Mostly it's the overall size and weight of the package, chain drive can be built with 30 speeds (10r+3f sprockets) in a very light and compact package. A belt with the same power transfer abilities in a single speed, needs an assembly roughly the same size and weight as the chain drive for 10.
I put 400 miles a week on bicycles, and wouldn't think about a belt drive on any of mine (8 at last count), but feel cogged belts do make a lot of sense in a boat application where room is available (and gear changes aren't required or can easily use a gearbox). They are quieter and would last longer in a wet environment.
Only issue with a belt is that they have to be carefully sized, so replacements for each belt has to be carried, with chains as long as they have the same link size you can buy in bulk and cut your own. Belts are also not tolerant of alignment errors, a chain will handle errors that would shred a belt in minutes without a problem. (they will have slightly reduced life, and a bit more noise though)
Ken.
> To: electricboats@
> From: matthew@acfr.
> Date: Sat, 28 Nov 2009 06:18:56 +1100
> Subject: Re: [Electric Boats] Bearings and power transmission
>
> danbollinger wrote:
> > Cogged/synchronous belts are in the 96-99% efficiency range, so don't discount them. They are lighter, and don't need lubrication.
> >
> >
> Cyclists are still largely using chains and a mechanism to bodily rip
> the chain from one cog to another to change gear as the efficiency of
> the simple belt/chain transmission/
> The chain systems are in the high 90s% efficient. The hub gear systems
> tend to be some what lower - mid 80s to mid 90s% efficient.
> Like our e-boats, cyclists want maximum power transfer with the minimum
> of transmission losses.
>
>
>
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