Direct drive is certainly the most efficient, but is it the most effective? The MARS motor I'm using runs flat out at about 3600 RPMs or something close to that. That's about the same range that the ICE was running so the gear box should be a good fit. That's way too fast for the propeller to be effective at moving a big heavy boat at slow speeds.
From what I understand, the ideal condition for a prop is the slowest speed and the largest diameter that will use the power available. A reduction gear is important in that equation for getting the speed of the motor down and for the thrust bearings that can take the prop pulling and pushing against the boat and the water.
If there was available a slow speed electric motor with thrust bearings it would be an idea solution. Lacking that, sometimes we've got to cobble together what's laying around the garage:)
I remember an old Buster Keaton movie in which he was zipping around in a little motor launch with a make or break two-stroke thumper and he was constantly starting and stopping and reversing all the time, it was really a treat to so someone play one of those little engines like that.
David
On 13/10/10 03:08, Peter wrote:My boat didn't even have a gearbox on it's original ICE - there was
> 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.
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only a clutch between the two stroke petrol engine and the prop.
Thus I learned how to dock a motor boat with out the aid of being able
to use reverse as a brake.....
The boat could run backwards - the engine being two stroke, could be
started in either rotation, but it certainly wasn't something you could
do fast enough to use reverse power to slow down. :-)
My electric installation is direct drive as well, now not even
requiring the clutch. No belt, pulleys or gearbox.
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