There is at least one bow thruster out there that uses a tooth-belt drive, and a I think at least one pedal boat that uses a twisted bicycle chain (so the system is not unknown). However I don't see much if any mechanical advantage over a shaft. You still have the bearings at each end of the drive train, and I think the enclosure required for a chain or belt drive with it's sprockets or pulleys would be larger (with more drag) than that required for a skinny shaft. A shaft drive incorporates the reduction in the lower unit gears, which are there anyway. A reduction gear at the top would add more bearings, complexity, and friction, defeating the whole object.
For an electric drive I suspect the "pod" with the motor in the pod is probably the most efficient. No gears, shafts, belts, chains, or cooling pumps required.
Willie
--- In electricboats@yahoogroups.com, John Green <v_2jgree@...> wrote:
>
> Thanks for that, Tom.
> Interesting. Seems they have the reduction gearing done at the top,
> allowing a smaller lower sprocket.
> This could also apply to a modern toothed belt drive, which would be
> more durable in the water.
> Another possibility is to have the prop blades as an integral part
> (spokes) of the lower sprocket, allowing a lower profile presentation to
> the water current.
> Note also the size of the prop compared to the overall size. Seems that
> the design might have been unhampered by a lack of ICE design
> characteristics mindset.
>
> John
> 1a. Re: chain-driven outboards?
> Posted by: "Tom" boat_works@... boat_works
> Date: Thu Apr 26, 2012 12:28 pm ((PDT))
>
> It looks it has been done at least once. About 130 years ago.
>
> http://archive.org/stream/electricalboats01sachgoog#page/n18/mode/2up
>
> -Tom
>
>
>
>
> --
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