"The main thing with any electric motor is to run them within 75% of their rated RPM. If you run the motor much below that, then your turning quite a bit of power into heating the windings, which is a waste and not good for the long term health of the motor, if you run it higher then you're probably not getting your moneys worth."
True enough. Although it may be clearer if you had said "around 75%".
"I personally like direct drive where it is feasible- geartrains add an extra layer of complexity, cost and it's yet another thing to wear out."
Also true but it's really just a matter of personal preference. Besides, a large motor adds a lot of weight relatively high in the pressure hull which, on a smallish boat, can cause some trimming problems. That said, I'll repeat. It's all a matter of personal preference.
"I find belt drives especially costly, although they are silent, but a 9:1 belt drive is not an off-the-shelf item is it?"
No. it's not. But then, I enjoy making all kinds of weird, off the wall kind of stuff. On top of which....I had a bunch of pulleys and belts at the time and no gears. You gotta "run what ya brung" sometimes.
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