# Small electric sternwheeler catamaran

Discussion in 'Boat Design' started by YotaTruck, Mar 30, 2016.

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### Village_IdiotSenior Member

As Gonzo alluded to, much of it is in the gearing, or gear ratios.

I've mentioned it on the forum before, but I'd like to see a large, slowly-rotating paddle wheel driven by electric motor via gears. This would consist of a large ring gear that is the same diameter/circumference of the paddlewheel, being directly driven by a tiny gear on the electric motor. If that wasn't enough down-gearing, an additional gearshaft could be implemented for extreme torque multiplication. I am envisioning a paddlewheel turning at just a couple rpm.

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### gonzoSenior Member

If the diameter is very large, the RPMs need to be low. The tangential speed is what you need to calculate. At the same RPM a wheel 10 times larger will have a speed 10 times faster.

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### Village_IdiotSenior Member

Yes, that is why the gearing and motor would be at the perimeter of the paddlewheel.

Let's say that the electric motor has a 15-tooth gear on its shaft and spins at 1850rpm. You would need to calculate the number of compatible gear teeth on the paddlewheel perimeter to get the paddlewheel rpms down to 2-3rpm. The diameter/circumference of the paddlewheel will be the major variable here. If it is too extreme, an intermediate gearshaft will be needed, which will reduce efficiency.

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### SamSamSenior Member

At 2-3 rpm, you'd need a wheel somewhere about 100 feet in diameter.

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### Village_IdiotSenior Member

Then we'd need a 10:1 reduction gearshaft in between...

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### RurudyneSenior Member

While it wasn't an electric motor: the local feed store is being turned into a feed store themed eatery (yes, my town is now officially urban and more gentrified and therefore sucks) and as a result their lovely old hit-or-miss engine is still beyond reach....

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### Village_IdiotSenior Member

Maybe you could pick up an overpriced one from antiquearchaeology...

Or scab the engine off of an old "B" John Deere...that would sound pretty cool rollin' down the river...

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### SamSamSenior Member

Let me re-phrase that...2-3 rpm is way too slow.

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### Village_IdiotSenior Member

Then we'll go 10rpm on a 10-12' wheel. That should give decent tangential speed, assuming there's enough paddle in the water to get a good bite.

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### SamSamSenior Member

Ok, say a 10' diameter wheel. 3.14 x 10 = 31.4' .That's the circumference. times 10 rpm = 314 feet per minute the outside of the wheel is moving at. Times 60 minutes = 18,840 feet per hour. Divided by 5,280 feet (one mile) = 3.56 mph. Assume 50% slippage, 3.56 mph divided by 2 = 1.78 mph.

I'm thinking that at such a low rpm, at such a slow speed of wheel to water inter-action there would probably be even more losses of efficiency somehow, so maybe the result would be like less than 1 mile per hour of speed.

Life is pretty short to be going 1 mph.

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### RurudyneSenior Member

When I consider hit-or-miss powered boats I sometimes think of the launch in that one Gilligan's Island episode that stayed afloat just long enough to get the cast back to their island home after they escaped the mad scientist and his mind switching machine.

Actually, as I recall it was a lovely little boat ... I wonder what eventually happened to it in real life?

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### SamSamSenior Member

You can't hardly 'scab' a John Deere B engine off a tractor. The engine, clutch, transmission and rear end are all pretty much one thing and they also form the frame/structure of the tractor. It's the same with most tractors. Here's one with the head removed.

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