Double Duty

https://www.google.com/patents/US4276033

Peter Krovina’s “sailing system,” patented in 1981, replaces a conventional sail with an adjustable windmill — while it’s driving the boat forward, it’s also storing power in batteries.

The batteries serve the boat’s need for electricity, powering the running lights, the cabin lights, space heaters, and the cooking stove.

Best of all, they eliminate the need for an engine — an electric motor drives the screw.