First, fixed foils won't work/fly. The foils have to be modulated because the weight to lift is constant but the ability to generate lift increses with the speed of the boat squared. Once a craft is foilborn and accelerating something has to control the lift or else the lift will continue to increase until the foil stalls and then crash. Once a foil craft climbs up on its foils something has to keep the total foil lift constant as the craft changes speed while up on the foils. This is acheived by changing the angle of attack of the entire foil or by varying a trailing edge flap on the foil to control lift. The secret to foil boats is not the foil shape; it is to "control the foil" to generate constant lift, boat plus sailor, over a useable speed range.
Bill,
This is correct if the goal is to sail the boat fully "foilborne" - to fly supported solely by the foils.
If the goal is to reduce wetted surface, fixed foils designed to lift less then the total vertical load seem to work fine. At least this is the way I understand they work in the Open 60 tris (up to 20 to 30% lift) and in the Catri (up to 90% lift).
But maybe things work different then I understand, and in this case I look forward for today's lesson!
Cheers,
Luiz
