The 70 lb thrust may be overkill, but some have advised that even a 55 lb
trolling motor is inadequate if there is much wind or current, so I will
probably have to carry my Seagull OB when I'm on big water. I intend to use
the electric whenever possible and mainly at low speed settings to prolong
the battery charge. I expect to use full power only when I need a little
extra push to get through turbulence under a bridge, to cope with a patch
of stronger current, or to get out of the way of the barge that's coming
faster than I thought. There are several reservoirs south of SF Bay that
now prohibit gas outboards but allow electrics, so I'll be able to sail
those lakes without the prospect of paddling home if the wind quits.
Even if I only use the electric to get in and out of marinas and to potter
around in quiet coves and lakes, I think it will be worth it. The Minn-Kota
will be quiet and nonpolluting, will start instantly with the flip of a
switch, and has both forward and reverse - none of which are
characteristics of my 1967 Seagull Forty Plus, which is noisy, vibrates,
leaves an oil slick; oozes gear oil; and has no neutral, no reverse, and no
autorecoil of the starting cord.
But the Seagull drives the Potter strongly, weighs only 28 lb and fits in
the lazarette, so I can carry it with me when it seems like a good idea.
Hopefully, having both motors at the stern won't have too much effect on
the trim since I'll have about 120 lb of batteries forward and low, and my
lateen mast is 11 inches forward of the original mast..
The RT-70S, like all the more expensive Minn-Kotas, has the Maximizer
circuit, which controls the power by pulse-modulating the 24 volts, which
is more thrifty with battery charge and offers continuous, unstepped speed
control. The Riptide model has added protection against saltwater.
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.
By the time I pay for the motor, 3-stage charger, deep cycle batteries,
boxes, and wiring, I will have spent enough to buy a pretty good gas
outboard, and it's going to be a lot of work to put it all together, but
it's something I've been wanting to try for a long time.
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?
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.
Harry Gordon
P14 #234, Manatee
Mountain View, CA