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The Electric Outboard Makes Waves

The Eska Electra electric outboard conversion has finally had its chance to push something. In July of 2010 we attached it to a San Juan 21 sailboat and ventured out of Gig Harbor on wind and electric power only.

The construction and initial test of the Eska Electra occurred well over a year before it was given a proper sea trial. During the initial tank test I utilized an ammeter to verify that the electrical draw did not exceed the motor or controller's rating. In June of 2010 another tank test took place. I wired up some of the batteries I intended to use. Running the motor at full throttle I monitored the voltage drop of the battery set to get a rough idea of running time. These tests led me to believe we would have adequate range for our short cruise.

In my original electric cruiser conversion brief I mentioned a goal of 4 knots for 5 hours with 200 lbs of batteries. This cruise included only 50 pounds of battery. With less battery capacity we certainly wouldn't be able to make our 5 hours goal.

We also failed to reach 4 knots. Full throttle was more than 3 but less than 4 knots. The test was somewhat skewed, however. The boat's bottom was decidedly unfair with many layers of ancient bottom paint partially flaked off. Towing a Laser and a Blackberry rowboat didn't help either.

San Juan 21 with DIY asymmetric spinnaker

When the San Juan 21 had wind she sailed faster than she could motor. This was especially true when her $5 DIY asymmetric spinnaker was hoisted.

On the positive side I can say that neither the motor nor the controller showed any signs of stress. Both were relatively cool to the touch at all times. My GPS batteries ran out before the Eska Electra's did so I can only guestimate how much work the electric motor did. Our cruise include two nine mile days. The Eska's batteries were recharged after each day. I would estimate that the motor pushed the boat at an average of two and a half knots for about four miles on each of the days. The wind did the rest.

Initial conclusion:

1. Without an adequate amount of battery the motor is not likely to meet expectations. Efficiency goes down with higher current draw. For this reason, having more batteries to share the load results in better electrical efficiency. Basically adding more batteries gains both in total capacity and electrical efficiency.

2. Not as fast through the water as we hoped. Some of this may be caused how much additional drag we added in a poorly maintained bottom and _two_ additional boats being towed. Because of our limited battery capacity on this trip we cruised at 1/2 or 3/4 throttle most of the time. With more battery capacity (see #1 above) we would have been more comfortable running at full throttle (which was still less than our goal of 4 knots).

While I can't say the project has met it's goals, it is possible, with a few changes it might come close.