I find
that I can maintain a greater speed in my longer boat than in my shorter boat. So I guess we have a stalemate.
No stalemate
– Last Updated: Jun-16-16 10:28 AM EST –
I started out that post pointing out that shorter boats with less wetted surface area move through the water with less effort at slow or moderate speeds (don't lose track of what was said in the post you initially replied to - that's where the distinction was made regarding what speeds this comparison applies to), but that has nothing whatsoever to do with the topic of maximum speed, which was the topic I switched to a few sentences later. If the only thing you want to focus on is maximum speed then you should just ignore boat comparisons having to do with slower speeds. The two topics are not the same. Of course longer boats have greater top speed, and that's exactly what I said in both of those posts.
That makes a comparison irrelevant two different
paddlers.
If my hull does 7 mph I sure as hell can’t cruise at 6.25 mph.
Hull speed is a measurable characteristic. This is not anecdotal stuff.
White water boats have allover lower hull speeds, for a good reason. Rec boats faster but not as fast as typical 16 to 17 ft sea kayak. Tacing tuned long boats like Epics fastest.
I have to disagree with this — hull speed as traditionally defined is a (too) simple parameter calculated based on water line length only. It does not taken into account any other hull shape parameters, and is not really a measurable quantity, per se. What you say about white water, rec boats and sea kayaks is all correct, of course, but the variation is not really captured by the calculated hull speed parameter.
Hull resistance increases with speed in a complicated way based on the different rates of increase of skin friction and wave-making resistance, which together sum to the total resistance.
Resistance curves are typically exponential; over a certain range of speeds the resistance will exhibit a more rapid increase. The calculated hull speed is usually within that range of speeds (not always). But there is no fixed and identifiable speed at which this happens, hull speed is just a general indicator, so is not really used in naval architecture nowadays. It is a decent way to compare similar hulls, but beyond that is not too useful quantitatively.
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OPer asked if sea kayaks were faster than unnamed other category of boat, but it would be strange for someone coming from racing or WW boats to ask that. In both cases hull speed is an normal factor in talking about a boat. So they pretty much had to be referring to rec boats.
One factor is the minimum volume necessary to float a person. That is static and doesn’t change.
A short boat must be fatter than a long boat to meet that volume. That makes it plow through the water. It is especially true with current design ideas of wide shoulders and hips, so anyone will feel safe in them.
There are two hull types, planing and displacement, that makes comparison almost impossible.
Hull speed is defined by the point where the bow wave frequency is the same as the length of the boat. Though it was originally worked out for sailboats, it comes close in kayaks. The efficiency of the boat can make a select few go past hull speed with little extra effort.
Part of that efficiency is in the rigidity of the hull. Soft hulls are slower because of changes to the hull and interfering with the bow waves.
Comparing the speed of different boats is apples and oranges. At a few races people in plastic boats and occasionally Hobie pedal drive enter. Without exception they take longer to do a five mile race than a boat built for speed takes to do a ten mile race. It also takes much more effort for them to do that.