There were two secrets to the AC's cup foiling system. The first was that they used curved foils that reduced lift as they rose out of the water, to prevent the foil from coming completely out. If the foil comes completely out of the water it loses lift and the drag increases dramatically. That is one of the causes the pitchpoling.
The second bigger secret is that they turned with the foil (just like a forward rudder) to resist leeway. That combination of turning and variable lift stabilized the height of the foil. . . . . . and the boat. Exactly the steering system the HP already has.
Also their system is hydraulically controlled to hold the foil in a precise angle. Everything has to be within a few degrees and not vary. A standard NACA foil can be used, it works fine in the opposite direction, except that it has a smaller working AOA range. Probably on a Proa the rounded edges should be facing outwards and the foils should be independently steered.
Also the nice thing about putting foils on the HP is that foils ventilate, once the hulls are out of the water it doesn't matter whether the top of the foils started out below the water line or not.
The only real issue is designing the curvature and chord (and foil selection) for the target speed.
Talador
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Posted by: taladorwood@yahoo.com.au
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