homemade outboard engine


Old 08-21-10, 11:58 AM
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homemade outboard engine

Okay, I know this will sound crazy, but this morning I converted a weed eater into a small boat motor (boat is a bass hunter 8 ft. plastic pontoon boat. It's rated for a 3 hp motor). After some machining, I got a trolling motor prop attached to the weedeater drive shaft and it is well-secured. I thought I was finished, but when I tried to dip the prop in the water with the weedeater running, the torque killed the motor. I tried dipping it while the motor was idling and with it wide open, but no difference except the size of the splash when it hit. Tried starting it with the prop in the water, but no go there either.
I realize that some sort of clutch assembly would help, but not sure how to rig it up. Also thought of cutting down the prop blades to a smaller size. Any other thoughts? If I get this working, my little boat should zip right along! Thanks in advance.
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Old 08-21-10, 12:12 PM
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I think that you pretty much answered your own question - no torque.
Old 08-21-10, 12:12 PM
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Too late now, but you might have to go to a straight shaft. A lot of them have a centrifugal clutch.
Old 08-21-10, 12:55 PM
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Yep...weedwackers run by speed not torque. Cut down the blades or find a smaller prop. Actually...something like an small electric fan blade might be a possibility.

Trolling motors are normally electric..max torque at 0 rpm.

Lots of small boats overseas have a setup like you describe...but they use all sorts of 4 cyl and even larger 4 cycle motors. They just have them extremely balanced to dip in and out of the water.
Old 08-21-10, 01:16 PM
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I thought about the small electric fan blades, but the ones I saw didn't seem very sturdy. Plus, I'd have to find a way to mount it backwards because the blades are pitched opposite for pushing air.
A straight shaft weedeater has a centrifugal clutch? Huh! I'll have to see if I can find a cheapie on Craig's List. That would most likely do the trick. Thanks!

Old 08-21-10, 01:46 PM
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there was a guy on eBay selling plans for something like that a few years ago . you might want to see if he is still there
Old 08-21-10, 03:57 PM
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This guy has figured it out.

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