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post #11 of 34 Old 04-05-2011 Thread Starter
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chainplates

John et al.
I,ll try to answer your questions in order:
The chainplates are indeed 1/4" SS 306,they were the original factory installed in 1982.The boat is a Pacific Seacraft not a Cruising Consultants boat and was factory finished and commissioned at Washington NC in 1983 as Salem.The chainplates are all common ground to a grounding plate.I will try to upload some pix of the chainplates shortly.

Dianne and Chuck Burke S/V NiftyNickers C37 #139
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post #12 of 34 Old 04-05-2011 Thread Starter
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chainplate fotos

This is an attempt to send some pix of the chainplate.Note the hairline cracks near the break and the rusty brown color of the metal at the break.I repeat when this was removed we did a dye test on the plate and it showed NO problems or cracks.If this saves someones rig I,ll be a happy sailor.

Dianne and Chuck Burke S/V NiftyNickers
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2050_1231Oct20080017_edited.jpg   2050_1231Oct20080019_edited.jpg   2050_1231Oct20080016_edited.jpg  
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post #13 of 34 Old 04-05-2011
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Chuck,

Thanks very much for the follow-up info, and the excellent high quality photos. Yikes!

Quote:
Originally Posted by niftynickers View Post
...The chainplates are all common ground to a grounding plate....
I suspect this is the culprit, in your case. I would humbly suggest that you disconnect that ground. I have heard of similar chainplate issues (on non-PSC boats) and in every case they were grounded. The chainplates on our 31 are not grounded and I would not want it any other way.


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Pacific Seacraft Crealock 31 #62

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post #14 of 34 Old 04-05-2011
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Wow! That's pretty crazy, good to know.

1971 23' Oday Pop Top
S/V Frida

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post #15 of 34 Old 04-05-2011
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Thank you for the cautionary information Chuck, and I appreciate you are sharing to be helpful to the rest of us. So I can get the maximum information out of this though, I'm confused about what I am seeing with the condition of the chainplate around the hole for example. My untrained eye sees that as significant corrosion that wouldn't require a dye test to observe. I must be missing the point. Was this not so apparent while on the boat, or is the message that we shouldn't just write that off as surface corrosion if we see something similar?

John - After three boats were struck by lightning in our marina last year, I thought it was a good thing my chainplates were grounded. Some argue this might just be asking to be struck though. Sounds like you'd take the extra risk with lightning to avoid this insidious long term corrosion risk. Why hasn't someone come up with the perfect solution to all these issues yet?
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post #16 of 34 Old 04-05-2011
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Quote:
Originally Posted by JohnRPollard View Post
Chuck,
I suspect this is the culprit, in your case. I would humbly suggest that you disconnect that ground. I have heard of similar chainplate issues (on non-PSC boats) and in every case they were grounded. The chainplates on our 31 are not grounded and I would not want it any other way.
My 31 has the lightning protection, chainplates are wired to the keel, but isolated from anything else.
The seacocks are not wired, ie electrically isolated as well.
The engine is wired to the 12v DC Neg
I don't have a ground plate.
Tom

PS31#111 Cielo Azul
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post #17 of 34 Old 04-05-2011
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Guys,

I was reluctant to comment about the grounding issue, but I felt it's worth pointing out that this is a variable not common to all boats.

Chuck has posted a very helpful cautionary note here, replete with photos. If we want to talk grounding and/or lightning protection, it's definitely a good topic of discussion, but maybe we could start another thread? Or revive one of the many old ones already running here on Sailnet.


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Pacific Seacraft Crealock 31 #62

NEVER CALLS CRUISINGDAD BACK....CAN"T TAKE THE ACCENT
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post #18 of 34 Old 04-05-2011
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Dear Friends,

Stainless steel, particularly 302/304, is fickle stuff. It crevice corrodes and work hardens, both invisible time bombs on a boat. IMHO, we don't really need to look at factors other than these to find cause here. Personally, I begin to look at any stainless steel rigging component with distrust after 10 years, even less in the tropics. This includes wire, turnbuckles, toggle straps, tangs, etc. Stainless steel chainplates with bends in them that work every time tension comes on the rig are even more suspect.

As Annie Van De Wiele reminds us, "The art of the sailor is to leave nothing to chance."
Better to swap it out early.

Dave Mancini
s/v Swan PSC34 #305
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post #19 of 34 Old 04-05-2011
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Quote:
Originally Posted by DaveMancini View Post
Dear Friends,

Stainless steel, particularly 302/304, is fickle stuff. It crevice corrodes and work hardens, both invisible time bombs on a boat. IMHO, we don't really need to look at factors other than these to find cause here. Personally, I begin to look at any stainless steel rigging component with distrust after 10 years, even less in the tropics. This includes wire, turnbuckles, toggle straps, tangs, etc. Stainless steel chainplates with bends in them that work every time tension comes on the rig are even more suspect.

As Annie Van De Wiele reminds us, "The art of the sailor is to leave nothing to chance."
Better to swap it out early.

Dave Mancini
s/v Swan PSC34 #305
Good points, Dave.

Although they are about eight years newer than Niftyknicker's, I know I'm going to be keeping a closer eye on ours thanks to Chuck's helpful alert. Thanks Chuck!


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Pacific Seacraft Crealock 31 #62

NEVER CALLS CRUISINGDAD BACK....CAN"T TAKE THE ACCENT
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post #20 of 34 Old 04-07-2011
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From the photos it looks like an intergranular corrosion to me. If the plates are truly 304 SS (as opposed to the low carbon 304L or one of the stabilized 18-8 stainless steels) and if the chainplate was heated to place the bend below the eye then not annealed or if it was mis-annealed at the mill (unlikely), it could have been sensitized in the heated area. While hot, the carbon in the alloy would be precipitated out the near the grain boundaries as chromium carbide leaving the outsides of the grains depleted of chromium and subject to corrosion. This sort of corrosion eats away the metal between the grains leaving them unattached to each other. Until the part began to fail mechanically, there would not be enough of a crack to detect at the surface with dye. If this was the cause of the crumbling of the metal when it was sheared, it might be common among similar chainplates.

Chloride induced stress corrosion cracking could also be present. When under tensile stress and in the presence of chlorides, any of the 300 stainless steels can develop cracks that go deeply into the metal. I used to see this in bolts which appeared to have been purposefully cut in half. Dye testing might have caught this before mechanical failure began.

There are three ways to handle chainplate maintenance: wait until it fails then replace it, wait until testing shows it has started to break then replace it, or replace it when it nears its known service life regardless of its apparent condition.

Bill Murdoch
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