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  #21  
Old 04-07-2011
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It sounds as though Bill has detailed knowledge of the subject and I certainly wouldn't argue with his conclusion.I can tell you that this piece was being cut from the lower end of the chainplate,the part nearest to the water and possibly submerged when heeled.The bend was at the other end which has not yet been cut (but will be).
I sort of comfort myself by thinking that there were four bolts above this part of the metal and it probably wasn't stressed too badly.
But I sure am glad that I did replace these chainplates before that failure that Bill speaks of.

Dianne and Chuck Burke S/V NiftyNickers C37 #139
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  #22  
Old 04-07-2011
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Quote:
Originally Posted by wsmurdoch View Post
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
1988 PSC 34
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Well sure Bill, everybody knows all that! (just kidding - appreciate the information.) As we're deciding where to purchase new chainplates from, what questions should we be asking concerning how they're fabricated? Any particular known-good sources? Or, should we by from a reputable source (like PSC) and just plan to replace them every N years regardless?
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  #23  
Old 04-07-2011
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Quote:
Originally Posted by wsmurdoch View Post
...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
1988 PSC 34
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I like the third approach that Chuck took!!
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Pacific Seacraft Crealock 31 #62

NEVER CALLS CRUISINGDAD BACK....CAN"T TAKE THE ACCENT
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  #24  
Old 04-07-2011
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Quote:
Originally Posted by niftynickers View Post
I can tell you that this piece was being cut from the lower end of the chainplate,the part nearest to the water and possibly submerged when heeled.The bend was at the other end which has not yet been cut (but will be).
I notice the hole is round. PSC must not have been using the carriage bolt holes at that time, or am I missing something?

Dave Mancini
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Old 04-08-2011
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Dave,
As you noted the holes are round but the bolts were carriage bolts.The corners of the square part of the bolts fit into the holes which are 5/8".I thought that that was a rather strange way to mount them but on the other hand it worked for over 25 yrs.
I seem to remember a post some time ago from someone else noting the square shouldered carriage bolt in a round hole and theorizing that perhaps the square shoulders caused stress and corrosion where they cut into the hole.I did not see evidence of that having happened.
When I replaced my chainplates I oted to use standard hex head bolts in 316 SS and 316 SS chainplate material.
Dianne and Chuck Burke S/V NiftyNickers
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Old 04-08-2011
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I vote with you. I've noticed that a number of riggers, including Brion Toss, have issues with the carriage bolt square hole in a chainplate. Good choice with the 316, also. Wish I'd done the same.

Dave
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Old 04-09-2011
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Seems like I have read discussions over the years (probably here on SN) about some SS supplied on boats built in Asia (70's-80's?) that was suspect. I don't remember the specifics or which boats/models were involved. Has anyone else heard anything similar?
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  #28  
Old 04-10-2011
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I have followed this chainplate discussion with interest because we too have an older Crealock 37 (1983). My one big question to those who have actually done this replacement on PS boats is: how do you remove the old chainplate from behind the teak rub rail that runs down the side of the hull?
Dave
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  #29  
Old 04-10-2011
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DMD,

With just a little coaxing (wiggle for and aft), mine pretty much just slid right up and out (1996 PSC34).

Dave Mancini
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Old 04-11-2011
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As Dave said a whack with a heavy hammer and some wiggling and some prying worked for me.Make sure that you clean out the groove that the chainplate is in with a putty knife and then drive the chainplate upward with a drift pin and hammer. More difficult was getting to the nuts inside the salon.Trying to remove the teak battens without destroying them is very difficult.
I'm now looking forward to replacing the stem piece for the headstay.The more I think about that job the more dubious I get.The stem fitting is integral with the bow rollers and must be removed as one piece and of course the nuts must be accessed thru the anchor locker.I'm trying to convince my tiny wife that the anchor locker is really a nice place for her to work.
Good luck with that, right.

Dianne and Chuck Burke S/V NiftyNickers C37 #139 1982
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