Homemade mud motor

Josh Schwenger

Josh Schwenger

Active member
I wanted to share my mud motor I built testing it today I need a cavitation plate the prop is ventilating I was only able to achieve 9mph. The engine is a Subaru 7hp in its stock configuration. I copied the frame from a company called PPF. I copied the bearing system from backwater. The lower bearing housing was built from 303 stainless steel it has three sealed bearings. The upper bearing has a single sealed bearing and I used a chain coupler because it allowed for slight misalignment. View attachment 4D5FAD97-027B-46FE-BC1C-CBFEFFB027B6.jpegView attachment EC70EDCC-6B24-40D3-BE5C-FFB13E9F045A.jpegView attachment 180CED58-98F8-4A02-B14D-099B3FA653C8.jpegView attachment 6E868FFE-2DA6-440D-9985-C4B60EA54DF0.jpegView attachment D9C895C9-0BA9-41C6-B376-5D620E6CF1A6.jpeg
 
Pretty dang, cool, nice looking motor!
I'd like to see a closeup of the coupler.
Lower bearing & seal sure look beefy.
 
Josh

That rig would be a natural fit in my area, and it gets style points. I look forward to more reports and pictures. Keep up the good work.

Eric
 
Josh Schwenger said:
The upper bearing has a single sealed bearing and I used a chain coupler because it allowed for slight misalignment.
Click to expand...

Josh,
Did you have a particular reason for choosing the chain coupler, over another flexible coupler like a Lovejoy style with the rubber spider? Just curious what factor(s) were driving your choice? I understand you said "misalignment" which many style of flexible couplers handle just fine, just wondering why you choose the chain type.
 
The chain coupler was copied from a company called PPF wood duck they used one so I figured I would give it a try. I planned to make my own coupler from stainless but I dint have enough extra material after I made the bearing housings. The Garvey is only ten feet but I would like to make one that is 4 feet wide 12 feet long. I took the throttle from a junk jet ski and I spent 150 on a back water prop. I only have 150 in everything else I bought a lot of bearings that did not work out I ended up with three 7204 bearings in the lower housing and a larger single 3/4 ID bearing in the top. The bearing housings were made on my lathe but I don?t possess the skill needed to thread on the lathe so they are held together with set screws and o ring sealed. The set screws are 1/4-20 and I broke three taps attempting to thread the housing. That was by far the most frustrating part of the process. Today I hope to work on a cavitation plate.
 
Very good looking build!
You are already doing very well with 9 mph from a 7 hp longtail. Adding the cav plate will make it easier to keep the prop in the ?sweet spot? just below the surface for best speed without cavitation or blowing out to the surface, which will make driving less of a chore.
If you are driving standing up then add a grab bar or a grab rope to steady yourself. And always wear your kill switch hi
 
A word of caution in the cavitation plate. Make certain it is sturdy and a good distance from the prop. I made a few mini mud motors and added a cat plate to one of them. When I got into heavy weeds the cav plate got pushed downward and the prop rubbed on it. Didn?t notice it at the time but it chewed up the prop to where it wasn?t that useful anymore.

Mark
 
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It was a night and day difference. With the cavitation plate i can drive it with one hand. Without the cavitation plate i had to hold it into the water. I switched boats for testing so i am able to stand up and run the engine. In the next few days i will get the tachometer and look into improving on my speed a little bit. The prop is a 7x4 from back water with a recommended Hp range of 7-10 Hp. The PPF wood duck uses a 6.5X4 and those guys seem to get about 14 MPH. Backwater sells their kit small kit with a 6x4 prop. What i am rambling at here is i think i am over propped and my engine is not reaching the correct RPM range to produce its power.
 
Josh Schwenger said:
It was a night and day difference. With the cavitation plate i can drive it with one hand. Without the cavitation plate i had to hold it into the water. I switched boats for testing so i am able to stand up and run the engine. In the next few days i will get the tachometer and look into improving on my speed a little bit. The prop is a 7x4 from back water with a recommended Hp range of 7-10 Hp. The PPF wood duck uses a 6.5X4 and those guys seem to get about 14 MPH. Backwater sells their kit small kit with a 6x4 prop. What i am rambling at here is i think i am over propped and my engine is not reaching the correct RPM range to produce its power.
Click to expand...

I have a PPF with a stock 212cc motor on a 12' aluminum boat that weights 175lbs plus me at 234lbs I'm getting a steady 10mph. Most everyone I've talked to using a stock motor with my size boat and those I've talked to running Four Rivers Refuge Runners are getting about the same with a 6.5X4 prop. I have talked on the phone with Jake the owner at PPF and he's telling me they can hit 14mph on a 12' flatbottom but they are not using stock motors either.

Good job on putting yours together.
 
A 7" wheel probably drops your rpms down a good bit. A tachometer would be great to have while testing your rig.

I run a homemade straight shaft mud motor and lost 600 rpms when my prop man triple cupped my wheel. My motor is 25 hp tho. I don't have a cav plate or skeg so it's a beast to drive but will go just about anywhere.
 
I tried this configuration today running without the air cleaner and a homemade straight pipe I cobbled together. I took the carb jet one size larger but will leave it as is until I get a plug reading. I install a tach and averaged 3800-4000 rpm. The boats top speed was 11.8 mph. The boat was not loaded during testing just me and necessary safety equipment. Before I go any further I will add a second person to the testing. The mud performance was great and I went over a few logs. One thing I will have to do is shorten the skeg it?s a bit to long. View attachment DC3F2615-93C9-43AD-A857-5B39E942F1B0.jpeg
 
Yeah that?s a old aluminum V Hull. I?m going to put it back on the sneak box and try that again. I have had that Hull since I was 12 years old. Do you think a flat bottom would be that much better.
 
A mud hull is ideal but an old vee hull will work, just won't ever be a speed demon. I ran an old 9 hp Godevil on a 1965 vee hull 20 years ago.
 
Cool motor, you did a great job.

My old hunting partner had a Koehler 35 longtail on his GD 16x54 mud boat. We'd get 12-14 mph tops fully loaded in shallow water, dropped down once to 10-12 mph once we got in water over 1" deep.

My experience is a flat and wide hull is the best for mud motors but then flat wide jon boats are not the best if you have to cross open water.

A guys I hunted with a few times had a 1448 blunt nosed jon with a 9hp long tail, great boat, could move around in 4" of water with no effort.
But he got caught having to come up river when the wind came up one morning. He was lucky/smart enough to find some calm water to run right next to the bank.
Shipped a lot of water, decoys were floating inside the boat when he got it back to the ramp.
He sold that boat the next week, just didnt cut given the rivers we had to run to get to the shallow bays..
 
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