wind power

I met up with Matt Kleban (NYU) to discuss our dormant project on the physics of sailing. Our conversation ranged around many different things related to sustainable power. In particular, we discussed whether it was possible to take a energy or power point of view on sailing, which has to do with the work that the sailboat is doing on the water and on the air. I feel like there will be some symmetries in play there. We also discussed power generation with wind farms, including the Betz limit (which is a limit on how much power you can get out of the wind). Is there an equivalent of the Betz limit for a sailboat? Finally, Kleban made a remark that is simultaneously obvious and deep: If you have a propeller turning in a fluid (like air), it might be a turbine (generating power from the wind) or a fan (using power to make wind). The question of turbine or fan has a frame-independent (relativistically scalar) answer.