Mud Motors

[DuckHunterJon]

First off, I wasn't sure where to put this, so if it needs to be moved, please feel free. I built my duck boat a couple years ago and have tried several motors on it. It's 12', flat bottom, v front (Glen-L Duck Boat Too for those familiar). I've tried several motors on it, and while they are all decent, I'm finding myself getting into shallower water with it and sucking up a ton of mud in the motors. This past weekend, I killed my 1966 merc 60 (trust me, it wasn't far off before the incident) by injesting enough mud to block the impeller. The motor cost me $25 if that's any indication to it's shape prior to this.

Anyhow, I'm faced with rebuilding the motor (will probably do anyway), or spend the same money and build a 4 stroke mud motor. I was just curious if anyone here had any insight about these motors, either home made or commercial (beavertail, go devil, etc). Any thoughts about the long tail vs. short tail motors? Any issues with direct drive and no reverse? Any tips, thoughts, otherwise about building one from scratch? I have a 6.5 hp Honda motor that is begging to be put to use, and I don't see it much work to build a drive shaft, housing, and mount for it. Just looking for other ideas. I've seen the plans on EBAY and a few others that have built them, just figured I'd check around here for opinions. Thanks!

 

[Home Cookin']

Re: Mud Motors

the old merc's were more delicate than the old OMC's (by reputation): If you want to get there fast, get a merc; if you want to get home, get a Johnson. So maybe another old OMC? Or two?
Perhaps an air-cooled outboard?
Maybe a jack plate? Should be an easy fit on a small motor
I don't know that they run go devils on 12' since you drive standing up, but I could be wrong.
We just run the OMC's and Yami 2 strokes at our club, through a lot of mud and sand.

 

[DuckHunterJon]

Re: Mud Motors

Thanks for the info Home Cookin'. I have been a little worried about the whole standing up part. I'm thinking of making a mount plate that will move the motor back about 6" from the transom, and still allow me to sit will running. I know the reason for standing is to have a better view of logs and stumps - but where I run, it's entirely a mud bottom. A very shallow mud bottom.

I'm keeping my eye open for another motor, and might entertain the idea of a jack plate, but still have the problem of not being able to run the prop half out of the water. I took a trip to Harbor freight yesterday and looked at their honda clone motors. Pretty darn impressive for $105. I then went to tractor supply company and priced up a U joint at $70. Looks like the most expensive part will be the prop ($150) unless I can come up with a way to make one.

Any other thoughts are welcome. Thanks again.

 

[shrew]

Re: Mud Motors

You need an air boat. A pole or a good set of waders to walk to where you're going wouuld get the job done to. LOL (JK).

Honda 2 HP air cooled would work in such shallow waters, but don't expect to ge there quickly. That is pretty skinny water, even for a 12' jon boat. I think your going to be limited in your options, and it sounds like you've already listed them out.

 

[Home Cookin']

Re: Mud Motors

get some used props cheap.
or a used 15 hp for $400.
The bottom line is that no prop motor will run in mud. A strong motor will tolerate some hits or dragging.
My theory is that when you are moving forward, stirring up mud, you aren't sucking it up but leaving it behind. Not so, of course, going idle speed, when stuck or reversing, or plowing. You zip over mud on a plane and you are OK, until you run out of water, drop off the plane and get stuck until the next tide. But if it's too shallow for the prop and you aren't on a plane, the duck-bill shove pole is your friend.
What I'm saying is, you can't solve the shallow water problem entirely with a different motor.

 

[tx1961whaler]

Re: Mud Motors

Sounds like you need a Mud Buddy:
http://www.mudbuddy.com/about.htm

 

[rollo1002]

Re: Mud Motors

I'm with tx1961whaler an avid duck hunter myself the surface drives are the motor of choice. mud buddy, go devil are the two I would look at if I were you.

you're buddies will be jealous as you get into those spots they wish they could. These motors have been well tested in the bayous of Louisiana and they work.

 

[dg512055]

Re: Mud Motors

I have a long shaft motor with a 25hp Kohler. It is home built by a local guy here. I can tell you that if you need to go a long distance, the long shaft is not comfotable to operate, especially at a speed above idle but below planing. When you turn at this power setting, the handle will pull like crazy to the outside of the turn. You MUST install a handle in the boat to hang on to. On the plus side, if you get into a spot where there is little or no water showing, you can lift the prop out and put in down in a differnt spot. You can also use the motor as a "oar" to spin the boat around in a different direction. I have run mine in 4" of water with a HARD bottom. It is on a 1652 F&F flat bottom boat. They will run in deep wet mud all day long. I would look at the ProDrive. They seem to be built like tanks and I have seen these run on Reelfoot Lake. They will push a john boat at 25 to 30 MPH in stump infested waters with no worries about hitting them. They just bounce up and back down. They also leave a neat rooster tail due to the surface running propellers. Watch some of the videos here.

http://www.prodriveoutboards.com/

 

[DuckHunterJon]

Re: Mud Motors

Thanks for the real world experience DG. That's the first I've heard of the handling. It's concerning to me as my boat likely won't ever see planing speeds. Maybe I need to rethink the long tail vs surface drive. Both seem pretty simple to build. I have heard the surface drives are better for higher speed, but was leaning towards the long tail as it's easier to build and I don't need high speed. My 4 hp pushes the boat along at a comfortable 6 mph which is faster than paddling - right up till I get in less than 8" of water, and as duck hunters know, that's just were the fun begins! Most of my hunting is in shallows, mud bottom, no stumps, logs, anything to hit. My longest trek is about 2 miles. Most of them are less than a mile.

Seems I need to weigh the pros and cons of SD vs long tail before I go much further. Any other comments on this anyone? Thanks!

 

[Home Cookin']

Re: Mud Motors

Saw a 4 hp briggs and stratton on our CL for $400 today....

To me the long tail is a liability, but I hunt in narrow winding creeks. Even the 17' canoe is too long at times. So if you add a long tail, you've lost some versatility, especially if you jump shoot (my 13' canoe is deadly, operated solo). I don't know your whole situation but for me, some paddling or shoving is inevitable. And less likely to spook ducks.

I often pull the canoes behnid a larger boat to cross the bigger water/long creeks then jump off to paddle the small creeks--maybe a combo of boats is what you want? A man can't have too many boats....

 

[QC]

Re: Mud Motors

First off, I wasn't sure where to put this, so if it needs to be moved, please feel free.

Hey Jon,

Thanks for the concern. Seems pretty general, so we'll leave it here. I know it can be confusing, I was thinking General OB, but this is more about an application than a power source.

I have a Briggs 5 bhp air cooled OB and it is fine for what it is. Biggest benefit is they are cheap and they are aircooled. Other than that, they kinda suck . . .

 

[dg512055]

Re: Mud Motors

DuckHunter, if you are going to use a smaller motor and don't get in a hurry, you will probably be happier with a long shaft. My brothers-in-law built a small one with a 3.5hp B&S that they use after running 2 miles up a small river with a 25hp outboard boat. The carry the small motor over a levee and clamp it to a 12 ft boat hidden in the bottom. They use it to travel through shallow water with mud and weeds a few hundred yards to the blind. It is not fast but it is better than a push pole. The smaller motors are mush easier to handle than my 25HP. I gaurantee the long shaft will be more versitile in your conditions. Eight inches of water is plenty as long as the boat doesn't sit on the bottm. If it has a flat bottom and you keep moving, you can run in much shallower water. The main thing to learn is that momentum is your friend. Plan your route to maintain forward movement as much as possible. The other thing to learn about a long shaft is they are happiest when going in a straight line. You will learn not to fight the motor, but to work with it. When you learn these things and with a little practice, you will be amazed at where they can get you.

 

[DuckHunterJon]

Re: Mud Motors

Thanks again DG, I'm currently leaning towards a longtail. I spend some time yesterday drawing up some designs, and think I have everything figured out except how to preload tapered bearings on the shaft to take the prop thrust. Otherwise, seems pretty simple. My thought is to build it for a fun project, and see how I like it. If it doesn't work on my boat, I figure I can always break it back down and use most of the parts for a surface drive build. The one thing that's pushing me towards a long shaft is most of the surface drives I see are much bigger motors, I'm not sure if that's a need to go fast, or that the surface drive props need the extra torque to work. The motor i have is 36 lbs, I'm targeting less than 60 lbs with a quick disconnect to remove it from the boat. As you said, lightweight is key.

I'll post some progress on the build as I go, and of course testing results.

 

[gonefishie]

Re: Mud Motors

Sounds like you need a Mud Buddy:
http://www.mudbuddy.com/about.htm

Wow! to heck with jet drive. I want one of those.

 

[DrLugOD]

Re: Mud Motors

Saw this today on the local craigslist:

http://stlouis.craigslist.org/boa/2091508041.html

 

[dg512055]

Re: Mud Motors

The older and smaller long shafts did not use any thrust bearings in the shaft tube. They only have needle bearings in each end with oil seals. Be sure to use 2 seals on each end. If you use only one on the bottom, and install it to hold the oil or grease in, it will pump water into the tube. The thrust is taken by the motor bearings through the u-joint. My motor is rated to take this kind of thrust. I think most small engines will. The tube on mine is just a piece of pipe that has been bored at each end to take a needle bearing assembly, the oil seals, and a snap ring. The u-joint is from NAPA I think. The shafts are almost universally 3/4" with threads on the prop end. I would look at a Mud Buddy prop. If you can, get a good material for the shaft. 80,000 psi cold rolled is kind of fragile in this application. I made a shaft from a steel call Miraloy, about 160,000 psi I think. This is after bending 2 cold rolled shafts on stumps.

 

[gonefishie]

Re: Mud Motors

I've always wondered about these motors. I've seen them in Asia with the long shaft and small prop. These boats were on big river and the motor appeared to be water cooled because I saw a pee stream. Are they basically the same thing? I don't understand why they don't use regular outboards if they're not running in mud.

 

[DuckHunterJon]

Re: Mud Motors

Interesting DG that they don't use thrust bearings. I wouldn't think the U-Joint would hold up too well at 3400 RPM and a hefty thrust load. I may just make it with out and see how it does. A friend has a lathe, but isn't sure he can get the shaft housing into the headstock, so I will probably make up ends for the bearing/seals, then weld that onto the shaft housing.

Thanks for the info on the shaft housing, I'll look into a stonger alloy for sure. Another qestion, if I may - I've been debating on whether to go with 3/4 or 1/2" driveshaft. 3/4 is pretty standard on the prop end, but I could sleeve it up to 3/4 if need be. Any thoughts?

Thanks again.

 

[dg512055]

Re: Mud Motors

Thinking about a 1/2" drive shaft, it may not be a good idea. In addition to the standard torque load from the engine, there will be impacts with hard objects, and the shaft must withstand these inertia loads as well. When using the single yoke u-joint, there will be cyclical rpm variations seen at the joint end of the shaft. Depending on the lenght and torsional stiffness of the shaft, there can be some severe harmonics at certian RPMs. These will leave you scratching your head when the shaft snaps off for no appearant reason. You also have to consider shaft whip. Depending on the length again, there will be an RPM range where the not-perfectly-straight shaft can bend in the middle under centrifugal load. This will go un-noticed until the shaft rubbing the inside cuts the drive tube in half. This will of coarse happen when you are 2 miles into the boonies with no cell coverage. Having experience with these motors, and having seen these failures firsthand, I will have to say that the shaft is the last place to skimp on robustness, (if that is a word). The 3/4' shaft that I have made could not be threaded with a normal die. They were cut on the lathe with a single point tool.

 

[DuckHunterJon]

Re: Mud Motors

Once again, thank you for the insight. 3/4 shaft it is. That works out better anyway as the ends have to be stepped to allow me to thread a section for a bearing preload nut. My current design (changing daily) has 5/8" ends, stepping up to 3/4" for the main section. The first 1/2" of the 3/4" section will be threaded (need to use fine thread 3/4" to clear the stepped section) to allow the use of tapered roller bearings and preload them from either end (the OD of the bearings will sit against a step in the shaft housing). Shaft seals will ride on the 5/8" step portion at either end. I know this will require the use of a 5/8" id prop hub, but Hill props on Ebay says he'll supply either 3/4" threaded or 5/8" pinned.

You bring up another point I've been thinking about - shaft whip. I see some manufacturers use a bushing at the mid point of the shaft to control whip. I'd like to do that, but I'm not sure how it's held in place. Perhaps something as simple as lock collars on the shaft? Any ideas on that?

Sorry for the 20 questions, but being an engineer, the design is half the fun!