Just a note, most all outboards of usable size are 2 to one gearing, I would love to find one with gearing up for higher prop rpm. Watch the torque output figures, you might need a bigger lower end for both prop size, and that the torque can get high fast -- if grounding at some point. Mine based on a 50 hp Evinrude, puts out more than the torque of a Chevrolet 2200 Vortec, 4 cyl.at 140 ft. lb. – just the speed is lower of course in the electric – the max efficiency at 3861 rpm VS the Vortec at 5k or so. That's at 48 volts, and 175 amps, from the size 27 marine deep cycle batteries I get as a sales rep sample. Cruise speed of choice is a lot less of course.
In my reading, I ran across an article that proposes that no gas motor should be in close proximity to any non-sealed electric power head, ( I assume non-sealed batteries too ) particularly any with brushes – I guess that sounds good. A hot motor or generator spark in the engine room doesn't appeal to me. Being casual with some cheaper gen sets, maybe could cause an explosion ??
later, Cal
Sent: Monday, September 08, 2014 9:10 PM
Subject: [Electric Boats] Re:New Member and question about displacement
Have been thinking about motor speed and gearing. Since I am not so concerned with attaining hull speed seems like running the motor up towards it's max at my fastest normal cruising speed and having a higher gear ratio would be the way to go. My prop calculations say that with a gear ratio of 2.5:1 I can run an 11 x 9 prop which I think should push the boat better at slower speeds. I think you also with the increase in gear ratio you get more torque at at the prop at lower amps at the motor(?) .
Probably the way to go is to use a lower end from a 20-30 hp motor to fit the larger prop size. Just does not seem like the little prop from a small motor would do the job.
I do want a generator at some point so probably will just spend the $$ for brushless.
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Posted by: "cal" <h20dragon@centurytel.net>
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