I haven't read this thoroughly (I'm in the middle of my work day), but this article seems to explain some of the physics:
http://members.xoom.virgilio.it/mfcatamaran/hull.htmlFWIW, if I take the hull speed formula from the Annapolis Book of Seamanship and apply it to my Prindle, which I think is 16 feet at the water line, I get:
Maximum Hull Speed = 1.34 * LWL1/2
= 5.67 knots
I can go a lot faster than that with both hulls in the water in pure displacement mode. You don't have to lift a hull to exceed this kind of speed. The Annapolis Book of Seamanship says that the normal hull speed limitations do not apply to catamarans. I think that catamarans normally are displacement boats, even when flying a hull, but the oversimplification normally used for dinghy's just ain't applicable when analyzing the way our favorite displacement boats work.
I found some other interesting links that I need to read in more depth. Here's one on optimizing hull shape for drag and other characteristics:
http://www.basiliscus.com/CaseStudy/geometry.htmlAh well, back to work ;->
Jonathan
