Sorry if this has been discussed before, but most of what I've seen here over the years relates to high efficiency running with props in the 1k rpm or less range, and motors in the 2kw or higher range. With proper reduction, it doesn't seem to be too hard to hit the high efficiency 'sweet spot' for such systems.
What I'm looking for is a motor configuration that will drive a light, long boat (24' x 2' at WL, under 500lbs all up) at high efficiency (90%+ for the motor), with prop speeds in the 300-700 rpm range. I would like this boat to be capable of both high speed (relatively, say 8 to 10 mph) at around 1 to 1.5 kilowatts, and long distance cruising at very low power levels - 50 to 100 watts. I wouldn't necessarily need both at the same time, so changing reduction or even motors and reduction to achieve one or the other for a particular outing would be acceptable.
I am able to find DC motors that will operate at 90% efficiency at the upper end of this speed range, with appropriate reduction, but have been unable to find a motor that will maintain that level of efficiency at power levels less than 200 watts, if I'm reading the specs and performance charts correctly. Many that do 90% at 1 kw or higher appear to do 50% or less under 200 watts...
This boat should be capable of very long runs in the 3 to 4 mph range with only modest battery sizing, if I can figure out how to get the motor to work efficiently at such low power levels.
Any suggestions?
Neil S.
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