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Chainplates

11K views 32 replies 20 participants last post by  Hush34 
#1 ·
Just acquired a 1978 Crealock 37. Chainplates look good but I know they are going on 40 years old. Is it possible that they could still be trustworthy?
 
#3 ·
Only way to know for sure is to pull them off. If you have any design on offshore sailing then it is prudent to replace them. Standing rigging as well. All this before the huge inverter, watermaker, A/C, and the other luxury items. Might pull the mast too and give it a good going over. How's that rudder doing? Thru hulls? Sails? The important stuff that will keep you out here. Good luck.
 
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#4 · (Edited)
That's a item that is addressed in the Westsail maintenance manual and like aeventyr60 says pull it and find out . However , are there rust stains around the chain plates ? If not I wouldn't worry about it to much . Does the Crealock 37 have a history with problem chain plates ? Westsails have problems with the boomkin tangs for one thing they get under water and the early ones weren't wide enough they rusted and cracked around the thru bolt . But you just got the boat , enjoy it and watch stuff .
Awesome boat ! CREALOCK 37 (PACIFIC SEACRAFT) sailboat specifications and details on sailboatdata.com

PS welcome to Sailnet hope to hear more about you and the boat .
 
#6 ·
Replace them. Be safe. Its a seriously fantastic boat. I'm envious. But don't risk your rig on 40 year old bits of metal that have almost certainly brittled over the years. And as others have noted...check out those thru hulls, seacocks, and of course the standing rigging.

1. Make sure it keeps floating.
2. Make sure the rig doesn't fall down.
3. Make sure the keel doesn't fall off.
4. Sail.
5. ???
6. Profit!
 
#7 ·
Enjoyed your response. The plan is to leave in four years. In the meantime, I spent all my money and more, so I have to enjoy it. Eventually, I will heed advice and pull plates. I will sail it in SF Bay and thereabouts to get my skills down and to see what falls apart. It is dry and solid thus far and manageable for me.
 
#9 ·
I replaced 9 chainplates from my boat. Not because I saw anything bad, but other owners of similar boats have and I wanted to make sure mine were good. When I went to remove the last one from the boat, it bent in my hand and cracked wide, at a point where only one bolt was essentially holding a stay to the boat.

Once off the boat, I bent it a little more and it broke. 1/4" thick piece of metal.

Here, you can see how bad it was, and there was no visible sign of failure before it was pulled.

Replace and have piece of mind. Better than having a failed rig while at sea.
 
#10 · (Edited)
The stainless steel typically used for chainplates has a 'severe' lower limit of fatigue endurance. Most 300 series stainless will have a fatigue endurance limit of 30% ultimate tensile strength ... UTS at about 90,000 psi. OR a Fatigue Strength at only 30,000 psi.
What this means is that if the chainplate is strained beyond/above 30% of UTS (loading to or greater than 30,000 psi), it will begin to rapidly fatigue; if kept below 30% UTS it will be virtually indestructible vs. 'fatigue'. If possible, always 'oversize' (thickness) when possible.

For the "blue water" typical design which (should) includes an inbuilt 3:1 Safety Factor ... historical 'scantlings' will show that NEW chainplates should have a high probability of successful service for ONE circumnavigation - about 25000+ sea miles.
For the typical 'coastal' design with a 2:1 inbuilt factor of safety - about 2/3 of ONE circumnavigation or 17000± sea miles, then a high probability of failure thereafter.
Fatigue Endurance limit for 300 series stainless is: 1,000,000 'load cycles' that exceeds 30% of Ultimate Tensile Strength .... on a blue water boat this load cycle max. occurs at ~40-45° angle of heel. On a 'coastal' design ... about a ~30° heel angle.
Even with new chainplates, once you accumulate 1 million load cycles at or above 30% UTS, there is a high probability of sudden catastrophic fatigue failure.

Crevice corrosion - an ADDITIONAL failure mode that WILL shorten the service life and reduce the load bearing value. Even when the stainless is being formed in the mill, micro-cracks will be formed. These cracks, plus cracks due to additive fatigue cracks will begin to form internal corrosion of the metal - thus an additional weakening and besides any simple accumulation of developing fatigue.

Suggestion for long distance sailing:
• For any boat with an unknown in-service life ... replace the damn chainplates.
• For any boat with chainplates over ~12 years old ... replace the damn chainplates.
• For any boat with chainplates - that have a 'designed' KINK or 'bend' in them ... replace at ~8-10 years.
• For any chainplates that have 'multiple' holes for bolting to knees, hull, etc. ... pull them off and inspect them for small/teeny cracks inside the bore holes that emanate perpendicularly from the axis of strain (looks like a 'smiley face' ... | -O- | ) replace immediately.
• Immediately replace any studs or bolts that have developed 'rusting', especially 'blackish'/dark rusting. Ditto, any chainplate that has developed 'zones' of black rusting. Ditto, for any polished chainplate that has developed a zone of noticeable 'dullness'.
• Inspect 'old' chainplate studs/bolts with a torque wrench ... torque to about 60-70% of the maximum torque value for the bolt or stud. If any 'break off' at or below ~60-70% torque value ... replace ALL of them for that 'station'.

Life extension of new chainplates.
• Suggest that you use 316 SS .... if you can afford it, get your 316 with "MILL SPECIFICATIONS" for 'chemicals and physicals' (so that you're 'sure' that you're not buying 'crap').
• POLISH the entire chainplate to a mirror-like surface. If you have the extra-$ available, then have the already mirror-polished chainplates - 'electro-polished'.

hope this helps.
 
#20 ·
or-like surface. If you have the extra-$ available, then have the already mirror-polished chainplates - 'electro-polished'.

hope this helps.
That is an amazingly comprehensive block of data.

How did you come up with that information?

I guess what I'm asking for is industry references if you have them handy even though what you wrote has the ring of truth to it and is consistent with my own limited experience.
 
#11 ·
I am not going to quote Rich because his post is too long, but ther is a lot of wisdom there.

Corrosion is the normal failure mode of chainplates, because stainless suffers from intergranular corrosion which leads to stress crack corrosion. In salt water this just has to be assumed to occur, and once it starts it can progress incredibly fast, as in months not years.

But you can't forget about fatigue failure. For most boats the salt will kill them before fatigue is an issue, but for older fresh water boats fatigue really is an issue. It accumulates slowly over time, and is impossible to inspect for, and the only way to know for sure if your chainplates are suffering from it is to put them under tension until they snap then compare the mbl of the metal to where they actually snapped.

These days, though I wouldn't use stainless of any variety. G5 titanium isn't that much more expensive, simply doesn't corrode, and doesn't suffer from fatigue at loads experienced on boats (the rigging will snap before the cycle loads get high enough to matter). Switching to titanium chainplates really is a lifetime fix for them.
 
#12 ·
We replaced all of the chainplates in our 1984 34 two years ago. They all looked good on the boat, and for the most part, off of the boat. We did find one crack in the backstay chainplate on the edge of one of the bolt holes. For the most part, they still seemed serviceable. We did not stress test any of them, as we were already planning to replace them as part of the refit.

These were not the original chainplates; the former owner had replaced them around '99. (We are the second owners of the boat, having bought here from the original owners, and have had her since '03.) But at 40 years of age, and no confirmation of replacements, I would highly recommend replacing them.
 
#13 ·
Congratulations on your purchase.

There are extensive comments on the subject of chainplate replacement at the link Bill Murdoch posted. Note that Cruising Consultants built the first 16 C37's between 1978 and 1979. Whether there are significant differences between the chainplates on the PSC boats and the CC boats I don't know; just something to keep in mind. See this link for CC details: The Pacific Seacraft Crealock 37 Sailboat : Bluewaterboats.org

Some other items to consider on older C37's that we found:
1. Re-rigging - LeFiell, the spar maker for the early C37's, sells new mast tangs, bolts, spacers and T-bolts for the turnbuckles. We replaced all of these when we re-rigged. The bronze turnbuckle bodies were still usable.
2. Mast step - the older boats did not have a stand pipe for mast wiring as part of the aluminum deck plate the mast sits on. Water intrusion down this wiring hole leads to soft wood at the base of the compression post and some owners have had to replace their posts. We managed to stabilize ours with penetrating epoxy before it got too bad. LeFiell sells an upgraded, aluminum mast step with stand pipe that takes care of this problem. When you pull the mast I recommend this upgrade. This link has details: http://www.sailnet.com/forums/pacific-seacraft/249913-splitting-compression-post.html
3. Internal halyards - while we had our mast out for painting (the third time) we cut holes for internal halyards. There are sufficient sheaves at the mast head to double the number of halyards if that is of interest.

I hope this is of some use to you.

John Newcomer
s/v Pelagic
1981 C37 Yawl (#22)
Seattle, WA
 
#14 ·
When I got my 1983 Orion, there were signs of rust stains coming from around the chainplates. On closer inspection, I noticed a crack coming from the corner of some of the carriage bolt heads. Ended up that most of them were about to give way from complete breaks. I had to replace all of them by local SS fabricator. The original bolts being carriage bolts had square holes in the chainplates and the cracks looked to start at the corner of the square hole. But it was a bear to get the bolts out due to carriage bolts having round heads (can't get a wrench around them). So do a close inspection of old PSC's.
Jim
 
#16 ·
That boat should be from before Pacific Seacraft obtained the molds, Cruising Consultants? I know of a boat from that vintage that had all their chainplates replaced, then on a crossing from Fla to Bahamas their forestay chainplate (i.e. bow roller piece) snapped. Miracoulously they did not lose their rig.
 
#18 ·
Pacific Seacaft provided my 6 new SS316 shroud chainplates with square holes (slightly rounded in the corners). I used new SS316 carriage bolts, nuts and washers when I installed them. I polished the heads of the bolts to match the finish of the chainplates,

The cracks in my chainplates did not generally originate in the corners.


This is a typical hole with its cracks.

Bill Murdoch
1988 PSC 34
Irish Eyes
 
#22 · (Edited)

This is a typical hole with its cracks.
Thats known as a 'saddle stress' load bearing FAILURE .. extremely poor structural design.

Square holes in dynamic (repetitive stress) structural finite elements have been universally and strictly avoided since the days of the infamous UK Comet (aircraft) disasters. Such corners are notorious 'stress risers' which concentrate and vastly magnify the stress tensors at those abominable 'corners'.
For 'round' holes the saddle stress load bearing FAILURE will typically look like: -O- with the cracks running transversely from the holes and 'across' the plate.

Even round holes drilled or 'punched' through such 'plates' are 'bad' for stress concentration and on an 'elastic basis' do NOT transmit the applied stress on an equal hole to hole to hole to hole basis. In such 'design' with multiple holes (in line) in plates, the 'first' hole/bolt takes up the majority of the strain as the plate elongates under strain, the 'rest' of the holes/bolts doing very little 'stress-wise'. If a chainplate fails, it usually fails at the very first bolt hole in the series.
Metals are 'elastic' .... think what would be correct if one was designing this in RUBBER material!!!!
Group Benneteau, quite brilliantly, changed over to T-bolt 'trunnions' and mirror-polished rods in 'pure tension' for their chainplates about 15 years ago - and for damn good reason: no kinks, no bends, no multiple in-line 'holes'. Beneteau removed all the 'stress risers' in their chainplates.
 
#19 ·
Thanks - a picture says a thousand words! I had one that cracked right through and put one on with a round hole that I got built locally at the end of the last cruise. I still need to do the rest before I go anywhere else.

I'd support the OP replacing theirs too - cheap peace of mind. It wasn't that hard a job.
 
#21 ·
Such comes from 35+ years in the engineering experience of stainless steel and other metals, etc. in high pressure bio-pharma, microelectronics, ultra-pure chemicals and nuclear industries and such process (chemical. etc.) engineering. And quite a bit of metallurgical 'red metal' experience before that when I was a working student.

All that I posted is quite common but still evolving state-of-the-art knowledge for all of those industries, which are often regulated to conform and comply with such 'state of the art' and 'current good manufacturing practices' - cGMP. What happened is that those industries were pursuing ever cleaner and cleaner (purity) processes with less 'surface-chemistry' produced micro and nano contamination ... and what unexpectedly 'popped up' as a result was stronger, more chemically 'inert' surfaces and structures, and with higher fatigue endurance or less premature fatigue failure.
I was just lucky to be at the right place at the right time of such hyper-evolving innovation .... all such is pretty much now over-regulated & in serious decline since the politically forced(?) decline of the US 'free market'; but, which now continues mostly 'offshore'.
 
#23 ·
My Pacific Seacraft 37's chain plates were cracked all over the place, just a horror show. I used high pressure water cut square holes with rounded corners. The bolts are polished 316 coach bolts but I machined the under side of each head in the lathe so that they were perfectly true and included grooves for sealant so some thickness remained. I wouldn't use regular bolts. The head surface area is much smaller, the sheer load will go on the thread in the chain plate (yuck), the spanner will be impossible to hold perfectly still so the surfaces will be scratched and possibly some minute parts of the hardened steel spanner will be left behind promoting corrosion. The polished plates and dome heads look lovely and authentic to the boat at little extra cost. AND, I was able to replace two of the plate by myself with the boat in the water. You can't do that with regular bolts.

Andrew
 
#25 ·
There a lot of stress-truth in what you describe in your excellent post.

However, the true function of 'bolting' in such structure is to provide FRICTIONAL forces between the plates and their 'mating' parts ... the friction generated by the bolts that drives these faces together (in compression) is what transmits the stress load from the rigging. Again, in pure and reliable stress design, the bolts only provide compression hence frictional forces that prevent the surfaces from 'movement'. There is 'no way in hell' for 4 or 5 bolts to equally and simultaneously to support a (cyclically applied) load at 90° (shear load) to such bolts, etc. ... and that's the probable reason that 'flat' chainplates universally FAIL at the 'first' bolt (closest to the rigging) of the chainplate surface.
A properly set up/designed and properly torqued (and with proper factor of safety applied) 'friction join' will transmit such stress over the entire mating surfaces between the chainplate and its 'mating surface'. To do otherwise automatically puts those bolts in vulnerability of 'shear' ... and is MUCH less strong and with LESS ability to adequately support such loads vs. 'fatigue' (of both the bolts and the plates, etc.); plus, results in the development of the localized 'saddle bearing stress' failures (@ the bolt holes)... where one usually sees 'smiling happy face' micro-cracks developing and emanating from those drilled bolt holes in those plates.

Further, add any bend or kink to those plates to meet the needs of the rig geometry .... another place where 'stress risers' in that plate go WILD.
 
#24 ·
Makes me likse the way CS did it. We have a T-plate for shrouds through bolted into a welded bracket attached to the bulkhead. Tension loads on the Bolts. Sandwiches the deck. The Bolts are on my preventative replacement list can be done anytime I just need to slack the shrouds a bit and change one at a time, of course I could remove both parts and polish on die check if warranted.
 
#26 ·
Sounds like a trade-off between the square hole and the right bolt head - probably no right answer.

Normally I'd say that the carriage bolt solution has been proven for 30 years and go with that, but it looks more like a known problem.

I am leaning towards round holes and hex drive rounded head screws: https://www.mcmaster.com/#98164a418/=14sc8ew. I wish they came with bigger heads. I'm not too fussed about being able to fit them single-handed.

Thanks,
jb
 
#27 · (Edited)
I came to a little different conclusion about the cracks in my chain plates than RichH. Pacific Seacraft tells me that my old shroud chain plates and their bolts were ss304. They were 18”x2”x1/4”; much larger in cross section than the 9/32” diameter ss304 shroud that each supported.

The cracks in the photo I posted were at the top of the uppermost bolt hole on the starboard aft chain plate.

Looking at the six shroud chain plates: None of the chain plates had cracks near the round clevis pin hole. Four chain plates had cracks near the top square bolt hole, three at the second hole, two at the third hole, and one at the bottom hole. By far most of the cracks were on the outside surface. Some passed completely through the thickness of the chain plate. Only a few were on the inside surface. It was rare to see a crack meet a square hole in its corner. Some cracks reached the edges of the chain plate. Some cracks met the sides of a square hole. All of the cracks had a portion of the crack under or immediately adjacent to the area covered by the carriage bolt head. The was no pitting or general corrosion.

All of my ½” carriage bolts were tightly drawn up. The chain plates should have been held to the outside of the hull by friction and caulking. The bolts should not have been in shear.

I believe the chain plates cracked due to chloride induced stress corrosion cracking. The stress came from the slight deformation of the chain plates caused by the tight carriage bolts. The chloride was from the evaporated seawater held around and under the carriage bolt heads. The chain plates had been in service for over 25 years.

I took the advice of Pacific Seacraft and replaced the chain plates with ones of their manufacture made from ss316 which should have better resistance to chloride induced stress corrosion cracking. I replaced the ss304 carriage bolts, nuts, and washers with ss316 carriage bolts, nuts, and washers.

Bill Murdoch
1988 PSC 34
Irish Eyes
 
#30 ·
I came to a little different conclusion about the cracks in my chain plates than RichH. Pacific Seacraft tells me that my old shroud chain plates and their bolts were ss304. They were 18"x2"x1/4"; much larger in cross section than the 9/32" diameter ss304 shroud that each supported.

The cracks in the photo I posted were at the top of the uppermost bolt hole on the starboard aft chain plate.
Bill, if the cracks were indeed at the top of the uppermost bolt hole, I believe your analysis is correct. When I first saw the image, I also assumed that the cracking was caused by bearing stresses. Even the direction of the inclined crack is more or less in agreement with the stress field caused by a contact. But given that the cracks are above the first hole, that failure mechanism is not really tenable, and stress-corrosion fracture is more likely.

My chain plates are about 22 years old, so I am also starting to wonder if/when I need to replace them. Of course living in New England, we use the boat only about half the time. Given that, how obvious were the cracks when you decided to replace the chain plates? Were they mostly hidden by the heads of the bolts, or were they clearly visible? Thanks!
 
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