"Michael Daly" ) writes:

On 9-Jun-2004, Marsh Jones wrote:

knots =(1.3*((SQRT)LWL)) which means that a 16' boat can go about

5.2Knots regardless of how much power you put to it. (Unless you can

pop it over the bow wave and get it planing).

Not really. Olympic class paddlers, as one example, routinely take their

canoes/kayaks well past hull speed without any evidence of planing. Hull

speed isn't a speed limit, it's a point where paddling gets tougher, faster.

It seems to have more relevance to big fat vessels (like keel boats) than

to long, skinny paddle craft.
the "hull speed" of 1.34 times the square root of the waterline length

only applies to deep displacment hulls. canoes and kayaks are such light

displacement narrow boats that they can go faster with low power. long

narrow hulls like catamarans can also "sail through" their displacement

wave and exceed the 1.34 number with low power.

we were discussing power requirement in another thread. if you multiply

the total resistance in pounds times the speed in knots times 0.003072 you

get the power requirement in horsepower to sustain that speed. a knots is

1.15 times a mile per hour. the problem is finding out what the total

resistance is. there might be sophisticated hull design programs which

will predict more than the wetted surface and wave-making resistances but

I am not aware of any. you will also find differences in computed wetted

surface and volume for the same boat among different hull design programs.

I don't know how precise you can expect to predict teh power requirement

for any boat. Perhaps if you do the calculations for two boats using the

same hull desing software you will get a pretty good comparison. So

comparisons of calculated numbers from the same manufacutuere might be

pretty close. If there are big differences in teh numbers for the boats

you are interested in then there is probably a basis for making a choice.

But if the differences are small I would not trust the nubmers.

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