Cavitation Damage on Propeller
- Thread starter Marley
- Start date
Cavitation, 100%. No question.
ship happens
Well-Known Member
Yep those pics define much more then the originals for sure. That's a tough one. How tight is that prop nut? What kind of propeller you have there?
Aquaholic
Crew Member
Shaft play is normal. You have classic cavitation as described in some of the online material that you can find. They often say it can be the hull style amongst a few other causes. Even some videos on YouTube. Unfortunately I don’t see how the dealer is going to warrant this cause they will ask you to find the cause of the cavitation. Sorry man, this is weird.
What prop were you running before this and did it have any marks? I have a three blade you can try.
I am running the same prop, but I have a foil on mine.
ship happens
Well-Known Member
Props should be tight. Not loose. Tight.
zurk
Well-Known Member
put some dole fins on it and check the RPM at WOT -- make sure its not over engine RPM. dole fins will prevent ventilation damage.
but yeah if you have pure cavitation damage. your boat doesnt like your prop. i doubt it can be warrantied either. worst case switch to a 3 blade.
make sure you have 95-110 ft lbs of torque on it -- check your outboard manual for exact torque specs.
but yeah if you have pure cavitation damage. your boat doesnt like your prop. i doubt it can be warrantied either. worst case switch to a 3 blade.
make sure you have 95-110 ft lbs of torque on it -- check your outboard manual for exact torque specs.
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Marley
Active Member
I was running a 3 blade but RPM was low at WOT and I wanted more stern lift. I still have the 3 blade I could put back in the interim. I sent all the info to the dealer and they are going to get back to me. In the meantime I need to change the gear oil anyways so I will pull the prop and the. Re tighten the nut.
Aquaholic
Crew Member
Do you know what the pitch was for the three blade and also for the four blade? I have a 17 pitch three blade and the matching four blade spitfire. It was the correct propeller size for when I had the 90 on my boat, but now I have a 115.
mbowers
Well-Known Member
Funny that he gets cavitation and ventilation terms correct but incorrectly uses the term "air". Cavitation produces steam not air.
The cavitation case I've seen in person had a prop that was way too big for the motor / engine combo. I think it was like 40 percent off. The boat would barely plane and once on plane the speed would not increase as RPM increased. I would guess a big difference in pitch between the OP 3 and new 4 blade. Maybe somewhere the wrong prop got in the wrong box. Definitely check the pitch on the prop and compare to what's on the box and the 3 blade..
Depending on the hub, prop torque might be more like 55 ft lbs.
Trying to get rid of prop play can be foolish as I found out the hard way. I mentioned to the "mechanic" at a "dealer" shop in Langford that the prop had some play in it. When I picked up the boat this "butcher" had roughly sawn down the hub and said it was fixed. I didn't trust that fix so I took the boat from there straight to Vector in Sidney. The competent mechanic there said the hub should have play in it and should never be cut so I had to buy a brand new hub kit and had Vector install it.
Just saw this posted from an excellent mechanic Don Weed which backs up Vector.
DO NOT modify or grind on the parts of the hub kit! Flo-Torq IV hub kits are DESIGNED to have play in them- that is what helps to absorb the prop/clutch rattle at lower RPM's, delivering you a quieter, more enjoyable boating experience.
If your dealer made ANY modifications to the hub kit- ask them to replace it with a new, UN-MODIFIED one.
Marley
Active Member
I think I found the problem with some advice from another member. The prop bore gasket is broken and letting exhaust by which is causing cavitation. Looks like the part is cheap and it will be an easy fix.
I was thinking of filling the damaged areas with JB weld and sanding smooth.
I was thinking of filling the damaged areas with JB weld and sanding smooth.
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Aquaholic
Crew Member
does that mean the prop was possibly flexing sideways within the casing?
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Aquaholic
Crew Member
My boat just now. I had the Spitfire similar prop plus this exact foil on my old 90, this is the 115 (so it’s similar in many ways) with no cavitation burn. You’re getting 5800 on a 6000 redline so the pitch seems okay. Dr. Google explains a couple of other ways that the cavitation can happen.
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RevyG
Crew Member
Thanks for this post and figuring it out!!! I have identical issues on mine, just made and appointment, they better warranty it! Thanks again,
turbomack
Well-Known Member
the theory is that escaping exhaust from between the gear case and prop is getting to the blades causing them to cavitate
mbowers
Well-Known Member
Exhaust gases cause ventilation not cavitation and would not expect much, if any damage from ventilation.
https://www.tacomapropeller.com/what-causes-ventilation/
@RevyG did you have any gasket issues fixed or just received a new prop?
Either way a new and different prop was installed so there is something else going on besides leaky exhaust gases. Since RPMs seem right, the overall pitch is probably right but maybe there is a progressive pitch. If the angle of attack / pitch at the front is way off that could cause cavitating props. A thin leading edge is more efficient if it's working at its design point, but a thick, beefy leading edge is much more tolerant to errors in the angle of attack / pitch at front of the prop.
Would love to see pics of the new beefy prop at the same view as pics of the previous skinny prop to hopefully see some differences. Also if the mechanic can provide an explanation why a new prop was installed that could answer some questions.
https://www.tacomapropeller.com/what-causes-ventilation/
@RevyG did you have any gasket issues fixed or just received a new prop?
Either way a new and different prop was installed so there is something else going on besides leaky exhaust gases. Since RPMs seem right, the overall pitch is probably right but maybe there is a progressive pitch. If the angle of attack / pitch at the front is way off that could cause cavitating props. A thin leading edge is more efficient if it's working at its design point, but a thick, beefy leading edge is much more tolerant to errors in the angle of attack / pitch at front of the prop.
Would love to see pics of the new beefy prop at the same view as pics of the previous skinny prop to hopefully see some differences. Also if the mechanic can provide an explanation why a new prop was installed that could answer some questions.
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