We ordered a Whisper 100 Marine wind generator from Southwest Windpower this spring. We'd done a lot of research and had decided that it had the best price performance of any saltwater-resistant wind generator.
However, we were unable to mount it on Scream, our heavy 45 foot cutter with a wide beam. The blades are just over 3 feet in radius, and we thought that we could accomodate that at the stern. What was not listed anywhere was the length of the tail, 5.5 feet. After a detailed consultation with a shipyard we determined that there was no practical means to mount the generator. Anywhere high enough to have the 11 foot swinging circle would need to be supported by guy wires on all sides, which would involve major hull modifications.
So the whisper 100 would work for large power boats, or enormous sail boats (well over 60 feet), but isn't an option of most of us.