Wayne,
You gave us a lot of necessary data but not two important points - How fast do you NEED to go and how far.
You can go 5 mph with 2 hp or 1500 watts or 40 amps at 36 volts. (3) gp31 batteries (about 65 lbs each) would give you 7 miles range at 5 mph or 13 miles at 4 mph. (6) 6v batteries would be a good choice too; 2X weight and 2.5X range.
The problem with the MK or any "trolling" motor for that matter, is that the prop is too small to be very efficient and too low pitch to load the motor at the speeds you will be capable of, kind of like driving in low gear all the time. It will work just fine but not give as much speed or range as something with a more appropriate prop.
A Torqeedo OB would be a better choice if you don't mind an OB hanging on the transom. Even their little 801 model would give you 4 mph. If your budget can stand it, I'd go for a Cruise 2.0.and (4) 6V AGM batteries
An inboard E system could be installed in very little room but would involve orders of magnitude more work on your part. The parts would cost as much as the Cruise 2.0.
You will want to put the batteries in the middle of the boat if possible; all that weight aft in the gas tank locker will trim the boat too far down by the stern. A six gallon tank full of gas only weighs about 40#; even add the 80ish# OB and you only have the weight of 2 batteries.
Good luck - your boat sounds like a good candidate for E power.
Denny Wolfe
----- Original Message -----
Sent: Tuesday, May 11, 2010 11:04 AM
Subject: [Electric Boats] Electric power for a Freedom 21
I would like to convert my Freedom 21 to electric power. I am currently using an 8 HP Johnson Sailmaster OB. The Freedom 21 has a LOA of 21' 8", a LWL of 17' 8", a beam of 8', a draft of 3' 9" and a displacement of 1800 lbs. The OB provides more than adequate thrust for docking maneuvers and, naturally will cruise under power for hours.
My plan is to install an electric trolling motor with twin motors/props. Offered by Minn Kota, it's specs are: Model RT202/EM, Maximum Thrust - 202 lbs., Max. Volts - 36, Amp Draw - 98, Recommended Boat Length - 22' – 26' .
There is plenty of room for batteries including, but not limited to the area previously reserved for the gas tank.
Any comments or suggestions? Any help or advice will be much appreciated.
Thanks for your help,
Wayne McKenzie
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