I'm thinking about adding a trolling motor to my boat but I dont want
multiple batteries. I have ENOUGH batteries to take care of around here as
it is.

My motor requires 360 CCA, the 50# trolling motor I want requires 47 amps
(max draw). I doubt I would ever use the trolling motor more than 2 hours
at a time and most likely would have the outboard running off and on during
that time. I am thinking I will buy the biggest deep cycle/starting battery
I can find and just use it.

The trolling motor has a built in battery guage so running the battery down
too far to start the motor shouldnt be a problem. Anyone else out there
doing this?

Thanks.

My motor requires 360 CCA, the 50# trolling motor I want requires 47 amps
(max draw). I doubt I would ever use the trolling motor more than 2 hours
at a time

You'd do well to plan 300 amps of battery for your trolling motor alone.

Sounds like a lot, but there's why:

2 hours at 47 amps = round to 100 ah.

It's best not to discharge a l/a battery below 50% of its rated capacity, so
100 X 2 = 200.

Then you have to make an allowance for the "sweet spot" in the recharge curve.
If you're discharged to 50%, the battery will
recover to 80% fairly quickly but the remaining 20% of charge to full takes
considerably longer. Unless you will always have ample recharge capability
between uses, you can only "count" on using 30% of the battery's
capacity....(that portion between the 50% floor you want to avoid discharging
below and the 80% charge state that you can recover fairly quickly. The "belt
and suspenders" approach is to take your amp hour requirement (about 100) and
multiply it by three. 3 X 30% = 90%, probably close enough for jazz.

"CCred68046" wrote in message
...

My motor requires 360 CCA, the 50# trolling motor I want requires 47 amps
(max draw).

The rate at which you use the energy (amps) is not any indication of how
much energy (amp-hours) you need.

I doubt I would ever use the trolling motor more than 2 hours
at a time and most likely would have the outboard running off and on
during
that time.

Are you saying that you only go out fishing for two hours at a time?

It is hard to get an idea of exactly how many amp-hours you will need
because the common useage of a trolling motor is to apply just a little
thrust here, a litte thrust there. In that two hour period you may have
only been operating the trolling motor for a few minutes.

On the other hand, you can pretty much ignore any charging from the
outboard. Most outboards have very small charging output. If you are
starting the outboard often it may not even be able to put back what it
takes for starting, let alone replace what the trolling motor takes.

The trolling motor has a built in battery guage so running the battery
down
too far to start the motor shouldnt be a problem.

I wouldn't rely on the battery gauge. It will warn you that you are about
to run out of trolling motor use, but it doesn't know what your outboard
needs to start.

You approach can certainly work, but it has a major hazard associated with
it. If you can rope start your outboard then there isn't any big issue
(yeah, my outboard came with a rope too. I suggest you actually try it
before you rely on it!). If you are relying on the electric start, then you
are gambling that everything works the way you expect.

The motor has to start reliably, every time.

You better not lose track of time or how much you have been using the
trolling motor.

You better not run lights, stereo or other current drains.

The eventual pitfall, however, is that the battery loses capacity with age.
It may do fine this year, and next year. But the year after that you will
go out and do the exact same thing you have been doing for the last two
years and you won't be able to start the motor when it is time to come home.

The real hazard here is that you will discover this at the worst possible
time. Most people will discover that their battery is shot when they get to
the launch ramp and can't start the boat. They might be ****ed off, but
they can just drive to the nearest autoparts store and buy a new battery.
You will discover that your battery is weak when it is time to go home. You
will be out on the lake and it will probably be getting dark. If you can't
start your motor you may be spending a cold wet night on the boat. If the
wind picks up you could be in serious trouble.

For the cost of a second battery you could save yourself a lot of trouble.

Rod