On Fri, 2 Apr 2010 19:35:35 -0700, "CalifBill"
wrote:

On a planing hull, maybe not much difference in fuel burn, but still have to
move water. On a displacement hull, thedifference will be dramatic. Yoou
have pretty much effectively double the hull length, giving a higher hull
speed. This should add both performance and fuel economy.

The secret to catamaran efficiecy is light weight combined with a high
length to width (beam) ratio. A typical ratio for either a
displacement powerboat or sailboat is about 3:1. The hull of a
catamaran however might be twice that or even greater. At high
ratios the formula for hull speed goes out the window because wave
making/hull drag is greatly reduced similar to what you'd experience
with a canoe hull or a rowing shell. Basically you can think of it as
being more streamlined. Naval architects refer to it as a lower
prismatic coefficient.

With regard to capsize issues, most cruising sail cats are under
rigged with short masts and small sails. That greatly decreases the
liklihood of becoming overpowered in a wind gust.

I've never heard of a power cat capsizing but it certainly could
happen with the right wave conditions, as it can with any other
powerboat.