T-Pain Is On A Boat: Re: [Electric Boats] trolling motor size for a Stiletto 27 Catamaran

Thursday, October 6, 2011

Re: [Electric Boats] trolling motor size for a Stiletto 27 Catamaran

I think you are a bit light on the amperage capacity with setting up two banks one for each motor if you went with twins. Twins is the way I would set it up for the reason of better control.

If I was going to set the system up I would run 24 or 36 volts mainly to keep the amp draw down, so you can also use smaller and lighter wire.

What I'm going to say comes from people that drive electric cars and trucks that get good battery life out of them. Do not discharge a lead-acid battery past 50% if you want to get the life out of it. As soon as you can recharge it. The max discharge most of them will do is 60%... In short think of a lean-acid battery as a fuel tank that every time you over discharge it the fuel tank get's smaller. And I'm told this is very true of AGM batteries because you burn the plates and there is no place for the ash to fall and you boil the jelled acid.

So with that said let's set up your batteries up as two banks of 24 volts. Voltage times amprage will give us wattage. 24 volt x 48 amps gives us 1152 watts really it's 1152 watt-hours meaning you can pull 1152 watts for one hour or 1 watt for 1152 hours.

But holding the the 50% discharge rule you have 576 watts to play with. Okay so call it 600 watts. They say 750 watts to the horsepower but in the real world it's more like 800 to 900 watts, some motors are higher then that per horsepower.

The big thing I see is windage you will have to counter to push it into the wind under power. To size your motors take the boat out in the winds you mostly sail in and see how much drag you have with a large pull scale then you can work from there on how much thrust you need. Mind you, you will want to do that with sails down.

When I was working at Marine Service Center in Seattle Wash. there were a couple of small (21or so feet) sailboats with full keels that used the 45 or 60 lb thrust trolling motors to get in and out of their slips as well as across the lake when the wind was down and they seemed to work rather well.

femm

--- On Thu, 10/6/11, Ken Rogers <ken@OmegaAtomizers.com> wrote:

Can anyone share their experience in using a trolling motor as the primary auxiliary pusher on a light weight catamaran?

I bought a Stiletto 27 this weekend. Weighs in at about 1200 pounds with some gear in it, more of course with passengers. Two long skinny hulls that draw about 9 inches. It currently has a 8hp Honda 4 stroke on it that only needs to run at idle / low throttle to push the boat into the wind. Of course, I'd like to get rid of the "gas stink pot" and go electric.

Looking at Minn Kota models they come in ranges of 30 up to 100 pounds of thrust, 12 volt to 36 volt supplies, Variable speed "maximizer" vs. 5 forward speed & 2 reverse speeds, salt water vs. fresh water, bow mount vs. transom mount. I have 4 AGM 48AH batteries from another project, so I'm set for any battery combination. Being a catamaran with a 14' wide max beam, and 8' wide across the rear deck of the rigid floor cockpit, it might be great to have two motors, one on each side spread apart so that it would drive like the big cats with twin separated screws. I'd have to devise a way to rewire both throttle controls to a central mounted dual shifter control unit.

Ken Rogers, in Fort Worth