T&T: Horsepower

[Jim Ague]

> The usual NA rule of thumb figure for propelling a displacement yacht at 
> hull
> speed is 1 hp. per 500 lbs. of displacement. Add 20% more power for
> emergencies and that's all the power the boat can reasonably use.

After doing some very, very extensive research (reading the latest, June 
2007, boat reviews in the glossy Sea magazine that arrives unsolicited in my 
mailbox monthly), I find that the above 500 number is way, way off. From the 
magazine:

Marlowe Explorer 82, 105,000lbs, twin 1500 Cat C30s, 1 hp per 35 lbs

Nordic Tug 42, 31,400lbs, 540hp Cummins QSC, 1 hp per 58 lbs (and it gets 
"just under 5nm/gal"!!!!!)

Krogen 58, 96,830 lbs, twin John Deere 154, 1hp per 314 lbs (actually JD 225 
derated to 154)

Silverton 33 Sport Coupe, 16,300lbs, twin Yanmar 315, 1hp per 26 lbs

So as you can see, except for the Krogen, that 500 number just isn't right, 
by a factor of 10.

Ouch! (Just bit my tongue.)

-- Jim Ague