Talk:Knot (speed)

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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)

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)

Contents

[edit] Wrong data?

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)

[edit] Locale

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)

[edit] Examples

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.

[edit] Text cut and pasted from other site

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)


[edit] Why?

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)

[edit] Velocity made good?

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)

[edit] Still do not understand

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)

[edit] Missing information

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)

[edit] Surplus information

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)

[edit] abbreviation for knot

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)