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davidpm 10-24-2011 09:56 PM

Chain plate metal bad
 
1 Attachment(s)
Hopefully boatus will not mind my posting this letter.
It seems to be important.
I'm not sure I knew that good stainless can just go bad and not show it.

RichH 10-24-2011 11:23 PM

... a common problem with 300 series stainless which has been widelly known since the mid 1970s = embrittlement or fatigue failure.
Although 300 series stainless has an ultimate tensile value of 90,000psi, it will quickly fail by fatigue failure at any repetitive loading (1 million cycles) above 30,000 psi ... known as the fatigue endurance limit.
The reason for all this that many who apply 300 series stainless steel do so via 'cookbook' values, not from a 'knowledge basis'. ... and thats why there are structural codes for 'critical stuff'.

davidpm 10-25-2011 03:04 PM

I have read that too Rich but Pacific Seacraft is known for building a good blue water boat and I believe there hardware is oversized.

I'm not sure I can really explain or know what to do with this knowledge.
If you pull a chain plate and it looks like it is in perfect condition but it is junk and there is no non-destructive way to tell what do you do?

RichH 10-25-2011 06:21 PM

Quote:

Originally Posted by davidpm (Post 790180)
I have read that too Rich but Pacific Seacraft is known for building a good blue water boat and I believe there hardware is oversized.

I'm not sure I can really explain or know what to do with this knowledge.
If you pull a chain plate and it looks like it is in perfect condition but it is junk and there is no non-destructive way to tell what do you do?

Fatigue is characterized by microscopic fractures in the 'grain' or surface of the base metal. Fatigue is evaluated by microscope, by magnetic or dye-penetrant methods such a 'magnafluxing' or other metallurgical analysis.

No one is stating that PSC built lousy boats ... ALL metals in cyclically loaded applications that exceed their 'endurance limits' will FAIL (sometimes catastrophically) by fatigue FAILURE.

bwindrope 10-25-2011 07:30 PM

Caution is advised
 
Given what we know, and what we don't know, most sailors err heavily on the side of caution with these things. I'm just now replacing my chainplates for this very reason. I pulled them out and expected to see crevice corrosion after them being in for 20 years, and was surprised to see that they looked like new even between the deck sections.

I pulled them out anyway, and ordered new, thicker chainplates from Garhauer to replace them. I didn't need a metal test or microscope to know that 20 year old chainplates should not be trusted for another 10-20 years. NO matter what they look like.

When in doubt, replace stuff!

davidpm 10-25-2011 07:47 PM

Quote:

Originally Posted by bwindrope (Post 790265)
I pulled them out anyway, and ordered new, thicker chainplates from Garhauer to replace them.

Sounds like a good idea.
BTW how are you making the thicker chain-plates fit the forks on the turnbuckles?

josrulz 10-25-2011 07:57 PM

For what it's worth, I also got chainplates from Garhauer (they did a great job for a good price), but I didn't oversize. My chainplates had lasted 27 years--another 27 with these new ones will do just fine. Of course, this was not for a PSC, but rather a Sabre.

But my real point is that Garhauer did a great job, and I would recommend them for chainplates.

davidpm 10-25-2011 08:20 PM

Quote:

Originally Posted by josrulz (Post 790279)
But my real point is that Garhauer did a great job, and I would recommend them for chainplates.

Good to know.

bwindrope 10-25-2011 10:02 PM

I had replaced all my standing rigging, piece by piece, a few years ago, and the chainplates were the last piece of metal in the system to have not been renewed since my ownership. The previous plates were 1/8 thick, and I ordered the new ones at 3/16. True, the old ones had lasted, but since I was replacing them and the cost difference was insignificant, I went larger.

The Hayn Hi-Mod fittings I use have 3/8 or 1/2" pins and so the 1/8" chainplate was quite thin on them. The depth of the pin is not affected by the width of the chainplate, and neither is it even close to being at the width of the fitting itself. I'm not being very clear here, but the bottom line is that it is no problem.

Just FYI, I paid about $250 for two chainplates, each about 20" long, 3" wide, and with the usual bolt holes.

It will give me immeasurable peace of mind to know that these chainplates are not remotely a weak link in my system! I've seen too many pictures of fractured chainplates and lost rigging to want to experience that in 35 knot SE winds in the Straits of Georgia!

mitiempo 10-26-2011 02:28 AM

I just pulled my chainplates after 34 years and they also looked good externally. I had new ones made of 316 which I purchased myself and had machine shop cut finish and polish. They are the same thickness - 1/4" - but longer with one extra bolt through the bulkhead. The old ones are now the backing plates instead of the thin backers that were original.

Could I have re-used the originals - maybe but I didn't want to take a chance.

1/8" thick on a Gulf 32? That definitely seems too thin.


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