Air and water are both fluids, so the hull drag goes up with respect to velocity squared as well. That's why planing and hydrofoiling craft are able to get up to these high speeds- they reduce surface area as their speed increases. So in this case, a catamaran does not act the same way as a planing craft because it's surface area does not decrease with increased speed.

My point however was that you can't look at weight alone because here we have two craft (YPE and windsurfer) that are able to travel at roughly the same speed yet one weighs about 10 times as much as the other. We could throw Hydroptere into the equasion and probably have another boat that weighs about 10 times what YPE weighs.

The critical issue (and one that effects catamarans as well as any other sailboat) is that the total weight essentially contributes to both drag and power. The trick is to maximise the power-to-weight(drag) ratio something that YPE and windsurfers have done quite well. This means having minimum boat weight, but not necessarily minimum overall weight.

sm