Yes, I saw a two-blade job obviously made out of an alternator with a beefed up shaft on a Westsail 32 about three years back in Cobourg, Ontario. (Everything else on deck looked a tad "home-forged" as well, but it obviously worked!).
You can get a number of designs, ideas and troubleshooting tips from the ecology and "off the grid" crowd of homesteaders and green types who build straw-bale houses atop of hills just to get at the wind to power CD players pumping out those pan pipes. Hey, electricity for free is good!
If you restrict yourself to "fair-weather amp making", you could hoist something off the deck hanging from the backstay. That's what the fellow I saw did.
I mean, it's an alternator with a prop and special windings. All the other stuff can be black boxed prior to charge entering the batteries. Experiment away. Learn how to wind rotors. Learn how to shape prop blades. Just wear a helmet and goalie mask for the first 25 knot "field test", OK? There are enough ugly sailors as it is.