Cavitation Plate

Brandon Bolling

Brandon Bolling

Active member
I have a question about a cavitation plate for a long tail mud motor I just finished building. I originally thought the purpose was to keep the prop just below the water while running at higher speeds by riding on the surface with the prop just below it . After reading up some, it said that the purpose was to keep water around the prop while in weeds or thick mud. Could someone please define the purpose and give me the correct placement. Thank you in advance. Here is a picture of what I had but removed after deciding it looked wrong.

FinishedLongtail007.jpg

 
Here's my understanding of it, but I'm sure there are guys on this site who know more about this than I do, so it will be interesting to hear from some of them.

The cavitation (or anti-cavitation) plate is supposed to prevent cavitation by directing water flow around the prop to minimize air bubbles that can create a loss of power and damage the prop. It's especially important on a long-tail because the prop enters the water at an angle whereas the plate runs parallel to the surface of the water when it is just under the surface.

I don't see anything wrong with the cavitation plate in your photo. Was it set at the wrong angle?

Rick
 
After reviewing some videos on youtube I concluded the same thing. The angle that I had it set on was still significantly up when placed at estimated water level. I am going to scrap the angle iron and use a piece of .25 X 1, it should offer a little smoother ride through the water, and if it is to keep the water around the prop it should make less turbulence, now i just have to figure out the angle
 
Brandon,
Put it on your boat and have someone hold it where it looks to you like the prop will be just under the water line. Then just weld the plate as close to the same plane as the bottom of your boat as you can get it. You will end up having to bend the end of the plate up or down to get the motor to ride in the sweet spot. Shawn
 
You will end up having to bend the end of the plate up or down to get the motor to ride in the sweet spot.
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After you get the plate set where you want it, you can then tack the brace back in place to hold the plate from further bending if you wish. Having the angle set just right for your set up, takes all the work out of operating a long tail mud motor.
 
This is a straight shaft design that is belt driven with the motor facing forward. I started off with the cavitation plate mounted directly to the drive shaft housing, however after some review and attempts to get the right angle I think that the only way to get it is to raise the plate above the housing. I am building this for a sneak boat that sits very low in the water so the straight shaft should work well, the problem lies in the angle of the cavitation plate being significantly close to parallel with the shaft obviously not exact but if I am to achieve the angle that you are telling me I would have to raise it or I will be cm from the prop. Thank you very much Rick, Shawn, and Dave for your help, I truely appreciate it. I think if the plate starts above the housing it should still function the same, or at least I hope it will.





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Cool design!!! How are you tensioning the belt? Just shims at the pillar block? I see what you mean about the angle. You might try it without a cav. plate. Some of the small h.p. motors I have seen on the net do not use one. Shawn
 
Shawn,

Actually that was the plan, but when it was all said and done a 22in belt fit perfectly, no shims needed, so imagine my surprise when the first belt l tried fit with no adjustments needed, it actually made my day and my trip to the hardware store a lot shorter than anticipated.
 
I agree with Shawn. I tried with and with out no performance difference deep or skinny water. But I have a smaller motor. Cool design: if you ever decide to build a shorty,I think you can apply your design quite well.

James Roberts
 
I don't think you'll have any problems with the cavitation plate, but I don't think you'll like the tiller bent like that. I might be wrong, but you've got to be periodically pushing down on that tiller to get the prop out of the water to clear it, and to get over obstacles, it takes quite a bit of force to do it, so I think the bent tiller is a bad idea. Also, straight tail mudmoters are a MF to steer. They will wear you out if you've got to spend several hours running around in a boat with one on the back. The way you've got that tiller, you're going to be torquing it all the time. That can't be good.

Ed.
 
Also, straight tail mudmoters are a MF to steer. They will wear you out if you've got to spend several hours running around in a boat with one on the back.


Ed.

Ed,
Is this why scavenger uses the loop handle? They look like they would be easier to run, but the handle could get in the way in a small boat. Shawn
Click to expand...
 
I don't know about Scavengers, except for pictures I've seen on the internet. I've run GoDevils and Mudbuddys. Maybe the thing with the loop handle is you've got to lean way out to cut the motor hard to one side or the other. With the loop handle, you wouldn't have to lean as much and the boat would be more stable in a turn.

Ed.
 
Robert,

I appreciate the diagram, surprisingly its the same picture that I put into my head. I cut the old one off and this is the new approach. It looks like a match up to what you laid out. Official test day is tomorrow, we shall see what happens. With the new design it will be way easier to adjust. Hopefully I will have enough push for it to make a difference.

Ed,

I hope that I don't fight this motor the entire way to my spot. Pulling the boat over dikes is hard enough, I don't want anymore trouble from the motor. I have never used a mud motor, I looked at one once, and thats about the extent of my knowledge other than asking tons of questions on the web and looking at countless pictures and videos. This project is completely trial and error, I expect to have some set backs, I hope to be able to solve them as they arise. I could not afford a mainstream model so I figured i would try it on my own, that beautiful little girl I am holding is worth every penny, there is just not a whole lot left over. I appreciate your input, what is a solution to making the motor easier to handle for long distances? The scavenger handle is just too big for my boat, any suggestions would be great. Thanks in advance!

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cavitation plate:

For what it's worth - I mount the plate so that in the running mode the plate is parallel to the water's surface or close there to. The plate makes it possible for the prop to "fly" just below the surface of the water. This holds the angle of the driveshaft as straight forward as is possible with this design concept. While it's true that the prop will push the boat forward while it submerged a long ways, The straighter or closer to parallel that the driveshaft is the greater the forward thrust is. If the prop is "flying" properly the tiller takes almost no effort to handle.

If you look at the mount of the forward end of the plate on my motors you will see that the end of the plate is anchored above the driveshaft houseing. The plate is also a bit longer than the norm to facilitate getting this angle parallel to the water's surface.

The sides of the plate are curved ar bent down to confine the water around the prop. The trailing lip of the plate also extends past the prop a bit to dierect the prop spray to the rear instead of letting it disperse in an uncontrolled arc.

I am in the process of crafting one for my Ultra-lite motor as well as I think they serve a serious function on even small motors.

Good luck with your project.

Mark F. Cheney
 
How hard is it going to be to change your tiller? If not that hard as I would expect, leave it as is and go out and try it out in some shallow area like where you're going to hunt. I wouldn't give up on my design without a trial. If you think it's a problem (I'd be very aware of the torquing issue), then replace it with a conventional tiller like you see with Mudbuddy or GoDevil. You see how those tillers are pretty straight? I guess the GoDevils have some bends in them, but not to the degree that you have. GoDevils are also very heavy and that tiller shaft is probably a big heavy piece of iron. The handles are oriented in the same axis as the drive shaft, so with the palm of your hand you can push it down to get over obstacles or bring the prop up out of the water to clear it, which we have to do frequently down here due to the thick vegetation, I'm guessing won't be something you'll have to do as much up there.

Ed.
 
The tiller on my rig is adjustable through a wide arc. It is made out of aluminum tubeing and doesn't weigh much. Some people stand, some people sit, so put it where it is comfortable for you.

Mark F. Cheney
 
I'm surprised someone doesn't make an adjustable cavaitation plate as ll boat transopms are not the same height. On the smaller motors the angle of the plate probably isn't as important but on the larger hp motors, I would think the angle of the plate into the water would make a huge difference in performance. Just a thought.

Mark W
 
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