I'll bite. Why not connect a generator to the prop shaft and generate electricity that way?
Because a propeller is designed to push water, not be lifted by it. It's camber and pitch are exactly reverse what they need to be for efficient power generation. We are talking fractional horsepower, here: the best of the breed, the W&S mentioned by Jon, produce 1/3 to 2/3 hp (250-500W) at full tilt. Maybe a thousand sqft of sail driving 5-10 tons of boat, you get the equivalent of 15-40A from the best-engineered, purpose-built hydrogenerator out there.
ANYTHING that adds suckness to the equation will destroy that output. Poorly designed rotor; belts, pulleys, or gearboxes; transmission drag; trying to use a wind turbine in water; or so on, or so on. Some large vessels have used a drive shaft to some effect, esp with the Autoprop, whose blades can be rotated into a lifting configuration. Broadly speaking, a hydrogen has to built from square one for that express purpose, or it will suck.
You can't generate electricity for your home by setting a box fan outdoors, either. Sorry. Physics does not care what you want to be true.
Good things about hydrogenerators:
* They make good, steady watts on passage, keeping your AP, nav gear, and possibly radar going w/out burning diesel.
* Not as affected by rolling or apparent wind or shadowing as wind gens.
* Weight & drag down low & aft.
Bad things about hydro-gens:
* They do zilch at anchor, on a mooring, or in a slip -- where sailors spend 90% of their time.
* They are less useful coastal cruising, as the hops tend to be short and motoring is common.
* They are an electrical appliance submerged in salt water. Doh! Reliability has historically been poor. Many VG boats had trouble with the electrics, debris strikes, or prop fouling.
We all welcome any entrant into the field of sailboat renewable energy. But the physics has to be there! If the OP's prototype doesn't look quite a lot like the W&S, it's automatically suspect. There's good reason all (modern) commercial wind turbines have three blades on a horizontal axis. Design converges toward what works. There is probably a small market beyond RTW racers: some hardcore passagemakers, some gear junkies for whom cost is no barrier. Most coastal sailors will find $4-6000 USD for a power source that only works for the <10% of the time their boat is actually sailing to be poor economics. With PV power densities improving and prices below $3/watt....