On yahoo there's a blurb about NASA's experiment using 18 electric motors mounted in the leading edge of a wing with 18 little props just ahead of the wing. So the entire wing is awash w prop wash and w flaps must create some serious lift probably reducing the size of wing required. But if the wing was made much smaller gliding w/o power would be an extremely low performance event. But thinking of gliding harks back to my ultralight flying days and it's a very rare event for an airplane to need to glide ... usually just before crashing.
Some of this may not be of benifit to boats but I've thought in the past that 6 to 10 props across the bottom of a boat would have some benefits. Prop damage would be more likely but draft would usually be reduced. If the props were close together some tip loss would be reduced and prop-walk would be basically eliminated.
Powering the props would probably be an engineering nightmare unless one used and electrical source like batteries and a generator. With B&G control would be easy and offer great manerverability w a little sosphistation in the wireing.
Vibration may be much less especially re the pounding the bottom takes when each blade slams water onto the bottom of the boat. High frequency harmonics could be a significant problem unless the props could be electrically synchronized to turn at the same speed.
Don't see any really big advantage to so many props but perhaps others have some ideas. This is not something I've thought much about. Comments ?
North Western Washington State USA