RE: Electric Outboard for Manatee

Eric Johnson (
Wed, 9 Sep 1998 09:07:16 -0700

- - - - - - - - - - - - - - - - - - - - - - - - - - -
West Wight Potter Website at URL
- - - - - - - - - - - - - - - - - - - - - - - - - - -
> I plan to run large diameter wires from batteries to motor to minimize
> voltage drop since it will be a fairly long run from the transom to the
> cabin. That will be less of a concern on a 24-V system since it requires
> only half the amperage to deliver equivalent power of a 12-V system. The
> two batteries in series at 24 V should give me about the same operating
> time as the same two batteries in parallel on a 12-V system.

Be sure to use marine-grade wire for this - its usually tinned for its
entire length. And don't forget to fuse everything.

> I have no previous electrical system in the boat so I plan to use
> the motor
> batteries for lights and such also. Do any of the electrical experts out
> there know if there would be any problem for me to draw some 12 volt power
> off one (or both) of the batteries, which will be wired in series to
> produce the 24 volts for the motor. That could result in running down one
> battery more quickly than the other, but is that a concern?

Probably not, if you have a good charger that can handle multiple batteries.
IMHO however, I'd suggest getting 24V bulbs. They're not terribly hard to
find... most standard automotive bulbs are available in a 24V version, so
you can buy standard lights and replace the bulbs with the 24V ones. A lot
of diesel vehicles and military vehicles have 24V electrical systems, so 24V
bulbs are plentiful. Carry spares though - its spooky to lose nav lights in
a crowded harbor. A lot of accessories (my GPS, for instance) can run off
24V just fine.

> I'm also wondering if it would be practical to use my tow vehicle's
> alternator to recharge the boat batteries as I drive. That would
> be nice if
> I'm traveling and can't always stop somewhere with an electrical hookup to
> power my charger.

That may be a little trickier since you'll have a 24V system, but I've
contemplated the same thing... you might want to rig a parallel-series
switch with an isolator so when towing its only technically a 12V system,
but we're getting pretty complicated now. You could go simpler by having
some switch so that you're only charging one battery at a time, and on a
trip, when you stop for food or gas or whatever, that battery should be
charged and you could switch to the other one.

A small solar panel does wonders for topping off the battery charge when
you're not using the boat, but I don't run a motor off my system so I don't
know how well it would work for you, since you'll be demanding a lot more
power from the battery than I do on mine.