Cavitation prop damage?

[My Limit]

I just bought a 1998 Sea Sport with the 5.7GS Volvo Penta motor. <br /><br />I noticed the skeg is slightly bent to one side as if someone forgot to put it up when pulling the boat out. <br /><br />I also noticed the prop had a bunch of bubble looking patches on it. I thought it was were someone welded it to make a repair. I now know that damage to my prop is from cavitation.<br /><br />Do you think a bent skeg would cause this prop damage. <br /><br />When I took the boat out it was awesome and drove great except at high speeds when turning right it would make a vibration that caused the railing to move slightly. No, problem when turning left at high speeds.<br /><br />I'm going to get the skeg straightened first. Then I will sand off the prop and repaint it. <br /><br />Hopefully that will solve my problem. Any other ideas?<br /><br />If my shaft was bent wouldnt I have problems or vibrations even going straight?<br /><br />Because this only happened at high speed I'm hoping it's the bent skeg.<br /><br />Thanks,<br /><br />ML

 

[rodbolt]

Re: Cavitation prop damage?

what drive are you running ?

 

[My Limit]

Re: Cavitation prop damage?

duoprop I'll see if it has a number for the drive.

 

[jaybirdtx]

Re: Cavitation prop damage?

The vibration is most likely the u-joints.

 

[rodbolt]

Re: Cavitation prop damage?

its normal for the duo-prop to cavitation burn the hub area with AL props. its just how it works, see it all the time and so far no one has come up with a solution other than stainless or periodic prop reworking.

 

[My Limit]

Re: Cavitation prop damage?

It's not just the hub area that's got cavitation burns. It's the blades. The boat, motor and outdrive only have 120 hours. Wouldnt something have to be causing massive cavitation to cause all those burns?<br /><br />I'm thinking about buying a new prop to see if anything will change before I have them take my outdrive off and inspect gimbal bearings etc.<br /><br />Any thoughts?

 

[My Limit]

Re: Cavitation prop damage?

I took the boat in yesterday to a Volvo Penta dealer. They checked the gimbal bearings and u-joints. They were fine but needed greasing. <br /><br />The mechanic found the prop shaft was bent. He put the motor in gear and had me hold a long screwdriver against the shaft with the shaft turning. I could see the screwdriver bouncing up and down about 3/4 inch indicating a less than straight shaft. <br /><br />He said $800 worst case scenario to replace the entire prop shaft. He said they might be able to straighten it, which would be cheaper and just as good.<br /><br />Thanks,<br /><br />ML

 

[My Limit]

Re: Cavitation prop damage?

After pulling the prop shaft he said he found the gears were damaged from what ever bent the prop shaft. He called it "compression damage". I need new gears and a prop shaft. <br /><br />What would it cost to rebuild that lower unit as opposed to buying a new or rebuilt one?<br /><br />Thanks