Electric propulsion for boats is a mature and growing industry. The
range is from abysmally simply (and naive) single solar panel
direct-wired to a 15LB thrust Minnkota on a 10-foot plastic-coated foam
Sunflower that I tried in 1988 (worked well until a thunderstorm came
up and I paddled against the wind two miles back to launch point) to
working boats carrying passengers for hire. Most must recharge
batteries dockside after heavy depletion, eight hours or so at 4-5
knots. Most use solar panels primarily for topoff.

Briggs & Stratton made a Permanent Magnet (PM) electric motor from a
high-energy magnetic material that I can never spell that got a lot of
press and use. The draw was that no electricity was required to
energize the field coils. 10HP motor now retails at about $400. B&S
have converted the motor sales to completed electric outboards.

New solar panels with higher efficiency and greater current output are
available. Converting a good sailboat hull of 19-25 feet to carry solar
panels as cabin hatch cover and sunscreen, and battery bank as ballast
can get you an overnighter that is (in lower latitudes, say below 34
degrees North) energy independent. For guaranteed return home, a
dropdown 7 or 9HP longshaft as any experienced blowboater knows is
essential. The electric motor can replace existing aux propulsion
almost as a drop-in.

Hurricane Katrina stripped the rigging from a lot of good small
sailboats here in Gulfport, MS. Since the bottoms of our waterways are
littered with debris and too dangerous to wade-fish, getting out to the
barrier islands is necessary. Fuel prices being what they are, solar
collection seems to offer a path, if you're not in a hurry.

If you are in a hurry, just buy the fish and be done.

Whil i havent ever used a boat with this setup myself i have read
accounts of people who have, and i believe the advantage has not much
to do with cruising or motoring... the batteries give you enough juic
to get out of your mooring only, not for much more, but things get
interesting when you set these things on 'hybrid mode' (might be called
something else, cant remember)...

In this kind of mode, you set the motor to a certain speed, say 5
knots. When the boat slows down, the motor kicks in instantly. when
it goes above this, the motor goes into generate charge mode. This
might sound pretty useless, but imagine yourself in medium to big
seas... boat sails through a trough, up a wave face and starts to slow
down (sails emptying)... motor starts and *automatically* powers you
up the wave face. you reach the crest, sails fill, you surf down the
other side, motors charge. Its my understanding that this sort of
sailing gets a lot more pleasant with a motor like this whereas people
with diesel only might just be motorsailing constantly. From what i
read i think the batteries would support a whole day of sailing like
this pretty easy.