BoatBanter.com - View Single Post - Electric motor to power a dinghy revisited

In article ,
says...
SNIP some good arguments
True but the battery does offer some advantages. It's quiet
and you can place the weight of it anywhere in the boat you
want.

Think of that 50-pound trolling battery as a gas tank that holds (the
equivalent energy of) a pint of fuel, takes all day to "fill" (recharge),
costs $$$, and wears out in a few years.

That seems rather pessimistic. A plain old lead-acid battery
can easily run thousands of charge-discharge cycles if it's
treated properly. And the power equivalent is much more than
a pint of gasoline, especially if you factor in the woeful
inefficiency of internal combustion engines.

If you discharge your lead-acid battery to the 50% or 80% level,
you are unlikely to get thousands of cycles. 400 to 500 might
be a better upper limit.

As for power equivalent: a 100AH,12V battery at a reasonable discharge
level is equivalent to about 1.3HP for one hour. My own experience
with a battery of about that size and a trolling motor is that
you can propel a very light boat for about two hours at perhaps
1-3 knots on one battery. I think I would get about the same speed
with my 4HP Johnson OB at a fast idle. Whether that would take more
than a pint of fuel is a good question.

A big difference between charging a battery and driving an OB
is that the pollution from the motor goes directly into the
water. That can be a problem on some lakes.

http://www.windsun.com/Batteries/Battery_FAQ.htm

Fresh Breezes- Doug King

Mark Borgerson