Talk:High-performance sailing

Sailing downwind faster than the wind

See also: talk:USA 17 (yacht) § VMG in 1st race

I know that this section seems hard to believe. Please read the citations and study them carefully before posting comments to the effect that this section is obviously wrong. I too did not believe that this was possible, until I did the research and found the citations given in this section. Others (including a physicist) were also skeptical, but then became convinced, see [1] and [2].--Gautier lebon (talk) 08:39, 10 December 2009 (UTC)

I've posted some responses in talk:sailing. Another interesting topic is sailing directly into the wind. I've never seen a turbine / prop craft "work" directly upwind in what I consider to be a controlled test - the so-called proof has been less than convincing. The "spork33" device can be simply adapted to demonstrate that this is possible on land. It's just inefficiency of props and turbines that make it hard to get something to work on water, as there's no fundamental law to say it can't work. In a thought experiment, this can be extended to make something work on water by say dropping and raising large sea anchors, and using energy from the wind through a gearing mechanism to winch the boat forward against the sea anchor, but necessitating the use of a complex device to drop sea anchors "upwind" and raise them with minimal energy loss if sustained progress is to be made. There are other possible variations of the same idea (really not so different from a turbine-prop in principle). Using a sea anchor to hold a boat in position with a turbine harnessing wind energy, storing the energy (ie in a battery) and then using it to propel the craft forward so that progress is made is fine, but this isn't continuous uninterrupted progress, and is somewhat unremarkable. —Preceding unsigned comment added by 202.180.87.174 (talk) 23:56, 14 December 2009 (UTC)

I'm not sure what you mean by "continous uninterrupted progress". Hardly any boat progresses at uniform speed. Variations in the strength of the wind and waves cause any boat to advance at varying speed. As you say, the wind-and-anchor driven device that you describe is not particuarly surprising and demonstrates that it is possible to advance directly into the wind while using only energy captured from the wind. What seems to puzzle people is the claim that it is possible to progress downwind faster than the wind. But the trick is to think in terms of apparent wind. High-performance boats go so fast, with respect to the true wind, that they are sailing upwind with respect to the apparent wind, even though they are going downwind with respect to the true wind. Seems paradoxical, but think of a boat that is on a 90-degree reach and has accelerated to the point where it is close-hauled with respect to the apparent wind. If that boat bears off just a little, would its speed start to drop off until it equalled the speed of the wind? No: why should there be a sharp discontinuity in the speed/course curve? In reality, the boat will accelate even more (unless it is already at hull speed), until it is again close-hauled with respect to the apparent wind.--Gautier lebon (talk) 12:30, 18 December 2009 (UTC)

Indeed the discussion in Talk:Sailing#Downwind_faster_than_the_wind should be read by anybody interested in this topic.--Gautier lebon (talk) 12:16, 18 December 2009 (UTC)

In partcular the summary.--Gautier lebon (talk) 11:26, 13 January 2010 (UTC)

I just removed "Sailing dead downwind faster than the wind" section as there is no agreement on that in the discussion Talk:Sailing#Downwind_faster_than_the_wind as Gautier lebon is well aware of. The section should not be added unless a reliable source is referred to (not likely as it is impossible to sail dead downwind faster than the wind). Prillen (talk) 10:23, 19 January 2010 (UTC)

Thank you for your edits. Regarding the section in question, please specify what exactly you are objecting to. There was NO disagreement regarding the theoretical possibility. There was skepticism regarding whether or not the propeller-driven cart was was a hoax or not. You (and others) state that it is impossible to sail dead downwind faster than the wind, but I have not yet seen anybody explain why this is theoretically impossible, nor have I seen anybody explain why the thought-experiments that I provided are not correct. And please note that what I wrote is not original research, it is merely a summary of the various sources that I cited. In my view, it would have been more appropriate to flag the section and to discuss the matter further before deleting it. Regarding clean-up, I am all in favor of improvement. What specific items would you suggest?--Gautier lebon (talk) 13:25, 19 January 2010 (UTC)

What to be cleaned? Here are some suggestions:

• The introduction is too much about speed records.
• The drawings are nice but have a too large font size and the arrow indicator on the wind vectors are pointing the wrong direction.
• The headings "Sailing on a broad reach" and "Sailing perpendicular to the wind" should use the same terminology (angle -vs- reach/broad reach).
• "Normal cruising boats yachts can sail at a about 45 degrees off the apparent wind (50 to 60 degrees off the true wind)." is (still) not representative for a modern yacht (40-50 degrees off true wind is more the case).
• The tables should use a more standard layout (i.e. without border).
• "Further Reading" should be cleaned up.
• The language should be clarified/shortened in general. Prillen (talk) 10:43, 20 January 2010 (UTC)

OK, that seems sensible to me. I'm busy with other things this week, but I will try to work on it next week.--Gautier lebon (talk) 11:56, 21 January 2010 (UTC)

I have corrected the introduction and the terminology. Regarding the drawings, the arrows point in the correct directions for the vector algebra to work: just think of the case when the boat is moving directly upwind or directly downwind; I wear thick glasses, so I like the large font, and I presume that others will too, since it does not make the drawings any larger. Regarding performance of normal cruising boats, I just took the figure given in the sailing article; if you don't agree with it, then please update both articles so that they are consistent, and provide a reference. I like the borders on the tables, they are easier to read that way. I don't know what should be cleaned up in "Further Reading", maybe somebody can take care of that. Same regarding general improvement of the language: I've many revisions to the article, incorporating many good suggestions that were made on Talk:Sailing#Downwind_faster_than_the_wind. I don't know what more to do.--Gautier lebon (talk) 10:20, 29 January 2010 (UTC)

Common fallacies

If you think that anything stated in the article is impossible, please consider that the following two reasons have already been stated, and shown not to apply:--Gautier lebon (talk) 11:22, 11 June 2010 (UTC)

1) Velocity made good downwind cannot exceed the speed of the wind because of the laws of conservation of energy

2) Velocity made good downwind cannot exceed the speed of the wind because there is no force on the sails when the boat reaches wind speed.

3) If it were possible to go faster downwind by tacking, then why do people bother with spinnakers?

Conservation of energy

A balloon drifts downwind at the speed of the wind. It uses no energy to do that. Similarly, an iceboat can drift dead downwind at very close to the speed of the wind, because the friction of its runners on the ice is negligle.

That is, to proceed downwind at the speed of the wind requires essentially no energy.

If a boat can capture some energy from the wind, then it can use that energy to propell itself downwind faster than the wind. There is no violation of the law of conservation of energy because the energy captured from the wind is used to overcome the resistance of the surface (insignificant in the case of an iceboat) and the resistance of the apparent headwind induced by the boat's progress. As explained in the main article, when a boat sails at an angle to the wind, it can capture energy from the wind, even if its downwind progress is faster than the wind itself. This is because of the apparent wind shift, see below.

Also, it is easy to see that a device can be constructed that can capture the energy from the wind even when moving dead downwind, see below Talk:Sailing faster than the wind#deleted thought experiment.

No force on the sails

As explained in the main article, the forward motion of the boat induces a wind that must be added to the true wind in order to find that apparent wind that strikes the sails.

• Sorry, the apparent wind created by the downwind motion of the boat must be vectorially subtracted. At some point,the downwind vector of the boat velocity must be equal to the wind velocity, at which point. The only remaining wind vector is perpendicular to the wind direction and is entirely due to motion of the boat. At this point and beyond, the "wind" is created entirely by the motion of the boat and thus becomes a true perpetual motion hype.--QuietJohn (talk) 05:20, 14 June 2010 (UTC)
  • Sorry, you are confusing velocities with energy. To make a "perpetual motion" claim, you have to show that energy would not conserved. It is not sufficient just to state, that something about the velocity vectors seems counter-intuitive to you.Eyytee (talk) 09:12, 14 June 2010 (UTC)

You are correct, it is vectorially subtracted. The drawings in the article show this. You are correct that, at some point, the downwind vector of the boat velocity is equal to the wind velocity: for a specific example, see the drawings for 135 degrees below. You are correct that the apparent wind is created by the motion of the boat, but the motion of the boat is created by the TRUE wind, thus there is no perpetual motion. Think of a motor boat: it uses energy from its engine to create an apparent wind. That apparent wind could be used to drive a propeller-driven power generator. Similarly, a sailboat uses energy from the wind to create an apparent wind, which allows it to obtain even more energy from the wind. The point is that the energy required to drive the boat downwind always comes from the true wind.--Gautier lebon (talk) 09:03, 14 June 2010 (UTC)

If an iceboat sails dead downwind, then it will soon reach a speed close to the speed of the wind and the apparent wind on the sails will be nearly zero.

But if an iceboat sails downwind at an angle to the wind, there will be an apparent wind shift: the apparent wind will move forward. As explained in the main article, the iceboat will eventually find itself on a broad reach with respect to the apparent wind (apparent wind at 90 degrees to the boat's course). The apparent wind will still generate a forward force component, so the boat will continue to increase in speed and the apparent wind will shift even further forward. As explained in the main article, this can result in velocity made good (progress in the direction of the wind) that is greater than the velocity of the wind.

Note the key point: what drives the boat is the apparent wind, that is what the sails "see" and what the sails react to and what propelles the boat.

• The apparent wind is created by the boat. So what this sentence says is that the motion of the boat creates the apparent wind which then speeds up the boat. Once again, perpetual motion.--QuietJohn (talk) 05:20, 14 June 2010 (UTC)
  • The apparent wind is not just resulting from the motion of the boat but also by the true wind. Apparent wind is the air velocity relative to the airfoil, and it is the standard approach to use that relative velocity to calculate the force on an airfoil based on Angle_of_attack and Lift-to-drag_ratio. If you suggest, that we should compute the force on the airfoil WITHOUT using the air velocity relative to the airfoil (apparent wind), then I want to see your maths.Eyytee (talk) 09:12, 14 June 2010 (UTC)

It is not perpetual motion, please see the explanation above.--Gautier lebon (talk) 09:03, 14 June 2010 (UTC)

Why use spinnakers

Most sailboats cannot accelerate enough when they sail downwind so that the apparent wind shifts to come forward of the beam, and this because the resistance of the water is so large. That is, the resistance from the hull prevents the boat from moving fast enough so that the apparent wind shifts forward of the beam. Therefore, the apparent wind will always be aft of the beam and a spinnaker will increase the speed of the boat. However, downwind progress might still be faster if the boat gybes downwind, even with a spinnaker, and indeed most books on racing tactics say that it will usually be faster to avoid a dead downwind course and to gybe back and forth, even if the sailboat is using a spinnaker.

DDW faster than the wind thought experiment:

Most involved here in these discussions acknowledge that it's possible to steady state sail a traditional sailing rig at a fixed angle to the wind where the downwind VMG of the craft is greater than 1x windspeed (even 2x, 3x ...). Those who do not agree with this should review the data collected by NALSA (nalsa.org) on the topic. For those who agree with the above, I present the following thought experiment related to the DDWFTTW propeller driven vehicle that has also been discussed here. The following is presented in the hope of removing some of the related misconceptions and furthering the discussion regarding the section that prillen recently removed.e

Who are these "most"? Much above and below is wrong. Nowhere in the cited refs do I see good claims that the VMG towards the directly downwind point is greater than windspeed. Sure, an ice yacht can do 5 x wind speed but that is across the ground at a very shallow angle to the downwind point. A free floating balloon still beats the water/land/ice yacht to the downwind point. "Most" here seem to think that the angle and the speed can be chosen independently. No! Speed downwind (VMG to the downwind point) will never exceed cos(angle to the wind) x ground-speed. Paul Beardsell (talk) 06:46, 7 June 2010 (UTC)

First, a couple of design basics related to the DDW propeller driven vehicle (DDWPDV). The spinning airfoils are not acting as turbine blades. The blades do not drive the wheels. The spinning airfoils are acting as propeller blades and are *driven by the wheels". The force on the wheels is a braking force and the gearing between the wheel axle and the prop axle transfers this braking force to the spinning blades.

Second, since the topic of this page is "Sailing downwind faster than the wind", some dismiss the DDWPDV saying that it's not "sailing" and thus isn't relevent to the page in any case. The truth is, the airfoils on the DDWPDV are acting in the *exact* manner as the airfoil of a traditional sailing rig with its parent on a 'faster than the wind' downwind reach. Both airfoils are carving helical paths through the air -- the traditional rig is merely carving a helical path of MUCH greater diameter (the diameter of the earth) than those on the DDWPDV.

I will support this above assertion with the following thought experiment:

(I'm not a sailor so pardon me of I misuse a term here or there in the following. Also, as with all thought experiments, there are some simplifications.)

Imagine for a moment a world that rather than being shaped as a sphere is shaped as a cylinder. The cylinder 'world' is laying on it's side in our view and we are standing at the south "end" of the world on top of the cylinder. The entire surface of this world consists of one enormous uninterrupted dry lake bed with one wind blowing from the south to the north. Let's send a land-yacht on a 45 degree reach running to the NW. Without making a single gybe, this craft will 'corkscrew' it's way around the world as many times as needed to reach the far end of the cylinder. We know that if we release a neutral bouyancy floating balloon into the wind at the same time as the land-yacht, by the time the land-yacht has made one circumnavigation of the cylinder world and reappears to us on top it will be significantly farther downwind and 'downcylinder' than the balloon. This of course is just a simple matter of the craft having a downwind VMG greater than 1.0 wind speed .

Nonsense! That is a circular argument (not only a cylindrical one!). You prove the yacht will be ahead of the balloon by assuming that VMG > windspeed. It is not. VMG is never greater than (speed over the ground) * cos(angle to the wind). Paul Beardsell (talk) 08:01, 7 June 2010 (UTC)

Now, imagine that when the initial craft we sent on it's 45 degree path is halfway around the world (and now on the 'bottom' of the cylinder), we set another identical craft off on an identical 45 degree downwind reaching path. We start this craft off at the same 'longitude' as our craft already in motion. What we now have are two land-yachts on opposite sides of the world, going the exact same speed and carving the same helical path -- all the while remaining exactly opposite of each other on the cylinder. Every rotation they make they cross the DDW path of the drifting balloon and each rotation they get farther and farther ahead of it.

No, they do not. Their landspeed will be max windspeed/cos(angle). They will never ever ovetake the balloon. Paul Beardsell (talk) 08:01, 7 June 2010 (UTC)

Imagine now in this thought experiment that we begin to shrink our cylinder world a bit at a time. We have not changed the speed of the wind nor the speed of the land-yachts. As this 'world' shrinks, all that changes is the diameter of the helical path shrinks and the number of revolutions that the yacht makes in any given period of time increases. Keep shrinking this imaginary world until the wheels of the land-yachts are on such a small cylinder that they are essentially touching each other as they spin dizzyingly around and around -- their sails protruding in opposite directions.

If you are with me so far, you'll see that our two land-yachts are still achieving a downwind VMG of greater than 1.0 -- every time they rotate they increase their advantage over the floating balloon. Also, those sails spinning in a perfect circle are sure looking familiar (propeller anyone?)

Once again, this is the same circular argument! You assume VMG > windspeed is possible, and then you prove this very fact. How convenient! Paul Beardsell (talk) 08:01, 7 June 2010 (UTC)

Going a step further in this 'morphing' process, let's replace the chassis of both land-yachts with something more simple without making any changes to the spinning sails. We know that both the sails and the chassis are carving a 45 degree helical path so let's dump the frames and wheels of the land-yachts and replace both of those with a single, oversized threaded rod. This rod is equipped with grooves that match the sails 45 degree path and is aligned with the wind, taking the place of the 'pole' of our cylindrical earth. Let's spin on a matching oversized nut and drop the masts into holes in that nut. Now, without ever interrupting the spinning sails nor their downwind VMG >1.0 paths we have created the simplest DDWFTTW vehicle of all -- two spinning airfoils on a nut traversing a threaded rod. At the center of these rotating airfoils, we now have a nut that is going DDW and continuing to press it's advantage over the balloon with every rotation.

(Before taking the last step to our vehicle, it's interesting to note that the sole purpose of the keel mechanism on a traditional sailing rig is to force the airfoil to take an advantageous path through the air. In the case of a 45 degree reach, it's purpose is to ensure that for every foot that the airfoil moves downwind, it also moves one foot to the right (or left). It's this forced diagonal path through the air that creates the apparent wind needed to generate thrust. Of course the purpose of the non-articulated skates of an ice-boat, the wheels on a land-yacht and the threaded rod and nut in our above example serve the same purpose as the keel of the sailboat -- forcing the airfoil to maintain it's path diagonal to the wind.)

Last step: Once we reach the point that we have a pair of spinning airfoils happily pushing the nut DDWFTTW down a threaded rod, we need someway to translate this into a vehicle that can traverse any dry lake bed DDW. Realizing that to do this we only must find a way to force our airfoils to continue on their 45 degree helical path -- a path from which they have yet strayed, we arrange gearing between the wheel axle and the prop axle to ensure that for every foot the wheels roll across the dry lake bed DDW, the airfoil is forced through the air one foot to the side just as before -- and there you have it, DDWPDV -- a DDWFTTW vehicle.

As you can see, through this entire process the wind never changed directions, the angle of the apparent wind to the airfoils never changed, the speed of the airfoils through the air never changed, the downwind VMG of the airfoils never changed, the lift and drag vectors of any given airfoil section never changed -- in short, other than a slow change in the diameter of the helical path of the airfoil, all remained the same from "sail" to "prop".

Turns out that the airfoils of a traditional sailing rig on a faster than the wind reach and those of the DDWPDV are acting in the same manner -- one can *call* it sailing or not, but it's a distinction without out a difference from an aerodynamic standpoint.

Here is the 'Cliff-Notes' version of the above: The airfoils of the propeller are one loooong and continuous downwind helical reach while the chassis travels DDW. Adjusting the gear ratio between the wheels and the prop is the equivalent of adjusting your ground track on the land-yacht (and thus altering your sails path through the air) and changing the pitch of the propeller is the equivalent of adjusting the angle of the sail on the land-yacht.

Hope this helps:

ThinAirDesigns (talk) 00:11, 26 January 2010 (UTC)

What sophistry! Paul Beardsell (talk) 08:01, 7 June 2010 (UTC)

Dear ThinAirDesigns, thank you very much for this and your corresponding post on the Sailing page. I had figured out that the propeller on the cart in question had the same function as a sail set at an angle to the wind (just as a rotating helicopter blade has the same function as a wing) but I didn't know how to explain it. Your explanation is very clear and makes perfect sense to me. Would the skeptics now agree that the deleted section can be restored?--Gautier lebon (talk) 17:14, 26 January 2010 (UTC)

Well it is always interesting with a new scope, but I can not see that the thoughts are supported by evidence. As I understand ThinAirDesigns it equals that a wind turbine could generate power in calm weather if it had a foundation that could tilt it from side to side. And I rally can not imagine that happening. The only way I can see it should be possible to sail faster than the wind dead downwind would be to measure the wind speed at the vessel but use a kite much higher up and use the wind shear to generate the driving force. But I do not consider this as a true SFTTWDDW as the kite would fly slower than the wind (and it is only my thoughts – never seen any evidence). Prillen (talk) 20:08, 26 January 2010 (UTC)

Hi prillen. First I would like to say that I am new to WP and want to make sure that I contribute to the discussion according to WP guidelines. Currently I intend for my comments to fall under this quote from the WP talk page guidelines "to discuss how the different points of view obtained from secondary sources should be included in the article, so that the end result is neutral and objective (which may mean including conflicting viewpoints)." With that in mind, I'll continue:

To conclude that the thought experiment that I gave is not supported by evidence, one has to assume that the the plethora of examples shown in operation on YouTube are faked (which of course is always a very real possibility). However, if the only flaw you can find in my example is that "it's not supported by evidence", all you've done is create a circular argument where 'it can't be done therefore the evidence must be faked, therefore your arguments aren't supported by evidence, therefore it can't be done ...'

To break out of this circle, one must first consider the validity of the thought experiment. If the thought experiment is valid, THEN we look at the evidence and say "is it faked"? If the thought experiment has no flaws, one could rationally conclude that while all that YouTube evidence *could* be faked, it need not be and in fact it's easier to just do it than to fake it.

Do you refer to the YouTube video of the model on the treadmill? That does not do what is claimed. Say the wind is 10mph. So we set the treadmill speed to 10mph. What is the speed of the wind which ought to be experienced by mini-you, sitting on the model. Zero! We are travelling downwind at downwind speed. So why is there a dirty great fan behind you? Why does mini-you experience a tail wind on the model on the 10mph treadmill? Paul Beardsell (talk) 08:01, 7 June 2010 (UTC)

As an example of this principle: If we logically conclude that an ordinary car has the necessary power and ground clearance to drive over an ordinary speed bump, we might also easily conclude that a video of a car driving over a speed bump to be reasonable evidence of our conclusion. If 10 different people independently video a car driving over the speed bump it starts to look even better as evidence. And certainly if it's easier to produce a video of a car actually driving over a speedbump than to produce one that fakes a car driving over a speedbump, one begins to conclude that the videos may indeed be real evidence. Why would someone fake it after all when it's so easy to actually do?

I believe that extraordinary claims require extraordinary evidence, but the purpose of my thought experiment is to show that there is *nothing* extraordinary about the claim of the DDWPDV, it is merely non-intuitive. For over a hundred years now, reaching ice-boats have been able to achieve downwind VMGs higher than windspeed. For a quarter of a century now sailboats have been able to do the same thing. If you place two of these completely ordinary vessels doing completely ordinary things on opposite sides of a completely ordinary circle (be it the world or a rotating shaft) the reaching sails are not going DDW, but the center point between the two certainly is. Place an object on that center point, or hook an object to that center point, and that object is now going DDWFTTW.

Would you care to explain where in my example the downwind VMG of the airfoils drops below 1.0x windspeed? If we agree that from the outset the two airfoils (on the land-yachts) have a downwind VMG greater than 1.0 windspeed and you don't agree that in the end they are *still* achieving this, there must be somewhere in there you can point to the change.

Also, I'm also not sure where you got the idea from my land-yacht example that a wind generator can be a net producer of power on a calm day (no matter what the foundation does). I certainly hold no such position and in the example I gave, the air is always moving relative to the surface. Also, like you I would not consider your kite example to be true DDWFTTW. To qualify, the wind measured must be the wind used

ThinAirDesigns (talk) 21:40, 26 January 2010 (UTC)

I am sorry but I still do not get your point. As I see it your arguments can just as well be used for sailing "dead" upwind faster than the wind. And you write "I certainly hold no such position and in the example I gave, the air is always moving relative to the surface." but for a vessel moving DDW at the same speed as the wind the relative wind will be zero – just as for a wind turbine on a calm day. Regarding evidence I will off cause except that I am wrong if you provide a reliable source/evidence. And no, I do not consider YouTube as reliable evidence. But it could be interesting to watch them – do you have a link? Prillen (talk) 09:20, 27 January 2010 (UTC)

Dear Prillen, if a vessel moves DDW faster than the wind then the relative wind will not be zero: the vessel will be facing a headwind. Just as an iceboat that starts on a broad reach will accelerate until it sailing into the wind. Regarding sailing dead upwind faster than the wind, consider a boat that has no sails but uses a windmill to power a propeller. There is no theoretical reason why that boat could not advance dead upwind faster than the wind, although it might not be possible in practice given the efficiency of the windmill, the drag induced by the windmill, the efficiency of the propeller, the drag of the water, etc. Regarding the video, please look carefully at the videos that you will find at [3]. Regarding what to do with this, my proposal remains to include in the main article a section on this topic, noting that there is skpeticism, and referring to the talk pages where this discussion has taken place. Surely that is of interest to Wikipedia readers, and surely one can rely on them to make up their own minds, if the text clearly indicates that skepticism may be justified?--Gautier lebon (talk) 12:32, 27 January 2010 (UTC)

Hi Prillen, At the very top of my first entry here (the thought experiment), I stated that my presented exercise was for those who agree that there exist traditional sailing rigs which can achieve downwind VMGs of greater than windspeed while on a broad reach. There have been several highly regarded books and sites referenced which state this, published polars showing craft capable of doing it and at least one international sanctioning sailing organization collecting and publishing data demonstrating it being done in the real world. I'm quite certain that any and all of those sources meet WP standards for inclusion.

No! VMG greater than windspeed towards the directly downwind point is NOT possible on any sea/land/ice yacht. The cited refs do not support such an outlandish claim. So the whole argument vanishes into thin air. Paul Beardsell (talk) 08:01, 7 June 2010 (UTC)

Before directly exchanging comments with you I should have asked your position on that above paragraph. If you do not agree with it, then pretty much all of what I have written will not make sense to you as it is all based on that "traditional sailing rigs can beat the wind to a downwind mark" premise. Do you mind if before we continue, I ask you if you agree with the above paragraph? Thanks ThinAirDesigns (talk) 14:01, 27 January 2010 (UTC)

ThinAir has posted a comment on my user talk page. He draws our attention to the fact that a team of Aero students from San Jose State University, along with their Professor, advisers and generous corporate sponsors have set out to build a device that would definitely prove that it is possible to go downwind, faster than the wind, powered only by the wind(DDWFTTW), steady state, see [4]. This shows that qualified and educated people believe that the feat is not theoretically impossible, although it may be very difficult to achieve in practice.--Gautier lebon (talk) 10:31, 28 January 2010 (UTC)

The world is full of idiots. Linus Pauling won two Nobel Prizes and then staked his considerable reputation on the claim then Vitamin C could cure cancer, baldness and flatulence. Do not accept arguments from authority, academic or commercial! Conservation of energy is a higher authority. Paul Beardsell (talk) 08:01, 7 June 2010 (UTC)

Yes I do agree in the paragraph above. And I agree with Gautier Lebon that a section about the idea should/could be included, but describing it as a subject of discussion and without proof – not the way it was done. But it is interesting with the student project though. Prillen (talk) 12:17, 28 January 2010 (UTC)

OK, I will post a version of the section in question along those lines.--Gautier lebon (talk) 11:07, 2 February 2010 (UTC)

Hi Prillen, and thanks for your response. Above, you say you are unsure of the 'point' to my thought exercise and follow-up post. With your agreement that traditional rigs can achieve steady state downwind VMGs greater than windspeed, and that this achievement is documented according to WP standard the point of my thought exercise is this:

The exercise shows step by step that the airfoils on the DDWPDV are operating in just the same way that the sails on the described (and agreed upon and documented) land-yacht operate. Any documentation deemed WP appropriate for the propulsion of the VMG greater than 1.0 land-yacht is also documentation for the propulsion of the DDWPDV since they are propelled in the identical manner. For this not to be true, someone would need to point out the precise step in my exercise where it goes wrong. To date, no one has even touched on doing so.

If I stick an internal combustion engine in a new and odd looking vehicle, it's WP appropriate to use the same internal combustion engine documention and references as the other application use. Just because I put a normally operating sail on a new and odd looking vehicle (the DDWPDV) doesn't mean that I don't get to use the same sailing documentation as everyone else. Documentation for any tradition rig with a downwind VMG greater than 1.0 windspeed IS documentation for the DDWPDV. (as a note -- It was the realization that the diameter of the circle that a traditional sailing rig follows (the diameter of the earth) could be shrunk to something more manageable that led to the creation of the DDWPDV. True story)ThinAirDesigns (talk) 14:29, 28 January 2010 (UTC)

Deleted thought experiment

Dear Prillen, I see that you have deleted the text that I reproduce below. Can you please explain why you deleted it? I thought that it explained why the claimed device is theoretically possible, and so was worth including.--Gautier lebon (talk) 09:47, 3 February 2010 (UTC)

Consider a boat that has a very large spinnaker and that drags behind it a propeller-driven electric power generator. The spinnaker can be made suffiently large so that the boat sails nearly as fast as the wind despite the drag from the power generator. Suppose that the generated energy is stored in batteries. After a while, the boat can lower its sails and use the energy stored in the batteries to run a propeller to advance faster than the wind. Thus, on average, the boat can proceed dead downwind faster than the wind.

This scenario is highly theoretical and it would be difficult to achieve it in practice because of the high resistance of water. But a wind-powered cart running on wheels, on a flat surface, has much less resistance. Consider a cart that uses a very large spinnaker to run downwind close to the speed of the wind while driving an eletric power generator from its wheels (that is, the wheels are geared to a power generator). If energy from the generator is stored in batteries then, at some point, the spinnaker can be taken down and the energy from the batteries can used to power an electric motor to drive the wheels so as to propell the cart downwind at a speed greater than the wind. Again, on average, the cart can proceed dead downwind faster than the wind.

Dear Gautier lebon you put a lot of energy an enthusiasm in this article - good. But I do not like you add text I think is already discussed, and not agreed upon, to the article. So I deleted the sub-section of the same reasons as earlier: Because then it is not considered as "sailing" faster than the wind. It would be "motoring-faster-than-the-wind" although you would be using stored wind derived energy. That is why I deleted the sub-section. Prillen (talk) 11:04, 8 February 2010 (UTC)

Thank you for the kind words. There were various items that were not agreed, but it seems to me that the validity of the thought-experiment was not challenged. What was challenged is whether it was relevant. I think that we all agree that proceeding dead downwind faster than the wind is not "sailing" in the traditional sense. And the section makes that clear. It is indeed a form of "motoring" faster than the wind, using only energy from the wind. I would be happy to rewrite the material to make it clear that this is what is being described. I still think that it should be included because it expains why the dead downwind cart does not necessarily violate the laws of physics, which is not obvious at first sight. If you agree that some revised text would be appropriate, please let me know, and I will add it. Thank you.--Gautier lebon (talk) 11:20, 8 February 2010 (UTC)

I fear I may be doing this wrong. Trying to leave a comment here -spork-

From the start of this wiki page... "Devices that are powered by sails (such as sailboats, iceboats and sand yachts) can sail (that is, advance over the surface) faster than the wind. Of course they cannot do that by using simple square sails that are set perpendicular to the wind."

Actually, I'm pretty sure it IS possible to sail faster than the wind with a square sail set perpendicular to the true wind. However, the vehicle must be constrained to move at some angle to the wind. Consider an ice-boat on a downwind course 110 degrees off the wind. With a square sail and low enough drag, the ice-boat should maintain a *downwind* vmg of nearly wind speed with this configuration. That will give it a true speed far greater than wind speed. —Preceding unsigned comment added by 75.55.124.115 (talk) 05:21, 8 February 2010 (UTC)

Excellent observation. I will correct the opening sentence.--Gautier lebon (talk) 09:47, 8 February 2010 (UTC)

Is it possible to apply the trigonometry that leads us to believe in reaching downwind (under a fore-and-aft rig) faster than the wind in the vertical plane? Square riggers off the wind set their sails slack so that they are not stalled but have laminar flow from top to bottom, and vertical lift. The boat is certainly constrained to stay in contact with the water surface. --Nigelj (talk) 11:11, 8 February 2010 (UTC)

Of course some part of the boat has to stay in contact with the surface, otherwise you won't get the "wedge" effect and you will simply drift downwind. Also, there is an apparent wind generated in the situation of the 'downwind' iceboat described above. That has to be taken into account, so it would not be efficient to set the square sail perpendicular to the true wind.--Gautier lebon (talk) 08:56, 9 February 2010 (UTC)

Retracting my position: sailing faster *is* possible

I want to apologize for not catching on more quickly here and in the Sailing discussion. This article in Science Daily finally explained this in a way that made intuitive sense to me: [5].

Another thing that helped, after reading this article was to think of a spacecraft in space, in two situations. In one situation, particles are shot, all at the same speed, from a fixed location at an object that is floating freely: the object accelerates. At the point the object's speed reaches the speed of the shot particles, the particles can no longer catch the object: the object and the particles are moving at the same speed. In the other situation particles are again shot at an object in space, from a fixed direction, but NOT from a fixed position. All in the same direction -- across miles of space. ALSO, the object is riding on a fixed, straight rail. The particles are shot at 90 degrees to the object -- and at a "sail" that is faced 80 degrees away from path the particles, i.e, almost in line with the direction of travel. Each particle hitting the sail increases the speed of the object -- that is, up until the point where none of the particles can catch the object. That object speed will be MUCH faster than the speed the individual particles are traveling.

Both situations are analogous to a sailing boat. The "particles" are wind, in both situations. In the second situation, the role played by the "fixed straight rail" is similar to the role played by a the boat's keel. Duh. It seems obvious, now. Lol. Regards to all, Alpha Ralpha Boulevard (talk) 19:43, 9 February 2010 (UTC)

...all except for your penultimate sentence in the main para: the particles will always be able to reach the spacecraft as it is on a fixed rail parallel to the one the gun's on. The limit comes from your choice of an 80-degree 'sail'. "Each particle hitting the sail increases the speed of the object -- that is, up until the point where the particles begin to pass down both sides of the 'sail' without hitting it, or are as likely to hit the back or the front of the sail." Nice one. Well done. --Nigelj (talk) 21:07, 9 February 2010 (UTC)

Folks: thank you for your kind comments, but absolutely no apologies are required. As mentioned previously, I too was intially convinced that this was not possible, and it took me a couple of months of research and carefuly thinking to (1) document that is not only possible but commonplace and (2) figure out how it works. And I greatly benefitted from your skeptical comments because they helped me to figure out how to explain the situation more clearly.--Gautier lebon (talk) 13:31, 10 February 2010 (UTC)

New version of thought experiment

I propose to add back the following revised version of the deleted thought experiment. It would appear after the sentence reading "Note that a conventional keelboat's performance is also very much improved by a device other than the sail: its keel". Comments?--Gautier lebon (talk) 09:51, 11 February 2010 (UTC)

That is, consider a device that uses a mechanism in additon to sails to store energy obtained from the wind and then uses the stored energy to propell itself dead downwind.

For example, consider a boat that has a very large spinnaker and that drags behind it a propeller-driven electric power generator. The spinnaker can be made suffiently large so that the boat sails nearly as fast as the wind despite the drag from the power generator. Suppose that the generated energy is stored in batteries. After a while, the boat can lower its sails and use the energy stored in the batteries to run a propeller to advance faster than the wind. Thus, on average, the boat can proceed dead downwind faster than the wind.

This scenario is highly theoretical and it would be difficult to achieve it in practice because of the high resistance of water. But a wind-powered cart running on wheels, on a flat surface, has much less resistance. Consider a cart that uses a very large spinnaker to run downwind close to the speed of the wind while driving an eletric power generator from its wheels (that is, the wheels are geared to a power generator). If energy from the generator is stored in batteries then, at some point, the spinnaker can be taken down and the energy from the batteries can used to power an electric motor to drive the wheels so as to propell the cart downwind at a speed greater than the wind. Again, on average, the cart can proceed dead downwind faster than the wind.

Sorry but "Wikipedia is not a place to publish your own thoughts and analyses or to publish new information." Prillen (talk) 10:10, 11 February 2010 (UTC)

Correct. But it seems to me that the thought-experiment does not fall into any of the forbidden categories. It is not "1. Primary (original) research" nor "2. Personal inventions". It is merely an obvious explanation of why no laws of physics are violated if a wind-driven device moves downwind faster than the wind. I would appreciate comments from others regarding whether the material should be included in the article, or whether it would be more appropriate to add a note referring to the talk page.--Gautier lebon (talk) 09:40, 12 February 2010 (UTC)

There isn't a proper Wiki place yet for well-conceived teaching. That's a pity, because imparting knowledge isn't just statement of facts, but largely helping learners conceptualize, helping them to avoid pitfalls. I heard that in the 1800s calculus was post-graduate work. As pitfalls became understood, it moved to graduate level, then to undergraduate. Now, it's sometimes taught in high school. That clearly demonstrates that there is more to knowledge than presenting the verifiable encyclopedic facts. But yet: that is Wikipedia's charter.

I'd be among the first to be bold and say, "Then change that part of the charter!" Except ... I happen to have years of professional experience editing and writing troubleshooting documents, and my experience suggests there would be significant problems. The problems focus around three primary stumbling blocks: 1) People have a tendency to assume that a major, a breakthrough insight for them ... will also be an insight for others. But in practice, learners have all kinds of misconceptions ... and what is an insight to one person ... is totally obvious to another. The other has some other misconception. 2) People also have a tendency to assume that what is a transparently obvious example will be the same for others. 3) I'm not pointing fingers, this is not directed at the folks who have been in this discussion: Often learners who have had a hard-won insight assume they now understand the whole problem in context. That is, they've considered the social, political, practical ... and every other side. They are in a great mood, happy to share their new understanding. It's a great impulse! Often enough, they don't yet perceive context. So what happens is that these new enthusiasts confidently broadcast their new understanding ... not realizing how limited their perspective remains.

So the problem is both that teaching is important, and that it is far more difficult than typically imagined. Wiki takes the "safe" posture, which is to disallow teaching. Times will change, but for now, that's where we are. Regards to all, Alpha Ralpha Boulevard (talk) 06:26, 13 March 2010 (UTC)

The two vector diagrams

The two big vector diagrams in the article with the respective titles "Upwind" and "Downwind" seem to have the directions of the "true wind" arrows the other way round. For example, in the "Upwind" diagram, the directions of the "boat speed" and "true wind" are both pointing towards the right side of the page. If the boat is travelling towards the same direction as the true wind then it should be travelling downwind, not upwind. 222.153.241.153 (talk) 17:12, 12 February 2010 (UTC)

No, the arrows point in the correct directions for the vector algebra to work: just think of the case when the boat is moving directly upwind or directly downwind.--Gautier lebon (talk) 17:22, 12 February 2010 (UTC)

I think the problem is that the vector diagrams are adding vectors that shouldn't be added. It's a bit like adding torque and horsepower vectorily. We don't want to add boat-speed and wind speed to come up with the apparent wind. What we need to do is add the true wind vector to the negative boat speed vector to get the apparent wind. This is because the negative of the boat speed vector gives you the relative wind over the boat in the frame of the boat when there is no wind. It's simpler to subtract the boat speed vector from the true wind vector to get the apparent wind. I think that would be more conventional and less confusing. ~ spork —Preceding unsigned comment added by 173.13.177.205 (talk) 03:06, 13 February 2010 (UTC)

The true vector addition should be "boat speed" + "apparent wind" = "true wind", which means "apparent wind" = "true wind" + (-"boat speed"). So the two vectors are pointing to the same direction in the vector addition diagram because you are really adding the negative "boat speed", but the original "boat speed" vector and the "true wind" vector" should be point in opposite directions. What we have now in the diagram is that for the upwind situation, the "true wind" and "boat speed" are both pointing towards the right. Now how does it qualify it as the boat going upwind if the wind and boat are going in the same direction. 130.216.172.78 (talk) 07:40, 13 February 2010 (UTC)

I think that we are all saying the same thing. In the diagram, the vector labelled "boat speed" is actually the apparent wind induced by the boat's motion. That is of course pointing in the opposite direction of the boat's motion. That has to be vector-added to the true wind in order to get the total apparent wind. I would welcome suggestions regarding text to add to clarify and avoid confusion.--Gautier lebon (talk) 11:01, 13 February 2010 (UTC)

I think we can only do it accurately if we lable the current "boat speed" vector "negative boat speed". It's very difficult to explain it without saying it's a negative vector because the rigorous vector addition involves the addition of a negative vector.222.153.225.5 (talk) 15:38, 13 February 2010 (UTC)

>> I would welcome suggestions regarding text to add to clarify and avoid confusion

I would suggest the vector be labeled "relative wind resulting from boat speed". I think this would be less confusing and more accurate. spork —Preceding unsigned comment added by 75.55.124.115 (talk) 09:36, 14 February 2010 (UTC)

Seems like a good suggestion to me. I'm tied up for the next 2 weeks, so I might not get around to it right away (it is more troublesome to change the graphics than just the text), but I will do it in due course.--Gautier lebon (talk) 14:14, 14 February 2010 (UTC)

Finally it seemed to me difficult to add the full explanation to the charts without cluttering them up too much, so I've added a sentence in the text before each chart to explain what the vector "boat speed" stands for. Please let me know if you think that this is not sufficient.--Gautier lebon (talk) 15:00, 16 February 2010 (UTC)

Prillen's edit of 23 February 2010

The following vector diagram includes impossible combinations of speeds and angles. The max speed of a frictionless sail craft over the surface is cosine(alpha)*(true wind speed). That is exactly the same speed towards the windward point as a free floating balloon. Like it or not. Nothing is for free. You cannot independently choose the speed over the surface and the angle to the wind - they are dependent on each other according to the (max speed)=(cosine alpha)*(true wind speed) formula. All arguments below make that mistake. They are not independent variables. Paul Beardsell (talk) 17:24, 6 June 2010 (UTC)

I am removing the diagram from the article, therefore! Paul Beardsell (talk) 17:25, 6 June 2010 (UTC)

I feel that Prillen's edit of 23 February 2010 (deleting the vector diagrams) is not appropriate. As discussed above, the vector diagrams are correct, and text was added clarifying the labels on the vectors. If someobody thinks that the diagrams are not correct, then it seems to me that the topic should either be first discussed on this discussion page, and/or a different version of the diagram should be produced to replace then one that is claimed to be incorrect. However, I would like some reactions before reverting to the previous version that contained the diagrams.--Gautier lebon (talk) 14:40, 1 March 2010 (UTC)

I think a diagram would be very helpful in explaining these concepts and should be part of the article. How about this diagram?

--Paul (talk) 20:01, 1 March 2010 (UTC)

Paul, this is a good diagram, and I think that we can include it. But it does not replace the original diagrams. The purpose of the original diagrams was to show how elementary trigonometry can be used to derive the numbers shown in the tables. Without those diagrams, it seems to me hard to understand what is going on.--Gautier lebon (talk) 16:11, 2 March 2010 (UTC)

Hi. I did not delete the diagrams, nor the text. I merely commented them out as the diagrams are wrong. The section should be included, but as long the diagrams are wrong it is better commented out, but if somebody could fix (I do not do graphics) the diagrams it would be an welcome improvement. The suggestion Paul brings forth is better than the exiting file, but it is a pity it does not show the increasing boat speed with vectors. The vectors are about the same length although the text states different boat speeds. Perhaps the arrowheads for boat speed should only be an indicator of boat direction an placed under the "130.0°" and be a little larger and hence the small arrowheads on the boat speed vector removed? And the small arrows pointing at the vectors seems redundant. Prillen (talk) 09:04, 2 March 2010 (UTC)

Commenting them out is the same as deleting them, because nobody can see them any more. Which means that they cannot understand how the tables are computed. In my opinion, the proper procedure would have been to open a discussion item. You say that the diagrams are wrong, but you do not say in what way. I agree that the label "boat speed" was misleading, but this was corrected in the text. Please tell me exactly what you think is wrong and I will either fix it, or explain why I don't think a fix is needed. Regarding Paul's suggestion, please see my comment above.--Gautier lebon (talk) 16:11, 2 March 2010 (UTC)

Commenting the section out was a way of saying "the section is not right as it is now, but is important and should be included" - and you are right the proper way is to start a discussion. But here it is! Regarding the diagram Paul made I still think it replace this diagram from the section above the one in question here.

UPDATE: the displayed drawing is the new version, see below; the comment that follows refers to the old version. The problem with the the vector diagrams is the direction of the vectors and the lack of direction on the apprarent wind vector. If we take the "Upwind" diagram shown above. As it is drawn now the wind is from ca. SSW (210°) and boat is sailing directly east (course 90°) and that mean the boat is sailing downwind or more precise a broad reach! So the "True wind" vector might be wrong, but if we assume the "True wind" and "boat speed" vectors are correct the title is wrong and the "apparent wind" vector is wrong. The apparent wind would be something like SE (135°). And I think the "True wind = 1" should be removed or relation with boat speed and apparent wind should be added. The same problems apply to the "downwind" diagram. Prillen (talk) 09:24, 3 March 2010 (UTC)

Dear Prillen, thank you very much for your constructive comments. I see that the diagrams need to be clarified to state that the vectors are not showing compass directions, merely relative directions. The boat is moving in some direction, at a certain angle to the wind, and into the wind. The vector labelled "boat speed" actually shows the relative wind generated by the boat as it moves upwind. I added text that makes that clear. The label "true wind = 1" indicates that the other vectors are shown as multiples of the true wind. No numbers are shown for the other vectors, because they are indicative. I don't have a problem with removing the "1" from the "true wind" label, I can include the explanation in the text. So it seems to me that the chart is not incorrect, but can be misunderstood as you did. Would you agree that the problem can be solved by adding text to clarify what the diagram is meant to show? If you agree with the principle, I will add text and restore the diagrams, and we can then fine-tune the text. I will also add Paul's chart, which is valuable, but does not have the same purpose as mine, which is to show how vector algebra and elementary trigonometry can be used to derive the various quantities.--Gautier lebon (talk) 16:39, 4 March 2010 (UTC)

Ok, I think that make a bit more sense – "Boat speed" means "wind-generated-by-boat-speed"? And then the apparent wind vector is pointing up to the right and the title is then correct. Is this the way it should be interpreted? But if that is the case I still think is it not so intuitive because of the "wind-generated-by-boat-speed" vector. A "boat speed" vector is a lot more intuitive and easily understood by most people. And in other words; I think the diagrams should be changed, not the text. Prillen (talk) 08:06, 5 March 2010 (UTC)

Dear Prillen, thank you for your positive comment. I will now rewrite the section and restore it. In the meantime, I looked at Bethwaite's book again, and found a citation that supports the diagram: I will include that. I will also change the diagrams to try to clarify, aligning with the diagrams at apparent wind. The diagram is correct in terms of vector algebra, but you have to understand that the "boat speed" vector actually represents what you say above. I look forward to your comments on the new version. It isn't hard for me to modify the diagram, I just am not sure what would be best. Regarding "true wind speed = 1", I need that because the formulas use that value for true wind speed, in order to avoid an extra variable and extra complications. I will also explain that in the cover text.--Gautier lebon (talk) 14:46, 5 March 2010 (UTC)

Gautier lebon I see your problems with the algebra, but I think it is better to leave the "boat-speed" vector out of the drawing and explain it in the text to clarify the diagram. The apparent wind vector still miss the direction arrowhead. And why not call "alfa" and "beta" for "awa" and "twa"? Prillen (talk) 13:11, 8 March 2010 (UTC)

Thank you for your comments. I've aligned the diagrams to the one that appears in the apparent wind article. Isn't it better to maintain consistency with other Wikipedia articles? If yes, we should maintain the "boat speed" vector. I didn't put an arrow-head on the apparent wind vector because it is obvious and it would further clutter an already rich diagram. But it would be trivial to add. Since I'm a mathematician by training, I tend to use alpahs and betas for angles. That is pretty common.--Gautier lebon (talk) 17:52, 9 March 2010 (UTC)

I haven't been following this discussion in detail, but looking at the diagrams now, I wonder if they could be clearer still. What we want to show is vector subtraction between the boatspeed and the wind to find the apparent wind, am I right? For clarity and intuitive viewing, I wouldn't introduce the head-wind-due-to-boatspeed vectors, as these are artificial and just represent minus(boatspeed), which enables the subtraction. I would show boatspeed proceeding left to right across the bottom of both diagrams (L to R is more intuitive to us westerners I think) and the wind impinging onto it as a vector from above, ending at the right-hand end of the boatspeed vector in both cases. In both cases, the triangle is the same shape, just remove the extra head-wind lines and labels, move the arrow-heads to the other ends of both other lines and leave the labels 'boat speed' and 'true wind' where they are. There is another intuitiveness benefit in that, to my eye, it then looks in both cases as if the boat is actually "at" the right-hand corner where the two vector-heads meet, and the vectors show how, in the most recent unit of time, the boat and the wind actually reached this point. I hope my explanation makes sense - it's always hard to describe a drawing. I've just sketched the two new diagrams here and they both look fine to me that way. Arrows trailing after each other - vector addition; arrows meeting at a point - vector subtraction. You have arrows pointing off in different directions - they look to me like your going to do addition using a parallelogram diagram, but then you draw the 'wrong' diagonal in, and my eye gets confused. Is this any help? --Nigelj (talk) 19:54, 9 March 2010 (UTC)

Nigel, thank you for your helpful comments. I'm all in favor of redoing the diagrams so that they are easier to understand. I thought that what I had originally done is pretty much what you describe now, but I'm probably missing something. I have to confess that I don't quite understand what you propose. Could you scan your handwritten chart into a PDF and post it to this discussion page? I could then use that as a model to modify my diagrams? I do agree that vector algebra can be confusing, I was just helping my 15-year old daughter last night. And it isn't helped by the fact that there are different ways of doing things, with and without parallelograms, as you say.--Gautier lebon (talk) 12:30, 10 March 2010 (UTC)

I've been bold. I don't own a scanner, so rather than create new upload file locations, I edited the previous versions of your two files to show what I mean. This means that my versions have currently gone live into the article. Please feel free to revert them if you don't agree it's an improvement. If you do like the approach, there are some small errors in the position of the windspeed vector on the 'downwind' diagram that meant that I couldn't get the arrowhead to the end of the line without it disappearing. In the end, both of these diagrams will need to be changed to SVGs for clarity and that might be the best time to fix that. --Nigelj (talk) 13:36, 10 March 2010 (UTC)

Dear Nigel, thank you for having taken that initiative, I think it is helpful. But now we are back where we started: people will probably misunderstand the diagrams, since they won't understand that the true wind vector is being added to the not-shown head wind vector that is induced by boat speed. I suggest that we leave it like this for a little time, so see if we get any more comments. If nobody complains, then I'm satisfied. And then I will fix it up the details as you propose above.--Gautier lebon (talk) 13:56, 11 March 2010 (UTC)

I have now updated the charts as agreed.--Gautier lebon (talk) 16:03, 25 March 2010 (UTC)

Dead downwind faster than the wind

For those interested in this esotheric topic, please take a look at [6]. The graduate students have done it. Their device advances against a treadmill, meaning that it can progress dead downwind faster than the wind.--Gautier lebon (talk) 14:08, 11 March 2010 (UTC)thttp://tech.slashdot.org/story/10/06/06/0518216/Google-Backed-Wind-Powered-Car-Goes-Faster-Than-the-Wind

No! Maybe it is possible to do what is claimed but those students have proven nothing using the treadmill. Were (minitiarised) you sitting on the device on the treadmill you would not be experiencing a headwind but a tailwind. In order to travel downwind faster than the wind you must experience an apparent headwind as a passenger. If the students took the prop/fan off their model and simply put a flat square sail perpendicular to the wind it would still go uphill on the treadmill. What a joke that experiment is! Those postgrad students should be stripped of their undergraduate degrees. Paul Beardsell (talk) 14:05, 6 June 2010 (UTC)

A device with a flat sail would not be able to progress against a treadmill. Surely that is obvious. What happens in the experiment is that the treadmill causes the wheels to turn, which causes the propeller to turn. The propeller creates a backwards-moving stream of air, which is sufficient to cause the cart to advance against the treadmill. This is the equivalent of progressing dead downwind at the speed of the wind.--Gautier lebon (talk) 11:29, 11 June 2010 (UTC)

Your remarks are unsubstantiated and offensive. These students conduct systematic and exciting experiments. MrBeanBob (talk) 00:09, 8 June 2010 (UTC)

Those students are either fools or hoaxters! And you are taken in. Why, if the model is going faster than the tailwind, does mini-you on the model still experience a tailwind from the fan on the ground behind the treadmill. What should be experienced is an apparent head wind. I would like to substitute their model with mine. It has no rotating propeller but just a flat card as a sail to be pushed along by the fan on the floor! It performs much better in THEIR experiment than does their own model! Paul Beardsell (talk) 11:47, 8 June 2010 (UTC)

It is clear that you have not looked at the videos of the outside runs, made after the treadmill experiments. Indeed the cart accelerates until it encounters a headwind. This can be seen from the telltales on the cart, as well as from the speed data (charts) that are posted on the web page.--Gautier lebon (talk) 11:29, 11 June 2010 (UTC)

On Monday, March 22, 2010 the San Jose State University project overwhelmingly succeeded in demonstrating 'direct downwind faster than the wind' on the Ivanpah dry lakebed south of Las Vegas, Neveda. There were numerous NALSA (North American Land Sailing Association) officials in attendance and one NALSA BOD member (Bob Dill) was there for every run and collected his own rough wind and GPS data. All collected video and data corroborate the personal witnesses. To be clear, this was NOT a NALSA sanctioned event but was presented as a demonstration to the NALSA BOD that the vehicle was capable of ddwfttw. After the demonstration, the team is working out the details with NALSA for rules and instrumentation related to an upcoming official NALSA ratified test and record. The team expects to be able to certify a record according to these upcoming rules in the range of 3 times the speed of the wind powering the craft. www.fasterthanthewind.org ThinAirDesigns (talk) 18:52, 25 March 2010 (UTC)

I propose three cheers for ThinAir and his colleagues. Will anybody join me?--Gautier lebon (talk) 16:23, 26 March 2010 (UTC)

Thanks Gautier. There were many long nights. Still a few more coming up to get the ratified record. ThinAirDesigns (talk) 08:04, 27 March 2010 (UTC)

Without even saying sailing dead downwind faster than the wind is impossible (it is impossible) one can rightly pour scorn as I do above on the treadmill experiment. Let's say it is possible and that it has been done. So, what is the theroretical maximum speed. There seems to be no limit. No limit, something's wrong, no prize. Energy from nowhere. Paul Beardsell (talk) 16:20, 6 June 2010 (UTC)

The energy comes from the wind. It is used to drive the machine forward. The maximum speed depends on how much energy can be captured from the wind and on the resistance on the surface and on the resistance induced by the apparent head wind. There is no free lunch here and no claim that a device can achieve infinite speed.--Gautier lebon (talk) 12:35, 7 June 2010 (UTC)

Dead downwind faster than the wind: Formatting & References

I am concerned that this section of the article is running afoul of WP policy in several areas. First, it appears that some edits are coming directly from ThinAirDesigns. This appears to be a violation of WP COI policy.

The discussion in this section as a whole, and the sources cited, are questionable at best. This is both in terms of content, style, and use of references. As this has also (at least in the past) been a controversial topic, I'm also concerned that there may be a [[Wikipedia:Neutral_point_of_view|NPOV] issue here as well.

Per WP policy on [original thought], a WP article talk page is not a notable or or authoritative reference suitable for use in the article.

Much of the rest sounds like a description of personal experience at the event. This is not appropriate. "Primary sources or sources affiliated with the subject are generally not sufficient for a Wikipedia article," see Wikipedia:Reliable_sources. Rather, "Articles should be based on reliable, third-party, published sources with a reputation for fact-checking and accuracy." (Wikipedia:Verifiability) Please see Wikipedia:Notability and Wikipedia:No_original_research as well. --Oskay (talk) 20:03, 31 March 2010 (UTC)

For the record, to my knowledge, so far I haven't made a single edit on any WP article on any topic, ever. Again to my knowledge I have only commented on the discussion page. *IF* one can find an edit or addition on a WP article made by me, it was not intentional and was made when I thought I was on the discussion page. I'm pretty darn certain the record will support my assertion that I stick to the discussion page. ThinAirDesigns (talk) 20:47, 31 March 2010 (UTC)

The edit of the article dated 18:54, 25 March 2010 was performed under the account ThinAirDesigns. This was a significant edit to the article, adding the claim that the students had "overwhelmingly succeeded in demonstrating" this phenomenon. ThinAirDesigns, can you please clarify your relation (if any) to this research group? Oskay (talk) 00:59, 1 April 2010 (UTC)

I went and checked Oskay, and you are correct. For some reason I mistakenly posted that on the article page rather than the intended discussion page. I apologize as I had no intention nor realization of such until now. I have avoided editing (or at least *intended* to void editing) this topic because,

A: I am not a regular WP contributor and as such am not familiar with the rules to do such.

B: Until our team gets a record ratified by NALSA (in internationally recognized sanctioning body for wind powered land speed records) I frankly don't know if any of our findings meet WP standards. The fact that this is a project undertaken by a reputable and accredited University may or may not meet WP standards. Perhaps you know ... I do not.

C: We expect in the next few months to have a NALSA record ratified, so I've got no to reason to press the issue considering the relatively short time to this upcoming event.

As to my relationship with the San Jose State University project, I am a Guest Professor for the duration of this effort(this semester and last) and one of two SJSU defined Managers of the project.

Again Oskay I apologize for the edit to the actual article -- being new to WP I lost my way in the edit process. ThinAirDesigns (talk) 01:29, 1 April 2010 (UTC)

Dear Oskay: you are correct, ThinAir mistakenly posted the same material to both the talk page and the main article. I quickly corrected that, posting to the main article a somewhat modified version of what is on the San Jose team web site. Please note that there are now two independent sources showing that a cart using a propeller linked to its wheels can progress dead downwind faster than the wind. Surely this is worth inclusion in Wikipedia? Regarding "no physical law is violated", that is not original research, it is a fact, otherwise the device could not work. I agree that it is not an obvious fact, that is why I wanted to include the thought experiment explaning why no physical laws are violated. But there was resistance to including that thought experiment, so it appears only here on the talk page. Could you please make specific comments, apart from the various in-line comments that you have already provided, that would allow us to clean the article up and resolve the dispute?--Gautier lebon (talk) 11:22, 1 April 2010 (UTC)

What's needed for clean up should be very clear if you read the WP guidelines on style, notability, and references that I initially linked to.

The majority of the recent edits have been directly taken from material provided by first-hand sources. Whether ThinAirDesigns edited the material personally or whether someone else copied information from this discussion page or their blog is somewhat immaterial (except for the possible COI/NPOV issue): it's still first-hand experiences that are being described here. Wikipedia is not a publisher of original thought. The guidelines explicitly state that "Wikipedia should not offer first-hand news reports on breaking stories. Wikipedia is not a primary source."

In the absence of reliable, third-party references and verification, the San Jose team's efforts -- while interesting and possibly of historic value -- should be carefully portrayed so as not to give undue weight. Right now, that whole section of the article is a discussion of the San Jose team efforts-- this absolutely, without question, undue weight with respect to the full article.

With respect to "original research," there is a big problem here as well. I added that inline tag because the reference given was this talk page I don't know how you could possibly argue that a WP talk page is a verifiable third-party reference, or that a discussion page here is an authoritative reference on the laws of physics. Also, per WP guidelines, Wikipedia should not be used for discussion forums. A thought experiment does not belong here. These talk pages are for discussing the article itself, not for debating the substance of the article.

"there are now two independent sources showing that a cart using a propeller linked to its wheels can progress dead downwind faster than the wind." And there are hundreds of sources showing perpetual motion machines in operation. That doesn't make either more or less verifiable, does it?

"Surely this is worth inclusion in Wikipedia?" I didn't say it was unworthy, just that you need to do it correctly. You don't need to make that kind of implication. Come on: It's an encyclopedia, not a press release. Read some other WP articles, read the guidelines about WP style and the WP core content guidelines, and fix it up. Why are we debating this? Oskay (talk) 00:24, 3 April 2010 (UTC)

Dear Oksay, thank you for your very helpful comment. Indeed, I had read the various guidelines more carefully before your last post, and I now understand your point and agree with it. It seems to me that the material at [7] can be referred to under the guideline "Self-published ... sources may be used as sources of information about themselves", see Wikipedia:Reliable_sources#Self-published_sources_.28online_and_paper.29. That is, it should be made clear that the reference only supports what the source says. Regarding the thought expertiment, I still think that it should go in the main article, because it shows why the device in question does not necessarily violate the laws of physics, which is not the case for perpetual motion machines. But there was resistance to including the thought experiment. For now, I propose the following rewrite of the section. Please let me know what you think of this.--Gautier lebon (talk) 07:27, 3 April 2010 (UTC)

A team of aeronautics students from San Jose State University, along with their professor and advisers, have reported that they set out at the end of 2009 to definitively determine whether it was possible to build a vehicle which can go directly downwind, faster than the wind, powered only by the wind, steady state.

At first, it would seems impossible to sail dead downwind faster than the wind: a wind-driven machine cannot progress dead downwind faster than the wind using only sails. This is because the apparent wind will be zero if the speed of the boat equals the speed of the wind, so the boat cannot possibly go any faster than that.

However, in theory, it can sail dead downwind faster than the wind using only energy obtained from the wind while moving (that is, it does not need to stock energy while in the port). Some sort of mechanical device can be used to transfer energy from the surface on which the machine is moving in order to increase the speed of the machine. Some might say that this is not sailing properly speaking, because the boat's speed is influenced by devices other than the sails. However, it is 'sailing' in the sense that the boat is propelled only by energy obtained from the wind. Note that a conventional keelboat's performance is also very much improved by a device other than the sail: its keel.

And indeed it has been claimed that a cart can be built that would use a propeller linked to its wheels (without batteries or electrical power generators) to sail dead downwind faster than the wind. Such a cart has been built and demonstrated. At first, this was considered to be a hoax, but it was subsequently considered to be a legitimate demonstration of what is theoretically possible. Indeed, as explained above, sources indicate that high-performance sailboats and iceboats can sail downwind at speeds greater than the wind, in the sense that their velocity made good downwind is faster than the wind (that is, they will arrive at the downwind mark of a course faster than would a balloon released from the upwind mark). Thus there is no reason to conclude that any fundamental law of physics is violated by a device that progressed dead downwind faster than the wind.

The team from San Jose University claim to have built a vehicle based on the same principle: a cart whose wheels are linked to a propeller. The team reported testing their vehicle on 7 and 8 March 2010 on a motor-driven moving belt (treadmill), showing that it would avance against the belt, which means, according to the team, that it can progress dead downwind faster than the wind. On 24 March 2010, the team reported that it ran the vehicle on the Ivanpah dry lakebed south of Las Vegas, Nevada, showing that it could accelerate dead downwind from a standstill and reach velocities well in exceed of wind speed. That is, according to the team, the vehicle was progressing dead downwind faster than the wind. The team reported that there were North American Land Sailing Association (NALSA) officials in attendance and one NALSA Board of Directors member (Bob Dill) was there for every run and collected his own rough wind and GPS data. This was not a NALSA sanctioned event but was presented as a demonstration to the NALSA Board of Directors that the vehicle was capable of progressing dead downwind faster than the wind. The team reports that it is currently working out the details with NALSA for rules and instrumentation related to an upcoming official NALSA ratified test and record. The team says that it expects to be able to certify a record according to these upcoming rules which should show dead downwind velocity in the range of 3 times the speed of the wind powering the craft.

It is important to stress that even as the wind-powered cart referred to above is actually going "upwind", it would not move at all if the wind speed relative to the ground is zero. In other words, it requires the wind to be moving in the same direction as it does for it to work. If, for example, an initially moving cart enters a region where the wind speed relative to the ground is zero, it would eventually stop due to energy dissipation (e.g. friction) even as it is heading "upwind" within the region. The wind-powered cart referred to above therefore would not necessarily violate the laws of conservation of energy, nor is it a perpetual motion machine, as it harnesses its energy from the kinetic energy contained in the wind. If enough of the wind energy is harnessed, the machine can (at least in theory) use it to propel itself, even at speeds faster than the wind. The cart is an example of a device that, while respecting the laws of physics, appears at first sight to be in perpetual motion: a so-called apparent perpetual motion machine.

I have to say that I'm a bit confused by some of the WP rules on sources that have been brought up above. I don't currently have the time to research these rules and I certainly don't claim any standing to argue with them, but it appears from the discussion that for whatever reason, this source may be considered more reliable somehow than the original source. http://sailmagazine.com/racing/running_faster_than_the_wind/ ThinAirDesigns (talk) 13:56, 6 April 2010 (UTC)

You can report that such'n'such web site says this works but you cannot have WP say it works. Conservation of energy. Paul Beardsell (talk) 22:37, 6 June 2010 (UTC)

Conservation of energy is not a mantra that can be used to dismiss actual observed data. Paul has not explained how conservation of energy would be violated. Indeed it is not. The energy comes from the wind, and is potentially very large. The device in question uses energy from the wind to overcome the resistance of the surface and the resistance from the induced apparent headwind. That would violate conservation of energy only if the energy required to overcome the resistances were greater than the energy obtained from the wind. Where are the equations to show that this is the case? Or the citation to the relevant calculations? Why is the unsupported assertion by one Wikipedia editor sufficient to overcome the patient work of many others, others who provided citations? Why is one editor's opinion that multiple concordant citations are all wrong sufficient to deprive Wikipedia readers of the chance to obtain the information in question?--Gautier lebon (talk) 12:31, 7 June 2010 (UTC)

Revised treadmill experiment

We want to demonstrate that a device can sail or propel itself dead downwind faster than the wind. We decide to use a treadmill. We assume a tailwind of 10mph and so we set the treadmill at 10mph and we leave it flat - no incline required. We leave the electric fan turned off because, at 10mph, there is no apparent wind. We put out miraculous model on the treadmill and hold it there with our finger so it neither moves forward or backward. It's wheels are turning and they're geared to the model's propeller. We remove our restraining finger. Does the device accelerate forward on the treadmill and continue to move forward? That's the experiment I want to see. I know the result and I am offering long odds to all comers! Paul Beardsell (talk) 14:17, 6 June 2010 (UTC)

That is ancient history. [8] demonstrates progress dead downwind faster than the wind in real conditions, not on a treadmill.--Gautier lebon (talk) 08:38, 7 June 2010 (UTC)

No! It is a hoax. There are ten-a-penny hoaxers with gadgets and equipment AND WEB SITES peddling their perpetual motion machines. It's a hoax! Energy from nowhere. If their argument were true there would be no limit to the downwind speed achievable! Paul Beardsell (talk) 09:03, 7 June 2010 (UTC)

It is not energy from nowhere. The energy comes from the wind. There is a limit to the speed that can be achieved: that limit comes from the friction on the surface and the resistance from the induced apparent headwind.--Gautier lebon (talk) 12:26, 7 June 2010 (UTC)

The problem with the YouTube video

You're on the model, and the model is on the treadmill. We imagine a tailwind of 10mph so we run the treadmill at that speed. What would the real-life apparent wind be to (mini-)you? Zero. So why is there an electric fan behind the treadmill? [I do not refer to the fan on the model, but the fan on the ground behind the treadmill.] Assume further that the machine works as desribed. Now we are travelling faster (say 12mph) than the wind, downwind (10mph, say). [That is the claim!] What should (mini-)you experience on the model on the treadmill? A headwind of 2mph! So the electric fan on the floor behind the treadmill should in reality be in front of the treadmill providing the 2mph headwind. That is NOT what the YouTube video shows! Paul Beardsell (talk) 09:00, 7 June 2010 (UTC)

Forget the YouTube video. That is ancient history. The relevant material is at [9].--Gautier lebon (talk) 09:12, 7 June 2010 (UTC)

So you agree the YouTube vid proves nothing? In which case the only people who say they've made a nonsense of thermodynamics are the hoaxters themselves? And some here. Paul Beardsell (talk) 09:33, 7 June 2010 (UTC)

No, I did not say that. I said that the You Tube video has been superseded by more detailed and convincing evidence.--Gautier lebon (talk) 12:25, 7 June 2010 (UTC)

Perpetual motion

Another way to demonstrate the perpetual motion nature of this is to ask what the theoretically maximum multiplier of the downwind speed is. Downwind 10mph, what 's the limit of the vehicle's speed? No limit according to the reasoning presented! Paul Beardsell (talk) 14:33, 6 June 2010 (UTC)

That is not correct, of course there is a limit. But is is not easy to compute because it depends on many factors. As the article clearly states, the limit comes from the friction of the hull (or wheels or runners) on the surface, the resistance induced by the apparent head wind and the efficiency of the device (sail or propeller) that captures the energy from the wind. According to [10], a dead downwind speed of 3 times wind speed is possible. That seems reasonble when you look at actual performance data from iceboats. Please look at the cited references before concluding that things are impossible which are in fact well known to be routine to people who have experience with iceboats, sand yachts, and high-performance catamarans.--Gautier lebon (talk) 09:15, 7 June 2010 (UTC)

No, limits come not only from friction. E.g. the carnot cycle shows the absolute limit of a petrol engine as being far far less than 100%. We are not talking friction. There has to be a theoretical limit to the maximum downwind speed achievable by this contraption of yours. I say it is less than the windspeed. You say it is unlimited except by friction. Wow. Paul Beardsell (talk) 09:36, 7 June 2010 (UTC)

What does the carnot cycle have to do with this? We are not burning fuel here. It is not I that says that it is unlimited, it is a number of cited sources, which include actual observed runs. Whereas you provide no citations, only your personal opinion. Surely this is not how Wikipedia is supposed to progress?--Gautier lebon (talk) 12:24, 7 June 2010 (UTC)

Actually, the answer is simple: In a purely theoretical sense, there's no limit, but in practice, materials always limit you. It's like asking questions about the leverage provided by a lever. What is the theoretical maximum multiple of the speed at which one end of a lever moves that the other end moves at? There isn't one. What is the *practical* maximum? Depends on your materials. But, no, there is not a theoretical limit, because the limitations are purely a question of materials. Wikiseebs (talk) 18:31, 10 June 2010 (UTC)

Sailing faster than the wind, but at an angle?

Also, those who say that one can sail a boat directly downwind faster than the wind by not proceeding directly but at an angle are WRONG. A floating baloon still gets to the directly downwind point before you no matter how you tack. You tack a modern sailboat because it is quicker to do that and gybe to get to a point directly downwind than trying to do it directly but that's still not quicker than the balloon. Paul Beardsell (talk) 14:33, 6 June 2010 (UTC)

It is quite amazing that you come to such a strong conclusion against overwhelming empirical evidence (ice boats, Amarica's Cup multihulls, sand yachts). The whole beauty of the idea of sailing faster than the wind is that it seems counter intuitive, to run against the 'laws of physics' (It doesn't - if it would, the topic would be discussed on the front page of the New York times!). MrBeanBob (talk) 23:56, 7 June 2010 (UTC)

As I make perfectly plain below, of course you can travel faster than the wind. But by keeping the wind on your quarter. Assuming a no loss of speed gybe you still get to the downwind point after the floating balloon, despite your speed over the ground. Paul Beardsell (talk) 12:03, 8 June 2010 (UTC)

Sure, you can travel at 1.2 x the speed of the wind, downwind, in a modern sailing dinghy, but at a considerable angle to the wind, the distance you have to travel to get to a point directly downwind is considerable more than 1.2 times the direct distance! It's quicker if the angle is 60degs or less because the direct downwind sailing speed is at best 0.6 the wind speed. But quicker is the free floating balloon. Paul Beardsell (talk) 14:36, 6 June 2010 (UTC)

Please read the cited references, as others have. When you work out the trigonometry, you can indeed have downwind VMG greater than windspeed, and thus arrive faster than the baloon. You deleted numerous reliable sources that say that.--Gautier lebon (talk) 08:39, 7 June 2010 (UTC)

No! No source I have deleted has said that. You (and others) may have interpreted them as saying that but NO THEY DO NOT SAY THAT. They DO say they can travel faster accross the ground than the windspeed (and I do not deny it - having done it myself) but they DO NOT say that the VMG towards the directly downwind speed is greater than windspeed. I tell YOU, *YOU* work out the trig. The angle and the speed are inter-related by the inequality (speed across the ground)/cos(angle to the wind) < (wind speed). If the angle and the speed break that inequality then they are an invalid combination. Sorry! You cannot beat the balloon. Paul Beardsell (talk) 09:07, 7 June 2010 (UTC)

Paul, please read the source before saying that it does not say what it actually says. The trigonometry is indeed worked out, and anybody can see how it works, if you take the time. What is unclear is whether the theoretical trigonometry can be achieved in practice, because of resistance, inefficiency, etc. The cited sources give multiple examples of verified cases where it was achieved in practice, not least during the America's Cup.--Gautier lebon (talk) 09:18, 7 June 2010 (UTC)

America's Cup? No. I followed the refs and could not see the assertions claimed. It was WP:SYN by you or another WP editor. I suggest the downwind point was not DIRECTLY downwind. The course marks are set and then the wind changes, they do not change the marks. Even in top flight sport the basic laws of Physics remain unbroken. Strange that! Paul Beardsell (talk) 09:31, 7 June 2010 (UTC)

Actually there were direct quotations from the people on the boats to the effect that they went downwind faster than a balloon. Again, you cite laws of physics, but provide no citation nor any detailed explanation of why some particular law would be broken.--Gautier lebon (talk) 12:21, 7 June 2010 (UTC)

I saw nothing in the quote you provided to say any such thing. They said they went faster across the water than the wind, but they did not say they beat the wind to a point directly downwind. Paul Beardsell (talk) 12:04, 8 June 2010 (UTC)

You have not read the citations carefully enough. They do say that progress to the downwind mark was faster than the wind.--Gautier lebon (talk) 11:32, 11 June 2010 (UTC)

Disputed tags

What I dispute is the assertion made in the article and here that it is possible to sail downwind faster than the wind to reach a point directly downwind faster than a free floating balloon. This is impossible. The vector diagrams are incorrect in that whereas they presume to tell us that a sailing boat can travel at 1.2 times the speed of the wind through the water (or an ice yacht can travel at 5 times the speed of the wind over the ice) those making the argument fail to note the angle to the wind that must be travelled. Given zero friction, to travel at twice the speed of the wind downwind you must travel at an angle of 60 degs to it (cos 60 = 0.5). To get to a point directly downwind you have to gybe half way and you get there, with your 100% efficient yacht, at precisely the same time as the free floating balloon. Paul Beardsell (talk) 15:06, 6 June 2010 (UTC)

Your trigonometry is simply incorrect, and you have deleted the graphic that shows the correct trignometry. I find this most disappointing.--Gautier lebon (talk) 12:47, 7 June 2010 (UTC)

Why, therefore, you may ask, do sailors bother to travel at an angle to the wind downwind? Because their boats and sails are so abysmally inefficient directly downwind. Sailing with your wind on the quarter is quicker than directly downwind, but still SLOWER than the free floating balloon to reach a point *directly* downwind. Paul Beardsell (talk) 15:06, 6 June 2010 (UTC)

Hence the "disputed" tag at the beginning of the article. Paul Beardsell (talk) 15:06, 6 June 2010 (UTC)

Further I strongly suggest that the cited refs do not support the assertion that in the America's cup downwind progress was quicker than a free floating balloon. If it is WP:SYN I cannot see how it was synthesized. But that or WP:OR neither are acceptable. Paul Beardsell (talk) 17:05, 6 June 2010 (UTC)

The only OR here is your own: you say that things that are said by relilable sources are impossible, but you do not provide any source that supports your assertion. We have been there before, I find it puzzling that we have to have the same discussion over and over again when it suffices to read the cited sources to understand why it is indeed possible to have a downwind VMG greater than windspeed.--Gautier lebon (talk) 08:41, 7 June 2010 (UTC)

No the onus is the other way. You want to include something then if I challenge it you must provide WP:VSs. Not just some self promoting web site from some hoaxters with corporate sponsorship. No! SciAm or New Scientist would do me. There is no onus on ME to say why what you say is wrong. You want to include material, you must support it. Please read WP:VS, WP:OR and WP:SYN. Thanks. Paul Beardsell (talk) 09:11, 7 June 2010 (UTC)

Indeed, but there were extensive discussions at an earlier stage, and numerous Wikipedia editors agreed that the citations provided were reliable and so the material was suitable for inclusion in Wikipedia. You have a different view, and I do think that it is appropriate to discuss that on this page, and to include a "disputed" tag in the article. But I don't think that it is appropriate do delete what represents a lot of work by many people until we have further dicussed it on the discussion page.--Gautier lebon (talk) 09:23, 7 June 2010 (UTC)

I agree. And I leave unobjectionable but questionable material on the page. But material with irregular citing of the hoaxters to support the hoaxters' claims, the WP:SYN citing of refs which DO NOT support the assertions made in the text, that comes OUT. It is not worthy of remaining in the pedia pending discussion. I believe WP policy suports me here. As does the (lack of) quality of the argument here resulting. Paul Beardsell (talk) 09:40, 7 June 2010 (UTC)

But you have added a flagrant OR, namely that a boat cannot reach the downwind mark faster than a balloon. You have deleted all the citations showing the contrary, and you have added that totally unsupported statement. Surely this is not how Wikipedia is supposed to be edited? If you have a citation to support your statement, please provide it.--Gautier lebon (talk) 12:49, 7 June 2010 (UTC)

Remove it if you must, but I added it to allow the unsubstantiated sentence preceding to remain. It goes, that goes. Paul Beardsell (talk) 12:06, 8 June 2010 (UTC)

The previous sentence is not unsubstantiated, it is supported by numereous citations.--Gautier lebon (talk) 11:34, 11 June 2010 (UTC)

Fallacious text cut from article

I have cut the following text from the article and expect to cut more:

Note that, if a boat can accelerate until it is sailing at 45 degrees off the apparent wind when sailing 135 degrees off the true wind, then its speed will be 1.41 times the speed of the wind. Thus its velocity made good downwind will be equal to the velocity of the wind. If it can accelerate until it is sailing closer than 45 degrees to the true wind, then its velocity made good downwind will be greater than the velocity of the wind: see the more detailed discussion in the section Speed made good below.

No! Never, ever is it possible for the hull speed multiplied by the cosine of the apparent angle to the wind to exceed the actual wind speed. No citation is given, and if one is, it would still be wrong! You cannot choose the speed and the angle independantly! They are not independant variables.

It is of course advantageous not to steer directly downwind when trying to reach a point directly downwind. But that is because sails never work well directly downwind. Steering on a broad reach is better than attempting a direct course but still you will NOT beat a free floating balloon.

Paul Beardsell (talk) 16:41, 6 June 2010 (UTC)

Actually, there were several citations, but apparently you did not read them, in particular the citations to ice boats and sand yachts. Please read citations before asserting that material is nonsense.--Gautier lebon (talk) 08:43, 7 June 2010 (UTC)

I DID read what I could. Some refs are to offline books I do not have. But I did not want to read them as I understand physical mechanics and I know no mecano-set sailing machine is going to disprove conservation of energy. BUT NAD THIS IS THE POINT THE REFS DO NOT SAY WHAT YOU WANT THEM TO SAY. They do talk about 5*windspeed but not about VMG>windspeed. Except for the hoaxters' site. Paul Beardsell (talk) 09:14, 7 June 2010 (UTC)

It is not about conservation of energy, because the energy contained in the wind is very large. It is about how much of that energy you can harvest in order to overcome resistance from the surface and the induced headwind. That is explained in the cited sources, please read them again, more carefully. You assert that [11] is a hoax site. But nobody else asserts that. What is your citation to support your assertion, other than your conviction that such a thing is not possible?--Gautier lebon (talk) 09:21, 7 June 2010 (UTC)

The onus is not on me. You want something in the encyclopedia, YOU must find the WP:VSs. Paul Beardsell (talk) 09:52, 7 June 2010 (UTC)

That is not correct. I and others contributed material based on citations. You challenge the reliability of the citations, which include a book published by a reputable publisher and written by a well-known sailor. So it is up to you to provide citations that indicated that the original citations were not in fact reliable.--Gautier lebon (talk) 12:19, 7 June 2010 (UTC)

I deny your citations supported the text you provided. Alternatively, the citations were to thought experiments here, or they were to the web site of the supposed heroes themselves. None of that meets WP:V Paul Beardsell (talk) 12:08, 8 June 2010 (UTC)

As you can see from the discussion below, you are the only person who takes that view. Everybody else agrees that the material was supported by reliable citations.--Gautier lebon (talk) 11:35, 11 June 2010 (UTC)

Removed section

I just removed the whole section on sailing downwind faster than the wind. It's all nonsense. I did try fixing it a bit but the only refs which actually supported the argument were to this talk page. The rest of it is to a HOAX and a set of links to perpetual motion machines. Paul Beardsell (talk) 17:19, 6 June 2010 (UTC)

That is your assertion, again not backed by any source. Whereas the material that you deleted was based on reliable sources. Please do not substitute your original research for verifiable citations.--Gautier lebon (talk) 08:44, 7 June 2010 (UTC)

Not reliable as per WP:VS. Paul Beardsell (talk) 09:28, 7 June 2010 (UTC)

That is your opinion, not the opinion of the many other editors who worked on this article.--Gautier lebon (talk) 12:17, 7 June 2010 (UTC)

There is much of merit in the article. Those editors have not provided questionable sources for the material they have added. The material I have removed is supported only by the claims of the hoaxters/heroes themselves on their own website. Not WP:VS. Paul Beardsell (talk) 12:10, 8 June 2010 (UTC)

This is not correct. You removed a great deal of material that was supported by perfectly reliable citations.--Gautier lebon (talk) 11:36, 11 June 2010 (UTC)

Please help, aeronautical engineers

The "propeller machine" needs to be explained. If sustained faster speed (rather than quick "hops") is possible, then it can be modeled and an expert can explain it. If the wheels and propeller alternate as prime mover, then how is equilibrium reached? Does the craft ride on a pressure wave? Do the air vectors form a standing wave in relation to the craft? Storing momentum and then accelerating quickly is cheating. What minimum speed over what minimum distance proves the novelty of the case? Anthony717 (talk) 17:50, 6 June 2010 (UTC)

It is explained, in several different ways, on the talk pages. And it is demonstrated at [12]. There is no alternation, it is a steady state situation, in which sufficient energy from the wind is captured to allow downwind progress faster than the wind itself.--Gautier lebon (talk) 08:47, 7 June 2010 (UTC)

This claim is unsubstantiated. Paul Beardsell (talk) 09:22, 7 June 2010 (UTC)

There is no need for WP to explain the unexplainable. Or to attempt to. We can just wait for a reputable journal such as Scientific American or New Scientist to report that it works and reflect their report here. This is *not* Popular Mechanics, we do not need to speculate, this is an encyclopedia. So until then we need do nothing and, even then, there is no urgency. Paul Beardsell (talk) 22:30, 6 June 2010 (UTC)

But for those who ache to be told it isn't a hoax, its a hoax! Paul Beardsell (talk) 22:30, 6 June 2010 (UTC)

Furthermore, aeronautical engineers are in particular not required. The credibility of an engineer can only be damaged by endorsing a perpetual motion machine. Paul Beardsell (talk) 22:30, 6 June 2010 (UTC)

Again, this is your unsupported assertion. [13] proves otherwise. It is not a hoax.--Gautier lebon (talk) 08:47, 7 June 2010 (UTC)

Perhaps, perhaps not. But "unsupported assertions" may appear on a Talk page. They may NOT appear in the encyclopedia themselves. Any assertion in WP itself which is challenged must be supported by WP:VS or face removal. That is WP policy. The hoaxters web site does not qualify as WP:VS. I note even they shy away from using the word "proof" and that the NLASA does not (yet) support the claims. But NLASA is not NASA so who cares one way or the other! "NLASA says Second Law of Thermodynamics is invalid" is a headline we won't see anywhere reputable soon. Paul Beardsell (talk) 09:51, 7 June 2010 (UTC)

One feature of all hoaxes is that it must take some people in! I know this is not a compelling argument. But conservation of energy is something which nearly all people believe in. Paul Beardsell (talk) 09:27, 7 June 2010 (UTC)

You keep talking about conservation of energy, but you never explain why this is violated. Once again, the energy contained in the wind is very large. An efficient device such an an iceboat can capture more than enough energy to overcome the frictional resistance (from the surface and the apparent headwind) to go 5 or more times faster than the wind. When you work out the trigonometry, it is obvious that downwind VMG is greater than wind speed. There is no violation of conservation of energy or any other physical law. Please provide a citation that says otherwise.--Gautier lebon (talk) 12:16, 7 June 2010 (UTC)

You continue to get this the wrong way around. What must be supported by WP:VS is that which is IN the article. Not so supported? It can be removed. I removed it. The only sources given for the claims are those of the claimants themselves. It would be helpful were I to provide refs for my assertions here but do not have to: This is not a pedia page it's a talk page. Paul Beardsell (talk) 12:13, 8 June 2010 (UTC)

Again: you deleted material that WAS supported by reliable citations. And you did that on the basis of assertions that cannot be proved (such as violation of conservation of energy) because those assertions are incorrect.--Gautier lebon (talk) 11:38, 11 June 2010 (UTC)

More unsupported text removed

I have removed this:

Other sailboats (such as the 18ft Skiff) can make good downwind at speeds faster than the wind. Indeed, it can be seen from the polar chart for the 18 ft Skiff that it can make good about 12 knots downwind at a windspeed of 10 knots, by jibing back and forth at about 140 degrees off the true wind. The polar chart in Figure PS1 of the cited book High Performance Sailing shows that boats that were sailing in 1996 were able to make good downwind at about 1.5 times the speed of the wind.

I followed the 1st citation (the yoavraz2 one). It does NOT say VMG is greater than windspeed. It says you travel at an angle to the wind and sometimes at a speed greater than windspeed across the earth, but it does NOT say ANYWHERE that VMG > windspeed. Remember VMG is speed towards the directly downwind point, not speed across the earth. Further, an interpretation by a WP editor of a diagram quite possibly not drawn to scale or maybe exaggerated in order to illustrate an argument is not a WP:VS verifiable source.

Paul Beardsell (talk) 08:21, 7 June 2010 (UTC)

Please read the book before saying that it does not way what it does indeed say. It is not an interpretation of a diagram, it is a direct summary of what the diagram shows, and what the text of the book itself says in several places. The book is easily available: please go to a library and read it (or buy a copy and read it) before challenging the material in question.--Gautier lebon (talk) 08:49, 7 June 2010 (UTC)

You obviously have the book. You can quote from it, therefore? Even so, if I find a book that challenges the laws of thermodynamics does that mean I can make outlandish claims on the thermodynamics page of an ENCYCLOPEDIA. Sailing DWFTTW would be in contravention of 2nd law of thermodynamics / conservation of energy, by the way. Paul Beardsell (talk) 09:25, 7 June 2010 (UTC)

I did quote from the book, but you deleted the quotes! Please explain how the second law of theormodynamics or the law of conservation of energy are violated. To do that, you need to show that the energy used by the boat as it progresses is greater than the energy that it captures from the wind. Please produce a citation that gives the equations and calculations. I (and the other editors) have produced citations of actual observations of the phenomenon. Please produce a citationt to support your bald that all those references are wrong or hoaxes.--Gautier lebon (talk) 12:13, 7 June 2010 (UTC)

Please feel free to re-add anything you genuinely feel is WP:VS supported which I have removed erroneously. But as a discussion has opened up you do, I think, need to specifically justify that, here, when you do. Paul Beardsell (talk) 12:14, 8 June 2010 (UTC)

Reversions

Practically every change I have made to the article has been reverted. I justified every one of the changes here on the Talk page. The reversion is unreasoned. So I have unreverted. Note: Nothing can be in the WP unless supportable by WP:VS. WP policy must be obeyed, like it or not. It is not for us to engage in WP:SYN or WP:OR. Read these policies, please, and ensure you comply with them before re-adding deleted material to the page. Thanks. Paul Beardsell (talk) 10:12, 7 June 2010 (UTC)

This is not correct. Your edits were not supported by citations. The article now includes unsupported assertions and original research. It cannot be allowed to stand as it is. In my opinion, it is your edits that violate WP policy, and that is why I reverted them. In turn, I would ask you to adhere to WP policy, which is to discuss disputes on the discussion page and not engage in editing wars. Clearly we need input from other editors.--Gautier lebon (talk) 12:02, 7 June 2010 (UTC)

You do need to realise that I do not have to show something is false to remove it from WP. I just have to show it is not properly supported by WP:VS. The onus on citations etc is on the person adding material. Paul Beardsell (talk) 12:18, 8 June 2010 (UTC)

Please feel free to remove any material which is not supported by WP:VS and which you know to be untrue. Paul Beardsell (talk) 12:16, 8 June 2010 (UTC)

Paul, seriously. You're wrong. You're hilariously wrong. I've waved this past any number of physicists, engineers, and sailors. Every time, they say "oh, of course that won't work", and then they do the math to "prove" it, and they say "oh, wait. I guess it does work. Neat!" It's a brain-teaser. It is counter-*intuitive*. But intuition isn't science... That ships can beat the wind downwind is something we have known for literally *centuries*. It's surprising, sure, but it turns out not to be impossible or anything. Please stop massively editing an article in a field you apparently know nothing about and are unwilling to learn. If you really want to have this discussion, go to a *discussion forum*, talk about it, exchange arguments, and come back here once you've either persuaded people or been persuaded. Wikiseebs (talk) 18:35, 10 June 2010 (UTC)

Article directions

1) Paul Beardsell I spent years at a research center specializing in aerodynamics, and I made the same points to Gautier lebon that you did. I discovered on more careful examination that I was wrong, and he was right. There's no violation of conservation of energy involved. You're drawing a false analogy to an object floating free in space, where it cannot exceed the velocity of "wind" impelling it. A boat is not floating freely, it has a keel. I've explained this elsewhere, so I won't repeat.

2) Although WP:V is a Wikipedia core value, the fascination with ruthless application of WP:V to every date, name, and fact is the hobgoblin of little minds. The key phrase there is "This policy requires that anything challenged or likely to be challenged", and this is taken by hobgoblins to mean EVERYTHING. If it meant everything, then it would say everything. The fact you have a disagreement does not necessarily mean that Gautier lebon has to justify himself.

3) On the other hand Gautier lebon, Paul Beardsell has a certain point about WP:SYN. Another pernicious behavior in Wikipedia is believing that because something has been printed, it is encyclopedic. This runs into problems in academic circles, for example, where there are 100s of papers on a subject, and some Wiki editor decides to pick-and-choose which are the most important. In practice these often end up being recent ones published on the Internet. What they should be is the pivotal articles defining the subject that are well-agreed upon as authoritative by that professional community. The selection of those articles should come, preferably, from ANOTHER WP:V source. I.e., the reference source should be the one picking the most important references, not the Wiki editor. This is rarely done — unfortunately the level of scholarship of the typical Wiki editor often does not tend to a wide, professional level of competence in a field. Hence "one off" references tend to be accepted.

I would call out the cited report of the work the experiment-in-progress by San Jose State University as an example of what should not be included. The experiment could fail to prove the hypothesis. It is not necessarily a significant, peer-reviewed experiment. It is crystal ball WP:CRYSTAL.

4) Paul Bearsell is also correct that these paragraphs, for example, does not belong in Wikipedia:

"At first, it would seem impossible to sail dead downwind faster than the wind: a wind-driven machine cannot progress dead downwind faster than the wind using only sails. This is because the apparent wind will be zero if the speed of the boat equals the speed of the wind, so the boat cannot possibly go any faster than that. However, in theory, it can sail dead downwind faster than the wind using only energy obtained from the wind while moving (that is, it does not need to stock energy while in the port). Some sort of mechanical device can be used to transfer energy from the surface on which the machine is moving in order to increase the speed of the machine."

Wikipedia is WP:NOT a textbook (Section 2.7). And another Wikipedia article is not a valid reference (let alone a talk page discussion!) Phrases such as "At first, it would seem" and "However, in theory" and "some sort of mechanical device" are signals that the article is straying into being a textbook. These are things professors might say in a classroom. They are not the formal language of an encyclopedia. Read a few articles at random in the Encyclopedia Britannica to get an idea where to anchor your language. Regards to both, Alpha Ralpha Boulevard (talk) 10:59, 7 June 2010 (UTC)

The comments from Alpha Ralpha are constructive. I have no problems with improving the article, and indeed there has been a great deal of constructive work in the past. However, I strongly feel that the edits by Paul Bearsell are inappropriate because they are not supported by any citations and contradict material taken from reliable sources. In my opinion, the article should be reverted to where it was before Paul Beardsell edited it, and we should discuss improvements on this page. That will allow the article to be improved, as opposed to its current status, which is most unsatisfactory.--Gautier lebon (talk) 12:07, 7 June 2010 (UTC)

It is well-known that boats can sail faster than the wind. There are thousands of examples, and it is well covered in the physics-of-sailing literature. One good example can be found here Physics of Sailing in Physics Today Magazine (note also the notes to that article for other sources). (Here is another source for references on the subject). Recently (the last four years or so) advances in materials technology have allowed boat builders to build very light craft with reduced drag which not only can sail faster than the wind they can achieve VMG faster than the wind calculated dead downwind. This is a fact. Editors who are arguing here that on one hand examples don't prove anything because it is "original research" and on the other hand, vector diagrams and equations are out-of-bounds because "Wikipedia is not a textbook" are making it impossible for this article to exist. The article needs to explain both the physics of wind-powered vehicles, and to provide examples that prove the case. If folks don't think this article is written well enough to prove the point, they should chip in and re-write it and find better references, not use their discomfort as an excuse to excise large chunks of the article and thus "prove" that you can't sail faster than the wind. I don't mind editors adding tags asking for specific cites or clarification, but deleting things that are demonstratively verifiable facts, is wrong. I wonder what Wikipedia would have said about the shape of the Earth in ~1480?

Last point first. An encyclopedia may have said the world was flat in 1480. And that would be correct for an encyclopedia. An encyclopedia reflects established science (even if it is wrong), not controversy. There is no room for controversy here. When a WP:VS such as SciAm or NS says it works then WP will say it works. Until then most we can do is present the controversy. We are not allowed to engage in WP:SYN or WP:OR in the article pages. I am happy enough to see it here, on the Talk page, but it cannot leak thru to the article until established as fact by an external verifiable source that satisfies WP:V. Paul Beardsell (talk) 08:25, 8 June 2010 (UTC)

No, it would not have been correct for a 1480 encylopedia to have stated that the world is flat, because all educated people, and all sailors, knew that the world was round since at least 400 BC. The 1480 encyclopedia should do exactly what everybody except Paul Beardsell wants to do. It should have explained that the world is obviously round because if you watch a boat disappers off the horizon it does not get smaller and smaller; on the contrary, first the hull disappears, then the mast slowly sinks out of sight. I suppose somebody, in 1480, would have tacked on a "citation needed" tag. Those people would probably tack a "citation needed" tag on the statement "the sun rises in the East". The point here is whether Wikipedia should contain verifiable facts that contradict common folklore. The answer to that is obviously yes. Lots of Wikipedia articles contain information that is not known to people that haven't done the research for themselves: that is the very purpose of any encyclopedia, including Wikipedia.--Gautier lebon (talk) 08:44, 8 June 2010 (UTC)

How petty! The point is not about whether the world is flat or not and when the consensus switched from one to the other. The point is that an encyclopedia is NOT controversial. That we all agree, surely? If something is controversial better it is NOT in the encyclopedia as we must be able to rely on the pedia, that's the goal. [As an aside, some clever Greeks knew the world was round millenia ago, they just couldn't carry their point. Maybe that's what you downwind fantasists may have to console yourselves with here.] Paul Beardsell (talk) 09:02, 8 June 2010 (UTC)

Indeed, we agree that controversial, unverifiable statements should not be included. For example, the controversial, unverifiable statement "a boat cannot sail downwind faster than a balloon" should not be included. The material that you deleted was not controversial. It was developed over a period of months by people who actually took the time to study the citations and undertand the issues. There is only one person who thinks that the material is controverial: Paul Beardsell. And the only argument put forward is a supposed violation of conservation of energy. But, as explained below, there is no violation of conservation of energy. So we are in a situation where one person is using his unsupported assertion to block the patient work of many others. Further, that person even disputed the suitability of material taken from a book published by a reputable publisher and written by a well-known expert. Surely this is not consistent with Wikipedia policies?--Gautier lebon (talk) 09:16, 8 June 2010 (UTC)

Sigh! The text I removed together with supposedly-supporting citations from the expert was removed BECAUSE the citation did not support the assertion. An editor wrote something which I knew was wrong and what was written was supported, supposedly, by a citation. I followed the link, it said nothing of the kind! I removed the text and the assertion. And I said what I had done here on the Talk page. That is WP policy. Paul Beardsell (talk) 12:23, 8 June 2010 (UTC)

The above paragraph (according to the Talk history written by Paul.h) summarises the current editing situation very well. The proposal for an article structure with (at least) an evidence and a physics explanation section is excellent. The latter needs good diagrams like the one proposed by Eyytee below. MrBeanBob (talk) 06:29, 8 June 2010 (UTC)

Sorry, but the diagrams are illustrative but misleading. They do not show the vectors at their correct lengths or directions. They are not proper physical vector diagrams. The numeric quantity e.g. 1.5 on the diagram is not derived but merely guessed at. It is difficult to draw good diagrams, I grant you. But those are little more than pretty pictures, sorry again. Paul Beardsell (talk) 08:38, 8 June 2010 (UTC)

Simple Diagram

Many (including some editors) seem to have a problem understanding how achieving a downwind-VMG greater than true-wind-speed is possible. I propose to include a introductory vector diagram, that shows how the sail can produce a force with a positive forward-component that propels the boat, under this conditions. I cannot upload files yet, so I put the proposed diagram here: [14]. If the diagram needs improvement, I can change it. Eyytee (talk) 22:13, 7 June 2010 (UTC)

Your diagram is very good! Also the two force diagrams at the bottom are illuminating. Maybe you could add the lateral force of the water acting on the keel/hull/dagger board balancing the large lateral component of the sail force, which is essential for the whole argument (without it the hot-air baloon argument would be correct). In addition I much agree with your first sentence. MrBeanBob (talk) 23:38, 7 June 2010 (UTC)

Good start, but the force diagram needs a drag vector, so the true boat velocity can be derived, not just a given...--Paul (talk) 00:49, 8 June 2010 (UTC)

There is no need for that (nice as it would be). All they need show is that there is a forward component of the force on the sail in conditions where the free floating balloon is being beaten to downwind.

This is exactly what the proposed vector diagram shows. A forward component of the force on the sail while going with a downwind VMG = 1.5 true wind speed.

You don't mean VMG (i.e. velocity made good to the desired [directly downwind] point), you mean speed over the ground.

This is factually not true. The proposed vector diagram clearly shows a downwind VMG = 1.5 true wind speed.

I never said that speeds faster than true wind velocity were impossible. And that isn't a proper vector diagram showing proper decomposition of forces. It's just a sketch supposedly showing what you want it to. Paul Beardsell (talk) 15:13, 8 June 2010 (UTC)

There is none. The forward force on the vessel disappears when (speed over the ground)/cos(angle to the true wind)=(speed of the true wind). That's the argument in a nut shell. Impossible. And any CORRECTLY drawn vector diagram makes this plain. Paul Beardsell (talk) 08:18, 8 June 2010 (UTC)

Paul Beardsell seems to suggest that the proposed vector diagram is NOT CORRECTLY drawn. Yet he fails to explain what exactly is not correct in the diagram. He merely makes assertions without providing proof or references.

It's like when something is incorrectly spelt in English. The literate ones don't need to be told the correct spelling. Those mathematically and physically illiterate cannot be explained to, and those that are don't need to be told. But, if you need a few pointers (ha!), start by properly labelling everything, say what is being decomposed into what, make the lengths proportionate to the speeds, if that is what you're drawing, or forces, if that is what your drawing. You're strumming on a guitar without having even tuned it. Paul Beardsell (talk) 15:13, 8 June 2010 (UTC)

what a properly drawn diagram shows

At the point where (speed over the ground)/cos(angle to the true wind)=(speed of the true wind) the sail provides no forward force (i.e. in the direction of the keel / wheels / skates). The slightest friction brings the vessel gradually to a halt. But, if all friction is eliminated the downwind point is reached at EXACTLY the same time as the free floating balloon. Paul Beardsell (talk) 08:33, 8 June 2010 (UTC)

This statement by Paul Beardsell is Original Research. It is not supported by any citation. It is also incorrect, as shown by the citations that Paul deleted from the original article. I will post more on this later.--Gautier lebon (talk) 08:46, 8 June 2010 (UTC)

It isn't OR. It's Physics 101. And even if it were OR, we are on a Talk page, and we can write here what is NOT allowed in the encyclopedia pages. I will not allow OR there. And it is not me who wants to put WP:OR and WP:SYN material there but others such as GL. Anything there has to be properly cited as per WP:V. Here, we can talk and argue but EVEN IF WE REACH A CONSENSUS what goes on the page itself has to be WP:V. Paul Beardsell (talk) 08:58, 8 June 2010 (UTC)

It is not Physics 101, and you have not provided a citation to show that it is. Worse, you have added to the main article the statement “Nevertheless this remains slower than the time taken for a free floating balloon to travel the downwind track directly”. This is Original Research, not supported by any citation, in the article itself.--Gautier lebon (talk) 09:11, 8 June 2010 (UTC)

I will continue to remove material from the actual article which does not satisfy WP:V. Paul Beardsell (talk) 08:58, 8 June 2010 (UTC)

It seems many of the rest of you cannot do force diagrams properly, and seem to want to disregard 2nd law of thermodynamics, as if science is not a matter of fact but merely what you would like to believe. Paul Beardsell (talk) 08:58, 8 June 2010 (UTC)

It might be the other way around, given that all text books support the force diagrams that Paul Beardsell is criticizing.--Gautier lebon (talk) 09:11, 8 June 2010 (UTC)

No they don't or there's a revolution in physics happening and it all started in Yachting Monthly. Paul Beardsell (talk) 15:43, 8 June 2010 (UTC)

Conservation of energy

Paul Beardsell asserts (if I understand correctly) that VMG cannot exceed wind speed because to do so would violate the law of conservation of energy. But this is not correct. A balloon that drifts downwind does not use any energy (even though the wind itself does use energy, for example to overcome the friction over the ground). Thus a device can progress dead downwind at the speed of the wind without capturing any energy from the wind.--Gautier lebon (talk) 09:09, 8 June 2010 (UTC)

So what? Paul Beardsell (talk) 09:30, 8 June 2010 (UTC)

So a balloon does not use any energy to drift downwind at the speed of the wind. If a boat can capture some energy from the wind as it moves downwind, then the boat can progress downwind faster than the speed of the wind without violating the law of conservation of energy (since it takes zero energy to drift at the speed of the wind, not counting surface friction). The boat needs the energy to overcome the friction from the surface and, more importantly (especially for an iceboat) the resistance from the induced apparent headwind.--Gautier lebon (talk) 15:42, 10 June 2010 (UTC)

If a device captures some energy from the wind (or has an internal power source), then it can progress downwind faster than the wind. It needs the energy in order to overcome the resistance from the surface (if it is a sailboat or iceboat or sand yacht) and in order to overcome the resistance of the apparent headwind induced by its motion.--Gautier lebon (talk) 09:09, 8 June 2010 (UTC)

This is patently not necessarily true! It assumes the conclusion being "proven". And it's muddled, conflating force with energy. Paul Beardsell (talk) 09:29, 8 June 2010 (UTC)

All right, let's take it step by step. Energy =force x distance. The energy from the wind is required to overcome the resistance encountered by the device when it progresses some distance over some surface. Is that clear? If not, PLEASE go read basic text books which explain this.--Gautier lebon (talk) 09:44, 8 June 2010 (UTC)

Here we have no difference. Paul Beardsell (talk) 10:19, 8 June 2010 (UTC)

That a device can capture energy from the wind while moving dead downwind, and thus achieve dead downwind speed greater than wind speed, can be seen from Talk:Sailing_faster_than_the_wind#Deleted_thought_experiment. Thus, there is no issue related to conservation of energy.--Gautier lebon (talk) 09:09, 8 June 2010 (UTC)

I say the thought experiment is flawed as it takes as a premise that which it purports to prove, again. This is a circular argument. Paul Beardsell (talk) 09:29, 8 June 2010 (UTC)

The tought experiment does not take any premise. It shows how one can build a device that, by storing energy, can achieve average downwind progress faster than the wind.--Gautier lebon (talk) 09:50, 8 June 2010 (UTC)

There were several thought experiments. The one to which I referred were the corkscrewing sailors on the cylinder. Paul Beardsell (talk) 10:19, 8 June 2010 (UTC)

The real question is whether a real boat, such as an iceboat, can capture enough energy from the wind when sailing downwind to overcome the induced apparent headwind and the friction from the surface. That question cannot be answered theoretically, you actually have to build a device and test it. But that is precisely what has been done, for the past 30 years or so, and the original article had ample citations, including from Bentwaithe, who is an authority on the matter.--Gautier lebon (talk) 09:09, 8 June 2010 (UTC)

No it can be answered theoretically because I say it cannot be done, this downwind malarky, theoretically. For something to be done practically when theoretically it can NOT be done falsifies the theory. But the theory on which I am depending is Newtonian mechanics. That's what these downwind chappies say they are falsifying, whether they know it or not. I did start arguing this from a conservation of energy POV but GL said no, consider the force diagrams. Well, the magical force diagrams presented always have a forward force, as if this were a given. And they are mere sketches! I will present proper force diagrams. Paul Beardsell (talk) 09:29, 8 June 2010 (UTC)

So we should take your statement "I say it cannot be done" as sufficiently authoritative to conclude that Benthwaite does not know what he is talking about? You previously argued conservation of energy. You are now invoking Newtonian mechanics. But is is precisely Newtonian mechanics that explains why it is possible to achieve downwind VMG greater than wind speed. Again, the material that you deleted explained that to the satisfaction of many other editors, including several physicists. When looking at this from the Newtonian point of view, please consider that the only forces that count are those induced by the APPARENT wind and by the resistance of the surface.--Gautier lebon (talk) 09:50, 8 June 2010 (UTC)

No! You need take nothing I say on my authority alone. I am NOT trying to put questionable material into WP. You are. I am having a discussion about physical mechanics on a talk page. That's all. You are free to ignore what I say. Paul Beardsell (talk) 10:19, 8 June 2010 (UTC)

Yes, you are trying to put questionable material into WP. You inserted the sentence to the effect that a boat cannot outrun a balloon. You are not merely having a discussion on the talk page, you made major deletions to the article, including deleting all the citations that supported the opposite of your thesis. I am not free to ignore what you say, because you have said that you will continue to delete such material (and citations) from the article.--Gautier lebon (talk) 13:38, 8 June 2010 (UTC)

Further, a cursory examination of the actual performance of USA 17 during the 2010 America's Cup should convince anybody. The yacht covered its downwind leg at VMG of 19 knots, in winds of 5-10 knots. That is, VMG was well over 2 times wind speed. Granted, the wind shifted a bit, but the shifts were not large (less than 20 degrees) and not constant. So there is no way that a balloon would have drifted down to the downwind mark at anywhere near the speed of USA 17. Again, please consider the basic data: downwind VMG of 19 knots in 5-10 knots of wind. What more evidence is required, given that numereous citations (alas, deleted by Paul Beardsell) explain how this is achieved?--Gautier lebon (talk) 09:09, 8 June 2010 (UTC)

This is all unsupported baloney not supported by the citations given. Nowhere is this AC stuff said in terms presented here. It's WP:SYN which is why I removed it from the article. Paul Beardsell (talk) 09:29, 8 June 2010 (UTC)

It was not VMG toward the windward point, it was speed thru the water. All agree, speed thru the water can be faster than the wind. But only at an angle where (speed thru the water)/cos(angle to true wind) < (speed of true wind). And that means the free floating balloon will beat you every time to the directly windward point. Also in a yacht race the DW buoy is not necessarily DW directly as wind changes. The speed to the DW buoy can be greater than true wind speed if the DW buoy is not directly downwind. But a free floating balloon still beats you to the line drawn thru the bouy perpendicular to the wind. Every time. And no sailing book can truthfully say different and no cited reference has so contradicted this truth. Paul Beardsell (talk) 09:36, 8 June 2010 (UTC)

It was not speed through the water, it was speed over the ground. Downwind VMG is the time taken by the boat to cover the distance beween the upwind mark and the downwind mark. The wind changes were not significant enough to affect the calculations. Contrary to what you say, Benthwaite directly contradicts your assertion. Bentwaithe's book (published by a reliable publisher) flats states that downwind VMG can be greater than windspeed, which means that the boat reaches the downwind mark faster than a free floating baloon.--Gautier lebon (talk) 09:42, 8 June 2010 (UTC)

Speed over the ground is NOT REPEAT NOT VMG towards the windward point. Tides aside, speed thru the water and over the ground are the same. Bentwithe does not (from your supplied quotations) say VMG-directly-towards-directly-windward-point exceeds true windspeed. Paul Beardsell (talk) 10:19, 8 June 2010 (UTC)

Actually Bentwaithe does say exactly that: VMG downwind (meaning speed through the water/over the ground in the dead downwind direction) is greater than wind speed. If you had the book, you would see it.--Gautier lebon (talk) 13:36, 8 June 2010 (UTC)

Please feel free to quote him, directly, here. The problem is either you misunderstand or he is wrong, as the Great Bentwaithe has surely not overturned classical mechanics? Paul Beardsell (talk) 15:41, 8 June 2010 (UTC)

I already quoted him adequately in the material that you deleted. Nobody is overturning classical mechanics, the problem is that you are misapplying certain basic physical principles, as many have tried to explain to you, see below.--Gautier lebon (talk) 15:42, 10 June 2010 (UTC)

factual Dispute initiated and sustained by PB

This article was developed collaboratively over a period of many months. As seen above, there was extensive discussion and a stable version was finally produced. Recently, Paul Beardsell (PB) has asserted that the article is incorrect. This implies that all the people who worked on the article made mistakes. Of course that is possible and the matter should be discussed. But I do not think that we are going about this the right way, as explained below.--Gautier lebon (talk) 09:38, 8 June 2010 (UTC)

procedural issues

According to my understanding of Wikipedia policies, PB should have tagged the article as being the subjet of a dispute (which he did) and then discussed the matter on the discussion page. This is not what PB did. PB proceeded to delete material that was supported by citations, arguing that the citations were wrong. PB goes so far as to dispute information derived from a book by Bentwaithe, a known authority (the book is published by a reputable publisher). Surely this is not compatible with Wikipedia policies.--Gautier lebon (talk) 09:38, 8 June 2010 (UTC)

Worse, PB added to the main article the statement "[a boat's downwind progrss] remains slower than the time taken for a free floating balloon to travel the downwind track directly". PB does not provide any citation to support this assertion. It is thus Original Research that cannot be allowed to remain in the article. Further, the assertion is directly contradicted by the citations that PB deleted.--Gautier lebon (talk) 09:38, 8 June 2010 (UTC)

substantive issues

PB asserts that downwind VMG cannot exceed the speed of the wind, because that would violate the law of conservation of energy. He provide no citation to support that assertion. As explained above, there is no violation of the law of conservation of energy.--Gautier lebon (talk) 09:38, 8 June 2010 (UTC)

PB's hypothesis, if you work out the trigonometry, means that VMG must be less that 1/cos(gamma) times wind speed, where gamma is the angle between dead downwind and the course (that is, gamma = 0 if dead downwind). In terms of course with respect to the upwind mark, this means that VMG, in terms of multiples of wind speed, would be limited to 1 for 180-degrees (dead downwind), 1.1 for 155, 1.22 for 145, 1.41 for 135, 2 for 120, 2.9 for 110, 3.9 for 105, 5.7 for 100, and infinite for 90. Of course infinite is not possible, because friction and the limits of how close the boat can sail to the apparent wind will come in. So PB's hypothesis is that VMG, as a multiple of wind speed, must be less than the minimum of the numbers given at the now deleted section Sailing_faster_than_the_wind#Speed_made_good and the numbers given above. But that hypothesis is falsified by published polar charts and by information on iceboats, which can go 5 times faster than the wind while sailing lower than 100 degrees off the wind. PB claims that all those citations are unreliable and incorrect. But the fact remains that there are citations that contradict PB's hypothesis. Also, there should be a physical explanation to support PB's hypothesis: what physical phenomenon limits to boat to VMG=1? As noted above, it cannot be the wind, because what counts is the apparent wind, and that would not limit VMG to 1. And it cannot be conservation of energy. Please also note the following quote from ThinAirDesigns, who is apparently a graduate student in aeronautics: "Most involved here in these discussions acknowledge that it's possible to steady state sail a traditional sailing rig at a fixed angle to the wind where the downwind VMG of the craft is greater than 1x windspeed (even 2x, 3x ...). Those who do not agree with this should review the data collected by NALSA (nalsa.org) on the topic." (see Talk:Sailing_faster_than_the_wind#DDW_faster_than_the_wind_thought_experiment). As stated on their web site, several students, and a professor, have built a device that has proven that it is possible to progress dead downwind faster than the wind, see [15]. So, if PB's hypothesis is correct, then (1) a lot of people have gone to a lot of trouble to fabricate false or misleading reports and (2) many people, including graduate students and professors, have been fooled into believing the impossible. Further, as an experienced sailor stated:--Gautier lebon (talk) 09:38, 8 June 2010 (UTC)

VMG: Let's be clear. VMG is the speed towards your target point, not speed over the ground. GL and ThinAirDesigns seem to change the definition of this term from argument to argument, and this has led I believe to GL's misinterpretaion of Bentwithe (sp?). Boat speed can be greater than wind speed, yes. VMG can be greater than boat speed, yes, but not for all desired points! When the desired point is a point directly downwind, VMG (i.e. towards that directly downwind point) is never greater than windspeed, but boatspeed over the ground (i.e. currents aside, thru the water) may exceed windspeed while attempting to get to that dead downwind point. The angle at which you travel means however that (waterspeed)/cos(angle travelled to true wind) < (true wind speed), and that allows the free floating balloon to beat you, every time. Faster than windspeed has never ever been denied. What is denied is that you can independently choose your speed and your angle as implied by a diagram I deleted from the article. Paul Beardsell (talk) 10:36, 8 June 2010 (UTC)

What we are discussing here is downwind VMG, that is, velocity made good in the dead downwind direction (in vector terms, the component of the speed vector that points in the downwind direction). We are not talking about VMG in any other direction. You again assert that downwind VMG cannot exceed wind speed. But Bentwaithe says otherwise, and provides polar charts that show otherwise. The data from the America's Cup also shows otherwise. The diagram you deleted did not show that you can independently choose your speed and angle. It showed the relation that MUST hold between speed and angle, given the laws of trignometry. The question then is whether or not those particular combinations can be achieved in practice. Again, data provided in several references (all deleted by you) show that indeed those combinations can be achieved in practice by iceboats, sand yachts, and some high-performance sailboats.--156.106.202.4 (talk) 13:29, 8 June 2010 (UTC)

If your book says that, it is wrong. If the data says that, it is wrong. Yachting's achievements are many but overthrowing classical mechanics is not one of them. See new section below. Paul Beardsell (talk) 15:17, 8 June 2010 (UTC)

Nobody is overthrowing classical mechanics. The issue is that you are misunderstanding and misapplying the relevant physical concepts. Many of us have tried to explain this to you, see below.--Gautier lebon (talk) 15:44, 10 June 2010 (UTC)

"VMG, in terms of multiples of wind speed, would be limited to 1 for 180-degrees (dead downwind), 1.1 for 155, 1.22 for 145, 1.41 for 135, 2 for 120, 2.9 for 110, 3.9 for 105, 5.7 for 100, and infinite for 90" thanks for working those out. Very handy. So... I need to find a boat that will go faster than 1.41x TWS @ 135 degrees off the wind. Many boats can do that."

Name the boat. Paul Beardsell (talk) 10:26, 8 June 2010 (UTC)

Any iceboat. Look at the NALSA web site.--Gautier lebon (talk) 15:37, 10 June 2010 (UTC)

dispute: proposed resolution

I propose that we revert the article back to where it was before PB started editing it, but with a "diputed tag" and then use this discussion page to agree what, if any, modifications are needed.--Gautier lebon (talk) 09:38, 8 June 2010 (UTC)

The standard way forward

There is no need to personalise this. Nevertheless I stand by what I have done. I have removed text fromm the article not properly supported as per WP:V. Several citations were to thought experiments on this Talk page! Others were to the web site of the faster than the wind downwind device. It is those questionable assertions (to be polite) which I removed from the article. Also removed were those assertion resulting from WP:SYN and WP:OR. This is agreed (in part at least by GL) and others have said some of the text should not have been included. The GL-proposed solution is not the WP way. If you want to reinclude the some text then please DO SO, FEEL FREE, I WILL NOT OBJECT if it is either obviously non-controversial or if it is supported by what is obviously acceptable as per WP:VS. The WHOLESALE reversion of my edits would seem to imply that I have done nothing in value. Just do it on a one by one basis, being careful to state OBJECTIVELY and to back this up. Paul Beardsell (talk) 10:13, 8 June 2010 (UTC)

For example. "The XYZ Group claimed 33 remember 2020 that they had achieved faster than the wind downwind speeds.[3rd party citation]" is acceptable. What is not is "On 33 remember 2020 FTTWDW speeds were achieved.[XYZ Group]" Paul Beardsell (talk) 10:13, 8 June 2010 (UTC)

That might be a path forward, but it would result in the restoration of the entire section on VMG, which you have, so far, violently objected to. Let's give others a chance to comment, and maybe we can then agree a path forward.--Gautier lebon (talk) 10:16, 8 June 2010 (UTC)

Is is a standard way forward. You replace anything you like but only if not saying claims are facts, and as a VERY STRONG preference using 3rd party citations, not from the parties themselves. Please see WP:V. Paul Beardsell (talk) 10:22, 8 June 2010 (UTC)

I too was involved in lengthy discussions on many of these points at Talk:Sailing#Downwind faster than the wind. I was sceptical about the physics, as well as the references and the WP:OR. At one point I too tried to clarify the terminology, saying, "Let us agree at least that we are talking about sailing downwind faster than the wind, not just sailing faster than the wind, and also that we are not talking about coasting downwind faster than the wind immediately after a very fast beam reach."

The physics

In the end it was this discussion above that convinced me that we don't have a fundamental problem with the physics, or any requirement for previously-stored energy etc. Alpha Ralpha Boulevard's spaceship-and-gun model described above has the true wind at 90 deg to the boat and so there is no progress downwind. However, my contribution to that model shows that it is the boat's ability to sail close-hauled (while still overcoming friction and drag) that is the limiting factor. (Paul B, you mention above that there must be a limit, or we probably have 'perpetual motion' - that is it). It is only one more step to imagining the true wind at, say, 135 deg, the boat accelerating until it is again close hauled 10 or 20 deg off the apparent wind, and all the physics is in place for VMG downwind greater than the true wind speed, with gybes to reach a downwind point. All this talk about iceboats, sandyachts and spaceships on rails comes about because real sea-going boats rarely can sail much better than 45 or 40 deg off the apparent wind. Some modern ultralight catamarans may be able to do this in calm water.

The references, the OR and the SYN

Here I have to agree more with Paul B. Some of the sourcing here was not up to standard, and it needs to be. We cannot say that all this trigonometry, thought experiments, models and then real polar diagrams are 'just connecting obvious facts'. There is far too much synthesis required for some of the statements that have been removed. If all this is true and downwind VMGs are being recorded greater than windspeed, then it won't be long before they start appearing explicitly described as such in reliable secondary sources. Until that happens, I think we have to be patient and wait for these sources to appear. In the meantime, the title of this article is 'Sailing faster than the wind' and there is plenty that is well-sourced to say about that in general before getting into downwind VMGs greater than windspeed. I have not reviewed all the sources and so can't say how much of what we had was well-sourced, but some of it certainly was not. --Nigelj (talk) 13:09, 8 June 2010 (UTC)

Nigel: I can accept most of your suggestions. Regarding "it won't be long until they start appearing explicity described as such in reliable secondary sources", sorry, but this is all so obvious to the people who sail these machines that they don't see the need to write it up. That is also the reason why there aren't articles in refereed physics journals: it is too obvious to be published in a referred journal. I've scoured for write-ups, and found the Bentwaithe book and the NALSA web site. I agree that those are not exactly secondary sources, but it seems to me that they are close enough. In particular Bentwaithe summarizes data regarding various boats, so that part of his book is a secondary source.--Gautier lebon (talk) 13:34, 8 June 2010 (UTC)

Yes. You are going to have a hard time finding a paper in a physics journal on the revolutionary topic "Mixing red and yellow paint sometimes produces orange paint." Wikiseebs (talk) 18:53, 10 June 2010 (UTC)

There are other reasons why something doesn't get published in refereed journals. E.g. they're laughably wrong. Paul Beardsell (talk) 14:59, 8 June 2010 (UTC)

Yes, but this is not one of those situations.--Gautier lebon (talk) 15:45, 10 June 2010 (UTC)

Physical mechanics

I had started by saying this is WP:OR but no, that's giving me airs and graces. This is plain classical mechanics, unadorned. It's fact, plain and simple. There is no need to put this in the article, this below is the reason other stuff must not go in the article. This is high school physics only. This could easily all be substantiated from WP articles, but there is no need, as it so uncontroversial. If you disagree with it then you are not literate in the most basic physics. Sorry. Leave aside your beliefs that sailing downwind with a VMG towards the directly downwind mark is possible. Leave aside what you've read the skipper of Oracle in the AC as having said. Just stay with the physics. I write this just to try and shake your convictions ever so slightly.

In order for one object to propel another in a given direction (consider two moving balls, or whatever) the first must have a component of it's motion in that direction relative to the motion of the second object. If I am travelling south at 10mph and you collide with me and I end up travelling south at more than 10mph then you must have had a southerly component to your velocity of more than 10mph. Otherwise the collision would have slowed me down in that particular direction. Uncontroversial, and of course we can decompose any particular motion so that it consists of the sum of one NS vector and one WE vector. When considering changes in NS velocity the WE velocity of the colliding objects van be disregarded. That is what vector decomposition lets us do, and it's done all the time in high school and undergraduate physics. It's not controversial and it's not rocket science. (Well, actually it is rocket science, but you get my drift, no pun intended).

So when a particle of the air collides with my yacht and the yacht is accelerated in a particular direction, the particle of the air must have had a velocity component in that direction faster greater in magnitude than the speed velocity component of the yacht in that particular direction.

The question then is, and you should all have seen this coming, if the yacht is going faster than the air in a southerly direction, how can collision with the air accelerate it in a southerly direction? And, sorry to disappoint, that's a rhetorical question, there is no satisfactory answer. Therefore sailing downwind VMG faster than the air is impossible. QED.

Yes, we do need a diagram, the one showing how the true wind is shifted forward and becomes an APPARENT wind that allows the boat to accelerate past the speed of the true wind. Any sailor knows about apparent wind shift and the resulting decrease or increase in apparent wind speed. You deleted the diagram that explains this.--Gautier lebon (talk) 07:44, 9 June 2010 (UTC)

You don't need a diagram, do you?

Paul Beardsell (talk) 14:52, 8 June 2010 (UTC)

Then someone says oh yes you can! And they're the skipper of an America's Cup yacht. Or they have endless qualifications, and they've read every book on yachting, and they've maybe even written one. Or someone has a PhD in Physics and they disagree? Well, then they're wrong, they forget the basics, if they ever knew them.

Paul Beardsell (talk) 14:57, 8 June 2010 (UTC)

criticism 1

"So when a particle of the air collides with my yacht and the yacht is accelerated in a particular direction, the particle of the air must have had a velocity component in that direction faster greater in magnitude than the speed velocity component of the yacht in that particular direction."

If the above paragraph was true boats could not tack UP wind, which is an observed fact for centuries.(Eyytee (talk) 15:52, 8 June 2010 (UTC))

The wind force experienced by a sail is perpendicular to the set of the sail. That force is most conveniently decomposed into two forces at right angles to one another (the vector sum of which is the force on the sail). The first force is in the axis of the vessel i.e. in the rolling, ski-ing, keel direction. The other force is at right angles to that, the one that tends to tip the vessel to the side. When the set of the sail is such that the axial force is forward that drives the boat forward and vv. If on an upwind tack the keel/whatever is at 40 degs to the wind and the sail is at 20 degs then a proportion of the force experienced by the sail will be in a vessel-forward direction. If the keel is at 40 degs to the wind but the sail at 60 then there will be a backwards force. None of this contradicts the classical mechanics. We have found the component of the force necessary to explain the upwind sailing. Paul Beardsell (talk) 16:09, 8 June 2010 (UTC)

This is correct. And if you work out the force diagrams for an iceyacht sailing at 135 degrees of the true wind, you will see why it can accelerate to 6 times the speed of the wind, and thus achieve VMG far greater than wind speed. I will work out those diagrams and publish them here, but it will take me a few days.--Gautier lebon (talk) 07:47, 9 June 2010 (UTC)

It'll take longer than that. Paul Beardsell (talk) 08:07, 9 June 2010 (UTC)

No, it won't, because I have already done them by hand. What will take time is to make them pretty.--Gautier lebon (talk) 15:35, 10 June 2010 (UTC)

Nobody here claimed that tacking upwind contradicts classical mechanics. It just contradicts your initial statement on the top of this section. On an upwind tack the air doesn't have a velocity component in the direction of the boat's acceleration which is greater than the boat's velocity component in that direction. Therefore your statement, on which you base your entire argument, is wrong. Eyytee (talk) 22:22, 8 June 2010 (UTC)

We're comparing components of [vector] velocities in a particular direction, not [scalar] speeds (talk) 06:26, 9 June 2010 (UTC)

Then please explain what you mean by "faster" without invoking scalar speeds, when you say "velocity component in that direction faster than the speed of the yacht in that particular direction"? What do you compare and how? Eyytee (talk) 07:57, 9 June 2010 (UTC)

Give me just a little slack. It would have been technically more correct to say "greater in magnitude" than "faster", but I suspect you did know that's what I meant. I will make that adjustment to my original text, thanks. Paul Beardsell (talk) 08:07, 9 June 2010 (UTC)

I gave a new counter example to your claim based on your clarification. Find it below. Eyytee (talk) 11:14, 9 June 2010 (UTC)

and I am preparing example(s) to illustrate. Note also that 5 > -6 (if you find that patronising I apologise but there are lots of things that simple which I am having to explain), which is why sailing towards the wind presents no fundamental problem in my argument. It is DOWNWIND TO A POINT QUICKER THAN A BALLOON which is impossible. Examples in prep. Paul Beardsell (talk) 06:26, 9 June 2010 (UTC)

Don't spend too much time on it, because sail-powered vehicles CAN get to a point downwind faster than a balloon. Are you saying you don't believe yachts like USA-17 and almost any iceboat or land-yacht can't achieve VMG downwind at a multiple of the true wind speed????--Paul (talk) 06:45, 9 June 2010 (UTC)

You misuse the term VMG. By VMG we mean the velocity (not speed) towards the desired point, which in our case, is the point directly downwind, the point towards which the balloon is drifting. As to having travelled on a downwind tack faster than the speed of the wind I have done so myself! But the ice yacht travelling at 3x windspeed over the ice does so at such a shallow angle that it does not get to the downwind point before the balloon. The ice/land/sea yacht is constrained thus, downwind: (speed over the ground)/cos(angle to the true wind) < (speed of the true wind) (speed over the ground) * cos(angle to the true wind) < (speed of the true wind) The term on the left of the inequality is component of the yacht's velocity directly downwind, the term to the right is that of the balloon. If the inequality is not true then there is no possible impulse of the wind on the yacht in the windward direction. Paul Beardsell (talk) 07:18, 9 June 2010 (UTC)

There is progress here! You (nearly) talk about the same thing: VMG = (speed over ground)*cos(angle to the true wind) (I guess we all agree it should be * and not / : VMG < speed over ground and cos ≤ 1). The "only" remaining difference now is that VMG > speed of the true wind (parallel vectors pointing in the same direction) has been achieved by many crafts, not least USA-17! That's an empirical fact, and there are models ('explanations' if you want) in the framework of classical Newtonian mechanics. MrBeanBob (talk) 07:39, 9 June 2010 (UTC)

thanks for spotting and fixing my typo Paul Beardsell (talk) 07:51, 9 June 2010 (UTC)

You and others allude to this evidence and then fail to produce it. This does not surprise me: One can talk of the impossible, one cannot do the impossible. Paul Beardsell (talk) 07:47, 9 June 2010 (UTC)

No, the issue is that you are refusing to accept multiple citations that disprove your assertion.--Gautier lebon (talk) 15:35, 10 June 2010 (UTC)

Velocity = speed. Downwind VMG = progress over the water (or ground) towards the downwind mark = cos(ang) time velocity. USA 17 had VMG of 19 knots in 5-10 knots of wind. That is evidence. The models and explanations are found in the material that you deleted, which was all supported by citations, in particular to Bentwaithe's book. Benthwaithe provides polar charts showing VMG greater than wind speed.--Gautier lebon (talk) 07:49, 9 June 2010 (UTC)

No USA17 did not! It had a VMG to the mark but the mark was NOT directly downwind! This point has been made to you already by me and on another article's talk page by someone else. You did say you were sending me extract's from B's book. I have not received them. But no matter, I am sure. Paul Beardsell (talk) 07:54, 9 June 2010 (UTC)

I have sent you the extracts by E-Mail on the morning of 9 June. If you have not received them, then please send me an E-Mail to that effect. Re USA 17, the mark was dead downwind when the race started, and the wind shifts were not significant. So, for all practical purposes, the VMG to the mark was downwind VMG.--Gautier lebon (talk) 15:35, 10 June 2010 (UTC)

VMG <= boat-speed. Where the desired point is directly downwind, VMG <= windspeed. Note we talking about the component of the boats velocity directly downwind, not its speed over the ground. Have I said that before? Paul Beardsell (talk) 07:56, 9 June 2010 (UTC)

Yes, we understand what you are saying. The problem is that published polar charts show the opposite, as does data from USA 17, despite your skepticism (the wind shifts were nowhere near big enough to counter the fact that USA 17 had a downwind VMG of 19 knots in 5-10 knots of wind).--Gautier lebon (talk) 15:35, 10 June 2010 (UTC)

I have a very simple counter example that disproves PB's statement at the top of this section (in its current form) : Boat is moving perpendicularly to the true wind, and accelerates forward. The magnitude of the velocity component of the air in the direction of the boat's acceleration is zero. The magnitude of the velocity component of the boat in the direction of the boat's acceleration is greater than zero. This is exactly the opposite of PBs claim, that the magnitude of the air's velocity component (in boat's acceleration direction) must be greater than the magnitude of the boat's velocity component (in boat's acceleration direction) Eyytee (talk) 11:14, 9 June 2010 (UTC)

criticism 2

Paul Beardsell is making a fundamental error in the above analysis. He assumes that the boat interacts only with the air mass. He neglects the interaction with the water. While in reality the resulting acceleration of a boat depends on both forces(keel and sail), and vector diagrams show that the acceleration can be partially opposed to the apparent wind direction(Eyytee (talk) 15:52, 8 June 2010 (UTC))

Apparent wind direction is usually a red herring in this type of discussion. It is useful if you want to explain what is happening from the perspective of someone IN the boat. No, as physics allows me, I will continue to look at this from the stationary (in comparison to the ground) spectator viewpoint. (Otherwise that the ground is moving relative to the observer makes it more complicated - our target point would be moving too!) Having thus being allowed to discard apparent wind, where is the component of the wind pushing the vessel faster downwind than the wind itself!?!? There cannot be one. Paul Beardsell (talk) 16:14, 8 June 2010 (UTC)

Apparent wind is NOT a red herring. The sail sees only apparent wind and can react only to the apparent wind. This is elementary Newtonian physics.--Gautier lebon (talk) 07:59, 9 June 2010 (UTC)

What is also elementary is that the analysis can be done from a spectator's POV, one who is not in the boat and one who does not experience apparent wind. That is what is meant by the equivalence of frames of reference. Paul Beardsell (talk) 08:29, 9 June 2010 (UTC)

Apparent wind direction and velocity is not a red herring. It is part of the physics of what allows a sail powered craft to travel faster than the wind. The sail is an airfoil, not just a flat obstruction to the wind. An airplane does not fly because the wing is tilted at an angle such that the wind pushes the plane up, it flies because of a pressure difference between the top and bottom of the wing caused by Bernoulli's principle. For sailing craft that travel faster than the wind, the force generated on the airfoil by the apparent wind is an important part of the force driving the craft. It isn't a perpetual motion machine, first, because it won't work without wind, and second, it does have a limiting case where drag prevents further acceleration. I have been sailing for close to 50 years, and when I first heard that modern mult-hulls sail downwind with apparent wind forward, I didn't believe it. But I did some research, and read up on vector analysis, and saw the truth. Everyone has a bit of difficulty understanding how this can be, but it is. Did you read the Physics Today article I linked to, above?--Paul (talk) 16:37, 8 June 2010 (UTC)

Very much a side issue but your understanding of aircraft flight is also limited! Whatever the mechanism, Bernoulli pressure differnces, whatever, those are one step removed from the basics. Newton still applies. To exert a force upwards a force force downwards is required (Newton 3: every force etc). Whatever the mechanism, whatever the meta-explanation, airfoil lift RESULTS from the directing of the airflow downwards. Flight is not a special case: Newton applies. [Bernoulli simply helps explain the most effective shape of the airfoil.] Paul Beardsell (talk) 19:51, 8 June 2010 (UTC)

Paul H has it right. An aircraft's wing sees only the apparent wind. That is why you don't want to take off with a tail wind: it would take too long to accelerate enough so that the apparent wind allows you to take off. All pilots are well aware of the fact that only the apparent wind counts, please read any elementary manual on flying.--Gautier lebon (talk) 07:59, 9 June 2010 (UTC)

Standing at the side of the runway I see the true wind, I see the speed of the a/c relative me. I add/subtract the two. So what? Both POVs are equivalent, the pilot's and the spectator's. What happens in reality is the same in both frames. some things are easier to measure and calculate in one or the other frame. The pilot has it easier deciding his airspeed, the spectator has it easier calculating ground speed. As for the boat I want to monitor progress to a point fixed my frame of reference which is not fixed in the sailors. I'll present / I am presenting the maths. Easier for this particular purpose in my shore-based frame. Sail trimming? Easier if you're in the boat. Paul Beardsell (talk) 08:26, 9 June 2010 (UTC)

Well, if you actually do work it out, you will see that it is far simpler in the frame of the boat. The same hold for planes: pilots look at the relative wind speed, not speed over the ground plus or minus true wind speed.--Gautier lebon (talk) 15:49, 10 June 2010 (UTC)

Maybe the term red herring is not the most helpful BUT one has to decide what one's coordinate system is and then stick with it. By changing one's frame of reference one can become disoriented and start believing three impossible things before breakfast. If one chooses one's frame of reference to be the vessel then analysis becomes difficult. The ground is moving, not the boat! A course change requires everything else to swivel including wind direction, the movement of the ground etc etc. Paul Beardsell (talk) 19:34, 8 June 2010 (UTC)

This is not difficult at all. It is perfectly valid to use a reference frame where where the sail is at rest in order to compute the force on the sail. The air velocity in this frame is called "apparent wind". Since the coordinate transformation doesn't involve rotation, the force vector on the sail is the same as in the ground frame. Eyytee (talk) 05:55, 9 June 2010 (UTC)

It is perfectly valid but I will force you to do the maths if you insist on using that frame and you will find the trig more complicatedPaul Beardsell (talk) 07:44, 9 June 2010 (UTC)

Just to clarify: I'm not suggesting using the sail's frame for the entire analysis, just for the calculation of the force on the sail. This is the standard approach to calculate the force on an airfoil based on Angle_of_attack and Lift-to-drag_ratio. And this is not confusing because as I said: The coordinate transformation doesn't involve rotation, so the force vector in the ground frame is the same as in the sail's frame.

You on the other hand suggest, that we should compute the force on the airfoil WITHOUT using the air velocity relative to the airfoil(apparent wind). I will force you to do the maths if you insist on this non-standard approach.Eyytee (talk) 08:14, 9 June 2010 (UTC)

and I believe it will be difficult for readers to follow the maths. I am simply using another equally valid frame, as you acknowledge. And, as I am sure you must know, the RESULTS calculated in one frame are the same as those calculated in every other frame - that is what equivalence means in this context. If the boat does not beat the balloon in my "spectator on the shore" frame it does not do so in your "sailor on the boat" frame. Paul Beardsell (talk) 07:44, 9 June 2010 (UTC)

Easier is to choose one's frame of reference as the ground. Then the boat moves and everything else remains constant! Wind relative to the motion of the boat remains important to those IN THE BOAT but unimportant to those in OUR frame of reference. Physics (in particular certain conservation principles) allows us to analyse the system from any frame of reference guaranteeing the same outcome. That is why I suggest that the perspective of those in the boat be disregarded. We will look at this from the shore. The maths and the arguments become easier. In particular we can disregard APPARENT WIND as the only wind we will witness is TRUE WIND, i.e. wind relative to the earth. Those who do not follow this argument are disqualified from further comment. [If you want to discuss Shakespeare you must at least read the plays!] Paul Beardsell (talk) 19:34, 8 June 2010 (UTC)

Therefore I disregard any argument that depends upon apparent wind. Good bye! Paul Beardsell (talk) 19:34, 8 June 2010 (UTC)

This means that you fail to understand the basic physical principles involved. Which makes it difficult to see how to continue the discussion.--Gautier lebon (talk) 07:59, 9 June 2010 (UTC)

Paul Beardsell seems to deny basic physical principles like the equivalence of inertial reference frames, by suggesting the Earth's frame is the only valid one, and generally denying the validity of analysis which uses a different frame. Eyytee (talk) 05:55, 9 June 2010 (UTC)

No, I do not. My argument depends on the equivalence of inertial frames. I am grateful to you acknowledging this in advance as it avoids argument later. As every inertial frame is equivalent to every other I am doing the maths in the frame where the maths is easiest. No very complicated trigonometry is required im my "spectator on the shore" frame of reference: I do not even have to calculate apparent wind. Much easier. But I am glad you acknowledge the frames' equivalence as then you will not be able to come back to me and say "but, the apparent wind is different" as you will acknowledge, in my equivalent frame, there is no apparent wind, only true wind. Paul Beardsell (talk) 07:38, 9 June 2010 (UTC)

"In my equivalent frame, there is no apparent wind, only true wind". That is your fundamental fallacy. The sails see the apparent wind, not the true wind. If that were not the case, a boat sailing dead downwind with square sails would keep accelerating, becuase the true wind does not change. But you know perfectly well that a boat with square sails sailing dead downwind cannot sail faster than the wind: and this is precisely because the apparent wind drops to zero, so there is no more any force that can accelerate the boat. So the ONLY wind that matters is the apparent wind. Again, this is not OR, it is basic physics of sailing, explained in all textbooks, including those referenced in the material that you deleted.--Gautier lebon (talk) 08:13, 9 June 2010 (UTC)

This is fundamentally nonsense. I ask you to think again. I have explained why below where at criticism 4. You need to review your physics. In your sailing books they will be talking about sail trim, they talk about the POV of the sailor. I use an alternative easier but equivalent frame of ref. Equivalent. Please think again. 08:19, 9 June 2010 (UTC)

Sails are trimmed with respect to the apparent wind in order to optimize the force generated by the APPARENT wind. The sails generate a force, which drives the boat (technically, the force causes an acceleration, which results in an increase in velocity). The friction from the surface and the resistance of the APPARENT headwind generate an opposite force, so eventually the boat stops accelerating. The point is that the driving force, the one from the sails, is generated by the APPARENT wind, and that is what you have to use when doing the physics. Again, this is explained in all basic textbooks, which disuss not only trim, but also the forces and the speed vectors.--Gautier lebon (talk) 15:53, 10 June 2010 (UTC)

Hi Paul H (this is going to be fun - two Pauls!). If you look at Lift (force) you will see that the Bernoulli explanation of lift is now discredited. And anyway, thin cloth sails are so easy to understand, we do not need it. Paul B is nearly correct saying that, "The wind force experienced by a sail is perpendicular to the set of the sail". The force due to the wind on every square inch of sail-cloth has a component at a right-angle to the square inch, and another (hopefully much smaller one) roughly backwards along the cloth due to drag. The curve or 'belly' near the front of a close-hauled sail (the luff) contains lots of square inches facing almost forwards, and it is largely held full and pressurised by the existence of the rest of the sail creating a nice trailing edge for, and maintaining laminar flow over, this driving front part near the luff. This is what allows sailboats to do the apparently magical thing of making progress upwind. Overtaking the wind downwind is no more special than this. You are right that the key to it is to go so fast on a broad reach that you end up close hauled, but once you do, I'm sure, looking at that luff and imagining all the force-vectors sticking out of the forward-facing side of the sailcloth, it will make as much sense as when imagining them on a beat to windward. You can't overtake the wind in the same direction as the wind, but you can at an angle to it, provided you can sail very efficiently very close-hauled. So, my point is, there is no problem with the physics, we just need reliable sources that say people have done it, and hopefully to explain the physics as well (since we must not reference our own explanations). What I'm hoping to do is to convince Paul B that the physics is not screwy, so that he starts to help us find these references, rather than saying they can't exist. --Nigelj (talk) 18:15, 8 June 2010 (UTC)

Nigel: I already provided the references, but Paul Beardsell deleted them. Bentwaithe's book explains all this (and more) in excruciating detail. And explains how high VMG is achieved. Again, all I did was summarize what is in Bentwaithe and the other cited sources. But Paul Beardsell has deleted all of that because he thinks that he knows better. It this any way to run Wikipedia?--Gautier lebon (talk) 07:59, 9 June 2010 (UTC)

No, too difficult, I'm on the shore, you want to invoke relative (or apparent) wind without doing the very complex maths that requires. You're out of order! (Different argument: I use the "set of the sail" as a device to average out the sail's curvature and drag. There is no important consequence of this.) Paul Beardsell (talk) 19:34, 8 June 2010 (UTC)

Actually the math is not at all complicated in the frame of the boat (not the frame of the wind): it is elementary trigonometry and you will find it in the article. Again, you will also find it in basic texbooks on sailing. And I would appreciate it if you stopped using expressions such as "you are out of order".--Gautier lebon (talk) 15:56, 10 June 2010 (UTC)

Paul Beardsell is correct in saying that the frame does not matter. However, the vector algebra is easier in some frames than in others. The deleted material used the frames that are adopted by all textbooks, precisely because the presentation is simpler. I still cannot understand why Paul refuses to look at Bentwaithe's book, which explains it all.--Gautier lebon (talk) 07:59, 9 June 2010 (UTC)

I do not have the book. GL said he would send me extracts. Not received. Paul Beardsell (talk) 08:21, 9 June 2010 (UTC)

I have sent you the extracts by E-Mail on 9 June at 8:38 European time. If you did not receive them, then please send me an E-Mail to that effect.--Gautier lebon (talk) 15:28, 10 June 2010 (UTC)

criticism 3

Your criticism here [where? this used to be part of a different thread until moved Nigelj (talk) 20:04, 8 June 2010 (UTC)] is based on the 'conservation of velocity', which is not a recognised principle. 'Conservation of momentum' is, but as Eyytee says below [well, it's above now, but who cares anymore? Nigelj (talk) 20:04, 8 June 2010 (UTC)], in order to 'see' momentum being conserved as a sailboat goes by, you would have to 'see' all the disturbances left behind in the air and the water after the sails and the keel have done their thing. Racing sailors are very familiar with 'dirty air' downwind of another boat, but to me that is all too complicated to visualise in such detail. In answer to your rhetorical question, the yacht is going faster than the south-going air, but in a south-westerly direction. By re-using the same magic that allows it to sail upwind, say 30 deg off the wind, it has now overtaken the southerly vector of the wind and is using it's 'upwind' ability to sail 30 deg off an apparent wind that is made up mostly of the wind due to its own movement, plus a small reduction and an angle in that wind due to the angle between its movement and the real wind. Just like in the vector diagrams in the article. One thing that's weird is that, unusually, the wind due to the boat's movement is much larger than the real wind. The real wind mostly serves to add a small angle to the 'movement wind', an angle that this very efficient boat can continue to claw itself along by, close hauled, getting just enough drive to overcome its minimal hull-drag. --Nigelj (talk) 18:39, 8 June 2010 (UTC)

No, I never said "conservation of velocity". Yet you are wrong to seemingly ridicule the term, it is Newton One and is thus PROFOUNDLY TRUE. Nevertheless I did not invoke it. And you cannot exert a force in particular direction in collision with a 2nd object unless one is travelling faster in that directon than the 2nd object. That is why the wind cannot propel you faster than itself IN THE DIRECTION of the wind. I.e., to the physics-illiterate: that is why downwind sailing to the directly downwind point quicker than the free floating balloon is impossible. Paul Beardsell (talk) 19:16, 8 June 2010 (UTC)

Once again, you fail to undertand that the only relevant wind is the APPARENT wind, not the true wind. Have you actually ever sailed a boat? All sailors know that sails are trimmed with respect to the apparent wind, not with respect to the true wind. And that it is the force of the apparent wind that propels the boat. That's why it is so slow to go dead downwind with square sails: the apparent wind is pretty weak.--Gautier lebon (talk) 08:07, 9 June 2010 (UTC)

OK, I'm outa here. If you are going to start rearranging other people's helpful comments so that they make no sense any more, and flooding the page with your own disordered comments, and getting abusive ("physics-illiterate" indeed!) and SHOUTING, then you can continue to argue without me. After you're done, we'll restore the page to a consensus version, but this is not helpful to improving the article at the moment. --Nigelj (talk) 20:04, 8 June 2010 (UTC)

Play the ball. I moved your critique to a subsection to allow BETTER addressing of your points. Sorry about Newton 1, but that was your error not mine. Heat, kitchen etc Paul Beardsell (talk) 20:12, 8 June 2010 (UTC)

I am leaning towards agreeing with Nigel. As all of you know, I am very patient and more than willing to try to explain admittedly counter-intuitive concepts. But, given my two years of physics at MIT (followed by a BA in Math and a PhD from Harvard), I am beginning to be a bit tired of being told that I don't understand physics 101, especially when the physics in question can be found in any basic book on sailing. During the week end, I will try to produce the force diagrams that were mentioned earlier, and that show how an iceboat sailing at 135 degrees off the true wind will easily accelerate to a speed that results in VMG far greater than the wind. Those force diagrams will also show why there is no issue of conservation of energy. If that still does not convince Paul Beardsell, then we might have to envisage another approach.--Gautier lebon (talk) 08:04, 9 June 2010 (UTC)

criticism 4 =

Correct. But what counts is the APPARENT wind, not the true wind. That was explained in the material that you deleted.--Gautier lebon (talk) 07:44, 9 June 2010 (UTC)

Anyone with any physics (I know you have some) will tell you that all inertial frames of reference are equivalent. If you do the analysis from the POV of the sailor in the boat you will need to cope with his measurements of the wind, speed and direction, the apparent wind. If you do the analysis from the shore then the wind is the true wind. We all are assuming the true wind remains constant during our stopwatch-speed and balloon tests. In the shore-frame-of-ref the wind is always the same. In the boat it varies for every point of sail and every boat speed. The boat-frame-ref is difficult to analyse. The shore-frame-ref is EASY. But they are equivalent (=equally valid i.e. give the same results). That's basic physics. I choose the easy frame. If you choose the other frame I bet you cannot do the maths - no one here has done it so far. I can do the maths in the easy frame and I think you can follow. If you believe the assertion of the equivalence of the frames of ref. Paul Beardsell (talk) 08:16, 9 June 2010 (UTC)

Of course the frames are equivalent, but the easy frame is the boat's frame: that is why all textbooks use that frame. The shore frame is hard to get right, and that may explain why you are having trouble seeing this. Please try the following: imagine an iceboat that is sailing at 135 degrees off the true wind, and work out the speed and force diagrams relative to the boat as it accelerates. Then, if you wish, convert them to the stationary frame of the earth. The mathematics of the boat frame are simple, they are presented in the article. The mathematics of the shore frame are more complicated, which is why you won't find them in textbooks.--Gautier lebon (talk) 15:26, 10 June 2010 (UTC)

For the record

As this discussion becomes increasingly difficult to follow and no way forward emerges, I would like to make the following statement for the record: In my opinion the article version of 6 May 2010 did not contain (1) arguments violating the laws of physics, (2) any Original Research, nor (3) any not-permitted Synthesis. The many references amply supported the main - and intriguing - arguments that (a) velocities over ground greater than wind speed are possible and that (b) VMGs towards the dead-downwind direction greater than wind speed are possible (faster than the air baloon). Nevertheless a more concise text seems possible and desirable. (Please do not edit this paragraph.) MrBeanBob (talk) 21:44, 8 June 2010 (UTC)

I have been reading these arguments that Paul Beardsell has been making. When I was an engineering student at a major engineering university, I took a course in statics. We worked this exact problem. You get an extra vector when sailing at an angle to the wind. That vector adds to your speed. There are no "conservation of energy" requirements that says a vessel cannot tack back and forth and beat a boat (or balloon) sailing directly downwind. If the vessel has enough sail and enough keel and does not have too much friction, it can get lots and lots more speed. It is difficult for sailboats to do this, (some can, but just barely), but it is easy for ice boats to do it. Ice boats do it all the time, with room to spare. I suggest Paul Beardsell do some googles on ice boat sailing. Some of the ice boat forums address this exact issue. To solve this problem in a scientific (engineering) way, one needs to draw vectors. This is exactly what the author Gautier lebon has done. Paul Beardsell needs to take a class in Statics so he can understand these vector diagrams. Thousands of engineering students taking statics have solved this very problem. Thousands of ice boat racers have proven that an ice boat tacking back and forth beats an ice boat going straight downwind. It is a common ice boat race, then they switch positions and get the same results, with identical ice boats and closely matched pilots. Any good book on sailing theory will address the issue. There is no scientific question that Gautier lebon's assertions are correct here. The theory is correct and the experiments back it up! Revert the article to Gautier lebon's assertions and get rid of the factual accuracy is disputed. There is no dispute amongst engineers who are informed on this issue. What makes it hard to understand, is the correct answer is not intuitive in this case. To understand it, you need to understand the vectors, the sail and the keel. Pontificating on some "law of energy conservation" isn't the right way to understand the issue. The sail converts the wind into the force necessary to propel the craft. The keel translates some of that force into speed in the desired direction and dumps the rest off into friction and the vectors allow us to obtain theoretical numbers on how a "perfect" boat would behave. Good work Gautier lebon! —Preceding unsigned comment added by Aviatorpilotman (talk • contribs) 03:58, 12 June 2010 (UTC)

Hear, hear! I think we have a clear consensus here. There's no need to list all the people who agree against the one who doesn't. Let's fix the article. --Nigelj (talk) 10:30, 12 June 2010 (UTC)

Agreed. Whaleswatcher had already reverted the edits by Paul Beardsell. I will now remove the disputed tags and add a warning so that, hopefully, we will not get into this sort of conflict again.--Gautier lebon (talk) 13:39, 12 June 2010 (UTC)

There may be some useful ideas from all this PB controversy. When an uninformed reader come in he may ask himself a question such as: If a sailboat can outsail the wind by tacking on a downwind course, why then do they proceed on a downwind course and put up their spinakers? And they may assert the same arguments as PB did. You may wish to address these ideas. I also think some more emphasis on how important the keel is would be useful. Without a keel (a flatbottom sailboat), the sailboat could not do what it does. In my thought experiement I envision a sailcraft on a set or RAILS. A top rail and a bottom are laid at an angle to the wind, say for a 2 mile course. The top rail keeps the boat from tipping over. The rails are well oiled and have little friction. In a sailboat, the keel acts as such a "rail".

Re why put up a spinnaker: (1) some boats can and do tack downwind even with a spinnaker, but of course only if they cannot accelarate enough so that the apparent wind is forward of the beam; such is the case for most keel boats. (2) Most sail boats, in most conditions, cannot accelerate enough so that the apparent wind is forward of the beam; in that case, there isn't that much to gain from tacking downwind, so people don't bother, except in tight regattas. But you are correct that this should be explained, I've added it to the fallacies.--Gautier lebon (talk) 12:40, 13 June 2010 (UTC)

I have a statement regarding the propeller driven cart. A propeller is NOT a sail!! A propeller "tacks" through the wind! It has angles on its blades. Although I don't claim to completely understand their clever contraption, I don't think it is "sailing". Sailing uses sails, not props! The prop can use the same extra vector that a sailboat gets when it sail off the wind. I question whether such a device should even be in an article such as this. It is interesting but a bit distraction from the main points. Perhaps it needs it's own article? —Preceding unsigned comment added by Aviatorpilotman (talk • contribs) 18:32, 12 June 2010 (UTC)

Hello Aviatorpilotman. One of the very common misconceptions regarding the propeller driven cart is that it is somehow using it's airfoils different than a common sailing rig on a broad reach does. There are many ways to show that this isn't true and that the propcarts airfoils are nothing more than the common sail on a broad reach of a smaller radius than folk are normally accustomed to seeing. If I may, here is a link to an animation that might help you visualize this. http://www.youtube.com/watch?v=UGRFb8yNtBo The kicker here is that most folks (even sailors) hold the belief that a traditional sailing rig always acts as a turbine (slowing down air relative to itself) while in fact there are many points of downwind sail that a traditional rig acts as a propeller (*accelerating* air relative to itself). It's just one more of the many counterintuitive aspects of sailing that this topic has brought to the surface. ThinAirDesigns (talk) 19:02, 12 June 2010 (UTC)

As I understand it, it is the same as the difference between a rotating wing flying craft (helicopter or autogyro) and a fixed wing flying craft (airplane). Boats usually used fixed sails. The dead downwind cart uses rotating "sails". Theoretically, one could use rotating "sails" on points of sail other than dead downwind, see [16]. I agreee that most people would not consider a rigid propeller blade to be a sail. But from the functional point of view it is, in this context. Recall that old windmills used blades that were in fact very similar to conventional sails: cloth panels streched over a wooden frame. Modern windmills use propellers, but the function is exactly the same: to catch the wind, deflect it, and generate energy from that deflection. This is exactly what a conventional sail does, and what the propeller on the dead downwind cart does.--Gautier lebon (talk) 13:02, 13 June 2010 (UTC)

Question for Gautier lebon: In the article drawing labeled "Downwind", is the line labeled "sin(beta)" a vector created by the wind pushing at right angles to the keel? (The keel would be in line with your vector labeled "Boat speed"). If so this might be useful to someone trying to understand the vector diagrams. Also, it seems to me the line labeled cos(beta) is the magic 'extra vector' that allows the boat speed to exceed the wind speed. I am just pointing out some ideas that I see that are important for me to understand how the vectors translate to real world and vice versa. Nice drawings, BTW! —Preceding unsigned comment added by 75.70.3.228 (talk) 00:23, 14 June 2010 (UTC)

PB's arguments

As far as I can tell, Paul Beardsell presents the following arguments:--Gautier lebon (talk) 08:19, 9 June 2010 (UTC)

1) VMG > windspeed violates the law of conservation of energy. No source is provided to support that statement.

• No CREDIBLE source is provided to support the alternative view either.--QuietJohn (talk) 07:04, 14 June 2010 (UTC)

2) VMG cannot exceed windspeed because, if it did, there would be no force on the sails. This argument is based on the fallacy that the sails are sensitive to the true wind, whereas in fact they are sensitive to the apparent wind. The deleted material included numerous references to textbooks that explain this.

• What you are saying is that it is the APPARENT wind - created the movement of the vehicle itself which allows it to go faster. So the energy of the vehicle moving provides the energy to make the vehicle move faster.... Hmmmmmm? QuietJohn (talk) 07:04, 14 June 2010 (UTC)
  • No, you are confusing velocities with energy. The apparent wind is the velocity difference between the sail and the airmass. The apparent wind determines the force on the sail. The energy on the other hand, always comes from reducing the true wind.Eyytee (talk) 08:43, 14 June 2010 (UTC)
• Please provide a quote - along with citation (FROM A CREDIBLE TEXTBOOK) to support your claim that VMG downwind CAN exceed windspeed --QuietJohn (talk) 07:04, 14 June 2010 (UTC)

3) Because of some combination of the above, it cannot be true that USA 17 sailed from the upwind mark to the downwind mark at a speed of 19 knots over the ground in 5-10 knots of wind. Never mind the published accounts, which also state that wind shifts were relatively minor (less that 20 degrees).--Gautier lebon (talk) 08:19, 9 June 2010 (UTC)

• Again, provide your claimed "published account". Nineteen knots OVERGROUND isn't the same as 19 knots DDW -unless the boat course was DDW. --QuietJohn (talk) 07:04, 14 June 2010 (UTC)

4) Because of some combination of (1) and (2) above, the polar charts and other diagrams found in Bentwaithe's book are wrong. That is, the word of one person, unsupported by any citations, should prevail over a book by a well-known expert, published by a reliable publishing house.

Is something wrong here?--Gautier lebon (talk) 08:19, 9 June 2010 (UTC)

Sailing downwind with a downwind VMG greater than wind speed

This is a respond to PB's arguments above, put here to avoid further confusion and clutter. PB claims that sailing dw with a dw VMG > 1 is impossible (I'm setting wind speed=1). He asserts that if the analysis is done in the rest frame of the water/ice/ground, this is clear. So let's do it in that frame. I'll ignore drag, treat the sail as if it were flat (for ease in describing angles) and assume the boat can only move parallel to its keel.

Consider an iceboat sailing at 45 degrees to directly dw, with a speed of 1.414 (never mind how it got like that, maybe someone towed it to speed and has just released it). At this moment the boat's VMG=1. According to PB the force of the wind should act to slow the boat down, and according to everyone else it should speed it up (assuming the sail is trimmed correctly, of course). So consider a parcel of air moving at wind speed that collides with the sail. Because the boat (and sail) has a vmg=1, this happens only because the sail is also moving perpendicular to the wind - but it does happen. The collision pushes the sail in the direction perpendicular to its plane. Since the plane of the sail is nor parallel to the keel of the boat, this clearly accelerates the boat (again, assuming the sail is oriented correctly).

It's easy to see this if you draw a diagram. Make the wind blow towards 12:00 o'clock or 0 degrees, so it's blowing from 6:00 o'clock. The boat is moving up the page and to the right, at 45 degrees (so towards 1:30) with a speed of 1.414 as above. The sail is (say) at 15 degrees to the boat, so its tack (the corner closest to the mast) is pointing towards 2:00. Collisions with air push the sail and boat perpendicular to the sail, towards 11:00. That has a positive component towards 1:30 that accelerates the boat, and another towards 10:30 that is perpendicular to the keel and does nothing. Therefore, if friction etc. are small enough, the boat will accelerate to a VMG>1 and (with one tack/jibe) can beat a balloon to a point straight dw. Waleswatcher (talk) 11:50, 9 June 2010 (UTC)

It's very refreshing to see what is an obviously honest attempt to address the real issues, and very helpful, as it lets me immediately make some compelling points against a very plainly drawn example. Thank you. (1) "According to PB ...": You nearly have my POV correct but not quite. In the frictionless situation you describe I am NOT claiming that the vessel is slowed down, I am claiming that it is neither slowed down nor speeded up. V=sqrt(2)*(true wind speed) is the limit at 45degs. Obviouly, where there is no friction VMG = (true wind speed) is possible. I am arguing against VMG > (true wind speed). The argument made by others is that VMG > (true wind speed) is possible. It is not. (2) "The sail is at 15 degrees to the boat ...": This is your mistake. At such an angle the sail is luffed - the wind is blowing the wrong way against the sail and is slowing the boat down!Paul Beardsell (talk) 21:57, 9 June 2010 (UTC)

Not true. The air hits the boat from 3:00 in the given situation. Since the tack of the sail points towards 2:00, the air hits the correct sail side which faces 5:00. See computation below.Eyytee (talk) 00:03, 10 June 2010 (UTC)

At angle 45 degrees and speed 1.414 * (true wind speed) the sail must be set directly along the keel line! Draw the diagrams! Such a sail cannot have a boat-forward component of force. The sail along the keel line, at 45degs and V=1.414, has no effect. Setting the sail at 15degs to the keel line is a brake. Thus your argument fails.

To support the above assertion I enter "enemy territory" and calculate apparent wind (s_aw,a_aw) where s_aw is the speed of the apparent wind (i.e. relative to the speed of the boat) and and a_aw is the angle of that apparent wind (i.e. relative to the boat's direction).Paul Beardsell (talk) 21:57, 9 June 2010 (UTC)

Why so complicated? You don't need to rotate the reference frame to align it with the boats axis. Just attach the frame to the boat and keep the orientation (x->east, y->north). Or simply use the vector formula from Apparent_wind : apparent_wind = true_wind - boat_velocity = (0,1) - (1,1) = (-1,0). So the apparent wind comes from east or 3:00, and hits the side of the sail which is facing 5:00.Eyytee (talk) 00:03, 10 June 2010 (UTC)

It is, (as careful application of the Feynman Problem Solving Algorithm does show), ((1-sqrt(2))*(true wind speed),0). [Do you really really really want to see the workings?] The important figure being the 0. The apparent wind in the example given by Waleswatcher is (from the boat's POV = apparent) directly ahead! Any setting of the sail other than amidships acts as a brake. Paul Beardsell (talk) 22:17, 9 June 2010 (UTC)

"The apparent wind in the example given by Waleswatcher is (from the boat's POV = apparent) directly ahead! Any setting of the sail other than amidships acts as a brake." If the first statement were true, the second would be as well. But the first statement is false. The apparent wind velocity is the true wind velocity minus the boat velocity. In my example that's a vector pointing to 9:00 (i.e. the apparent wind is blowing from 3:00 towards 9:00), with magnitude 1. But the boat is pointed at 1:30, so the apparent wind is not directly ahead, it's blowing from 45 degrees to the starboard (right) side of the bow, and so the boat just needs to be close hauled with the clew on the port (left) side. See my comment below for more details and yet another frame.Waleswatcher (talk) 00:33, 10 June 2010 (UTC)

Thanks for the correction on your point of view. But we're still in disagreement, because I claim that the wind will accelerate the boat. I have drawn the diagram and my conclusions are that the boat will accelerate. Are you sure you have the sail oriented along the line between 2:00 and 8:00?

If you're willing to change frames, the simplest one to use is neither the rest frame of the ice nor that of the boat, but rather the rest frame of the wind. In that frame, the ice is moving towards 6 o'clock at speed 1, the boat is aimed at 1:30 but is drifting directly sideways towards 3, and of course the air is at rest. Meanwhile the tack of the sail is pointing at 2:00 (and the clew at 8:00). So forgetting about the hull for a moment, the sail is moving to the right while angled up-right to down-left. Therefore there is a force vector on it up-left, pointing to 11 o'clock to be exact. Projecting that onto the keel, that has a positive component pointing to 1:30 that accelerates the boat. So it's not a brake.

Note that if the sail was set the other way at 15 degrees to the hull, that is with the tack pointing at 1:00, then it _would_ act as a brake. But that's the wrong trim (which is clear if you imagine being on the boat, and think about the apparent wind).Waleswatcher (talk) 00:28, 10 June 2010 (UTC)

I drew a diagram. Please check it. Generacy (talk) 12:18, 10 June 2010 (UTC)

Looks good to me, thanks for drawing it. PB, what do you say? Convinced?Waleswatcher (talk) 13:24, 10 June 2010 (UTC)

Dear Generacy and Waleswatcher: thank you for your valuable contributions. Indeed, the graph that Generacy has drawn is along the lines of what I propose to do, but it might still take me a couple of days. As stated above, it all becomes clear when you draw the force diagrams. And that is not OR, such diagrams are found in many books on sailing.--Gautier lebon (talk) 15:23, 10 June 2010 (UTC)

Sailing at 135 degrees off the true wind

As promised, I've developed force diagrams that are meant to make the situation easier to understand. But I'm not convinced that what I have done can be understood easily. At first, I thought of making three diagrams, showing velocities and forces for three situations: (1) standstill (2) apparent wind at 90 degrees (3) apparent wind at 45 degrees. But then I decided to make separate diagrams for the velocities and the forces, with each diagram showing the three situations.--Gautier lebon (talk) 12:27, 11 June 2010 (UTC)

I would much appreciate comments on how to make the text below, and the diagrams, easy enough to understand so that they could be incorporated into the main article.--Gautier lebon (talk) 12:27, 11 June 2010 (UTC)

Consider an iceboat that is sailing at a course that is 135 degrees off the true wind. At the beginning, the boat is stationary. We will use the value "1" for the speed of the true wind. The apparent wind is equal to the true wind and comes from the same direction as the true wind. The velocity made good (VMG) downwind is zero. This is shown by the value "V0" in the chart below.

The boat will accelerate and will eventually reach a speed equal to to .707 times the speed of the wind. At this point, the apparent wind will come from 90 degrees (broad reach) and the speed of the apparent wind will also be .707. VMG is .5 This is shown by the value "V1" in the chart below.

At this point, the only resistance to forward motion is the friction of the iceboat's runners on the ice. But that is negligible.

• Unfortunately, not true. Wings (and sails) come with a penalty called drag in addition to lift. Lift would typically be perpendicular to airflow and drag in the same direction as airflow. So, in addition to runner resistance, you have aerodynamic drag which acts to slow the boat down. --QuietJohn (talk) 06:43, 14 June 2010 (UTC)

So the boat will continue to accelerate and will reach a speed equal to 1.41 times the speed of the wind. At this point, the apparent wind will come from 45 degrees (close hauled) and the speed of the apparent wind will be 1. VMG is 1. This is shown by the value V2 in the chart below.

That is correct. I should have referred to the lift, which is the force on the sails net of drag. According to Bethwaite, lift is about 2/3 of the total force. But this does not change the argument, because lift and drag increase proportionally, with the square of wind speed. So there is an excess of lift over drag, and there is still a forward force which will accelerate the boat past a beam reach.--Gautier lebon (talk) 09:12, 14 June 2010 (UTC)

If the forward component of the force on the sails is sufficient, the boat can continue to accelerate, the apparent wind will shift further forward, and VMG will be greater than 1, that is, greater than the speed of the true wind. That is, the boat will progress downwind faster than the speed of the wind. The text and charts below show the force on the sails and the forward component of that force. It is not possible to determine theoretically whether the forward component at V2 would be sufficient to accelerate the boat further; but measurements of actual iceboat performances show that indeed it is. Iceboats accelerate until they are sailing at about 10 degrees (or less) off the apparent wind, and thus achieve speeds of 5 or more times the speed of the wind. This is the case even if the boat is sailing at 135 degrees off the true wind. So the VMG (progress in the dead downwind direction) is far greater than the speed of the wind.

The chart below shows the apparent wind and the sails on the iceboat when it is at a standstill (V0), on a broad reach (V1) and close hauled (V2). The angle of the sail is half of the angle of the apparent wind, which is the optimal angle in terms of generating a forward driving force. The force generated by the apparent wind on the sail is proportional to the square of the speed of the apparent wind.

The chart below shows the forward force resulting from the apparent wind when the iceboat is at a standstill (V0), on a broad reach (V1) and close hauled (V2). The force generated by the wind is perpendicular to the sails. It can be seen from elementary trigonometry that the forward component of that force is sin(sail angle).

Thus, the forward force when the iceboat is close hauled will be 38% of the total force on the sail. Again, whether or not that is sufficient to accelerate the boat further will depend on the resistance caused by the apparent wind (the headwind induced by the speed of the boat). As stated earlier, in practice it has been found that the force is indeed sufficient to further accelerate the iceboat (and in fact also other high-performance boats, including sailboats, as explained elsewhere in the article).

VMG greater than windspeed section does not conform to Wikipedia specifications

First and foremost, there really don't seem to be any RELIABLE, VERIFIABLE sources. Secondly, what sources there are appear to be reports of original research, none of which has made it through a peer review process since they first appeared in November of 2008.

Wikipedia's recommendations are: Exceptional claims require exceptional sources

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Exceptional claims in Wikipedia require high-quality sources.

If such sources are not available, the material should not be included.

The major "sources" in the section are to self-published videos demonstrating original research.

This "issue" has been publicized since at least 2008 with no peer-reviewed publications of such a spectacularly counter-intuitive notion. It is VERY hard to believe that such a scientific breakthrough could remain an orphan with no better explanation than a very dubious "thought experiment".

As indicated in the Wikipedia recommendations for such unauthenticated exceptional claims, this section should not be included.

No problems with sailing faster than the wind - just with a downwind velocity made good greater than windspeed.--QuietJohn (talk) 06:17, 14 June 2010 (UTC)

The cited book by Bethwaithe is a perfectly reliable, high-quality source, that summarizes years of data and developments. The NALSA web site contains many references and data that show that iceboats routinely go downwind at VMG greater than wind speed, and it also explains why this is possible. The [[talk:sailing faster than the wind#deleted thought experiment] is hardly dubious, and certainly not original. In fact, it is trivial. The videos that you refer to pertain only to the propeller-driven cart that goes dead downwind faster than the wind. The fact that boats with conventional sails, such as iceboats, sand yachts, and USA 17, can achieve downwind VMG greater than wind speed does not depend on any videos: it is documented from reliable sources, as cited in the article.--Gautier lebon (talk) 09:09, 14 June 2010 (UTC)