I agree--that website's formula is really wacky.
I just asked it for the hull speed of the Elco 30,
which I designed for Elco in 1987--a classic fantail
launch and as you guys said, about as slippery as they
get. The answer the website gave was a hull speed of
9.3 knots--and with an engine of 26.5 HP. LOL!!!! In
fact, my extended calculations showed a 2 HP engine
would push the Elco 30 at hull speed (6.1 knots)in dead
calm/no current, though of course you'd want to double
that to about 4-5 HP for practical use. And of course,
4 or 5 HP is a long way from 26 HP, and the speed
of 9 knots...well, anybody ever seen a fantail
launch towing waterskiers?? Pass me another Mai Tai,
please.<br><br>Seriously, anybody contemplating using that website should
be warned their formula's all wrong. For fantail
launches and other slipperies, it ought to be about 1.2
times the square root of the waterline length; 1.25 if
your ego's involved. Forget displacement, forget
horsepower, forget fancy prop calculations (they are all
factored in when you guesstimate your block coefficient
and other stuff, which gives you an idea how much to
chip off the theoretical maximum of the formula 1.34
times sq. rt of waterline).<br><br>I have no idea how
the HP calculator on that website works--it's so far
out and there are so many other variables--it's not
even using the ol' 1 HP per 500 lbs. (or even 1,000
lbs) rule of thumb.
