Planing Hydrofoil
The attack angle is set at 6º.
It can be adjusted by the crew moving fore to aft, and depth of immersion can be adjusted by moving to leeward or windward. In light airs the foil can be removed altogether decreasing drag.
Features of the planing hydrofoil:
The anti-heeling force of the skipper hiking out automatically increases as wind speed and heel angle increase because the center of lift moves to leeward.
The lifting active area of the foil increases with increased crew weight.
As boat speed increases, the lifting force increases, and the boat rises from displacement mode operation to planing.
The dimensions and attack angle of the hydrofoil are chosen so that at windspeed of 4 knots and above, the boat rises to the water surface. Below 4 knots wind speed the foil is generally not deployed, i.e., left on shore, so it does not contribute skin friction and displacement drags. The lighter the crew the lower the speed for onset of planing.