On 22 Mar 2007 10:21:07 -0700, "
wrote:

Sorry, I missed one point that you had mentioned in your post. You
are saying that I really don't need the extra two batteries. I would
like to learn more. If I really don't need them, I will be able to
cut down at least one hundred pounds from the load, and this would be
a very good thing.

In order not to get the extra two batteries, I will need to use the
current two dual purpose batteries to do the following things:

o First dual purpose battery: I will need to use it to crank the
outboard and use it to power fishfinder, GPS, VHF radio,
livewell for baits, and _may_be_ a pair of trim tabs. I have
a feeling that one battery cannot handle that many tasks,
and I may need to split the tasks into two batteries.

o Second dual purpose battery: I will need to use it strictly for
trolling motor. This also means that I will need to pair it with
a 12-volt trolling motor, and this is limited to no more than
55-lb thrust.

Based on West Marine recommendation, 55-lb thrust should be enough for
a 18-ft 2000-lb fiberglass boat. But based on tech support in a
trolling motor company, they recommend 70-lb thrust for that size of
boat, and that will require a 24-volt system and two 12-volt
batteries. This makes me a bit confused. If I interpret this
correctly, this means more is better, and less is OK if I am not using
it in strong current or high wind situation. If I understand this
correctly, 55-lb thrust probably is OK for me, and this also means
that I probably only need one battery for the trolling motor.

In summary, I may only need totally 3 batteries instead of 4 batteries
as what I originally thought. This is good because I can cut down at
least 50-lb to 60-lb from the boat load. Thanks for getting me
thinking along that line.

The difference is 12 Vdc and 24 Vdc. 12 Vdc systems have reduced run
times as they will draw more current doing any task. With 24 Vdc
systems, that current draw is spread across two batteries increasing
efficiency and run times. Put another way, the higher the voltage the
less current draw.

For example, on my Princecraft, a 14 foot aluminum boat, I have a
single 12 Vdc battery to power the 45 lb. thrust trolling motor. It
does quite nicely in a wind situation and moves the boat along
quickly, but it will only last a half day's fishing is I'm on a small
pond and has zero power for cutting weeds. The 24 Vdc system (67 lb
thrust) on the Ranger runs all day pushing a boat 4 times the weight
of the Princecraft and I have reserve power up the ying yang.

Holding a boat against a wind or wave action with a 12 Vdc trolling
motor is going to tax your patience because you will not have the
power necessary to properly move the boat.

I would definetly opt for the higher thrust and 24 Vdc system.