[MHml] horsepower

[Alan Christoffersen]

Bill Gibbs skrev:
> Evan,
> Thanks for the offer.  But don't go out of your way for this.  It's only
> been one night of doodles so far. :-)
>
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> Bill,
>   

We used to use a simple guesstimate for fuel consumption for a given 
boat/engine/prop setup based on:

Fuel consumption  = K x n3,  where n is the rpm,  As fuel consumption 
and horsepower can be considered pretty much as a linear function, then  
you need around 8 times more horsepower to  double your speed.

N.B. This is only a guesstimate, and can only be used for displacement 
mode, not for
forced mode or planing hulls.

Years ago I bought an Iroquois Chieftain, 32 foot cat, weight around 2,5 
tons. It had 2 x 60 hp 2 stroke outboards, and could do 18 knots flat 
out.  I replaced them with 2  x 9,9 Yamahas. One of these could push her 
at around 7 knots flat out!

So I guess the formula is good enough for a ball park figure.

Good Luck

Alan Christoffersen