Split Voltage

Welcome to the forum Alan.

With ~70% more thrust--Do you have enough battery bank capacity to make your round trip (or possibly several trips over a weekend) between charges...

Just as a guess... Looking at 56 amps per motor. Discharging to 50% capacity of bank:

• 56 Amps * 2 = 112 Amp draw
• 4x GC batteries in series = 24 volt @ 232 AH
• 232 AH * 0.50 max planned discharge = 116  AH working capacity
• 116 AH working capacity / 112 Amp draw (max power) = 1.04 hours per charge of operational time

So--First question is does this work for you (~1 hour of operation between weekly charging)?

Next, yes, you can wire up the 4 batteries in series--Run 24 volts, then wire them back to 12 volts to charge--That will get "old" over time. Do you have other 12 volt loads for the boat (splitting off 12 volts from a 24 volt bank is not great--It causes the low vs high batteries to discharge at different rates and unbalances them--May be less of an issue if you plan recharging at 12 volts during the week).

I suggest that you may want to review your energy usage and solar charging... Guessing at Montreal Canada, summer usage, fixed array facing south:

http://www.solarelectricityhandbook.com/solar-irradiance.html

Montreal
Average Solar Insolation figures

Measured in kWh/m2/day onto a solar panel set at a 59° angle from vertical:
(Optimal summer settings)

Jan	Feb	Mar	Apr	May	Jun
2.37	3.39	4.31	4.81	5.03	5.37
Jul	Aug	Sep	Oct	Nov	Dec
5.35	5.08	4.28	3.00	2.05	1.87

Say May through August or over 5.0 hours (long term average) hours of sun per day:

• 55 Watt solar panel / 17.5 volts Vmp = 3.14 Amps Imp (rated charging current) @ 12 volt bank
• 3.14 Amps * 5.0 hours of sun per day * 5 days (weekday) charging = 78.5 AH per week average charging (ignoring 20% charging losses)

Depending on your "real" weekend AH usage--This 55 Watt panel may not be enough for your needs...

Typically, suggest 5% minimum charging current (10%-13% typical):

• 24 volts * 232 AH * 1/0.77 panel+controller deratings * 0.05 rate of charge = 362 Watt array minimum
• 24 volts * 232 AH * 1/0.77 panel+controller deratings * 0.10 rate of charge = 723 Watt array nominal

Just from what is "optimal" for the battery bank (larger battery banks need larger solar array), a much larger array would be better (for longer battery life). As well as providing more energy for your weekend usage. Highly suggest a minimum of 5% rate of charge... And 10% is recommended by flooded cell lead acid battery mfg. for best battery life.

If you go with a larger array and/or 24 volt charging--You need to make sure you always connect the battery power to the charge controller first, then the solar array. And disconnect solar first, then the disconnect the battery bank to charge controller. If you have solar power and no battery bank, the charge controller can get "confused" (not boot correctly, or make a 12 vs 24 volt battery bank configuration mistake) or even be damaged (lots of variables here--Just generic warning).

-Bill

The good thing with putting batteries in parallel--It is easier on the batteries. 1/2 the current draw, and 1/2 the depth of discharge.

Bad side, with A/B switch--If A "goes dead" and you need to travel--Switch to "B"... With A+B, if your bank goes dead, you are stranded until they get some charge back in them (it could take one day or two sunny days, at least, to get enough charge to make the trip from a "dead" bank).

Good the panel is mounted to the boat--No charger/battery switching issues. Solar panels are getting pretty cheap these days... A 300 Watt panel can cost you something like $150-$300 (at least south of the boarder) if you shop around (get a Vmp~35-40 volt panel for charging a 24 volt battery bank--Not a Vmp~30 volt panel) if you look around (watch for packing & shipping costs--Can cost a lot to send a single panel).

The smaller 150 Watt and less "12 volt" (Vmp~17.5 volt Vmp) panels usually cost a lot more $$/Watt.

If you go 24 volts--You would need another charge controller.

-Bill