Lots of interesting discussion on the wing shapes and drag here.
Just curious if any of you had any feedback on my theory for the roll stability vs wing tip direction. I have noticed that this effect also works across the entire wing, roll stable wings will have significant anhedral. Seems counter-intuitive given when in air anhedral makes roll less stable. Cheers.
I think I finally found an explanation for anhedral making hydrofoils more stable on roll:
If I want to turn left, I shift my centre of gravity (COG) to the left side of the board. This rolls the foil to the left. Because lift is always perpendicular to the wing, the lift vector now tilts to the left as well. A component of that lift becomes a side force, which makes the foil start to slip (drift) to the right relative to the water. In other words, the foil wants to keep moving straight ahead, but the tilted lift vector forces it into a curved path.
Once the foil is slipping sideways, the direction of the incoming flow changes: the water now arrives slightly from the right.
If the wing has anhedral, this sideways flow increases the effective angle of attack on the lower (left) wingtip in a left turn. The left wing therefore generates more lift and more drag.
This behaviour mirrors what happens in aircraft. A dihedral wing allows an aeroplane to turn using rudder alone: deflecting the rudder left yaws the nose left and creates sideslip from the right. With positive dihedral, that sideslip increases the angle of attack on the right wing, rolling the aircraft into the turn. Roll and Yaw are therefore positively coupled for dihedral wings, and negatively coupled for anhedral wings (making anhedral wings stable on roll).
In the mean time, I made some more wings and stabs with proper vacuum bagging. This is really fun, and I am sooooo much looking forward to test them next summer.
great work, looking forward for your results. I just published my webapp to calculate the power draw of foils, I believe you will like it 
