Electric Yacht

Libertine, Catalina 27

Libertine, a Catalina 27.  She belongs to Scott and Andrea McMillan of Electric Yacht.
(Written by Scott McMillan)

Libertine had a tired old gasoline engine when we bought her in 2005. This helped make the price “right”.  This was a move up from the Aquarius 23 she replaced.  We live in MN and sail on an inland lake (Lake Koronis) in central Minnesota.  The season here is short, but sweet.

In 2005, we installed a prototype system using the 10”x9” propeller that came with the boat and off the shelf components.  The results were encouraging, but not spectacular.

That encouraged me to develop a complete inboard system.  I have been an electrical engineer for many years and specialize in designing motor controllers.  In my view, one of the obstacles to people going electric is the lack of a complete system at a reasonable price.  I think our system solves this problem

Since we sail on a lake that is no more than 5nm in any direction, long range was not really a concern. For this reason, we are currently using four 12V group 31 batteries.  They have a capacity of about 100AH. Libertine has the “dinette” style interior that was available on the Catalina 27.  All four batteries are mounted under the aft dinette seat.  This actually balances the boat, since the water tank and galley are on the port side. A dc-dc converter converts 48V to 12V to power house lights and electronics.  We also replaced the beat up old 10x9 propeller with a good used 14x12 three bladed prop.

This combination has proven very effective on Libertine. After starting higher, I have now turned the maximum current setting down to 50A. This power setting moves the boat along at 5kts and gives all the power we need for maneuvering around the dock and mooring. It only takes 20A to move along at 4kts and 10A to putter along at 3kts. Sometimes I even set it at 4-5A. Just enough to quietly keep moving between puffs on very light air days. Do that with your old gasser or diesel!!

Though I would recommend a larger battery bank for most installations, this one serves its purpose. This type of “minimal” system should work for many lake sailors and racers who value light weight. Our total weight is about 300 lbs. I don’t know what the engine, gas tank, starting battery, house battery and exhaust system of the old installation weighed, but I know it was more.

Libertine is moored at our family lake property. Therefore, it was desirable to make her energy independent. To this end, we installed a 48V Air-X wind generator. Between it, and regeneration while sailing, I rarely plug into shore power anymore. We have all the power we need for weekend sailing.