Advice on prop shaft (metallurgical)

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Plevier

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Rather horrified looking at my prop shaft yesterday on a 9 yr old Jeanneau. See pics at https://picasaweb.google.com/106544940609481176193/20120221

My guess is that it was cr*p steel with inclusions and unless I see it eroding deeper it could now be OK and stable. There is enough meat left to take the power of a 19HP Volvo. It's a 25mm shaft and the big pit is maybe 2mm deep.

Our boatyard mechanic - always rather doom and gloom - thinks the shaft should be replaced urgently. I think it should be OK to put back and inspect occasionally. I'll clamp an anode on just in front of the P bracket so it can't all fall out!

Any thoughts please (Vyv are you there - again?)

Thanks
 
I would agree that at the moment it will be Ok however it is unlikely to get better! A new shaft shouldn't set you back more than about £150 if you find the right place to make you one however the main issue will be the ease or difficulty of removing the shaft. If the engine has to be moved to get the shaft in and out you will be into realignment etc. Personally I would go for it (but I would do it myself) then the job is done.

Yoda
 
Had the same on a Beneteau 25.7 shaft at 1 year old, only I had to change the shaft because corrosion was also in area of the volvo seal. So I think I'd recommend you pull the shaft and make sure the seal is not compromised.

Dealer thought it was Galvanic corrosion although I reckoned it was crevice corrosion. We came to an amicable solution in that he took the shaft out and I put a replacement in. He needed to be a contortionist to get it out, and actually couldn't get the shaft out of the tapered coupling so had to cut the shaft so I reckoned I got the easy bit.

Used a duplex stainless steel shaft and I isolated it electrically with an R&D coupling just in case it was galvanic, I also used a split coupling at gearbox end to make it easier to get the shaft out next time. Whole lot was about £150.
 
I looked at your photos yesterday, without understanding the cause of the damage. Looked again now and I still don't. It is clearly neither crevice (unless there has been fouling on the shaft for a considerable length of time) nor galvanic. The pits are large and deep, with sharp surfaces that have a high stress concentration. It seems to me that there is a strong likelihood that fracture could initiate from them. I would change the shaft.

If you would like to send me good quality close-ups of the pits I will have a look but I suspect that analysis might be needed to diagnose the problem.
 
Vyv
Not good news but thank you. I will send the photos in hi res to your website email address and will try and get macro pics tomorrow.
I didn't notice anything when I inspected the boat in Jan 2011 prior to purchase, I suppose I could have missed it. There clearly had been fouling see https://picasaweb.google.com/106544940609481176193/Troubadour#5564921258720433746 but it had been scraped off. She was launched in March so this seems to have happened very quickly.
I'll also send a pic as it was in May when I fitted a new prop and didn't notice anything amiss. The anode in that pic (new in March) fell off some time between May and now so the boat was anodeless for an unknown period. The anode position does not correspond with the corrosion.
I don't leave electricity connected. In any case it's a VP engine and the gearbox is isolated from the engine. The stainless steel brackets for the swing keel show no corrosion at all. I can't see any reason for galvanic corrosion. I can't see any reason for crevice corrosion.
You don't buy the slag inclusion theory?

PS Would it be worth trying grinding it out and smoothing the edges? If it's no deeper than say 2mm it leaves loads of metal, 19HP doesn't need a 25mm shaft does it? If it does go deeper then decision made!
 
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Troubadour said:
You don't buy the slag inclusion theory?

PS Would it be worth trying grinding it out and smoothing the edges? If it's no deeper than say 2mm it leaves loads of metal, 19HP doesn't need a 25mm shaft does it? If it does go deeper then decision made!
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slag is very unlikely in modern stainless steel making and the damage doesn't look like slag to me. It looks like porosity, which I would have thought equally unlikely in a hot rolled product but maybe something went wrong?

Your PS must be worth a try. Not much to lose if the alternative is a new shaft. It would be worth doing some dye penetrant crack detection if you know someone who can supply/lend the aerosols. You can buy the kit for about £50 from memory but hardly worth it for a couple of squirts. Maybe an NDT company would look at it for a bargain price.
 
Troubadour said:
Rather horrified looking at my prop shaft yesterday on a 9 yr old Jeanneau. See pics at https://picasaweb.google.com/106544940609481176193/20120221

My guess is that it was cr*p steel with inclusions and unless I see it eroding deeper it could now be OK and stable. There is enough meat left to take the power of a 19HP Volvo. It's a 25mm shaft and the big pit is maybe 2mm deep.

Our boatyard mechanic - always rather doom and gloom - thinks the shaft should be replaced urgently. I think it should be OK to put back and inspect occasionally. I'll clamp an anode on just in front of the P bracket so it can't all fall out!
Click to expand...
Why not get Lancing marine in for a second opinion ? The're only 10 minutes drive from the club and could give you a quote for a replacement at the same time. If it were me I'd just replace it because from your description of the circumstances there seems to be no way to get a handle why it happened and so no way to tell whether it will get worse.

Boo2
 
Boo2 said:
Why not get Lancing marine in for a second opinion ? The're only 10 minutes drive from the club and could give you a quote for a replacement at the same time. If it were me I'd just replace it because from your description of the circumstances there seems to be no way to get a handle why it happened and so no way to tell whether it will get worse.

Boo2
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Hi Mike

Yes I'm intending to do that tomorrow as the shaft is so easy to remove, I'll take it round to them. It's just another 200 ***ing quid on top of everything else that's all!
 
Here are a couple of pics taken last weekend illustrating prop shaft corrosion.
It was only identified when the rope cutter was removed.
Lucky the owner removed the cutter.
 
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It looks like chloride pitting, but on an unusually large area, I've seen it in smaller patches and a metalurgist suggested that's what it was. I'll ask our metalurgist expert to have a look at the pictures for his opinion.

Crevice corrosion can happen in 316 where crustacean have been attached, then when they come off they leave an area unprotected which forms a cell with surrounding material.

This is my understanding, but I'd talk to a metal expert.
 
My shaft had this damage two photos showing corrosion under cutter and other under shaft seal.

These were on a 1 year old Beneteau shaft. Ignore red stuff I was using shaft to hold the prop while I put propshield on it.

I find it interesting that its also from the Beneteau/Jeanneau stable.

http://www.flickr.com/photos/15986486@N07/sets/72157629430704753/
 
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Talulah said:
Here are a couple of pics taken last weekend illustrating prop shaft corrosion.
It was only identified when the rope cutter was removed.
Lucky the owner removed the cutter.
Click to expand...

Could be wrong, but that looks like a mild steel tube! Chap on the marina had same problem with a 70's broads cruiser. His snapped and that one was a 3 inch diameter tube. Not good, change it for stainless says I. :(
 
If you are intending to leave the shaft in place I would definitely try and polish out the sharp edges and round off any corners, to try and remove any stress raisers which would act as a potential initiation point for fatigue crack growth.

As Vyv said I would also recommend some form of NDT on the shaft. If you are intending periodic inspections it may be worth investing in some dye pen spray. There aren't really any other DIY NDT options available on stainless.

However, if it were my yacht I would probably leave it this year but plan to change the shaft next season when it was lifted out. But that decision really depends on how much motoring you are intending to do.
 
I had bad crevice corrossion on one of my Jeanneau (Mobo) shafts and it had to be replaced. The other question perhaps to ask is what are the consequences :eek: if it were to break in action? What are costs then on top of the shaft itself which is already going to be about 500 quidish for something reasonable.
 
davidwf said:
My shaft had this damage two photos showing corrosion under cutter and other under shaft seal.

These were on a 1 year old Beneteau shaft. Ignore red stuff I was using shaft to hold the prop while I put propshield on it.

I find it interesting that its also from the Beneteau/Jeanneau stable.

http://www.flickr.com/photos/15986486@N07/sets/72157629430704753/
Click to expand...

The fact that these are under the shaft seal and a cutter must have something to do with it. The rust marks look like they are from the cutter. Different metal from the shaft?
Was there any graphite or copper grease in the shaft seal? Don't know what difference it would make but just a suspicion.
 
Spyro said:
The fact that these are under the shaft seal and a cutter must have something to do with it. The rust marks look like they are from the cutter. Different metal from the shaft?
Was there any graphite or copper grease in the shaft seal? Don't know what difference it would make but just a suspicion.
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There was also damage to the shaft where it passed through the cutlass bearing in the P bracket, hence my thoughts that it was crevice corosion.

I do wonder if the shafts Beneteau an Jeanneau used were a bit suspect.
 
the metalurgists reply is that it may be a lower grade of Stainless or that it wasn't electrically connected to the anode, or both.

Just bad corrosion with signs of it all along the shaft.
 
Neil_Y said:
the metalurgists reply is that it may be a lower grade of Stainless or that it wasn't electrically connected to the anode, or both.

Just bad corrosion with signs of it all along the shaft.
Click to expand...

Are you referring specifically to one of the cases in this thread please? It's grown from my original one!
 
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