View Full Version : Cavitation or vibration issues?

08-12-2013, 01:50 PM
I am at my wits end so I'm looking to other experts for advice here. I have a 2000 Mooba Kamberra that has some pretty bad cavaitaion or vibration issues.. The problem is when under heavy load, such as towing a towable, the boat cavitates hard when truning right. I originaly tought the issue was cavitation so I had my prop refinished to no avail. The more load on the boat the worse the vibration is and the lake conditions don't seem to play into, it does it in calm water as well as rough water. Any suggestions or thoughts?

08-12-2013, 01:51 PM
Check your alignment first. Possible your shaft is just slightly out of round too.

08-12-2013, 02:00 PM
how difficult is it to pull the shaft?

08-12-2013, 02:00 PM
Check your rudder too for looseness. Sounds like something is loose or out of tolerance, like kane mentioned the shaft may be bent and you don't know it.

I know it sounds silly and simple and probably isn't your issue, but my boat has terrible vibrations when weeds get stuck around the prop, so I have to swim under and pull it all off.

New Guy
08-12-2013, 02:22 PM
How hard of a turn to the right? How fast?

08-12-2013, 02:39 PM
It does not matter the degree of the turn... I can backout of the turn slowly and the vibration lessens. I am leaning more towards a prop issue, if i apply trottle in the turn the vibratin gets worse. Also it does at relativly low speeds and faster speeds. We only experience this when pulling a towable tube.

08-12-2013, 02:49 PM
The Kamberra was v-drive right? Here is my top ten list for vibration troubleshooting. Start with #6. As old as your boat is, and the fact it worsens in turns makes this sound likely..

1. Bent or bad Prop (Maybe the prop wasn't repaired properly)

2. Bad Cutlass Bearing (Grab prop and see if you can move the shaft within the bearing)

3. Bent Shaft (Can't check this by eye)

4. Shaft out of alignment.

5. Bent Strut

6. Shaft coupling bolts loose (very likely).

7. Loose engine mounts.

8. Bad structure under engine mounts.

9. Failed thrust bearing (probably integral to v-drive)

10. Air in v-drive. (I have never seen this on a Moomba, but I know of it happening)

08-12-2013, 02:57 PM
Thanks for the list Nate, I'll dive into in the next day or so and see what I can find. I talked to the guys at ACME a few minutes ago an dthey mentioned the cup may be the issue... I'm wanting to change out to an ACME 1235 anyways but hate to do that and still have the vibration issues..

08-12-2013, 03:06 PM
Definitely check the coupling bolts. They do come loose and are easy to tighten if you have long arms. :o Also, swap props with a buddy and see how you run and how he runs with yours. If his runs smoothly the prop is OK. Likewise, if you are back to smooth, it's the prop.

08-12-2013, 05:48 PM
Worked through the list Nate gave me as best I could, "coupling bolts" can y'all give me an idea what these are and where they are located please? I did find 3 of the 6 motor mounts slightly looser than the others but not loose enough in my opinion to be the problem. I also went ahead and ordered an ACME 1433 from Nettles, I need an extra prop regardless.

08-12-2013, 10:38 PM
The coupling bolts are on the prop shaft coupling. Follow the shaft up out of the stuffing box until you hit a flanged joint.

It will have at least four bolts going through it.

The motor mounts being loose may mean you are out of alignment. Google engine alignment for inboards.

It is easy to check, and is done right at the coupling I mentioned.

Think about it. The v-drive is what the prop pushes against to move the boat. It has a bearing to absorb the thrust and transfer the work of the prop to the hull.

The v-drive is bolted to the trans and the engine. If the engine isn't bolted down tight, the prop will push it. If it pushes it at an angle (turning hard) it will vibrate. Badly.

Checking alignment will require a couple of wrenches and a feeler gauge. If the mounts were loose, it is probably off.

08-23-2013, 11:20 AM
I am happy to report my cavitation/vibration issues are gone!! I got a new ACME 1433 prop and the issue went away... Evidentially the company that refurbished my prop didn't do so well. The 1433 prop is AWESOME! It pulls great and the hole shot is amazing. Thanks to all for your input.

08-23-2013, 11:54 AM
I went through that a couple years ago. I had some other problems too but also had a poorly repaired prop. I sent it back to the outfit that repaired it and made them get it right and include a report on the balancing. They did get it right the second time. Scared the crap out of me though.