Thanks edt for your info and Tiago for that vid. What a great and simple way to demonstrate the affects of shape and drag.
I remember as a kid in the car, going down a motorway with a flat hand out the window. Flying it up and down just by adjusting the angle of attack, to find the sweet spot. to be able to hold the full weight of my arm in the middle of the window, happy days lol.
So basically the answer is yes you can use a flat wing for a hydrofoil and they are being used. But a foil shape reduces drag, which helps in gaining speed and thus enables a lesser angle of attack. This is more efficient and water is 784 times denser than air. Our speeds required for lift are a lot lower than an aeroplanes wing, also hydrofoils are a lot smaller. Being more efficient must make it nicer to use as well!
So it depends if you wanna cruise or rip?
It's all interesting stuff