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Posts: 50
| Any tuffy esox mag tiller users have any cavitation issues. My boat is 3 years old and it has a 60hp yamaha on it. The original prop and the backup both did this in the 1st year. On the pic of the prop, all 3 fins wear the paint off and it is real rough feeling there, like sandpaper. I took the prop back to the dealer and was told I must have hit some sand. I didn't think so. I had both props fixed/cleaned up and the same happened again. The boat dealer then told me to remove the intake filters (see 2nd pic) as this had been a problem with cavitation on these tuffy boats. I just put a new prop on and have motored only a few miles on it and again I have the wear issue. Any other esox mag users have this. Also, Steve W. , do you have any suggestions?
thanks Brian
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Posts: 5874
| The thing you are pointing at is not an intake filter. It helps force water into the livewell pump when on plane. It's not likely to be causing your cavitation issue, unless your motor is too high. Looks like you had two, and one is missing. It is adjustable and should only extend below the transom a very little.
You haven't given enough information. When does it cavitate? On acceleration? Once on plane and trimmed out? During turns? It's an aluminum prop. What pitch? What RPMs at WOT?How high is the motor mounted? Put a straight edge along the bottom with the motor trimmed level, and check.
Picture looks like it's hitting something because the paint isn't off the end, it's in a bit. Is it possible the blades are flexing and hitting the trim tab?
Provide some answers above, and I'd bet Steve( VMS) will have some answers for you.
Not heard of this issue on any Esox Mags, and I know quite a few guys that run them.
Edited by Shep 10/25/2013 8:26 AM
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Posts: 50
| Shep thanks for reply. I should have labeled them livewell intake screens, was told that they help keep out unwanted stuff to livewell pumps. In the pic, I'm holding it in place since I took them off this summer. The cavitation is heard on acceleration. I don't notice it on plane or trimmed out. The prop is a 12 pitch, 11 and 3/8. As far as rpms, when going wide open, I'm at around 5900. I don't believe the blades are flexing and hitting something. When I 1st noticed this the 1st summer, the paint was just gone in the same area on each blade. Shortly after that, those spots got "rough" feeling, like sand paper. I see the prop pic isn't the best. But this prop is new and one blade has shown this wear. I'm sure if I continue to use it, it will wear just like the others. | |
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Posts: 3500
Location: Elk River, Minnesota | Hiya,
This is a classic example of what cavitation really is. You definitely have a cavitation issue as what you are experiencing is an actual pocket (or cavity) forming on the back side of the blade as it goes through the water. It is an extreme drop in pressure between the blade and the water which causes the water to acutally vaporize, creating the pits you are feeling on the blade surface. That is also why you don't have it on the edge of the blade but rather on the fin itself.
In looking at your second picture of the transom, I have a feeling it could be a few different things that can lead to the issue you are having. Cavitation is a normal thing to happen, and most props will have some sort of cavitation..but not enough to actually erode the prop. Your case is excessive. What I see are a couple of items that can potentially create disrupted water reaching the prop: The transducer, and potentially those EZ pumps. In order for the EZ pump to work, it has to stick down into the water just a touch in order to create pressure and force-feed water to your livewell (much like many of the speedometers on the boat work...water pressure). In creating this, the water flow to the prop is disrupted (introduction of air to the water before hitting the prop...it is in the path of the prop, thus creating the pressure drop on the rear side of the fin. The Transducer could also potentially cause this as well.
The difference in ventilation vs cavitation is when you ventilate, you are actually introducing air into the water from either vent holes, or from piercing the surface of the water directly on the prop, whereas cavitation is dealing with air that is already trapped in the water and is passing over the blade surface. This is why when you turn quickly you actually are ventilating...not cavitating as you are creating a pressure drop on the water's surface drawing air into the prop fins. Or...if your motor is set too high, the prop can draw air in at the water's surface.
Think of ventilation like mixing a glass of chocolate milk. you spin in one direction creating a flow of milk in that direction. Then stop the spoon and you create a drop in pressure on the back side of the spoon because the direction of the milk will continue in the direction of stirring, and you are now changing the direction of flow.
My suggestion to consider: Remove the EZ pump covers, AND the transducer. Then, if you can polish the spots where the cavitation is happening, paint (with a zinc base so it etches into the aluminum...otherwise it will just flake off) and go for a spin...see if the cavitation occurs again. If not, put the transducer back on and retest... If no cavitation, then put the EZ pumps back on and remove the transducer...retest.
It could be the combination of transducer and the ez pumps creating a very wierd flow of water to the prop...you have water being forced in a couple of directions (sideways and down) from both parts, which could potentially create a flow of water that is actually spiraling between the transducer and ez pump....thus a low pressure area...leading directly to your prop.
Steve
Edited by VMS 10/24/2013 9:30 PM
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Posts: 32910
Location: Rhinelander, Wisconsin | That's an EZ pump, not a filter, Shep described it well. They do nothing at all to cause any cavitation, they are just at the surface under power and don't open the water up or disturb water flow in front of the prop coming to plane. It makes no sense that the wear would occur when powering to plane at all, what's your tach doing as you come up on plane, and are you keeping the engine trimmed all the way down until you come on to plane; what's your time- to- plane? Are these painted stainless or aluminum props? What you see there is happening when you are running on plane, I'd wager. The EZ pumps use head pressure to keep water flowing on plane.
As mentioned below, your transducer is in the wrong place. It should be mounted in the tunnel on the starboard side, I'd move that. The EZ Pumps are not the problem. | |
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Posts: 50
| I've ran all summer with the EZ pumps off and still cavitation. When powering up to plane, yes I'm trimmed all the way down. I can't say for sure what the tach is doing when powering up. I don't think its jumping around. I'm pretty sure I would have noticed this. The prop is aluminum. Wish I hadn't winterized the boat last week. Would like to pull the transducer off and try it. | |
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Posts: 5874
| What you can do now is take a yard stick and put on the keel and see where your cavitation plate sits compared to the bottom of the keel. I suspect it will be quite high.
I don't like putting a transducer dead center on the transom in front of the prop for exactly that reason. I've seen it many times on other boats. I'd move it out to the side, at least to the first chine.
I don't think the EZ pumps will cause the cavitation, especially since you said it still happened when the covers were removed. They really don't need to be below the transom much. Especially at low speed on acceleration.
I would also look into a SS prop. I agree with Steve's assessment that your burning the paint off.
Winterizing is easy enough to take it out for spin to check it out. You'll rest easier over the long winter knowing you resolved your cavitation issue. | |
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Posts: 3500
Location: Elk River, Minnesota | Glad Steve Worrall stepped in on this as well. I have not seen the ez pumps in person but understand how they work. Figured I'd cover all bases to try and deal with the cavitation problem..
That is what I love about this site...we all try to help each other out when we can.
Steve | |
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