Serenity, Cheoy Lee Bermuda 30 Ketch powered by Electroprop Mariner

Video – 5 Years of Electric Propulsion with Eric Dysart





My boat has more power and a higher top speed with the electric drive than with the 12HP Yanmar 1 cylinder diesel that was previously installed.



You should be able to get performance that is similar to mine, since I would guess that our boats are so similar. Using the Electroprop High Thrust 4 blade Propeller matched to a 2.55:1 gearbox, I have measured the following performance:

Average Results

Speed Amps Volts Watts
3.0 9.54 52.4 500
3.9 19.21 52.0 999
4.4 28.9 51.5 1488
5.0 48.5 50.7 2459
5.7 78.8 49.6 3908
5.9 106.2 48.7 5172


You can see that 4kts is right around 1kW. Don’t worry about the drag of your new prop, I’ve found that I typically sail with the motor running at less than 2A. This eliminates all prop drag and allows for minimal regen on blustery days.



I’m running 16 Thundersky 160A LiFePO4 cells connected in series to create a 48V nominal system. My voltage at rest is close to 53V, but with voltage droop from higher loads, I consider my system to average 50V, plus it makes the math easier. So I’ve got 8kW of total storage from a 200 lb battery pack. I consider the usable capacity to be down to 80% depth of discharge and using that figure, here are my various ranges adjusted for Peukert’s Effect:

Batteries - top

8 kWh LiFePO4 (6.4 kWh usable)

(16) TS-LFP160AHA – $3325 – 200 pounds

Peukert’s exp (LiFePO4) 1.03 1.03 1.03 1.03 1.03 1.03
Hour Rating 20 20 20 20 20 20
Total capacity (wh) 8000 8000 8000 8000 8000 8000
Depth of Discharge (%) 80 80 80 80 80 80
Usable Capacity (wh) 6400 6400 6400 6400 6400 6400
Speed (kts) 3.0 3.9 4.4 5.0 5.7 5.9
System Voltage 52.4 52.0 51.5 50.7 49.6 48.7
Discharge Amperage 9.54 19.21 28.9 48.5 78.8 106.2
Discharge current -watts 500 999 1488 2459 3908 5172
Usable Capacity – hours 12.72 6.23 4.13 2.46 1.53 1.15
Range – nm 38.2 24.3 18.2 12.3 8.7 6.8


In controlled performance testing, I have found that these numbers are pretty accurate.  Of course, your results will vary, but you should be able to get pretty close to these numbers.

I use an Elcon PFC2000+ charger (from Evolve Electric in Colorado), it can do a full charge in about 5 hours using a 15A 120VAC shorepower circuit.

For emergency backup, I have a Yamaha EF2000iS generator (50lbs) that can drive my charger to produce 28A at 54V. My boat can motor at 4.2-4.3 kts as long as the gas holds out, without using any battery charge at all. I’ve never had to use it to get home, but I have motored around for an hour as a proof of concept. The generator only comes aboard for longer trips, for day sails, I don’t carry the extra weight.

I think that you’ve come to the right place. James is great to work with. I’m not aware of any other vendor that can supply this type of real world data about their systems.

I’m sure that you will enjoy your conversion.

Fair winds,



Hi everybody,

I did another set of performance trials yesterday. I started at 12:00 noon, after the last rain shower passed. The process took about 90 minutes and I covered 6.35nm during the tests. I ran the same process as before, 1 pass in either direction at a particular throttle setting, progressively climbing through 6 settings and then repeat the process descending through the same settings until done. There was some wind by the end of the trials, but that should be offset through the pass in each direction. The results were more consistent than the last trials which had apparent tsunami surge that skewed some of the numbers.

Cheoy Lee sailboat with Electric Motor

Eric’s Cheoy Lee

Here’s this weeks results:

  • 495W = 3.0kts
  • 1,000W = 3.9kts
  • 1,500W = 4.5kts
  • 2,450W = 5.0kts
  • 3,905W = 5.7kts
  • 5,165W = 5.9kts

Slightly better at the low end and a little worse at the top end, but fairly close (+/- 0.2kts) to the previous tests. Because we had a conversation in the interim about motor temperatures, I recorded winding temps during the second half of the trials to see how quickly the motor would recover during the lower power settings. With a max observed winding temp of 74C at the end of the fourth pass at full throttle, the motor dropped to 52C by the end of the last 500W pass.

Right after the trials, I set the throttle to about 2500W and headed out of the marina, around the detached breakwater in open seas and then back in. 45 minutes later, at a constant power setting, the motor was stable at 60C and I had covered an additional 3.85nm. Apparently, the speed boost downwind is greater than the penalty going upwind resulting in an average speed of just over 5.1kts.

After messing about for 30 minutes or so at slower speeds, I brought her back to the slip. The entire day was 10.9nm with a 4.0kt average. The battery meter showed 107.7Ah consumed. After 15 minutes rest, the battery bank was resting at 52.35V. 4 hours on the charger, and she was fully recharged.

Fair winds,

Marina del Rey, CA