http://members.cox.net/sholley1/electric.htm

"A few years back I was impressed when I saw a "dock maintainance
barge" tooling around the cove in our Marina under the power of a
little 12 volt trolling motor. It was small, old, but the persistance
of the little thing moved the barge around quite well. I proceeded
down to my boat, and embarked on the following procedure to go
sailing."

"NOTE: There is no neat formula or correlation between thrust and
horsepower. However, I read a comparison that measured a 6 hp gas
outboard produced just over 130 lbs of thrust, so that would class the
107 Motorguide in the realm of a 5 hp gas (give or take a little).
Thats not a lot of power, but ample for my needs. I don't know how I'd
fare towing in another boat, but I'll include towing in "tests to
come"."

http://www.geocities.com/Yosemite/Fo..._outboard.html

Auxilliary Power Requirements with Electricity

"A typical trolling motor is designed to push a displacement hull at a
maximum of about 2 to 3 miles per hour. Therefore, I determined to use
the highest thrust 12 volt electric trolling motor that I could
purchase and see where that would lead. In this case, a Motorguide
model T47 motor with a 36 inch shaft length was commonly available at
the local Kmart stores. This motor draws about 50 amps at maximum
speed and is rated to produce 47 pounds of thrust. Replacing the
propeller with a two blade (power) design from the three blade (weed
free design) included with the motor should result in the required
combination of low shaft speed and high thrust. This motor, combined
with a bank of two new fully charged group 27 deep cycle batteries,
could operate at maximum thrust for about 2.5 hours. In theory, the
calculations said that this combination would propel my Com-Pac at
just under three knots. This would meet my stated goal of a 5 mile
range under power with some safety margin."