In practice, the typical electric drive reduction gear actually does two things in the typical axial installation. It converts a rotational speed and torque to a lower speed and higher torque, and it also afunctions as the thrust bearing. Most motors in common use as propulsion motors do not have thrust bearings, or at least do not have bearings rated for the dynamic thrust loading encountered in a boat. The prop turns, pushes the shaft forward. A direct coupling between prop shaft and motor shaft in the absence of an external thrust bearing will push the motor shaft longitudinally through the motor. A reduction drive generally incorporates a thrust bearing, so the forward thrust of the prop shaft is transferred to the hull by the thrust bearing in the reduction gear bolted to the mount. So the economic impact of the initial cost of a reduction gear is offset partially by not needing a separate thrust bearing.
Efficiency of well designed reduction gear setups, whether they be geared or belted systems, can be very good. I am using an enclosed gearbox filled with oil, and the cost was not prohibitive at all. It actually simplified installation since I did not need to build a thrust bearing mount. A mounting plate cut for a C face motor also of course accepts the C face reduction gearbox and the motor bolts directly to the gearbox. With my original small folding prop I should have been able to go direct drive, or i should say 1:1 but I installed the 2:1 gearbox anticipating a larger fixed blade prop, partly on the advice of the members of this board and I have not regretted it and do not anticipate regretting it now that i have what I believe is a much more appropriate prop. Looking forward to some testing!
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