[PCW] FP horsepower increase

[Alexander Veis]

Dear Pat
Thank you for your very detailed analysis. Generaly i agree but i cannot
understand in the case of Manta cat how is possible from 160hp to 225hp to
gain only 2kn (19-21kn) while from 225hp to 250hp (total increase 50hp
instead of 130hp) gainning 2kn as well (21-23kn).
Alexander

----- Original Message ----- 
From: "Pat Reischmann" <preischmann at msn.com>
To: "power-catamaran" <power-catamaran at lists.samurai.com>
Sent: Monday, January 07, 2008 4:02 PM
Subject: [PCW] FP horsepower increase


> I suspect the FP hull designs are very similar to the Manta, CS, Maine
cat,
> and other "displanning" hull forms as Pete Brady would call them. These
hull
> forms are very efficient in the displacement mode and the mid range 15-18
> knots semi-displacement mode. Adding more horsepower after a point doesn't
> seem to add much more speed nor efficiency. I think some people don't
> understand the distinction of difference between these hull designs and
full
> planning hull forms (symmetrical and asymmetrical).
> All out planning hull forms actually become more efficient at the higher
> speeds than the displacement type hulls, but don't enjoy the low speed
> efficiency, sea-kindliness, and fuel economy in the mid range of the
> displacement type hull forms. The Manta is a good example. With a pair of
D-3
> 160 hp engines top end is 19 knots, with the D-4 225 hp 21 knots, with the
250
> hp 23 knots.
> Based on overall efficiency, noise, etc we found the 225 hp to be well
suited.
> At 75% throttle the 160 would cruise at 15 knots,
> the 225 at 17 knots and the 250 19 knots. I think FP is probably giving
good
> advice about hp increases.
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