Hi Michael,
You're mixing two different issues but they can each be answered.
Reduction systems, belt and pulleys, gearboxes or chains are not significantly inefficient. My Browning greabox is 97% efficient, 2% loss to the gears and 1% loss to the seals, and it includes a thrust bearing. There are a number of belt drive systems that exceed 95% efficiency. I don't know about chains because I consider gearboxes or belt systems to be better, but some people have used them to some success.
While the torque from an electric motor is fairly constant through low RPM, the power generated is not. A motor that is overloaded will draw too many amps at low RPM and overheat. A motor that is underloaded will reach max RPM before drawing maximum rated amps resulting in an underpowered system. Using a reduction system allows one to match the motor output to the boat's resistance and the prop's ability to create thrust. For direct drives, AC induction motors are better suited for higher power at lower RPM, Solomon Technologies offers that type of solution.
Even though you didn't ask specifically, you may want to do a little research on the differences between BLDC and PMAC motors, they are subtle. Many people mistakenly believe that they are the same thing, but by correctly matching the controller type to the motor type, you should gain more efficiency than you might lose through your reduction setup.
It's good to see you coming up to speed, but for a while, you'll probably be missing something. Hang in there, it's not rocket surgery, but it is more complex than a set of oars.
Fair winds,
Eric
Marina del Rey, CA
PS. Anybody can put together a system that works, it's harder to figure out how to put together a system that works well....
--- In electricboats@yahoogroups.com, Michael Mccomb <mccomb.michael@...> wrote:
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> aren't belt drives inherently inefficient if one compares that method of connection to a directly coupled shaft?
>
> AND...
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> if electric motors produce the same torque at any rpm then why would one wish to gear an electric motor either up or down? wouldn't one simply want a slower revving more efficient propeller and then run a motor rated to run at 2400 rpm or more at 1000 rpm instead? i understand the cooling might be an issue with some motors due to the fans being an integral part of the motor but surely a secondary dedicated fan system could make up the difference for VERY little wattage
>
> again, am i missing something.... BLDCs do run at constant torque do they not?
>
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