Cavitation and Intake Grate Paint

[BoaterGuy]

Disclaimer: I've read all of the cavitation threads on both sites and the main summary I got was that the marine sealant needs to be smooth as possible with no ridges that could cause air bubbles.

That said I had some run-in's with sand last year backing on and off the beach. I'm pretty sure that caused my minor cavitation on acceleration. Its slips out of the hole every time on the port side and unless I ease the throttle forward, it will not bite. Obviously gets worse the more I weigh the boat down.

I pulled the pump twice and resealed everything all way down to the intake grate and around the outside of it. Also smoothed everything with my finger before it dried. I noticed no improvement whatsoever.

On thing I did notice is that the black paint is peeling in different spots on both the intake grate and ride plate. Could that be the culprit? If so what kind of paint should I get to fix it.

The least favorable solution could be to replace the wear ring. Can this be done without resealing the pump? Do you think that this is my problem?

I'll try and get out to the marina when the weather gets above freezing to take pictures of the pump and everything else.

Thanks!

 

[Murf'n'surf]

If the paint has a loose edge it may just be corrosion. If there's no flaking paint that you can peel easily it just might be from cavitation.

How does the clearance between impeller and housing look? Same distance on both pumps? Any deep gouges in the housing?

Bent impeller blades?

Pics would be nice....

 

[Scottintexas]

I do not think the paint or lack of would cause an issue. I would think either there is still an issue and you are sucking air or you have an impeller imperfection but even that is like a magic bullet to determine.

when you had the backing on off sand experience, was there any torque or did you have to use high rpm's thrust with little movement ? my cavitation / loose sealant happened when I tried to pull another boat off a sand bar, i had to rev my engines with little forward movement and the created enough suction to loosen the silicone,

what do your impellers look like?

 

[Cobra Jet Steering LLC]

Do you see any rub marks on the pump liner? I would believe your issue is either something wrapped around the hub of your impeller that you can't see, like fishing line or the impeller and pump liner have an issue with excess clearance or a bent impeller blade or a bad bearing in the pump itself.

 

[BoaterGuy]

There are no rub marks on the pump liner. I did give it some RPM's a couple of times as I was beached in a very strong current at an ocean inlet. Too dangerous to get in the water....

I guess my best chance of getting advice is to get pictures up. I'll see what I can this weekend.

I'm tempted to just take it to the dealer so I dont have to mess with it anymore. The impellers look fine too, but I dont have a trained eye so I may be missing something.

Its hard to tell for me if the gap between the liner and impeller is the same.

Hopefully these questions will be answered with pics. I'll check back, thanks guys!

 

[Murf'n'surf]

We are cheaper than the dealer! Get pics looking both ways with a flash.

 

[waterboy]

I had some cavitation last year I was dealing with. My silicone looked fine. I pulled the grate and did notice where the silicone was not adhered real well around the edges.

I know you said you pulled everything and resealed. What did you use? Silicone is a good "gasket" but really has no adhesion properties. I don;t mean to second guess your work but if the surfaces were not totally clean, maybe that could be an issue. Any issues would cause cavitation.

I ended up doing a quick fix and got lucky, it worked... I dug out some of the silicone out of the gaps all the way around. I used Permatex Right Stuff gasket maker and sealed everything up. I just applied it on the surface, getting down in the gaps best I could, and smoothing everything over real well. No issues at all last year with cavitation.

Just adding my experience. Hope it might help.

 

[BoaterGuy]

I havent pulled the grate yet, maybe I should do that first. Damn this cold weather!!

For the most part I used 3M 4200 but around the grate the factory used silicone, so I replaced it with the same marine silicone from the ship store at my marina.

 

[waterboy]

I guess now that I reread your note. You said you pulled the pump. I guess you mean the impeller part and not the shoe ??? So much for me reading closely and assuming...

I had loose silicone around the edges of the pump shoe (or whatever it is called) on one of my jets. The intake tunnel part. I pulled the intake grate (3 bolts that are bolted to the hull). Dug out some of the silicone and resealed with the product I mentioned above (just on the surface and as far as I could dig it out easily) all the way up to the impeller. The intake grate also has sealant around the bolts to prevent water from getting into the hull so be sure to get these too.

That seam in the intake tunnel can definitely cause cavitation if the silicone even appears to be loose. It will suck in air from anywhere. That is where my issues were and pulling a skier out of the hole was getting rough before I did this. Anyway, if you haven;t done that, I am betting that will fix your problem.

Worst case is to pull the intake tunnel pump shoe but that is a bitch from what I have heard. Recent thread from someone documents that PITA really well.

 

[MNdrifter]

Would you get cavitation if the seal on the clean out plug was torn or not sealing? I forgot to lock the plug once and it would not bite for beans.

 

[txav8r]

The seal on the clean out plug is critical. It must seal. The way the seal is designed, it gets tighter with more pressure. If the seal is not sealing, I suspect you would flood the clean out tray. It is very different than not having plugs in to begin with. If a plug isn't in or isn't locked, there is not restriction and all you get is cavitation. If it is locked but a bad seal or leaking seal, it will not have all the power it can generate and leak water at speed. Now at idle and no wake speeds, you may not notice a problem with a seal issue.

Anything that flickers, causes an eddy, or directly introduces air, will cause air and loss of load on the impeller. Loose paint could indeed do this if...it was a piece that was loose and flapping at high speed as you moved through the water or accelerated. But generally, unexplainable cavitation phenomenon ends up being something small in the pump, that couldn't be seen without pulling the pump. If the pump and impeller was clean, and absolutely nothing in it, you just have a rough edge probably in the intake tunnel somewhere, but it could be anything that disturbs water.

 

[BoaterGuy]

So I finally got some pics of the intake tunnel. For the couple of little pieces that are sticking up at the base of the impeller, I took a knife and smoothed it out to get rid of them and I'm still getting cavitation. I'm now moving towards a wear ring or impeller...

 

[Murf'n'surf]

Strange....the impellers look to be in perfect shape. I think your impeller to housing clearance is good also. Perhaps you have a bent impeller blade that's not noticeable until you pull them out?

 

[BoaterGuy]

I'll pull the pump again and take some more pics. I need to get this sorted out before Memorial Day. Thanks @Murf'n'surf

I also have @waterboy and @OperationROL helping me offline. You guys are the best!

 

[john94si]

How often are the wear rings needed to be replaced?

 

[OperationROL]

How often are the wear rings needed to be replaced?

Only when necessary

 

[Murf'n'surf]

When you say cavitation, are you hearing a noise only or are you noticing no propulsion on one side along with a noise?

Have you swapped cleanout plugs from one side to the other?

 

[BoaterGuy]

When you say cavitation, are you hearing a noise only or are you noticing no propulsion on one side along with a noise?

Have you swapped cleanout plugs from one side to the other?

The cavitation is both noise and lack of propulsion upon acceleration from a stop. Once I get moving, the cavitation either reduces to a tiny amount or goes away completely.

I have not swapped cleanouts, that is an interesting idea... I'll try it.

 

[Murf'n'surf]

Just for shits and giggles make sure your reverse gate is moving up and out of the way completely on its own.

 

[ratchetdu]

I've been having a cavitation issue (Loss of power and high rev noise until just after getting on plane and then it would smooth out and go away) since end of last season and was at a loss on what it could be? So, after doing everything i could think of (looking for random pieces of debris, pulling the pumps and impellers all the way out, re-sealing anything with silicone, etc), I determined my issue. And sure enough, it was one of the cleanout plug seals. Swapped from one side to the other and problem followed that engine. So, new plug repair kit being ordered soon...

Glad it was an easy fix and figured it out (I hope)!!!