RE: electric propulsion
- On a pure power boat, the energy density of batteries obviously makes them a poor choice for long distance/high speed.
On a boat that's primarily sail using it's motor for mostly for tight quarters maneuvering, I believe there's a different story.
First off, if the boat is one designed with inside ballast to begin with, there is absolutely no penalty for the weight of the batteries if used in place of the normal ballast.
secondly is the dependability an nonexistent maintenance, not to mention all of the safety, mess, odor issues of gasoline or diesel. Motors like the torqeedo are also immune to swamping and short term submersion, a nice feature when hanging low off of a transom with a following sea.
Having the regen setup would be the cats meow. I read about a catamaran set up with that. it powered for over an hour out of the marina and out the channel to the sea, put up sail and before long had cocompletely replaced the charge, at which point the props were feathered. it's my understanding that the throttle can also be set to "motorsail" to the point of minimum prop drag, but still slightly charging.
Like a wing or a sail, high aspect ration makes the most effcicient use of avaiable area my minimizing the percentage lost at the tip. The reason for 3 and 4 blade props is to get sufficient area on a shorter diameter, and in the case of higher RPM motors keep the tips from going so fast they cavitate. Low RPM, large diameter to deliver the same thrust requires excellent low RPM torque characteristics. The old "low speed deisels" that used to be in ships only turned about 90 rpm, achieved amazing mileage being directly connected to the shaft with no transmission at all. Current cruise ships use multiple deisel generators to turn electric thrusters.
The one big drawback at the moment is the cost for sure.