It s not installed yet. I have the shaft, prop, and reduction in place but the motor won't be installed till I m done with other things. I can tell you that under sail at 5 to 6 kts the shaft is turning pretty fast with the 3 blade prop. That said I don't expect miracles and all we really look for is enough output to recharge whatever we used on the short power run off the mooring or minimal loads like running lights
There are a number of hydro generator on the market used by long distance sailors and they are supposed to be pretty efficient. The are usually mounted on a bracket at the stern