Peter,
A gear box in a typical ICE installation serves two functions, its a reversing gear and its also a reduction gear. For our purposes its really just the reduction we're after. Diesels would still need the reduction too even if they were just stopped and reversed (which they and gas engines used to be before reversing gears became standard and RPMs went up.)
The transmissions from these small engines we're talking about are as simple as they can be. Its literally three helical gears and an idler. There is a friction plate clutch for pushing the two gears into and out of engagement but that's it. Some of the smaller gearboxes are even simpler.
The efficiency of helical gearboxes is usually cited as about 96%, about the same as belt reduction.
Reliability is a function not just of simplicity but also of durability. For a boat my size (32' and somewhere between 8k and 10k lbs), the durability and robust nature of an oversized gearbox is a big plus compared to aluminum plates and a toothed belt. The belt approach is an excellent one and very reliable but I would argue not as robust and durable as a gear box.
Boats are compromises and we all go with what we're comfortable with. I think its nuts that people use wheel steering on boats that can use tillers, but then I've also got a stayed rig instead of a freestanding one.
I think its probably a wash between gear reduction and belt reduction, neither is dramatically better than the other, if I hadn't already had the gearbox I probably would have built a belt set-up, but for cost reasons rather than efficiency reasons. Give me a few years of experience with electric boating and I'll probably have some strong opinions!
David
This is a great forum, and I've learnt a lot from lurking and reading through past posts, but the recent discussion on leaving in the original transmission has flushed me out into the open.
Converting to electric, one is looking for the greatest simplicity and efficiency possible. Running electric power through an ICE transmission, with it's cone clutch, gears, and oil bath, seems to me a poor idea. I'm sure if Diesel engines could reverse with the flip of a switch they would not have coupled them to a cumbersome gearbox.
Just my thoughts on the matter....
Peter.
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