The best way to cool an electric motor is with water, and the biggest heat sink in the world is only a few inches away from most of our electric motors, so it only made sense to make a water cooled electric drive.
We designed a copper water cooling coil to increase the output of our electric drives.
You can see a picture of the 7 KW drive at this link:
http://www.propulsionmarine.com/electric/7-kw-water-cooled-electric-drive
We are using the larger Sevcon controller and a larger gearbox to handle the increased amount of thrust that this unit develops.
The motor runs 30 degrees C cooler with the additional cooling equipment.
The copper coil is machined to fit between the gearbox and the motor. The system can be cooled with raw water or can be used to heat hot water, in which case the hot water tank acts as a large heat sink.
Cooling is an issue with any motor, actually, it is the limitation to most systems. This system works very well at keeping operating temperatures down during prolonged use.
This system is capable of continuous use at 7 KW in 70 degree ambient temperature and 60 degree water temperature. Actual results will vary with ambient temperature of the air and water and the underwater configuration of the boat.
We will make copper coils in the near future for anyone wanting to decrease the operating temperature of any Mars motor.
Cooling the drive also increases the efficiency of the system by decreasing the resistance of the windings of the motor. A very small electric pump of 20 watts or less is all that is required to pump the water.
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