oxygen starvation???

[WindDancer]

had my prop shaft removed to have rubber radiator hose like coupling replaced and was told that the shaft had "oxygen starvation" where it passed thru the cutlass bearing, probably due to long storage without running.

I had never heard of this, neither had my non-marine machinist friends. Is this for real? I was told that I could have it micropolished, but the cutlass bearing would keep wearing out prematurely and they recommended replacing the shaft.

I bit the bullet and had it replaced with new coupler and cutlass bearing, but am still wondering if I was scam'd.

Forrest

[hellosailor]

My BS detector is showing "11". Never heard of this, and I'd suggest you contact a shaft maker to ask if they ever have, as experts in the field.

When stainless steel is *submerged* in standing water, and deprived of oxygen, it can develop microcorrosion and suddenly fail. But a prop shaft (typically Aquamet or Monel) standing in the air? Hey, cutless bearings don't make a gas-tight seal, they actually allow some water flow.

I know there are some odd and obscure failure modes in marine work, but if this was a real storage problem, I think I'd have heard of it over the years.

[CaptainK]

Hey Forrest.

It sounds like BS to me too!!

I also second "hellosailor"'s recommendation, on asking and checking out a shaft maker. And ask them for some information.

Sounds to me the yard just want to make some extra money off from you!!

[Alan Wheeler]

Forrest, did you get the yard to point out the damage visualy to you? What did you see?
Hellosailer has stated some excellent points.
Did the yard leave you with the old shaft? I would be asking for it so as you could obtain a scond opinion.

[WindDancer]

Wheels, yes I did see longitudinal marks on the shaft that matched the cutlass bearing pattern. I have the shaft because a machinist friend of mine wanted to see it.(he has never heard of it either)

I did a search on google and found some info. A Yacht designer(Kasten Marine Design) did a paper on various corrosion problems and mentioned "oxygen starvation" so I emailed him and got the following reply:

Hi Forrest,

Your boat yard is correct, the oxygen starvation corrosion was from leaving the shaft sit in contact with the cutless bearing for an extended time. And yes, in all likelihood it would have caused premature wear on the bearing, unless it was very minor. Better safe than sorry...

Cheers,
Michael Kasten


I guess an old dog can learn new tricks!
Forrest

[hellosailor]

WindDancer, his site looks professional but his answer reminds me of too many doctors and surgeons I've heard.

What's the first and best answer a surgeon always gives you? "Needs surgery!" Hmmmm.....

Rings, slight rings, cut into the saft at the cutless would be normal, since the shaft does *not* make an airtight seat in the cutless bearing. It is normal and essential for seawater to lubricate the two, and that means debris will *always* get in the bearing and make some marks on the shaft.

Sounds like the guy is trying to be polite and keep out of someone else's (your) problem.

I'd still be curious to hear what some shaft makers and high end prop shops had to say about it. If this was endemic, I can't help but feel that someone out there would have said "If you're buying a yard queen, replace the shaft if it has been on land for more than xx months". Might be a good question to put to the folks at Good Old Boat magazine, right up their alley too.

[Richhh]

BS meter is reading in the 'high' zone.

Just take the shaft and 'dress' the shaft with emery cloth then crocus cloth to put a high/mirror polish on it in the area of the packing journal and the cutless .... and magically the oxygen starvation will ultimately over time dissappear as the chrome migrates back to the surface of the metal .... THAT's why stainless IS stainless. Just chuck up the shaft in a lathe and pull emery and crocus across until its 'clean' and very shiney. If you have deep galling or deep scratches that would allow too much of a hydro clearance for the cutless, then consider to replace the shaft; otherwise, polish it as best you can without taking too much 'meat' off and shove it back in.

Try to get as much of the circumferential scratches and lines (caused by the old cutless) out when you 'dress' and polish the surface ... and then let nature take its course for the chrome molecules to migrate to the surface. Once you dress and polish the shaft the chrome micro granes in the surface structure will reform at the surface.

Sorry but this is not a nuclear power plant you're working with here but a 25 or 30 mm prop shaft.
If you see NO gross color shade change of the metal surface in comparison to adjacent base metal after polishing ... then the advice you got was 'flim-flam' and hyper-hype to make you unnecessarily replace a shaft (The same type of person will also sell you a 'bottom peel' job too if you have 3 cosmetic blisters - in the 'trade' its called 'mining for dollars'.)

[DeepFrz]

Hmmm, what's so strange about stainless steel sitting underwater in a cutlass bearing showing crevice corrosion from oxygen starvation?

I just read an article about this very thing and it was even accompanied with pictures. The author was able to reverse the shaft as the tapers were the same at both ends. The pitting would have cut into and worn the cutlass bearing more rapidly than normal had he not reversed it.

This is a common problem on boats that sit in the water for long periods of time, especially in areas where there is little water flow. So if your boat sits in the water, run the engine and drive the prop on a regular basis.

Phil

[Pura Vida]

Corrosion on stainless can occur in a anarobic environment. Now if that effected you boat or not is another story. You may have made the right decision anyway depending on the cost and the condition of the other parts in the drive train. I recently had to replace my stern tube, prop and stuffing box and ended up changing every thing from the transmission back. I might have salvaged a couple of parts but it just didn't make sense.

[hellosailor]

DeepFrz-
Go back and read it again. This is *not* crevice corrosion, this is *not* underwater. This is storage in the air, on dry land, where that corrosion mode simply does not apply.

THAT'S what is so strange. A prop shaft, even in a cutless bearing, sitting in a boatyard is surrounded by air. Anaerobic corrosion should simply not be an issue. Stainless surrounded by grease or other materials that exclude air (like epoxy or urethanes, etc.) simply does not suffer. The problem you are thinking of comes from stainless being immersed IN STAGNANT WATER without oxygen.
Totally different environment.

[WindDancer]

Hellosailor

Yes, this is under water. The boat sat in the water for about a year before I bought it. The PO also used too big of packing when he replaced it according to mechanic and tightened it too tight when he repaired it resulting in it seizing to the shaft which ruptured the rubber coupling that started this whole problem.

Forrest

[hellosailor]

Forrest-
Oh, so it wasn't in storage, it was still in the water. Very different!

"Nevermind" [Emily Latilla]

[delmarrey]

I keep my boat's out of the water 90% of the time. But I couldn't imagine a dry cutlass bearing mess'n up a shaft. But now I see it's been rotting in the soup, that splains it. I'll bet the bronze around the cutlass rubber was crumbling also.

If you don't use it, you lose it..................................._/)

[BC Mike]

From the book. "The problem with stainless is crevice corrosion. Barnacles sticking to the shaft create ideal conditions for pitting; so do rubber bearings and many shafts have become badly pitted in way of rubber bearings. While the shaft is stationary the rectangular areas of the rubber fluting pressing against the shaft starve the metal of oxygen and pits can quickly form. When the shaft turns again the rubber is torn. Pitting can also occur on the taper or in the propeller nut thread "
That from Nigel Warren in his book Metal Corrosion in Boats.
Michael

[p_61@eim.ae]

Forrest, you were talking about the Aquamet 22 failing, yes this is absolutely possible. I built a 60 ft high speed dive boat a few years ago and it had twin 3" aquamet 22 shafts, she did 55 kts, till one day we thought we had some around the prop.it turned out the shaft had cracked right across right in the middle of the cutlass bearing, it was only held together by less than half an inch of metal. Needless to say we were not impressed, she was only a few months old and the old aquamet was supposed to be the bees knees. We chopped the bit out that failed and sent off to the supplier in the US, (they actually turned up the shafts for us) and they informed us no claim possible due to the fact that the failure has been caused by oxygen deprivation of the hardened face of the shaft. It was caused by the cutlass bearing, in fact the exact shape of the rubber fins was eaten around the shaft. The problem is exacerbated by high water temps and high salinity. The only way to slow down or stop it is turn the shaft, like every time you go past it or at least every few days depending on the weather factors in your area.
I changed our bearing over to Thordon and got completely away from cutlass and have never used them again. Thordon we are running direct drive on 1150hp V12 mtu's thru PP 160 jets at 2350 rpm and they have been going for 8 yrs now and instead of changing the bush we skimm it and fit an over size shaft end, weve done it once in all that time. Good luck. Steve.