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Old 05-07-2014, 10:46   #16
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Re: JB Marine Weld and Crevice Corrosion

There are actually some products made for repairing shafting. Shipyards use this stuff often, as a new shaft costs a huge sum...

For fixing cutlass bearings into ovaled out shaft struts, ITW makes Chockfast Orange.

For grooved and worn shafts, look at Phillybond. It depends on the kind of wear, but most of the time I see where the shaft has worn undersized, folks have a machine shop turn grooves into the shaft and then over fill the grooves. When you haul out and see the grooves it is time to re-do the job.

I would spend the money and have a machine shop magnaflux the shaft and make sure you don't have any crevice corrosion and cracking that the naked eye can't see. Stainless is funny, in that you can have a pit on the surface and the inside of the shaft is made of swiss cheese and looks like metal eating termites have gotten inside.

ITW Chockfast Marine | Industrial Grouts, Adhesives, Repair Products and Coatings
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Old 05-07-2014, 11:04   #17
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Re: JB Marine Weld and Crevice Corrosion

It won't fix your problem. You need to ensure that stagnant water is removed.

Stainless steels, both 3xx and 4xx series can suffer from crevice corrosion and stress corrosion cracking when stagnant chloride rich water is present.

Get rid of the water or make sure its not stagnant. Then monitor the area closely.

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Old 07-07-2014, 10:53   #18
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Re: JB Marine Weld and Crevice Corrosion

Quote:
Originally Posted by skipmac View Post
OK, rudder shaft. I was thinking prop shaft although a rudder post can also have a stuffing box.

So the corrosion was right where the shaft exits the rudder itself as in the part of the shaft that is normally exposed to the water?

What about down into the rudder as well? Did you dig out a little to see if the corrosion penetrated beyond the exposed, visible part of the shaft?

My understanding of crevice corrosion is that it occurs on SS that is enclosed in a wet environment where the water is stagnant and becomes oxygen depleted. SS exposed to open water I would not expect to show true crevice corrosion so I would question what caused the corrosion and if it will continue.

Either way, it sounds like it's not a wear area so answers that concern. My only question is whether or not the JB weld will absorb any moisture or allow moisture to seep under the margins of the repair and stay damp against the underlying SS shaft. That would just exacerbate the problem. Why not just leave it as is, exposed so you can keep an eye on it?
Skip,
I dug down around the shaft about 1/2" and it was clean with the exception of the shallow juncture between the shaft and the top of the rudder. I filled the void with epoxy thickened with hi-density filler and covered the repair with mat and roving. It looks bullet-proof.
And, again, the extent of the pitting/corrosion was so minimal and confined that only a neurotically obsessed mariner would even give it a second look(I hope I haven't shared any personal confession that will forever leave me vulnerable) as I was unfortunately impelled to do. So,
there's the rub. I have finally finished the installation which I have commented on in the Construction section under "Rudder Redux."
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