Postmodern Sysadmin

A blog about servers and junk

Adding Electric Motors to a Gemini 105m

I recently added a pair of electric motors to my Gemini 105m catamaran.

Although I don’t have any photos of the actual installation, here is what they look like:

These are a pair of Caroutte S400’s.

In theory they have a thrust of 180lbs each and a peak power consumption of 2.7kw each. Although it cannot be directly compared, the onboard diesel is a 20kw (27 Horsepower) engine. With both engine there are many different variables like transmission losses, propeller losses, etc. You just can’t compare these directly with specs alone. The pair of electric motors cost about $3k.

How well do they actually perform? I would rate it as OK considering what they are. With a 10 ton sail boat, I did not expect these motors to push this thing more than a couple of knots. Honestly if they were powerful enough to maneuver out of the marina and into the bay, I would be happy.

Here are two videos of them in action:

Unfortunately they are mounted too high, and will suck in air if I attempt to run them at full throttle. I’ll try to figure out how I can get them to go lower into the water.

While they can be controlled “tank style”, I found that the actual maneuverability of the two electric motors is worse compared to the vectored thrust of the drive leg of the diesel.

The power from the system comes from two large 330 watt solar panels.

Which run through a large 60 amp, 48 volt charge controller.

Which charge four 75amphour deep cycle batteries:

The batteries are certainly the weakest part of the system, but they were on hand (came with the boat). The batteries were half discharged after an hour of 3 knot motoring. In summary:

  • The pair of electric motors is powerful and inexpensive considering the alternatives
  • The pair of solar panels is as large as I think it can be for this boat
  • The charge controller is overkill, but high quality
  • The batteries are under-sized for this system
  • ~3 knots is pretty good for sun-powered propulsion