weedeater mud motor

Thread starter #1


Senior Member
I've been working on this for a week or so and I'm at a stand still.
1.Coming up with a way to mount the motor to the boat.
- used old trolling motor mount, grade 8 bolt, locking nut, square tubing and some conduit clamps. Plus relocated throttle trigger on to .5" conduit handle mounted on th shaft then bent around the motor towards the operator (like a tiller). Also I have to take the motor off the shaft and rotate it 180'. Pretty simple, shaft was slotted so i just cut another slot on opposite side and slid motor back on.
2. Flex drive shaft was too flimsy(it broke).
- replace with .25" steel rod w/ nylon bushings.
3.Motor spins clockwise @ 6000rpms or so.
- trolling motor props want work they are made for counter clockwise rotation. Also because of the high rpm too big of a prop or a prop with too big of a pitch will choke down the motor. THIS IS WHERE I'M STUCK.
any ideas would be appreciated. Thanks


Thread starter #3


Senior Member
Thats ok laugh it up, by the way I didn't know they let you have computers in the asylum. Just kidding, I got this idea off another forum and thought i would give it a try.


Senior Member
I think that is awesome. My only question is, if you can find a prop, will the little weed eater motor give you enough torque to propel the boat? I wonder what would happen if you put a lawn mower engine on that shaft.

take em

Senior Member
why not use all weedeater parts?i'm thinking maybe using the brush cutting blade(the one that looks like an x)and heat it up to twist the blades in the proper direction to make your own prop.you could set your own pitch and there wouldn't be any attachment issues.only problem that comes to mind is maybe a balance issue.let us know if you pull this one off..........
how about a 3 hp prop


Staff member
Looks like 30 days in rehab to me '-)
Me and a buddy had this same idea a few years ago. He wanted something light to put on his pirogue. Funny thing this is where we got stumped too. We never actually put it all together as you have . It seems like we found some sights on the net that you can find different size props, etc. . Sorry but i don't remember what sites we looked on. Try a search on google. Good luck!
I wonder if it will choke down when you put a load on it such as moss,stumps,mud. I ask this because mine in thick grass does. Say what you want if it works perfectly and you pull up to the boat ramp with this people are going to look some thing like this :rofl: . If you get it worked out let us know I have a 12ft boat for beaver ponds this would work great on. What about heating a trolling motor prop and reversing the pitch?
Thread starter #10


Senior Member
Well I welded a left handed nut onto a edger blade and started to cut away and shape the blade. At first with the whole prop the weedeater would not even crank. As I began to cut down on the diameter of the prop the better the motor ran. I cut it down to about the size on a trolling motor prop or maybe a little smaller and gave it alittle pitch by bending the trailing edge of the prop out. When i put it under a load in the water it would only allow the engine to rev to about half rpm, but it sure did cut some lilly pads. With this setup the boat was not moving very fast at all, about a knot or two. Next i cut about another inch or so off each end and gave the trailing edge a good twist outward. When i tried this setup the speed was good maybe 5 knots but the engine still was no where near full rpm. I guess i'll keep trying different sizes and pitches until i find one that works.
For more speed I was thinking about maybe mounting another weedeater beside this one in a twin engine configuration.
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there was a post on the refuge forums about this a while back. Great idea for a trolling motor, no battery to worry about. Do a search on it and there will be some info. They were getting there props from Youngs props. They have a website and are fairly reasonable. They did carry reverse pitch props. Great idea.:cheers:


Senior Member
I have a little bit of experience with weedeaters and small engines, as I tinker around with them every now and then. I think the biggest problem you are going to run into, as you may have all ready experienced, is the simple fact these small engines do not develop very much torque. Displacement on most of these is in the 25-31cc range, which is woefully small for your intentions.

Most all weedeaters rely on high RPM's to cut grass and weeds, not torque. Think about it, how many times have you been able to shove a weed eater into a pile of weeds and not have it choke down? Actually, look at it this way. When using a weedeater, you have to get it up to speed before you try to cut with it. If the engine isn't maxed out on its RPM's, it is not going to cut very effectively. Plus, even at its max RPM's, the motor is easily slowed by the smallest of brush. And this is in the open air with strings for cutters, which weigh less than an ounce.

Now, consider what you are trying to accomplish. You want to take the exact same motor, which has a hard time cutting a patch of weeds with two strings on dry land, and stick it in the water with a pitched blade to push around a boat and 200lbs of weight?

Here's the thing. If you can somehow come up with a prop that works, how fast do you think the motor will push the boat? Second, as mentioned before, a weedeater must be almost maxed on RPM's before it will work effectively. How do you plan on accomplishing that under water? Now, technically you could crank the motor with the prop out of water, and then drop it in. But, as you have found, you will not be able to maintain max RPM's once that prop is submerged. I don't think you realize how much torque is truly necessary to turn a prop and move a boat.

OK, for arguements sake, let's say you solve the prop problem. That's just the first of a multitude of problems that you have to overcome. How far do you think you can make it on 12oz of fuel? Sure, you could rig up a larger tank, but that may be irrelevant if you consider the next problem. What are you going to do about heat? All that resistance is going to play wordydirtywordydirtywordydirtywordydirty on the motor, and it is highly probable the motor would overheat in a matter of minutes. Sure, the engine is air cooled, do you think it is going to be able to keep up with the heat from overworking the engine with a pitched prop? Then, consider corrosion from water in the shaft. Most weedeater internals don't get along too well with water, and it would be difficult to seal. Water has a way of migrating, and it is entirely reasonable to assume it could make it to the engine. Hey, if it does, I guess you could then consider it a "water cooled" engine!!

Now, for giggles, let's pretend you figure out a way to combat the aforementioned issues. How fast do you really think this motor will achieve in a jon boat once its filled with waders, decoys, guns, people, and whatever else you need? Call me skeptical, but I highly doubt it would sustain speeds in excess of a few MPH's in open water. That's in calm open water, mind you. What do you think will happen if the water is a little rough? What do you think will happen once you hit the first lilly pad or patch of moss? Remember, this is the same engine that stuggles to cut a clump of grass with two strings on dry land. I've seen 25HP outboards choke down on this stuff, can you imagine what would happen to a 25cc engine?

I think the concept is a good one, but fairly obvious that it would never work. Now, you could go buy a heavy duty four cycle weedeater, such as a commercial Stihl or Husqvarna, but I don't think they would do much better. Plus, you are looking at $250-400 for a commercial grade unit (that still wouldn't work). Now, a lawn mower engine might work, but it would take some engineering.

Nevertheless, I commend your ingenuity!

Big Dawg

Senior Member
Hey man.......

If it don't work out for ya just weld some wings on it and fly up here to my place and I'll take you out in my boat.:rofl: :rofl: :rofl: I'm just messin' with ya dude. I hope you can get that to work. I would love to see it. Good luck.
Sticky I hope you do not take this personally. I really like the idea and would have tried it myself. With that being said I have to pull this up every day, it just brings a smile to my face. It makes me think of some of the ideas I have had in the past. Lawn mower engine may work scratch this idea and send us some pictures of the mower engine mounted on the boat.


GONetwork Member
I think the guy's name was Ikka on the second post #8 that said it chokes down every time it goes down in the water. Seems they are running into the same problem.


Senior Member
strap a back pack blower to the back of your boat n stick the nozzle in the water n off ya go ........
I have attually seen this setup before on GPTV a couple of years ago on an outdoor show they broadcasted and it has always stuck with me. I remember them going through a swamp and it would go really fast!