Talk:Knot (unit)

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Speed[edit]

knot is a unit of speed, not velocity. Speed is a scalar (distance over time) while velocity is a vector (displacement (direction vector) over time). A knot is obviously the former. Stewart Adcock 18:42, 20 Nov 2003 (UTC)

Name[edit]

I'm changing the name of the article to "Knot (speed)" from "Knot (nautical)", because the unit is used not only for nautical things but also in meteorology and aviation. GrahamN 15:12, 1 Apr 2004 (UTC)

How about nautical mile per hour? –radiojon 03:09, 2004 Apr 2 (UTC)

The thing is known as a "knot", not a "nautical mile per hour". What's wrong with "Knot (speed)"? GrahamN 16:38, 2 Apr 2004 (UTC)

Wrong data?[edit]

I've done some calculations, and unless I'm mistaken 1 knot equals 1.32 miles per hour, not 1.15 as the article states. Furthermore, I believe it would be more useful for international users if the equivalent speed in kilometers per hour (kph) was added, since it's a more familiar scale of speed, with which most people around the world can relate (not the case of miles per hour or metres per second). Regards, Redux 12:20, 14 Sep 2004 (UTC)

  • My caclulations agree with the article. (If you follow the link on the number in the article, you'll see that Google's calculations agree as well.) But as for kph, that's easy: 1852 m/h = 1.852 km/h! Isn't the metric system nifty? -- Toby Bartels 05:33, 14 Oct 2004 (UTC)
You were right about the knot/mph ratio, I had miscalculated. I'd remove the "precisely" after the kph conversion though, since 1.852 is a round up (the actual precise number being 1.851999985024). I'm glad to have been of assistance in the m/h v. km/h thing. Regards, Redux 20:06, 11 Dec 2004 (UTC)
Redux talked about 'metres per second', not 'per hour'. And timekeeping, alas, isn't that simple in the metric system. It's not decimal, but more like duodecimal or 60-base. But the article now already gives km/h, so what am I on about? DirkvdM 10:26, 21 August 2005 (UTC)

Though I'm neither a mathematician nor a sailor, I'd consider replacing the term "roughly" as the characterization of the conversions from knots to statutory miles per hour, at least. The reason? Because, worked out to six decimal places as it is, a difference of one digit in the last decimal place (e.g., 1.150780 mph instead of the stated 1.150779 mph) amounts to traveling 0.0634 inches (1.61 mm) more or less over one hour. To me, "roughly" in this context indicates a coarse measure. However, wouldn't the differences here be really difficult to measure in any practical situation. Wouldn't the phrase "almost precisely" be a better substitute? Am I missing something here? Anoneditor 22:58, 4 November 2006 (UTC)

I think the correct mathematical phrase is "is approximately equal to". The reason for including the phrase is to highlight the fact that one of the conversions (to 1.852 kilometres per hour) is exact and by definition; the others are only true to the accuracy shown. I agree that the current version is 'sub-optimal', but what do people think is the best way to express this? Maybe two lists, one with only that conversion in it? Maybe change the phrase introducing the current list, and keep the bold print just for that one? --Nigelj 10:10, 5 November 2006 (UTC)
OK, how about this?

== Conversions ==

1 (international) knot is exactly equal to 1.852 kilometres per hour, and is approximately equal to the following:

Looks fine to me. So good in fact that I have added it to the article. --Nigelj 21:40, 5 November 2006 (UTC)

I cannot believe "it looks fine to me" has been accepted as a reason to post something on a wiki! All information is required to be verifiable, there is no verified information on much of this article. Therefore all unverified information will be deleted by February 1st 2012 if it has not been fixed--75.17.205.29 (talk) 20:57, 28 January 2012 (UTC)Dr. S

Locale[edit]

where is the knot unit used? is it used outside of USA as well? Xah Lee 03:49, 2004 Oct 12 (UTC)

I'd guess that the knot is usually used at sea. ;-) Yes, it is widely used outside the US. It is used in Britain at least. Stewart Adcock 00:20, 15 Oct 2004 (UTC)
Knots are used around thw world for maritime and aviation purposes, like GMT is. Dolive21 11:34, 2 February 2006 (UTC)

Examples[edit]

I looked here to see what typical speeds of ships are. The Stad Amsterdam is supposed to be very fast with 16 knots. How fast is that for a tall ship? And what are typical speeds of other types of boats/ships? DirkvdM 10:26, 21 August 2005 (UTC)

For a clipper, that's fast. That's also a little faster than many naval ships typically go, but I know that Nimitz class carriers are capable of around 30 knots. BioTube 01:17, 24 September 2006 (UTC)

Most modern warships are capable of around 30 at knots full steam.

Text cut and pasted from other site[edit]

I just removed a big chunk of text which was added by user 69.58.224.12. This was because it was just cut and pasted, probably from this site. --Spondoolicks 09:43, 23 August 2006 (UTC)

Thanks. I've also now removed the 'CleanUp' tag that had been added because of this strange text. --Nigelj 18:51, 23 August 2006 (UTC)


Why?[edit]

Why do they still use inferior knots and not, m/s or km/h? --- Unsigned comment.

Read second paragraph of the "Discussion" section in article. --- Safemariner 14:56, 30 December 2006 (UTC)

Velocity made good?[edit]

Could someone confirm that velocity made good really refers to speed over ground. I am a ship science student, I have only come across velocity made good as meaning the velocity vector either to windward or toward some reference point (typically toward a waypoint in GPS's). —The preceding unsigned comment was added by 152.78.254.72 (talk) 19:03, 13 March 2007 (UTC).

It can be more complicated for a sailing boat: You might be beating hard on the wind, and so unable to sail directly towards your waypoint: VMG towards the waypoint is very different to SOG in that case. --Nigelj 20:19, 13 March 2007 (UTC)

From the text of the article it is not clear why Speed Over Ground SOG and Velocity Made Good are expressed in knots. Neither of them is speed relatived to the fluid and seems to be inconsistent with the rest of the article. Perhaps a dimensional analysis is needed here. Unsigned comment by User:72.213.32.110

Most speeds on boats and aircraft are expressed in Knots. This is true whether it is the speed through the water (STW), as measured in the past by chip logs or more recently by various patent logs, speed over the ground (SOG), measured by GPS or radar, or velocity made good toward the next waypoint (VMG), also measured by GPS or radar. No dimensional analysis is needed because they are all in the same units --
STW + (the component of the speed of the current parallel with the boat) = SOG
all measured in knots, paying attention to signs.
. . Jim - Jameslwoodward (talkcontribs) 13:38, 3 May 2010 (UTC)

Still do not understand[edit]

I looked this up for the origin of the term "Knot", which I still do not understand. —The preceding unsigned comment was added by 71.218.13.153 (talk) 03:56, 7 April 2007 (UTC).

The section on the origin of the knot makes it sound so precisely invented. In fact the use of a log was modified over time, with different distances between the knots on the line and different times measured (though I've never seen other than 28s and 30s). At one point, the British Admiralty defined the knot it terms of distance over time (as a result of measuring the distance along the meridian) and that resulted in one standard for distance between knots. Later refinements of the meridian length resulted in further refinements of the knot distances on the line as well as the time for the glass. Eventually, the results converged on the information stated in the Origin section.
The principle is simple - throw a log overboard and see how long it takes for the vessel to move some distance away from the log. The log has a line tied to it and the distance is measured by counting the number of knots tied into the line as the line passes over the stern of the vessel. The time is fixed at, say, 30 seconds. Knowing time and distance you can calculate speed = distance/time.Michael Daly 20:02, 30 August 2007 (UTC)

Missing information[edit]

The rational for the name "Knot" is absent from this article. It is allegedly derived from the number of physical knots in a log line dropped into the water and pulled astern by the way of the vessel that pass in a time period. But this needs citing prior to insertion in the article. Fiddle Faddle 22:57, 17 August 2007 (UTC)


-What i want to know is why they used 47 feet 3 inches between each knot tied in the line? It is kind of a random distance to use. —Preceding unsigned comment added by 64.19.242.245 (talk) 14:13, 25 October 2009 (UTC)

From the article you may determine that the distance together with the time interval used represented one nautical mile per hour. Fiddle Faddle (talk) 21:53, 25 October 2009 (UTC)

Surplus information[edit]

I do not believe the section Nautical examples as it stands today has any relevance to this article. It refers to displacement hul maximum theoretical speeds, not to knots per se. Fiddle Faddle 22:57, 17 August 2007 (UTC)

I agree that the section does not belong here. Based on misunderstanding and misinterpretation of the term hull speed and its (frequent mis)use, I question whether it should be included anywhere :-) - but that's another discussion. (It is useful if you want to discuss what Froude did and how speed vs resistance behaves in typical, but not all, displacement hulls). Michael Daly 20:09, 30 August 2007 (UTC)
See the section "Examples" above: an ordinary member of the interested public asked for some typical examples of use of the unit, so I supplied some. If it doesn't suit an extreme-expert's most pedantic sensibilities, then of course, you may delete as much material as you want. (It's much easier than adding any!) --Nigelj 18:19, 1 September 2007 (UTC)
Please don't take edits in Wikipedia personally. You are more than welcome to create an article about displacement speeds and place this information in it, but it is not in place in this article. I would welcome your creating it in a new article, I would welcome a link to it in See also. Please do not resort to name calling, and assume good faith in your comments. I removed, and am removing again, the section that two of us feel to be out of place here. Please just create it, and create it well, in a new article. The work you put in is worth preserving, but this is not the article for it.
While it was only a small consensus it certainly was a consensus for removal. We really do need the information you created, just not in this definitive article about the unit itself. Fiddle Faddle 19:09, 1 September 2007 (UTC)
Who is this 'we'? The Management Committee of Wikipedia-editors-who-just-know-what-is-needed? If you want a new article, then create it yourself, my friend. --Nigelj 19:35, 1 September 2007 (UTC)
The material has been transcribed to Hull speed. Fiddle Faddle 08:53, 2 September 2007 (UTC)

abbreviation for knot[edit]

If you have a view on what abbreviation(s) should or should not be used, you may be interested in reading this discussion. Thunderbird2 20:59, 4 September 2007 (UTC)

While I agree with the intent of your most recent change to the knot's abbreviation, I have a bit of a philosophical problem with the IEEE, of all organizations, as a prime reference on a measure of significant interest to the mariner.  :-) I'd prefer to see a prime reference (i.e named in the text of the article) that is primarily an organization that is nautical or specifically concerned with weights and measures. Chart 1 (Canada) or Chart 1 (USA) being the standard reference for nautical charts in those respective countries may be preferred. Michael Daly 06:00, 9 September 2007 (UTC)

I see your point. The counter-argument is that the IEEE is an international organisation, while the ones you quote are not. On this particular abbreviation they appear to agree though. At least the Canadian one uses kn, but I wasn't sure where to look in the NOAA document. Was I missing something obvious? Thunderbird2 09:53, 9 September 2007 (UTC)

While this is unreferenced, custom and practice when I was taught navigation was always "kt" and also the fact that it is stated as a plural "kts". Fiddle Faddle 10:01, 9 September 2007 (UTC)

Aha - I found the NOAA abbreviation (also kn). So if the IEEE as well as the maritime authorities of Canada and USA all favour kn, that sounds like it qualifies for an even stronger statement (favouring kn over kt) than the one we have already. Do you agree? Thunderbird2 11:50, 9 September 2007 (UTC)

I see every reason to state the total universe of abbreviations, noting the preference for kn and the existence of kt and plurals where used, and using {{cite web}} or other appropriate template to reference whatever is required. Fiddle Faddle 13:29, 9 September 2007 (UTC)

I edited the introduction. Is that OK now? Thunderbird2 15:55, 9 September 2007 (UTC)

Very good. :-) Michael Daly 16:08, 9 September 2007 (UTC)

I added a source reference for the 28-second chip log definition. Coould somebody more skilled than me check the reference formatting? Mleivo (talk) 19:29, 28 February 2008 (UTC)

Abbreviation kn reopened[edit]

I have redone the reference for the abbreviation "kn". The US (NOAA) document whose citation I have left in place, is, in fact, a document which incorporates IHO Chart INT 1 (the IHO does not publish its own charts), and, therefore, represents the international position on the subject. The Canadian document which was previously cited is essentially identical, as is New Zealand 201, British Admiralty Chart 5011, and similar publications from other nations. Although called charts, these are in fact 96 page A4 books. . . . . Jim . . . . Jameslwoodward (talkcontribs) 21:13, 19 December 2009 (UTC)

"Knots per hour" wasn't always an error.[edit]

While the expression "knots per hour" is considered erroneous today, this wasn't always so. If you look at 19th-century sources on maritime and naval matters, you will frequently see "knot" used not as a measure of speed, but of distance (synonymous with "nautical mile"), and speeds will often be given in "knots per hour". Searching Google Books for the phrase over that timeframe turns up plenty of examples, often in professional naval and maritime journals that presumably would be careful about proper usage of terminology. Of course, my mentioning this here counts as original research, but hopefully someone can find a discussion of this change in usage in a reliable source so that it can be mentioned in the article. --Colin Douglas Howell (talk) 00:26, 29 August 2011 (UTC)

ISO status[edit]

See #2, whose title is

"Non-SI units accepted for use with the SI, and units based on fundamental constants"

which makes the third sentence in the article backwards:

"The knot is a non-SI unit and not accepted for use with the International System of Units (SI)"

as it is clear that the knot is accepted for use with the SI. Therefore my change, eliminating the "not", appears to be correct.

Footnote (f) in the same cite says:

"(f) The knot is defined as one nautical mile per hour. There is no internationally agreed symbol, but the symbol kn is commonly used."

which is consistent with the change I made. Of course this reference may be wrong, but I see no reference for the claim that "kn" is an ISO standard symbol. Certainly all the navigators I know -- American, German, English, and Swedish -- use "kt", not "kn".. . Jim - Jameslwoodward (talk to mecontribs) 16:05, 11 September 2013 (UTC)

Looks good. Good catch. It's just possible that someone may confuse kt with 'kilo-ton', I suppose. --Nigelj (talk) 16:57, 11 September 2013 (UTC)
The statement "there is no internationally agreed unit" was probably correct at the time the article was written, but it is no longer so. That changed in 2006, when ISO published the International Standard ISO 80000-3. That standard defines the knot (I quote verbatim) as "knot (kn), 1 kn := 1 nautical mile per hour = (1 852/3 600) m/s ≈ 0,514 444 m/s". Dondervogel 2 (talk) 17:04, 11 September 2013 (UTC)
OK, thanks. Can we have a WP cite for that? And do you agree that the removal of "not" from the first sentence is correct? . . Jim - Jameslwoodward (talk to mecontribs) 17:18, 11 September 2013 (UTC)
I'm beginning to see where the confusion is coming from. That 8th edition SI document is also published in 2006, so perhaps the two organisations were not communicating well with each other. Given that ISO and SI contradict each other, do you think the article should include a statement to that effect? I think you're right about removing the word "not" (if you mean the second occurrence - the first one is correct ;-) Dondervogel 2 (talk) 17:33, 11 September 2013 (UTC)
Hmmm. Given that SI is stating a negative, while ISO is stating a positive out of its own book, I think I would run with ISO. The fact that ISO lists it says that SI is simply wrong, or out of date. I'd still like a cite for it, though. . . Jim - Jameslwoodward (talk to mecontribs) 19:29, 11 September 2013 (UTC)
I added a reference to the standard itself. Or did you mean a secondary reference? Dondervogel 2 (talk) 19:35, 11 September 2013 (UTC)

──────────────────────────────────────────────────────────────────────────────────────────────────── We can't make the statement that knot is "not accepted for use with the International System of Units (SI)" supported by a citation to the BIPM SI Brochure where a table called "Non-SI units accepted for use with the SI" includes the knot. That was a good catch, and I have fixed it again. There are other problems in that lede now, though. One is that we say that kn is the ISO standard symbol and that "The same symbol is preferred by the IEEE". What we don't mention is that SI says, "There is no internationally agreed symbol, but the symbol kn is commonly used", so they acknowledge or recognise it too. Secondly, we give kt and NMPH a great deal of prominence, when they are both clearly 'wrong' by modern day standards, and their mention is uncited. Fixing these would require quite a rewrite if the new lede is to be readable. It must also be remembered that this is the WP:LEDE and so should be summarising points made with citations in the main body pof the article. In other words, most of this detail needs to be moved down into the article, fully cited, and a summary placed in the lede. Lots to do. --Nigelj (talk) 19:53, 11 September 2013 (UTC)

Please be careful what you do with "kn" and "kt". The SI and its strict adherents tend to make pronouncements that completely ignore what ordinary people actually say -- does anyone you know say that it's 1.5 megameters between point A and point B? Of course not , we say 1,500 kilometers although that is wrong by SI rules. (My spell checker marks "megameters" and "megametres" as misspelled.)
While I fully recognize the limitations of WP:NOR, I am an experienced marine navigator and, as I said above, none of the people I know -- American, German, English, and Swedish -- use "kn". I think the use of "kn" is intended to avoid confusion with kilo-ton, but as a practical matter I can't see that happening -- we say that a large ship displaces 80,000 tons, not 80 kilo-tons. Also note that the FAA uses "kt" as the abbreviation for knot (see, for example 14 CFR 1 part 35 appendix B). On the other hand, Bowditch uses "kn". I would be comfortable if we said that both "kt" and "kn" are in general use. . . Jim - Jameslwoodward (talk to mecontribs) 10:57, 12 September 2013 (UTC)