Talk:Hull speed

message: The article is Hull Speed.  The introductory text on Speed Length Ratio is redundant as it is addressed in the referenced Froude number article.  This is also true for the History section - I think you would agree that the history of Hull Speed is what should be addressed here not the history of Speed Length Ratio.  I have no reference for the history of Hull Speed and would suggest deleting the section in its entirety.  The "Physics" section is somewhat misleading ... as discussed at length above, the physics of wave making resistance is incredibly complex and the "Physics of Hull Speed" is something that is at best, misrepresented in the present article.  Currently the attached graph adds nothing to the article as the "Hull Speed" point (i.e. Speed Length Ratio = 1.34) has no distinguishing characteristic at all.  This, I'm afraid, is the point that I have been trying to make ... Hull Speed is not a real thing at all.
I’m afraid my opinion is still that the present article does not describe the subject “Hull Speed” well and still has a significant amount of text that is not relevant.
At the risk of raising your ire, would you consider re-introducing the text I had put forward and enhancing the appeal to a general reader while still maintaining the technical validity?
Jmvolc 02:08, 27 May 2006 (UTC)
thread_title:  Still astray of the subject, I fear 

message: After reading the article (admiditly not very closely) I still do not have a clear idea of how the physics produces the effect. I do have a physics background, with a family background in sailing, so I have heard the term "hull speed" before - understanding it to be an emperical result - the top speed of a displacement hull set solely by the waterline length of that hull. After reading the article it does not seem completely clear why 1.34 is the magic number. Maybe we need a slightly stronger link between the "physics" section and the "hull speed" section? Is this a correct understanding: (a) The wavelength of the bow-wave is set by the waterline length. (b) The propagation speed of a wave is set by the wavelength. (c) The "hull speed" is the propagation speed of the bow-wave, since traveling faster than the bow-wave is really hard to do in a displacement hull. If this understanding is correct - should we have some wording to that effect in the article, or does the article already make it clear? j-beda 12:19, 8 July 2006 (UTC)
replies: text: Yep, that's right.  Basically, when you hit a speed/length ratio of 1.34, the hull speed, you have to basically climb out of the hole created by your wake.  The Savitsky paper I've been working from has some really good diagrams of this, and I'll try to re-generate them and get them in the article.  scot 21:52, 13 September 2006 (UTC)
thread_title:  Another Layman's Comment 

message: I wish the term hull speed would go away.  It is the most misunderstood and misused term among amateur boat users.
;Hull speed is a special case of a speed-length ratio:These are just two different terms for the same idea applied for the specific case of a vessel when the waterline length equals the wavelength of a transverse bow wave.
;Hull speed is not empirical: The hull speed equation has been derived by Froude based on a simple assumption - set the wavelength of a transverse bow wave equal to the waterline length of a vessel.  The reason is to determine the speed-length ratio where the two are the same.
:This is explained in Marchaj's Sailing Theory and Practice (pp 245-257).  I've put this derivation on my wiki at Hull speed.
;Hull speed is not a speed limit:It is an arbitrary point where the wavelength of a transverse bow wave is equal to the waterline length of the vessel.  It just happens that this point, when viewing a graph of speed versus resistance, corresponds to a point where the resistance increases a lot for a relatively small change is speed.  There is no "kink" or visual indicator of this point in graphs of typical hulls in towing tests.  Many vessels can routinely operate at speeds much higher than hull speed without planing.
;Hull speed does not result because you have to "climb the bow wave":You can no more climb the bow wave than pick yourself up by your bootstraps.  You can't climb a wave you are making.  The force increase is because you're pushing a lot of water around and the incremental increase at that speed is significant.
;Hull speed does not mean your bow rises sharply and stern sinks significantly:For some vessels, you'd have a hard time noting any apparent change of trim due to the bow/stern position.  ICF flatwater racing kayaks come to mind.  The pitching of the kayak due to the paddler's effort is way greater than any trim difference (such kayaks/paddlers win races around a speed-length ratio of 2.2).  In other craft, you can see a difference.
;Moving faster than hull speed does not result in planing:Planing requires an appropriately shaped hull.  Lacking that hull shape, the hull will continue to displace water in order to support its weight.
I really wish the term would go away. Michael Daly 22:57, 31 August 2007 (UTC)
thread_title:  Hull speed drives me nuts 

message: This article does not belong in physics, that's what the problem is. It belongs in navigation (boats, yachts, ships). Hull speed is called displacement speed in Swedish and that is actually a much better term, since it makes it clear that it refers only to the speed when a hull is traveling in displacement mode. It is still a fundamental factor in boating, especially sailing, though even though there are sailing boats that are designed to plane now (e.g. Volvo Open 70, Mini Transat) the vast majority of sailing yachts are displacement boats, and when sailing them you must take hull speed into account in the strategy of course selection, sail selection, and such. Thus I propose that this article be grouped with those dealing with boating and especially sailing, and removed from the physics articles, where it really doesn't have much significance. Dr Ulf Erlingsson (talk) 13:25, 4 December 2011 (UTC)
thread_title:  Reclassify article as boating related 

message: I took the liberty to change the flow of the article to streamline the opening a bit. Hope this helps!
02:31, 18 January 2013 (UTC)
thread_title:  Took liberty to change the flow of the article 

message: I think the above sentence is wrong. The size, or vertical amplitude of a wave has no particular connection to its wavelength. The wavelength is governed by the speed. So while I agree that the wavelength increases with speed, i am not convinced the size does, and even if it does increase, it does not affect the wavelength.Greglocock (talk) 23:23, 15 June 2014 (UTC)
thread_title:  "As boat speed increases from rest, the size of the bow wave increases, and therefore so does its wavelength" 

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