I would contend that on a beach cat longer is always better. Sure there is a speed at which shorter is better, for a 300kg displacement hull i.e. (150kg boat + 150kg crew flying a hull) it is above 25 knots, at 200kg it is above 20knots and at 100kg it is above 15knots. Below those speeds longer is better, above shorter is better.

So to say that an F16 is optimized at 5m is saying that it is optimized for a speed of between 20-25knots. When we are talking about faster boats in the context of a beachcat I think we are talking about faster around the course not straight line blasting, probably with an average speed of around 8-12 knots. At these speeds wave drag is very significant , for 300kg displacement (150kg boat) wave drag is the highest drag component up to about 7 knots. So long and thin is always best for low drag.

The other very important point is buoyancy distribution to enable the boat to carry the sail power. Here again longer is better.

Gareth
www.fourhulls.com