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Downwind faster than the wind[edit]

This paragraph requires revision:

Some extreme design boats are capable of traveling faster than the true windspeed on some points of sail and can even sail downwind faster than the wind, although this is not intuitively obvious[1][2]; iceboats can sail both upwind and downwind at speeds far greater than the wind.[3] Americascupfreak (talk) 20:41, 10 June 2014 (UTC)

1) Boats that are not "extreme" in design are capable of travelling faster than wind speed on a beam reach.

Indeed, this is correct, and the text should be modified accordingly. Please take a look at the proposed new article User:Gautier_lebon/Sailing_faster_than_the_wind and let me know what you think of that.--Gautier lebon (talk) 16:49, 8 December 2009 (UTC)

2) Iceboats may have been demonstated to sail on a downwind part of a course (which by definition is of limited duration) from "A" to "B" faster than the wind on a VMG (to wind speed) basis, but sustained downwind faster than the wind progress on a fixed bearing is not possible. —Preceding unsigned comment added by (talk) 00:46, 1 December 2009 (UTC)

That's what I thought too, until I looked up various references. Please take a look at the proposed new article User:Gautier_lebon/Sailing_faster_than_the_wind and let me know what you think of that. Indeed, usually downwind tacking will be required in order to go faster than the wind, but it is possible to construct a wind-driven cart that can go dead downwind faster than the wind, see the explanation and references in my draft article cited above--Gautier lebon (talk) 16:49, 8 December 2009 (UTC)
Absolutely. "Intuitively obvious", although the writer may not realize, means "it's obvious to me, I imagine it's obvious to others, so I don't want to explain it." As a professional editor, my response is "If it's obvious, then don't say it. If it might not be obvious to some substantial part of the audience, then explain it, don't tell people what amounts to 'Figure it out for yourself.'"
"Some extreme boat designs" belongs in a sports magazine, not an encyclopedia, where facts need to be verifiable. "Extreme" may mean something to the writer, but again, it may mean nothing to the general reader. (Me, for example. I couldn't guess what this means if you offered me free passage to Tahiti.) Cheers, Alpha Ralpha Boulevard (talk) 04:51, 6 December 2009 (UTC)

I'm not familiar with 'extreme' sailing machines, but I can see how moving faster than the true windspeed is possible while tacking downwind. What I can't see, is that you would arrive at a downwind mark faster than the windspeed would get you there if you just floated on it. In other words by deviating away at some angle you may get the 'rush' of going fast, but your VMG towards a directly downwind point, I think, will always be slower than the true wind speed from here to there. Is that right? If so it is a significant drawback, as few people sail just to get the rush of speed, most want to actually get somewhere, either to race to or to arrive at that point. --Nigelj (talk) 19:00, 8 December 2009 (UTC)

OK, I've just read your user-space article, and I see that I am right if we use an ordianry sailing machine. I think I;m right in the other two cases too, as I see the maths ran out long before the downwind speed-of-wind section. I believe that your 'huge spinnaker, negligible-drag towed generator' example has a kind of perpetual motion machine fallacy - if the towed generator is that small it won't make any difference, if its any bigger it'll slow the boat down more than it speeds it up. The downwind cart is the same - if you go at the exact speed of the wind, the propeller will stop. Nice try. --Nigelj (talk) 20:01, 8 December 2009 (UTC)
Dear Nigelj, I felt exactly as you did until I carefully studied various articles on the web. Please look at [1]. The reality of this device was debated, but in the end anybody can see that it is legitimate. For the debate, see [2] and [3], and please note that the initially skeptical physicist wound up admitting that he was wrong and that a wind-powered device can be built that will indeed sail dead downwind faster than the wind. The reason why this is not a perpetual motion machine is that the inherent energy in the wind is very large: if you can harness enough of it, you can do what you want. This is also explained at [4]. My motivation for writing the proposed new article was to assemble in one place the relevant references, precisly because most people would think that such things are impossible. Maybe my explanations aren't clear enough, but then I would appreciate suggestions on how to improve them.--Gautier lebon (talk) 09:30, 9 December 2009 (UTC)
Well if you motor your not sailing! End of story. You would not be sailing either if you have a windgenerator on your yacht charging your batteries while in port and later the batteries will power the yacht faster than the wind. Same thing, different approach. By the way, a yacht will point 45 deg to true wind not apparent wind. Prillen (talk) 10:46, 9 December 2009 (UTC)
A wind-driven machine cannot sail dead downwind faster than the wind using only sails. However, 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 (e.g. the wheels on a sail-driven cart can drive a propeller). I'm not sure whether you (or others) have actually read the citations that I provided. If not, please do so. Regarding pointing, a yacht's sails see only apparent wind, not true wind. So a yacht can sail at a certain minimum angle with respect to the apparent wind. If a yacht can sail at 45 degrees off the apparent wind, then it cannot sail at 45 degrees off the true wind, because of the apparent wind shift induced by the speed of the boat. Boats that sail at 45 degrees off the true wind achieve that by being able to sail closer than that to the apparent wind (say about 35 degrees off the apparent wind.--Gautier lebon (talk) 08:26, 10 December 2009 (UTC)
Sorry, but as long you have to store energy for later use you can't claim to sail faster than the wind. And my point about about 45 degree wind is just a modern cruiser will tack within 90 degrees i.e. sail at 45 deg to true wind. Prillen (talk) 15:19, 10 December 2009 (UTC)
We are on the same wavelength now. As we all know, how high a keelboat can point depends on a lot of things, including quality of the sails and how clean the hull is. I've rarely sailed a keelboat that could tack within 90 degrees in light air, but I've come close to that in stronger winds, because the effect due to the apparent wind shift is relatively smaller. Anyway, you are correct to imply that my text should match more closely what is in the main article on sailing, and I will modify it accordinbly.--Gautier lebon (talk) 07:56, 11 December 2009 (UTC)
Also, please be careful to remember that this article is called 'sailing', so be careful about giving undue (or any) weight to 'wind-driven machines' that do whatever they do by any means other than actually sailing. --Nigelj (talk) 18:50, 10 December 2009 (UTC)
Yes, this is a good point. There is a difference between sailing properly speaking, that is, a device propelled by sails, and the broader notion of a machine that is propelled by the wind. I've modified my text to clarify this. And, in any case, I was not proposing to include my material directly in the article on sailing, I propose to create a new article.--Gautier lebon (talk) 07:56, 11 December 2009 (UTC)

It remains my opinion that the claim and reference to iceboats sailing downwind (VMG) faster than the wind requires qualification (ie that this is not possible on a single bearing) or explanation of the method - accelerating to a velocity much greater than wind speed on a "reach", then turning downwind with minimal frictional loss of forward momentum as is possible with an iceboat, trimming sails to minimise wind resistance while at faster (VMG) speed downwind than the wind, and repeating this action in sequence if required by the duration of the course, to achieve verified progress (VMG) faster than the wind. I made the mistake above (and corrected it) of repeating the common suggestion that progress downwind faster than the wind is possible with an iceboat with "tacking" (gybing). Tacking may be practically needed to go from mark to mark on a fixed course, but it is also possible to achieve downwind faster than the wind (VMG) progress by altering course as described without tacking.

This is a good comment, I will incorporate it.--Gautier lebon (talk) 10:32, 14 December 2009 (UTC)

With regard to the cart with propellor connected by gearing - claimed to demonstrate that indefinitely sustainable directly downwind faster than the wind progress can be made (by "spork33" and others in a clever internet hoax apparently designed to "double-cross" the "Mythbusters" TV programme), the explanation given is inadequate, and the demonstration (videos) of the cart(s) in action does not revoke criticism that the machine uses energy stored in rotational movement to accelerate for a finite duration once "released" at wind speed. It is not capable of reaching wind speed on it's own. Energy "pushing" the cart forward (via the prop) must always be less than energy "braking" the cart (through the wheels) at any velocity. Despite attempts to argue otherwise, the only source of energy for the cart to accelerate is kinetic energy of the wind, which reduces to nil when it is at wind speed. The machine described and demonstrated is a worthy addition to the Wikipedia page on Perpertual Motion Machines. —Preceding unsigned comment added by (talk) 05:59, 14 December 2009 (UTC)

I don't see any theoretical-physics reason why the energy pushing the care forward must always be less than than the energy braking the cart at any velocity. It is clear that the only source of energy is the kinetic energy of the wind. But there is no reason in theory why enough of that cannot be harnessed to go faster than the wind. The thought-experiment involving the intermittent use of a towed electrical generator and batteries shows that there is no violation of basic physical principles in imagining a device that can go dead downwind faster than the wind. I note that the initially skeptical physicist later admitted that the cart in the videos is not a hoax. I don't see any published reference that still suggests that it is a hoax.--Gautier lebon (talk) 10:32, 14 December 2009 (UTC)
The towed electric generator thought experiment is a similar device. I'm deeply suspicious of the initially skeptical physicist who "changed his mind". The discussion became very heated at times and unnecessarily complex. Always it was accompanied by video seeming to demonstrate that the device "worked" as claimed, but these videos never clearly demonstrated that sustained progress faster than wind could be made. The demonstration of "duration" of stored energy release of intertia in the rotating componenents - by lifting the cart and measuring the time until the propellor stopped spinning due to frictional losses - was flawed, as it did not include the significant effect of momentum from forward movement of the cart which was transferred by gear drive from the wheels to the prop. It's hard to grasp forces/energy interactions in a dynamic moving system. I have drawn a diagram here [5] which I hope makes things more evident.
From looking at that diagram, several things should be clear:
1) That the energy "harvested" from the wheels must create more "braking force" than the "driving force" produced by the energy used by the propellor, regardless of gear ratios or velocity of the cart.
2) That in the demonstration, where the cart is held on the belt (equivalent to artificially accelerating the cart to wind speed in a wind tunnel), there is more kinetic energy put in to the total system (the device) than is required to accelerate the mass of the device to wind speed.
3) That this "extra" energy is stored as momentum in rotating components.
4) Release of that stored energy allows the device to accelerate when released. (that's how it "seemed" to work)
5) The energy will be "used up" (lost to friction), and the device will decelerate to below wind speed. (that was never allowed to be seen in videos)
6) That the device could never accelerate to wind speed unaided - exactly the same constraints apply as to any boat with a sail, sailing directly downwind.
I do believe that the device is worthy of inclusion in Wikipedia somewhere, perhaps to the Perpetual Motion Machines page, perhaps a separate page. It was clever - but probably a hoax rather than a mistake. To work as claimed, accepted laws of physics would be broken.
Note that this doesn't proclude making a device which could make sustained downwind (VMG) progress faster than the wind. Iceboats already do it. But not constantly - as when reaching to pick up forward momemtum the VMG progress is temporarily slower than the wind, and they cannot sail directly downwind faster than the wind on a continuous and sustainable basis. But between point A and a directly downwind point B, theoretically possible and evidenced by GPS plots. I was thinking to make a demonstration device to try and "prove it" in a controlled indoor setting, but it would be quite a complex device, and a bit pointless as the evidence from iceboats has already demonstrated that the theory works. —Preceding unsigned comment added by (talk) 23:08, 14 December 2009 (UTC)
I agree. 'Achieving a speed greater than the windspeed', is perfectly possible; and the momentum, or kinetic energy, so created can be used to coast temporarily directly downwind at such a speed too. This is very different to actually arriving under sail at a distant downwind point before molecules of air that were around you when you started. That is what I would understand by 'sailing downwind faster than the wind', and it is not possible without using some previously-stored energy. --Nigelj (talk) 12:54, 15 December 2009 (UTC)

Dear all: again, I thought as you did until I researched the matter. If you look at the polar diagram for the 18ft Skiff at [6], you will see that an the 18ft Skiff can indeed tack downwind faster than the molecules of air. And an iceboat can do so much faster. There is no need for previously-stored energy. If I understand the rules of Wikipedia correctly, one is supposed to report on what has been published elsewhere, not to provide original research. My objective is to summarize various articles and sources on sailing faster than the wind. Unless I misunderstand the rules, criticism of those articles is original research that does not belong in Wikipedia. But I do agree that it should be reported that there is some skepticism, and I've modified my user page draft to reflect that.--Gautier lebon (talk) 13:32, 16 December 2009 (UTC)

Well,in terms of WP:RS and other policies, we include things based on their weight in reliable, secondary sources. Someone's homepages on certainly don't qualify as that, nor do videos on youtube. The publication Catalyst sounds as if it might, until you read, "Opinions expressed are the author’s, and not those of AYRS ... Contributions are welcome from all." That does not sound like a reliable peer-review process at work. I also cannot find in that author's maths any conclusion about VMG downwind being greater than the windspeed - it all seems to focus on maximum speed achievable in whatever direction, and choosing the angle to maximise VMG, but does not contain the text you want that I could see. But it doesn't matter, as it's not a 'reliable source' anyway. I think the best we can say is that there is controversy and individuals continue to try to prove it, but others still disagree with their findings and conclusions (with refs on either side). What we need, to state this as a fact, is a textbook, published by a mainstream publisher (they have review processes) or an article in some other mainstream publication that does stand by what they publish, to actually say it. --Nigelj (talk) 14:32, 16 December 2009 (UTC)
I take it that you both agree that the device presented by "spork" and others does not work as claimed in theory, and has not been demonstrated to work in experiment, so can be eliminated. There seems to have been consensus between some people involved in discussion elsewhere that if the "spork" device can do it, then iceboats can do it, and vice-versa. There are some documents here [7] also claiming to show downwind faster than the wind (averaged point A to point B, VMG) performance recorded by GPS. But there are flaws in this data. One is that there's no certainty that wind direction and velocity is recorded accurately. Another is that speed of the boat after rounding the top mark does not drop to below wind-speed according to recorded GPS data - so some energy stored as momentum from the boat's upwind tack is carried through. This data was from 2004. Hand-held GPS have become more affordable, much more common, and much easier to use, so it's surprising that some more recent data isn't commonplace - or at least more easy to find. —Preceding unsigned comment added by (talk) 19:53, 16 December 2009 (UTC)
What your source say: It's possible to do a VMG downwind faster than the wind. But thats not the point. Thats well known I guess, but you (Gautier lebon) claim it is possible to sail dead downwind faster than the wind. And that's the problem – it is not possible. Prillen (talk) 07:46, 17 December 2009 (UTC)

Thank you for the good comments. I do agree with Nigelj's comment that the article should mention that there is some controversy. But, again, I haven't found any articles anywhere (peer reviewed or not) that suggest that sailing downwind faster than the wind is not possible. It seems to me that the following statements are not controversial and are amply supported by reliable citations: (1) boats can sail faster than the wind on some courses, notably at 90 degrees to the wind; (2) some boats can make good downwind faster than the wind, by tacking downwind, notably iceboats and the 18ft Skiff (and in February 2010, when the 2010 America's Cup takes place, we will have reliable published actual data on velocity made good downwind by high-performance multihulls); (3) no physical law is violated by a boat that makes good downwind faster than the wind. In addition, the following statements seem correct to me: (4) it is possible to conceive of a theoretical machine that would use devices other than sails to capture the energy of the wind in order to sail dead downwind faster than the wind; (5) some people claim to have built and demonstrated such a device, but there is some skepticism regarding the legitimacy of that claim.--Gautier lebon (talk) 08:24, 17 December 2009 (UTC)

By the way, I didn't start by trying to claim that it is possible to sail dead downwind faster than the wind. It is quite the opposite: I was trying to prove that such a thing is NOT possible. What happened is that I got into a discussion with a very experienced sailor regarding the peformance of the giant multihulls that will race in the 2010 America's Cup. He told me that those boats would sail downwind faster than the wind. I scoffed. He insisted. So I decided to prove him wrong by finding polar curves that would show that no boat can go downwind faster than the wind. Much to my suprise, I found exactly the opposite. So I started to think about the physics and to do more research. You've seen the results. For what it is worth, I've asked a physicist to look at my draft page, and he says that it seems correct.--Gautier lebon (talk) 08:24, 17 December 2009 (UTC)

If you believe that it is not possible that a device could sail dead downwind faster than the wind, then you must believe that such a device would violate some basic law of physics. But I don't see which one would be violated, so I would appreciate specifics comments on that.--Gautier lebon (talk) 08:24, 17 December 2009 (UTC)

For directly downwind faster than the wind, powered by the wind, it is absolutely violating laws of physics. Even if a device could be constructed that had no frictional losses, then it is constrained to sailing downwind almost as fast as the wind, as the energy required to overcome the intertia to accelerate the device to wind speed is always greater than the kinetic energy available that can be transferred from the wind to the device. It can get closer and closer, but never quite to wind speed, unless mass of the device was nil, or size of the sail (and amount of steady wind!) was infinite. The device cannot accelerate to and beyond wind speed directly downwind using the wind as sole source of energy. But I agree with you that a device can be constructed that can make VMG downwind progress directly downwind faster than the wind. Take the device with no frictional losses, accelerate it to well beyond windspeed (iceboats can do 5x wind speed on a reach), then turn to point it directly downwind, and it then travels directly downwind much faster than the wind, powered by the wind, and it can do this indefinitely. In reality, add some frictional losses and it's still possible - unless the combined frictional losses make it impossible. It's not possible in my 8 metre sloop, but in an iceboat or the giant America's Cup multihulls, or 18 foot skiffs perhaps, there's no fundamental reason why it isn't possible. But where is the reliable data to show it has been done? —Preceding unsigned comment added by (talk) 09:39, 17 December 2009 (UTC)
You say "the energy required to overcome the intertia to accelerate the device to wind speed is always greater than the kinetic energy available that can be transferred from the wind to the device". This is not obvious to me. Again, take the thought-experiment of the boat with a very large spinnaker that tows a propeller-driven electric power generator behind it. Theoretically, there is no reason why you cannot use a spinnaker that is sufficiently large to overcome the drag from a generator that provides significant energy. Store that energy in batteries, then drop the sails, and use a propellor to sail faster than the wind. Your average VMG dead downwind can be faster than the wind speed. Of course this is not achieved with sails alone. But I don't see what physical law would be violated by such a machine.--Gautier lebon (talk) 12:12, 18 December 2009 (UTC)
Regarding what has actually been achieved in by real boats or iceboats, I agree that it would be good to have more reliable data. In February, we will have the actual data from the 2010 America's Cup. Does anybody seriously believe that those boats will not make good faster than the wind on the downwind run?--Gautier lebon (talk) 12:12, 18 December 2009 (UTC), that is a very good explanation of the physics. But don't go soft at the end! If you accelerate to 5x windspeed on a reach, then turn into a measured, downwind course, and remain going faster than the wind for a while, that means nothing about sailing downwind faster than the wind. You are simply entering the timed course with previously-stored energy. You might as well allow batteries that were charged the night before and an electric motor, or a diesel engine with 40-million year-old sunlight for power. Starting from A, using no stored energy from before, and arriving dead downwind at B faster than the wind from A to B at the time is impossible.
As I've pointed out before, the polar chart for the 17-foot Skiff [8] shows that it can start at a standstill and tack downwind, arriving at the downwind mark faster than the wind. That is, it makes good 14 knots downwind in 10 knots of wind. That is no more impossible than it is to sail on a reach faster than the wind.--Gautier lebon (talk) 12:12, 18 December 2009 (UTC)

The polar chart for 18 foot skiff shows boat speed of about 7 knots directly downwind (180 degrees) and about 14 knots at about 145 degrees. Now that's claiming around (a little less than) 12 knots (VMG) progress directly downwind (not 14 knots - that is boat speed). On a constant bearing of ~145 degrees, that is not possible, an error has been made in the polar chart. The "bulge" around 145/215 degrees is surely (claimed/estimated) speed with spinnaker set - and as such, either speed stated or angle to the wind must be incorrect. The original reference is to a book published in 1996 (The Symmetry of Sailing / Ross Garrett / Sheriden House) - predating GPS with selective availability off, and common availability of small hand-held GPS units. It is almost certain that the information is incorrect. Furthermore, it is not referenced here [9] and if referenced on the sailing page, a comment should be added that the reliability of the data is disputed. —Preceding unsigned comment added by (talk) 06:58, 19 December 2009 (UTC)

You are correct, the polar chart for the 18-foot skiff shows velocity made good of 12 knots, not 14. I made a trascription error. It is indeed possible, and there isn't necessarily an error in the chart. I realize that I didn't explain things clearly enough. Please look at the new section User:Gautier_lebon/Sailing_faster_than_the_wind#Sailing_on_a_broad_reach. The energy available in the wind is essentially unlimited compared to what is required to propell an iceboat (or a high-performance boat). Energy is not the lim[iting factor. What counts is the force produced by the sails compared to the force exerted by the surface. There is a very good explanation at the bottom of the page [10]. Surely that can be considered a reliable source? I also found several other new citations, which I think can be considered reliable, see the footnotes at the end of the introductory paragraph of my draft article. The 18-foot Skiff never uses a spinnaker because it can always accelerate enough so that the apparent wind is ahead of its beam. Same as an iceboat. Same as the giant multihulls that will be used to race the 2010 America's Cup: they don't have spinnakers because the apparent wind will never be behind the beam.--Gautier lebon (talk) 16:04, 21 December 2009 (UTC)
So, at 145 degrees (with wind on the port side) the polar chart claims 14 knots true speed, about 12 knots VMG speed downwind in 10 knots of wind. So the apparent wind direction moves foreward, and apparent wind speed drops, when accelerating at this angle. But that position indicated on the polar chart isn't possible as the apparent wind direction has shifted to about 2 knots on the starboard side. So the chart is absurd and clearly wrong. The 18 footers here use a type of spinnaker - asymetric "reacher". —Preceding unsigned comment added by (talk) 20:29, 21 December 2009 (UTC)
I don't understand your comment. The polar chart shows only boat speed and direction, not the apparent wind. The apparent wind is not 2 knots. See the vector diagram in the section "Why are eighteen footers always sailing upwind?" in the article at [11]--Gautier lebon (talk) 09:25, 23 December 2009 (UTC)
Gautier lebon, just be aware that everything you say in your middle post at 08:24, 17 December 2009 (UTC) is WP:OR and so, while interesting, inadmissible on Wikipedia articles. --Nigelj (talk) 12:19, 17 December 2009 (UTC)
Yes, I am aware of that, and was not proposing that anything like that be included in an article. But I thought that it was worth including in this discussion.--Gautier lebon (talk) 12:12, 18 December 2009 (UTC)
'If you accelerate to 5x windspeed on a reach, then turn into a measured, downwind course, and remain going faster than the wind for a while, that means nothing about sailing downwind faster than the wind'
It's quite possible to start from zero velocity, reach to gain speed faster than the wind, then turn downwind to "coast" during progress on the downwind leg. If distance lost (relative to windspeed, VMG to wind direction) during initial acceleration and "reaching" is less than distance gained when "coasting" at above windspeed, then (VMG) downwind speed faster than the wind is possible averaged over the duration of a course. It seems likely that this can be achieved with iceboats. But I can't find any evidence to show that it has been achieved. The iceboat GPS plots I have seen start with upwind legs, so momentum is always carried through the top mark. —Preceding unsigned comment added by (talk) 21:24, 17 December 2009 (UTC)
When you say "coast during progress on the downwind leg" you seem to be ignoring the effect of the apparent wind. There will be significant apparent wind, due to the speed of the boat, so the sails would have to be close hauled even on the downwind leg.--Gautier lebon (talk) 12:12, 18 December 2009 (UTC)
Yes agreed. Is that what this whole discussion has been about? In that case if we change the phrase to "Appearing to have sailed downwind faster than the wind" I would have agreed from the start. --Nigelj (talk) 21:38, 17 December 2009 (UTC)
I'm not sure what would be meant by "appearing". A boat starts from an upwind mark and reaches the downwind mark some time later. Thus it has a certain downwind VMG. The question is whether the downwind VMG can be greater than the windspeed. Either it sails faster than the wind or it does not. Or maybe we have an issue with terminology here. What I mean by "sailing faster than the wind" is "the boat's speed is greater than the wind speed". There is a separate phenonmenon, which is "the boat's speed make good downwind is greater than the wind speed". I take that that nobody disputes that boat speed can be greater than wind speed on some courses, in particular a 90-degree reach. I trust that everybody accepts that certain high-performance boats (and iceboats) can have downwind VMG greater than wind speed, by tacking downwind, even if they start at a standstill at the upwind mark. I agree that VMG on a dead downwind course cannot be greater than windspeed for a device that uses only sails. So, presumably, the only disagreement is whether, through the use of devices other than sails, it would be possible to build a machine that can use only energy from the wind in order to achieve VMG greater than windspeed while on a dead downwind course. Incidentally, I presume that everybody knows that a windmill-powered boat (with a propeller in the water) can sail directly into the wind, which is of course not possible for a boat that uses sails.--Gautier lebon (talk) 12:12, 18 December 2009 (UTC)
Yes, I think it is what it is all about - my original questions / statements at the commencement of this thread - particularly 2). There are several places in Wikipedia, where the claim is made - without qualifying the claim by stating "appearing to" as you suggest - that downwind (VMG) faster than the wind is possible, including the statement in the main sailing page : "Some high-performance boats are capable of traveling faster than the true windspeed on some points of sail and can even sail downwind faster than the wind[5][6]; iceboats can sail both upwind and downwind at speeds far greater than the wind." This needs to be deleted or further explanation provided. One of the links provided [12] is a hoax. Even the diagram of the device provided on that link completely ignores the "braking" force of driving the prop on the wheels. The device demonstrated on video has larger and heavier components than the original "spork" device - the duration of release of "extra" energy (than is required to propel the mass of the device to wind (belt) speed - so is artificially put in to the device in the video demonstration) is longer, so it appears to be even "more convincing" on a necessarily fixed length treadmill demonstration, but it is still the same hoax, and should not be referenced from the sailing page, except as a curiosity perhaps. —Preceding unsigned comment added by (talk) 05:16, 18 December 2009 (UTC)
You are correct, the reference [13] that appeared in the main sailing article should not appear there. I have corrected that mistake and provided the correct reference to support the statement in the main article. Thank you for having spotted that.--Gautier lebon (talk) 12:12, 18 December 2009 (UTC)
See above for comments on 18 foot skiff polar chart.

The argument seems to vacillate between inappropriate extremes of being a hoax, or a fringe theory about perpetual motion. But also, any subject that is under so much dispute does not belong in Wikipedia. What something "appears to do" is subjective, a perception based in ignorance, and inappropriate for an encyclopedia. The references cited were not professional, reliable sites that are subject to peer review.[14], [15], [16]. As such, the material and references were deleted. My honest mistake. I didn't consider this.[17] Alpha Ralpha Boulevard (talk) 05:32, 20 December 2009 (UTC)

Folks: it is not a fringe theory that sailboats can sail faster than the wind. That is a well-known fact. What some of you are finding hard to believe is that this can happen even if the boat starts off downwind. Please read the explanation at User:Gautier_lebon/Sailing_faster_than_the_wind#Sailing_on_a_broad_reach.--Gautier lebon (talk) 16:04, 21 December 2009 (UTC)

Oh, and P.S. before you go there, Gautier lebon, I worked for years at a NASA center specializing in aerodynamics. We regularly got letters from well-intentioned people who wanted us to explain how their elaborate theories for anti-gravity boots or faster-than-light drive were incorrect. The answer? It isn't NASA's job to disabuse people who have confused themselves with theory. Nor is it Wikipedia editor's job to do the same. There's plenty of material to be contributed to this article from published, reliable sources. Again, I was mistaken.[18] Alpha Ralpha Boulevard (talk) 05:56, 20 December 2009 (UTC)

Indeed, and I am trying hard to provide an understandable explanation of why and how boats can progress at speeds faster than the speed of the wind, by citing what sources I can find. I've found some more reliable sources now, please look at the latest version. For what it is worth, I did 2 years of physics at MIT before switching to mathematics and eventually got a PhD from Harvard in statistics.--Gautier lebon (talk) 16:04, 21 December 2009 (UTC)
Under the selection removed is another contentious paragraph:
"Some non-traditional rigs purportedly capture energy from the wind in a different fashion and are capable of feats that traditional rigs are not, such as sailing directly into the wind. One such example is the wind turbine boat, also called the windmill boat[5], which uses a large windmill to extract energy from the wind, and a propeller to convert this energy to forward motion of the hull. A similar design, called the autogyro boat, uses a wind turbine without the propellor, and functions in a manner similar to a normal sail [6]."
The page referenced for the Autogyro boat has been removed (it seems to have been a personal home page Yahoo/Geocities). The links to the wind turbine boat seem to come to a dead-end, with no real evidence that the device has been shown to work, and links to forums and discussion and a grainy video of a device that doesn't really show anything to substantiate the statement that they can sail directly in to the wind. (talk) 10:06, 20 December 2009 (UTC)
That material was a little closer to being on-topic, but again, there's so much "core" material of the sort that's available in standard texts that could be added to this Wiki article that at best, these kinds of things belong in their own article. I note, for comparison, that Automobile doesn't mention "generator", even though it's an essential part of most cars, nor does the rather technical Steam locomotive seem to mention anything about the secondary and tertiary functions of the motive power: To generate electricity for lights, and to heat passenger coaches. I.e., the articles focus on main functions only.
Noting that wind power on a sailboat can be used for other things than driving the vessel might be worth noting in passing, in a simple sentence, or with a link to another Wiki article, but as a developed topic is seems to complicate, rather than clarify, here. Regards, Alpha Ralpha Boulevard (talk) 15:21, 21 December 2009 (UTC)
This was my intent: to have a short sentence in the main article that would link to an entirely separate article.--Gautier lebon (talk) 16:04, 21 December 2009 (UTC)

Some of you have suggested that an iceboat could turn downwind and use its momentum (kinetic energy) in order to proceed downwind faster than the wind. Although this is theoretically possible, I doubt that it can be done in practice. As explained at the bottom of [19] an iceboat continues to accelerate when moving downwind because there is essentially no friction to stop it. The kinetic-energy approach is easier to understand if you use formulas. Let V be the windspeed, VB the boat speed, VMG the speed made good downwind, D the distance from the upwind starting point to the downwind mark, TR the time spent running downwind, and TS the time spent reaching to accelerate and accumulate kinetic energy. That is, suppose that the iceboat starts at the upwind mark, reaches back and forth for total time TS in order to attacin maximum V, then, when it is back at the upwind mark, turns dead downwind. We are interested in the speed made good downwind including the time required to build up the kinetic energy, that is, we start counting the time when the boat starts moving. So VMG=D/(TR+TS). But TR=D/VG. If VMG>V, then (if you work out the equations) V/VB+V*TS/D < 1. If you plug in realistic values, you will see that this is not likely to hold. But, again, what an iceboat does is not at all to use its momentum to go fast downwind. On the contary, it builds up momentum as it accelarates downwind because of the force of the apparent wind, which does decrease as it accelerates, but remains sufficient to accelerate the iceboat. See the bottom of the page [20].--Gautier lebon (talk) 16:04, 21 December 2009 (UTC)

Gautier lebon, the comments you added throughout this discussion today alternate between arguing that 'a boat can sail faster than the wind' and that 'a boat can sail downwind faster than the wind'. No one that I can see is disputing the former, it's the latter that we disagree about here. Boats sail across the (true) wind faster than the wind because of the trigonometry of doing so. If you put a tapered wedge into a tapered gap, you can (with enough force, and little enough friction) force the wedge out quite fast by closing the gap quite slowly. There must be a word for that, but it is just like gearing or leverage. Of course it normally is used mechanically in reverse, pushing in a tapered wedge, to apply large sideways forces slowly. Back to sailing, a boat or iceboat that cannot move sideways will shoot off quickly across the true-wind direction, until the apparent wind is so far ahead of the beam that friction and drag prevent further acceleration (as the sail inefficiency increases close-hauled). If you turn that boat downwind, all that gearing, or leverage, or cherry-pip-squeezing effect begins to deteriorate with every degree of turn. For every degree you go off the wind, the 'wedge angle' increases: the first few degrees may increase your SOG (even if already greater than windspeed) as available propulsive force increases, but your VMG downwind is still nowhere near windspeed, which is how the trigonometric 'gearing' is working at these angles, to enable SOG above windspeed. As you approach pointing directly downwind, the trigonometric magic totally disappears and you end up, at best, 'floating' at windspeed with your biggest sails up. At no point in this 90 degrees of possible course angles does your VMG directly downwind exceed windspeed. All of this assumes a long course so that momentum gained on the beam reach is not just used to coast downwind significantly. If all you mean is that the momentum of a fast reach can enable you to coast quickly in any other chosen direction, then that is not, to my mind, "sailing" in that other direction.
Thank you for this good comment. Your analysis is perfectly correct up to the sentence "If you turn that boat downwind". You are correct that the "cherry-pip-squeezing" effect is diminished on a downwind course. But it is not zero. Please read carefully my explanation at User:Gautier_lebon/Sailing_faster_than_the_wind#Sailing_on_a_broad_reach and the references. Since the "cherry-pip-squeezing" effect is not zero, it can produce enough force to still accelarate a boat that has very little resistance, in particular an iceboat. Whether or not VMG exceeds windspeed depends on the course and the speed of the boat. If a boat is sailing at 135 degrees off the true wind, and its speed exceeds 1.41 times the speed of the wind, then it is making good downwind faster than the wind. Your sails are not "floating" because you are close hauled: don't forget the apparent wind shift. Again, iceboats etc. do not use spinnakers because they always accelerate until the apparent wind is well forward of the beam. Momentum has nothing to do with it: as I pointed out above with a formula, it isn't possible in practice to build up enough momentum to make good downwind faster than the wind.
I think the reason these arguments go on for hours at every yachtclub bar, is that there are so many options that ever-increasing alcohol enables most people to forget half of the options, half of the time. 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. --Nigelj (talk) 19:25, 21 December 2009 (UTC)
Yes. Lashings of wishful thinking reinforced by anecdotes - instead of good quality data. (talk) 20:48, 21 December 2009 (UTC)

Dear all: thank you for your comments, which are helpful. Indeed, there is no disagreement that a sail boat can sail faster than the wind. The Hydroptère record proves that conclusively. And indeed, as Nigelj says, the matter which seems to raise doubt is whether (1) the wind can power a sailboat on a downwind course so that it proceeds faster than the wind and (2) whether it can go fast enough to make good downwind faster than the wind. I have finally found a citation which appears to me to meet the high standards that you require, namely the official report of the 2009 land speed sailing record [21]. That report includes (at the end) a diagram of the yacht's course. As you will see, the record (about 3 times wind speed) was set on a course about 120 degrees off the true wind. Hopefully you will all agree that this citation is sufficiently reliable, especially when taken together with the explanation of why this is possible? I refer here only to the question of sailing downwind on a broad reach. I agree that the question of sailing dead downwind is a different issue.--Gautier lebon (talk) 08:56, 22 December 2009 (UTC)

Taking your figures: The course is 120 - 90 = 30 deg lower than a beam reach (true wind). The downwind component of speed (VMG downwind) is 3 * sin(30) = 1.5 * windspeed. The component of speed across the wind is 3 * cos(30) = 2.6 * windspeed. So these figures do show VMG downwind greater than windspeed. I'm sure that we cannot use your figures in WP - they're not mentioned in the source and anyway that is not a reliable secondary source. I'm not really sure that we could use these calculations either, they're WP:OR. To help with googling, I said the 'cherry-pip-squeezing effect' must have a name - it's related to Galileo's 'inclined plane' and to 'tapers' in engineering as well as to wedges. The Sin and Cos stuff above is the way you 'resolve vectors into their components'. --Nigelj (talk) 13:44, 22 December 2009 (UTC)
Thank you for having confirmed that my calculations are correct. The source mentions wind speed and direction and boat speed and direction. Why do you consider that the official report of a record recognized by a national association is "not reliable"? The calculations are elementary trigonometry. They are not original research: they are taken from the references given after the opening paragraph of the draft article, see in particular [22], the very bottom of that page [23] and [24]. Anybody can reproduce the calcuations, and please note that I provided links to the relevant bits of Wikipedia on trigonometry and vecor algebra. By the way, a good explanation of the "cherry-pip-squeezing-effect" is given at [25].--Gautier lebon (talk) 09:25, 23 December 2009 (UTC)

Summary of downwind discussion[edit]

If I understand the discussion above correctly, it can be summarized as follows.--Gautier lebon (talk) 11:23, 13 January 2010 (UTC)

  • There is consensus that high-performance boats can and do sail faster than the wind on some points of sail.
  • Skepticism was expressed regarding the ability of a sail-driven machine to achieve speeds greater than the speed of the wind while sailing on a downwind course. I provided various citations to support the claim. The initial citations were felt to be insufficiently reliable. However, I have not seen any criticism of my last citation, to the world land speed record, at [26].
  • Subsequently, I have acquired the book High Performance Sailing by Frank Bethwaite (Adlard Coles Nautical, 2007). This book confirms the trigonometrical calculations contained in my draft article User:Gautier_lebon/Sailing_faster_than_the_wind and provides, on page 405 and elsewhere, data showing that sailboats can indeed progress faster than the wind on a downwind course.
  • There was also skepticism regarding whether a wind-driven machine can make good faster than the wind by tacking downwind. The detailed data regarding the land speed record shows that this is possible. Further, the polar chart at page 405 of the cited book High Performance Sailing shows that, already in 1996, high-performance sailboats were able to make good downwind at 1.5 times the speed of the wind.
  • Finally, there was skepticism regarding the possibilty of building a device that, while not powered by sails, would use only energy from the wind in order to advance dead downwind faster than the wind. Such a device would not violate any basic physical law because, as shown above, a sailboat can, by tacking downwind, make good downwind faster than the wind. However, it is not obvious that such a device could be built in practice. I provided references to a web site that demonstrates a propeller-driven cart that apparently uses only the energy from the wind and that can advance dead downwind faster than the wind. Some comments were posted to the effect that this must be a hoax, but public references to the web site in question indicate that independent viewers consider that it is not a hoax. Nevertheless, I agree that some skepticism regarding this cart may be justified.

Interested parties should take a look at Sailing faster than the wind and talk written with a biased point of view (in my opinion). Prillen (talk) 10:23, 19 January 2010 (UTC)

As to achieving a steady state downwind VMG of greater than 1.0x windspeed with a traditional sailing rig, I don't understand why there is still debate. All that is required is a sufficiently optimized rig and hull. All standard ice-boats and land-yachts do it easily, and as has been shown from readily available polars, there are a pretty fair number of sailboats that can do it as well. As some claim above, it is not necessary to use KE (turn DDW temporarily) to achieve this and can be done on a fixed heading for as long as there is wind and room.

There's no more of an authority on land sailing performance than the folks at NALSA ( and their site is littered with references, article and real world examples of this regular accomplishment:

Note #3 in faq: "The 'velocity made good' down wind is often over twice as fast as sailing directly down wind."

In an NALSA article titled "putting numbers on iceboat performance", Bob Dill (Nalsa BOD member) Bob has recorded GPS data (and includes plots and diagrams from said data) showing DN class craft achieving sustained downwind vmgs of ~3.5x windspeed lap after lap of a NALSA sanctioned race.

As was pointed out before, the NALSA data recorded during the rather recent Greenbird land sailing world record shows sustained downwind VMGs (more than a mile) of greater than 2x winspeed in spite of the fact that the craft was taking a path optimized for ground track speed rather than vmg speed.

(all of the above raw data is available from NALSA btw).

ThinAirDesigns (talk) 22:02, 25 January 2010 (UTC)


  1. ^
  2. ^
  3. ^ław_Marchaj Czesław Antony Marchaj (born in Słomniki, Poland, on July 9, 1918) is a Polish ...Aero-hydrodynamics of sailing, ISBN 0-229-98652

Bringing the article into complance with wiki policy[edit]

My take on the current article is that it reads as a how-to or instruction manual in many places. I'd ask my fellow editors to take a look at WP:NOTHOW for details on the policy, and I'd like to see the article cleaned up to bring it into compliance with these guidelines.

Several recent edits, although well meaning and basically correct (if un-cited), have taken the article deeper into "how-to" territory. Let's try to move teh article in the other direction. Mr. Swordfish (talk) 22:09, 5 February 2015 (UTC)

'Trim' Section[edit]

Any particular reason that the first letters are bolded in this section? Am I missing something? 1414domination (talk) 17:15, 5 November 2015 (UTC)

Maybe it's someone's memory aid? There are no sources and the whole thing is written like an essay, so it's impossible to know. Kendall-K1 (talk) 21:51, 5 November 2015 (UTC)
It's just one of many things in this article that needs fixing. Please be Bold and rewrite it to conform to WP:MOS. User:HopsonRoad 00:05, 6 November 2015 (UTC)
I would if I had the sources. I do have a copy of Chapman's, maybe I'll take a stab at it. Kendall-K1 (talk) 01:06, 6 November 2015 (UTC)
That's great, Kendall-K1. That should cover it, for instance you can find a discussion of sail trim here. Cheers, User:HopsonRoad 03:05, 6 November 2015 (UTC)

English variant[edit]

We should pick a variant of English and stick to it. Right now we've got "centreboard" but "jibing"; someone changed the section heading but "jibe" is still used more in the article. Kendall-K1 (talk) 21:20, 15 November 2015 (UTC)

I propose that we use the first variant at Glossary of nautical terms. I feel (as an American) that we should be using British English for basic terminology—this honors their maritime tradition that far exceeds others and it is presumably applicable to other English-speaking sailing countries, like Australia, New Zealand and Canada. I propose that terms for more modern gear and techniques employ the English variant that prevails in the country where that advance may have been made. If the sailing advance was made in a non-English-speaking country, then the term that gets the most hits might apply. If there is some dispute about which variant should be the first variant, the discussion should occur first at Glossary of nautical terms. It seems chaotic to write articles in the variant that the initiator happens to use. Any alternative ideas? Sincerely, User:HopsonRoad 23:04, 15 November 2015 (UTC)

Kiteboarding and windsurfing?[edit]

This is to invite discussion about whether mention of these topics is within the scope of this article. User:HopsonRoad 01:31, 23 July 2016 (UTC)