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**raythompson** · 05-24-2006, 11:37 AM

Cavitation

Cavitation, if that is indeed what you are experiencing, is caused by air reaching the propulsion system. In this case your propeller. Cavitation happens more readily on an I/O or outboard than with a propeller that is under the boat.

With that said it would be difficult to get enough air under the boat to cause cavitation when you have all that weight in the back. It is possible that you have too much weight and the bow is too high scooping air under the boat. Perhaps spreading the weight around and keeping the boat in more of a level attitude would help.

I would not put anything in a transmission beyond what the manufacturer recommends. If the seals do expand they may exert too much pressure on the shafts and cause premature failure of the seals. Also brake fluid does not have the high pressure qualities that would be required in transmission fluid and is most certainly not the right viscosity. Brake fluid also absorbs water and that will not be good for your transmission. I would not want your GM mechanic friend working on any of my vehicles if he is giving out that kind of advice.

**TeamAllen** · 05-24-2006, 01:14 PM

I have the same model boat. I do not add any ballast, so I'm not much help on that. I did replace the prop though, last year. I used the original prop for 8 years. I decided to get a spare. I replaced i with a new ACME propeller. Model #653 13 X 11.50 .060. That new prop was smoother than anything. It is the best improvement I have done to the boat.

The thing is, I never noticed is was not smooth before. Maybe with the added weight you are using, magnifies the problem to the point you really notice it.

If you don't have a spare prop, I suggest you try that first. ACME can dial in a prop specific for your needs. If you do have a spare prop already, try switching them.

I would replace the tranny fluid before I added anything else to it. It can't hurt.

**Tequilasun** · 05-24-2006, 01:33 PM

I guess I don't understand, are you getting cavitation, or do you have a tranny problem?

Team allen has a great suggestion, Acme can indeed dial you into a prop that will work better for a ballast heavy boat. In fact, they have some specific props just for that.

I would not put brake fluid in the tranny, that's the first time I have ever heard anything like that.

**dogbert** · 05-24-2006, 01:43 PM

Teamallen is right, a new prop will make a huge difference. If yours is still the original, props have come a long way. I'm on my 3rd prop...still have the original. Each time the new prop design was an improvement. One of these new ACME 3 blades will make a huge difference.

**skyski_tige** · 05-24-2006, 01:57 PM

I am not sure if it is a cavitation or tranny problem. I would assume that if it was a tranny problem then it would happen more often. I am trying to determine what is really causing the cavitation at this point.

This is actually my spare prop. I have a 4 blade that I just got repaired but I like the wake with the 3 blade over the 4 blade.

I usually don't run the boat with any weight. I ride a hydrofoil and really don't need a huge wake but I have been surfing lately and need some additional ballast. This boat does not seem to need much weight to enhance the wake.

I will put the 4 blade prop back on and replace the tranny fluid to see if that helps.

Hope this clears some things up.

**dogbert** · 05-24-2006, 02:01 PM

Originally posted by skyski_tige
I am not sure if it is a cavitation or tranny problem. I would assume that if it was a tranny problem then it would happen more often. I am trying to determine what is really causing the cavitation at this point.

This is actually my spare prop. I have a 4 blade that I just got repaired but I like the wake with the 3 blade over the 4 blade.

I usually don't run the boat with any weight. I ride a hydrofoil and really don't need a huge wake but I have been surfing lately and need some additional ballast. This boat does not seem to need much weight to enhance the wake.

I will put the 4 blade prop back on and replace the tranny fluid to see if that helps.

Hope this clears some things up.

Did you hit something with your other prop? If so, I'd have a dealer check out the shaft and strut, because that may be your problem. If the shaft is even the slightest bit out of alignment, it could be causing some problems with the strut (there are some bearings inside there).

**skyski_tige** · 05-24-2006, 02:13 PM

I have hit a couple of stumps in the past 12 months but did no visible damage to the strut / shaft.

I would assume that if the shaft / strut was damaged then this would happen all the time.

**dogbert** · 05-24-2006, 02:20 PM

Originally posted by skyski_tige
I have hit a couple of stumps in the past 12 months but did no visible damage to the strut / shaft.

I would assume that if the shaft / strut was damaged then this would happen all the time.

I wouldn't be so sure. I hit a submerged log in about 20' of water and it bent my shaft one way and the rudder the other (it got caught between the prop and the rudder). The boat seemed fine until I pulled it out of the water and took a look underneath. The prop was barely bent. My dealer said it would run for a while, but then it would start damaging the strut and my V-drive over time.

If those bearings in the strut finally do seize up, then you could lose the entire shaft (along with your prop) or worse. It would be a bad day on the lake.

**Tequilasun** · 05-24-2006, 03:20 PM

ok, now we have something! I would have your shaft and strut looked at by a pro. It takes very little to knock those things out of alignment. And it is a pretty easy fix. If you bent the shaft, or the strut, then that's another problem. But if you haven't noticed big vibrations then your probably just a little out of alignment.

Either way, you need to get it fixed (if indeed it is a shaft/strut problem) because it will vibrate the tranny and then you will have a much worse problem on your hands.

Is the prop you have on the boat now Stainless?

**skyski_tige** · 05-24-2006, 04:44 PM

I do have a stainless prop on it right now. The 3 blade might not be the original prop but it was the spare when I got the boat in 2000.

I just setup an appointment to get it looked at on Friday. Thanks for the advice and I will let everyone know what he finds.

**dogbert** · 05-24-2006, 04:59 PM

The stainless is probably what came stock with the boat. My '99 came with a stainless 3-blade

**Tequilasun** · 05-24-2006, 05:23 PM

The stainless prop might be a bit of your issue then. Stainless is much harder then nibral and because of that you will feel more vibration with a stainless prop than you will with nibral.

It might not be the whole issue though, so good call on getting it checked out.

**talltigeguy** · 05-24-2006, 08:28 PM

Please forgive me for not understanding - please clarify - I assume you mean that the tranny slips and the engine revs under the circumstances you describe above?

I have only seen or heard of cavitation when the boat is turned very hard or in big waves.

It sounds to me like the tranny is slipping, not cavitation. I think it is a good idea you are having it looked at.

**lee** · 05-25-2006, 11:22 AM

If you are having cavitation with the prop, how does putting brake fluid in the transmission stop cavitation?

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Cavitation with weight in boat or at slow speed

Cavitation with weight in boat or at slow speed

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