While I accept it's possible, I have trouble wrapping my head around it. Windsurfers can tack, right? I don't get the rigid airfoil, it must be toed-out or toed-in or something. In the picture it appears to be convergent.
This I can Understand:
Edit: I've thought about it and have decided it's like the
Wells turbine used in the
Ocillating Water Column power plants.