# Homemade surface drive mud motor



## Cdewolfe

Built my own surface drive mud motor last year. Bought some plans off eBay for a 6.5hp build and then beefed everything up to handle a 13hp. Cut all my own parts with a 4.5 inch cut of wheel which added a ton of time to the build. If I do another one I will be having it cut by someone with a waterjet. A friend powder coated the transom mount. Welded tabs onto the tunnel for the transom mount and cut out an angle to access the top pulley. Cut slotted holes into tunnel to mount engine and for belt tension adjustment. Measured height down to bottom of boat and cut off tunnel. Cut out a window on bottom for prop shaft to mount through. Welded skeg and mounting plate to prop shaft. Pressed in brass bushings and installed grease zirks. Mount prop shaft onto tunnel and bolt on a bearing in tunnel on the end of the shaft and tack weld the pulley on. Had threads cut into the 3/4 prop shaft for prop. Welded bottom of tunnel on. (You can see my improvement in welding over the duration of the project in that picture) prepped everything for paint and used por15 for a base coat and then went over with flat camo paint. I have a few videos on YouTube uploaded of the build and test runs.
https://m.youtube.com/channel/UCjlOfMwBuK1NvOozqbabq_g


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## Darryle

Looks good, I would like to see some better pictures of the completed motor. 

I bought those same plans, but ended up going this route 







I will eventually build one as I am slowly acquiring the parts and materials, except I am using aluminum.


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## Crazyboat

I have NO time on a mud motor, but it seems to me there is a lot of stuff blocking the free flow of water to that prop, what am I missing?

Other then that it looks like a very quality job.


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## tomme boy

These motor only have to have the bottom of the prop in the water. And they are extremely fast for what they are. The Copperheads are as fast or faster than the same hp outboard. Many times way faster in the smaller versions


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## Crazyboat

tomme boy said:


> These motor only have to have the bottom of the prop in the water. And they are extremely fast for what they are. The Copperheads are as fast or faster than the same hp outboard. Many times way faster in the smaller versions




So one running say a 20 HP drive will top out over 25 MPH on a small light boat?


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## Darryle

Here's a 12hp just like mine on a small skiff about 12-13ft pushing 23mph 

https://m.youtube.com/watch?v=4ekyx3zwl6A&feature=youtu.be


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## Sinkingfast

Darryle said:


> Here's a 12hp just like mine on a small skiff about 12-13ft pushing 23mph
> 
> https://m.youtube.com/watch?v=4ekyx3zwl6A&feature=youtu.be




I just can't get my head around this. I'm sure your phone is correct but the water doesn't seem to be going by at 23mph though. It does make 12hp worth of noise...

Hmmm.I've got a 18hp vtwin in my shop waiting for a project..


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## Darryle

There are guys who get upper 20s with a 23hp and a 14-16ft boats


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## Cdewolfe

If you got the link in the original post I added a video of the motor in open water. After the video I checked my stored and I was getting 18 mph. As you can see in the video I didn't have my trim set right as the entire prop was under water and the tunnel was dragging a lot slowing me down. Once I fixed the trim I was right at 20.


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## Cdewolfe

Couple more pictures of the motor finished. Sorry they are so dark.


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## Darryle

Looks like a V-Belt drive? What is your final drive ratio? Any issues with slipping? 
You did a heck of a job and your tenacity is to be commended. Using a cutoff wheel to fab parts is no small task.


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## Cdewolfe

Thank you. I ended up with a 3 inch top pulley and 3 1/2 bottom. Right now it is v belt but will be getting changed over chain this summer. When I was alone no slipping issues but with 3 guys, 8 dozen deeks and all our gear it slipped a bit if I accelerated to quickly.


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## CedarRiverScooter

A notched (aka timing) belt might be less maintenance than a chain.

You can get any size you want from Mcmaster Carr


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## Darryle

The Copperhead I have has a Megadyne Platinum 1224 PLT8 cogged for a drive belt, it's a beast and pushes a 10 1/2" 10 pitch prop, thing looks ridiculously big on the back of the motor


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## Cdewolfe

The belts I could find but was having a harder time with pulleys. Especially since its a 1 inch bore output shaft on the motor and 3/4 on the prop shaft. I would prefer to use a cogged belt though


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## Darryle

You buy hubs to fit the shafts and then you can buy the pulleys in what ever configuration you need.


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## Cdewolfe

I ended up selling the motor to fund building the boat I picked up so I guess I don't have to worry about the belt anymore.


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