Prop cavitation/corrosion - 48 Sundancer

[Bear Paws]

As they were getting ready to launch me today I received an email with these pics. What are your thoughts about the cavitation/corrosion on the props (besides not being good)? Should I not launch and replace immediately, launch and replace, refurbish?

 

[Henry Boyd]

On the specifics of the whether props can be repaired or not is a level of knowledge I don’t have. I assume last year the props looked fine? So that would suggest this damage happened after six months in fresh water. I’ve got four NiBrAl props the same age and seasonal use that have existed to roughly the same age used exclusively in salt water that look brand new. So my reaction is you’ve got a serious corrosion problem that goes beyond the condition of the props.

The conundrum is besides being Corrosion caused by some kind of electrical charge created by your boat, it could also be faulty dock wiring, or one of your neighbors. Again starting to get above my pay grade. But it would seem some in water testing is needed where you keep the boat. If it was me I’d be loath to risk damaging a new set of props, so I’d be checking with a good prop shop to evaluate the props to see if they can be fixed and used until you can find the cause of the damage.

 

[TNT8808]

As they were getting ready to launch me today I received an email with these pics. What are your thoughts about the cavitation/corrosion on the props (besides not being good)? Should I not launch and replace immediately, launch and replace, refurbish? View attachment 83605 View attachment 83603 View attachment 83604 View attachment 83605

I had the same/similar issue twice, and was told they were cavitation burns due the hull design and high pitch of the props. I had them repaired and put back on once and the second time they reappeared I had them repaired and put in the storage area under the master bed and bought a new set of Acme props.

-Tom

 

[Bear Paws]

I had the same/similar issue twice, and was told they were cavitation burns due the hull design and high pitch of the props. I had them repaired and put back on once and the second time they reappeared I had them repaired and put in the storage area under the master bed and bought a new set of Acme props.

-Tom

Tom, did you go with the same specs or modify?

 

[M Prod]

As Henry mentioned, appears to be stray current in the water somewhere near your boat. Where that's coming from is anyone's guess. Also check all of your bonding connections. I had something similar happen to me and it turned out to be a corroded connection in the aft of my bilge. Im in salt though, so likely not your issue is my guess. Still worth a go over.

Can't really comment on whether you should run it for the season as is. If the damage is strictly cosmetic (and limited to the prop) it should be ok ...but you'll want to figure out if there is stray current near your boat once you're at the slip. You'll also want to plan on replacing that prop next winter.

 

[TNT8808]

Tom, did you go with the same specs or modify?

I went with the same size, and pitch on the new props but added variable pitch and .045" of cup. I've not had anymore cavitation burns, and at the same RPM as previous I gained about 2 MPH.

I was told by two different prop shops the cavitation burns are common on the EQY props on the 48DA's. I have no way of confirming this, and can only tell you what happened on my boat...twice.

-Tom

 

[Sea Gull]

A good prop shop will be able to repair these cavitation burns AND should be able to tweak the props to lessen the chance of it happening.

I went through a similar process on a 58DB. It took a couple of iterations to get it just right.

 

[carterchapman]

A good prop shop will be able to repair these cavitation burns AND should be able to tweak the props to lessen the chance of it happening.

I went through a similar process on a 58DB. It took a couple of iterations to get it just right.

Jeff, I seem to recall you telling me the 58 originally had 28x37's that had the cavitation burning, and Sea Ray replaced them with 30x33's to solve the problem. I have 30x33's and that's what the spares that I got from you are...my memory may be fuzzy on that...

My Dock mate's '05/55DB (same boat and engines) has 28x36's, so they may have been tweaked from original...We seem to perform equally.

 

[Henry Boyd]

After looking at some old industry publications on ship propeller cavitation damage, I still believe that there is a strong indication there are electrical issues at play. What bothers me is that very deep cavity highlighted by the screwdriver and the lack of trailing edge damage on the blade tip. Deep cavity material losses are more of an indication of failure due to electrolysis (stray current) than cavitation that tends to be a surface condition. Cavitation is also prone to the trailing edges and pressure surfaces of the blades in addition to blade root damage. The lack of photos showing blade damage suggests blade surface damage is not present. Keep in mind the water pressure that exists at the blade root that can create the cavitation effect also exacerbates material degradation caused by electrolysis. Or said the other way, electrolysis can exacerbate the effects of cavitation.

 

[TNT8808]

Attached are a couple pics of my props that I was told by two different prop shops were cavitation burns.

-Tom

 

[Highliner]

Sorry, just a little cavitation humour. Must be the COVID getting to me.

 

[Sea Gull]

Jeff, I seem to recall you telling me the 58 originally had 28x37's that had the cavitation burning, and Sea Ray replaced them with 30x33's to solve the problem. I have 30x33's and that's what the spares that I got from you are...my memory may be fuzzy on that...

My Dock mate's '05/55DB (same boat and engines) has 28x36's, so they may have been tweaked from original...We seem to perform equally.

Your memory is perfect! Sea Ray finally supplied props with significantly different measurements. The speed and fuel burn numbers were similar.