The fellow who builds the Cape Horn wind vanes has a great DVD of his
circumnavigation. He had a stern pulpit mounted alternator with a prop
trailing on a line. It appears to have done a good job of supplying his
electrical needs since the boat didn't have an engine. This was in the
early 80's so it was probably just an automotive alternator.

A shark ate the trailing turbine and, after doing without power for a while,
he fabricated a new one from stuff he found on board. The improvised rotor
is beautiful and a testimony to what human ingeniuity can do with minimal
materials and tools.

--
Roger Long