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Old 08-03-2003, 02:41 PM
pung pung is offline
Join Date: Dec 2002
Location: Toronto
Posts: 67
Convert a gas trimmer to a canoe motor?

My father is convinced that he can buy a cheap gas trimmer and turn it into a canoe motor. Can he do it?

He has been using an electric trolling motor for a few years but the batteries are very heavy and the motor is slow.

Web searches lead me to an old Usenet thread where a person claimed that they were able to perform this operation to power a catamaran. The person said the bearings had to be replaced and that the propeller needed to be ground down until it no longer stalled the engine (torque problem I suppose).

So the question: Can someone with very little mechanical knowledge and no metal working tools do this? Are any instructions available online or in print?
Are there any other inexpensive ways to stick a motor onto a canoe?

... oh, yes he's aware that the accepted way to power a canoe is with a paddle. It's no use arguing with him, he wants to enjoy the canoe without any sort of effort on his part.
Old 08-03-2003, 04:04 PM
DougC DougC is offline
Join Date: Mar 1999
Location: IL, USA
Posts: 5,209
Gas trimmer motors are very small. Like, small as in one-quarter horsepower or less -- and they are simply not designed for sustained loads even at that power level--look inside one sometime, the "crankshaft" is usually a single-sided stack of sheet metal plates spot-welded together. In the US, many odd places around are selling "blade"-style scooters now that are powered by these tiny "weed-whacker"-type 2-cycle engines, and the top speed with one typical-sized teenager on board is only about 12 MPH. That same kid can pedal a 10-speed bicycle faster than that. And then you'd have the problem of finding some way to seal the submerged bearings on the actual prop drive.
- If he absolutely wanted to try to do this, I would advise either get a trolling motor and run it off a battery as usual, or rig up a small generator somehow to power the electric prop drive of a trolling motor.
Old 08-03-2003, 04:52 PM
Finagle Finagle is offline
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Location: Somewhere near Boston
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One of the biggest problems would be the noise -- gas trimmer engines are very noisy. If the canoe is for fishing, you'll scare every fish within miles, not to mention making enemies for life of everyone else on the river/lake.
Old 08-03-2003, 06:54 PM
stamcon stamcon is offline
Join Date: Aug 2003
Location: So SF
Posts: 9
Pung, I had a friend that converted a weed wacker to a boat motor. He used it for his dinghy. He had to try a couple of different sized model airplace propellers to get one that worked properly. One of the big problems with this setup, as Finagle stated, is the excessive noise.
Old 08-03-2003, 07:29 PM
pung pung is offline
Join Date: Dec 2002
Location: Toronto
Posts: 67
Alright, thanks guys.

I saw the noise issue mentioned in another Usenet discussion (discovered after posting here) and it's nice to see you confirm it.

Weed Whackers are simply too loud to take onto the water.

I've convinced him to buy a cheap second hand boat motor instead.

My dad is happy that his idea was somewhat plausabile.
So everyone wins

The usenet discussion I mentioned in case anyone is curious:
Old 08-03-2003, 11:20 PM
scr4 scr4 is offline
Join Date: Aug 1999
Location: Alabama
Posts: 14,114
Originally posted by DougC
Gas trimmer motors are very small. Like, small as in one-quarter horsepower or less...
That in itself shouldn't be a problem, I think. One-quarter horsepower is a bit more than one human-power.
Old 08-04-2003, 02:10 AM
AskNott AskNott is offline
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Join Date: Mar 1999
Location: Anderson, IN,USA
Posts: 14,634
On the Amazon, and some rivers in South Asia, the unpredictable snags make conventional outboards useless. The motors they use look a lot like weedeaters. The concept might seem impractical, but, hey! I live in a town where a public park houses a tiny circular track where men from all over the country race little hand-built racecars at 120mph. By "little" I mean between 12 and 18 inches. The engines look like they're from model airplanes, but these guys machined the teensy mills from aluminum and steel.

Ahem. I got sidetracked. If somebody other than pung's father is still interested in this daft, but interesting project, I'd recommend shopping for a prop in the model boat aisle rather than going for an airplane prop.
Old 08-04-2003, 08:48 AM
Philster Philster is offline
Join Date: Aug 2000
Location: Location: Location:
Posts: 10,486
Weed trimmer motors are popular for model power boating, power boats up to five feet in length and up to 60 mph. They could handle a canoe.
Old 08-04-2003, 10:46 PM
Northern Piper Northern Piper is offline
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Join Date: Jun 1999
Location: Je suis Ikea.
Posts: 25,645
pung, I'm thinking these guys might be able to help you.
Old 08-05-2003, 01:48 AM
antechinus antechinus is offline
Join Date: Dec 2001
Location: Sydney
Posts: 2,265
Originally posted by Northern Piper
pung, I'm thinking these guys might be able to help you.
So this is where the kids in the Mad Scientists Club retired to.

Further to AskNotts post ... in South East Asia the motor is mounted onto a post in the back of the boat (you could rig it so the snipper can be simply sat on the post). This acts as a pivot and holds the weight of the engine. The weed-cutter is much lighter than the SEA version, but your dad wont be using a harness to hold the cutter....will he.


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