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  #11  
Old 10-18-2009
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Chainplate maintenance on a PSC 37

On our 1983 PSC 37 rust stains ran down the hull from the chainplates. We cleaned the reachable portions of the chainplates and realized that the majority of the rust was coming from the shrouds and shroud fittings. We decided to inspect the chainplates more thoroughly because we were planning to take the boat offshore.

To remove the chainplates, we had to do the following:
1. Remove the teak battens in the salon. The teak battens extended behind the trim pieces on the forward and aft bulkheads, which required removing the teak trim end pieces. On our 37, we had the old style interior which did not include the bookcase and lockers--the battens extended the length of the settee. Removing the battens exposed the area where the chainplate bolts were. Our bolts were finished over with a few layers of woven roving/fiberglass, preventing our seeing them or accessing them.

2. We used a hole saw with the pilot bit removed to cut the roving away from around the nuts. The hole saw was large enough to remove the woven roving over the nut and leave a big enough hole that a socket could then be fitted down flush over the nut.

The nuts for the aft and center chainplates were relatively easy to get to using this method. The forward chainplate nuts were much more difficult. The starboard forward chainplate nuts were barely accessible through aft end of the sliding door cabinet in the head. Reaching the nuts was difficult, but possible.

The port side nuts were somewhat easier, being accessible through the hanging locker on the port side. This hanging locker had the carpeting lining the hull, so we had to peel back the carpeting first.

If you're lucky, you will have carriage bolts attached to these nuts. If you're not, you'll have some unlucky person standing outside to hold the bolt head while you unscrew the nut. We had ordinary round-head bolts in round holes in the chainplates. Fortunately, the bolts were tight with old caulking and held their position while we removed the nuts.

Putting the nuts back on required having someone on the outside with vise grips held flat against the hull, gripping the bolt head so that it wouldn't turn.

3. Once the nuts were off and the bolts forced out, we broke the chainplate free from the hull. Each was caulked firmly to the hull. Caution: don't try to chisel underneath the chainplate because you'll bend the chainplate.

We removed ours by using the rigging and turnbuckles like this:
- Loosen all six shrouds: port and starboard forward and aft lowers and the two uppers.
- Working on one _lower_ chainplate at a time, tighten the shroud on that chainplate until you get a couple of inches sideways bend in the mast (this means that shroud is very tight). The chainplates for the lowers should break away before you have to tighten their shrouds this much. If a chainplate won't break free and you've tightened as much as you dare, get a piece of wood--2x4 or 4x4 about 2 feet long--a very brave assistant to hold the wood almost flush with the side of the hull with the end of the wood against the very bottom of the chainplate, pushing up against the bottom of the chainplate. Use a sledgehammer and strike the wood with several (it may take as many as 8-10) taps to break the chainplate free from the caulking. You will know when it breaks free because the chainplate will move and the mast will snap upright. It's pretty obvious.

- Break all the lower shroud chainplates free the same way.

- Because the upper shroud has a longer chainplate and because it goes underneath the rub rail, it's harder to deal with. The same technique will work--be patient and fearless.

One last potential trick: if you can, worm a very thin wire between the chainplate and the hull and saw it back and forth to cut the caulking away as much as possible.

Once our chainplates were free, we inspected them and found them to be sound after 20 years. We did, however, have them cleaned and polished to a
high polish to help retard further oxidation.

Reinstallation uses the opposite steps, minus the sledgehammer, and is fairly straightforward. If you don't have carriage bolts, you will still need someone holding the vise grips flat against the hull, with the head of the bolt held by the sides of the vise grip jaws, not the end.

If you have square holes and carriage bolts, we envy you.

We did not get to the chore of removing and inspecting the forestay and backstay chainplates. Our assumption is that if you have the strength of Samson and the arms of a gorilla, and are familiar with maintaining a Jaguar XKE, you should have no problems.

Good luck.

Sue
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  #12  
Old 10-18-2009
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Just a personal preference . . . if I were going to all the trouble of removing chainplates this old, I'd take a good look at the cost of new ones while I was at it. After supporting the rig over all this time there's likely some undetectable metal fatigue. Supporting the rig is such a critical function, and at this point you've done most of the hard work associated with this task. For me it'd be nice to have the peace of mind of having new chainplates installed on a 20+ year old boat, especially if you're thinking of using it offshore. You'd be good to go for many years to come and likely wouldn't need another iteration of this onerous task anytime soon.
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Old 10-18-2009
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We just finished replacing all the shroud chainplates on our 29 year old C37 yawl. We did this with the mast up and the boat in the water in Mexico. A few tips follow. If anyone wants more details feel free to email us at: pelagic_sails@hotmail.com.

We had cracks in two shroud chainplates that started with crevice corrosion on the sides against the hull and migrated across the edges to the fronts of the chainplates. You could feel the cracks with a fingernail. We pulled the lowers on one side and replaced them then did the opposite side then the uppers.

Yes, you can pull a chainplate out using the shroud it's attached to as mentioned by Sue. Just tighten it up and lean on the wire. We didn't need a sledge and didn't loosen them all at the same time.

All of our chainplates went under the rubbing strakes. Cleaning out the 5200 was a chore made possible with a Fein sander with narrow saw blade attached and Debond Marine Formula. It really does dissolve 5200. Since we went with 5/16" 316 instead of the original 1/4" thick material the Fein tool allowed enlarging the pockets in the rubbing strakes for a perfect fit.

We didn't want square holes in the chainplates and didn't like the idea of the original square shouldered carriage bolts in round holes either. Both lead to stress risers in the chainplates (confirmed by Don Kohlman). Our preference was to use button head, socket cap screws but the threads run all the way to the head on these and we didn't want threads bearing on the chainplate holes either. We had some carriage bolts modified by a machine shop to take the square shoulder off. We then put two flats on the heads so they could be held with a wrench.

We had the new chainplates made locally in Mexico with a water jet cutting system. Very nice work and very precise with no saw, drill or heat induced stresses in the material. I told them to make 1/2" holes +.003 over and they were all dead on. They were all buffed to a high gloss and bent like the original ones.

We used Lifecaulk instead of 5200 and tighted the bolts in two passes waiting about 10 days between initial and final tightenings. The caulk cures slowly when it's under a chainplate and we didn't want to squeeze the glue line down too thinly.

The Fein tool with saw also allowed us to cut the interior teak slats (we do have the cabinetry and book bins installed) so short sections could be removed.

We removed, cleaned, polished and inspected the four mizzen shroud chainplates and the two backstay plates (split backstay). Using the same modified carriage bolts as for the main shrouds, we had some SS sleeves made to press into the original backstay chainplates that were 1/2" ID. This got rid of the square shoulder in a round hole as originally built. We used the original mizzen shroud bolts.

We didn't mess with the stemhead fitting yet but there are no rust stains so we figure that can wait a while.

Hope this is of some use to someone taking on the job.

John
s/v Pelagic
C37 #22 (1980)
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  #14  
Old 10-18-2009
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Wow.

The amount of good info in this thread is impressive. Many thanks to the folks who've tackled this job for taking the time to walk the rest of us through it.

Ours (Crealock 31) have not shown any sign of issues, but we'll be sure to watch them.


Quote:
Originally Posted by jnewcomer View Post
... Since we went with 5/16" 316 instead of the original 1/4" thick material the Fein tool allowed enlarging the pockets in the rubbing strakes for a perfect fit....

Hope this is of some use to someone taking on the job.

John
s/v Pelagic
C37 #22 (1980)
John, Great info. You were wise to upsize the chainplates given that you went with 316 stainless replacements instead of the original 304, which is a stronger alloy. Did you consult with someone to determine which dimensions would provide comparable strength, or was this an educated guess?
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Old 10-18-2009
s/v Pelagic
 
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Going to 5/16" thick 316 chainplates was an easy decision since it was the only material available at the time. Plus it seemed that bigger could only be better and 316 has better corrosion resistance. The tables I looked at show 304 and 316 to have the same tensile and yeild strengths but that 304 has slightly better shear strength than 316 (10.7 vs. 11 Gpa). Even it it wasn't the only thing available we still would have opted for the 5/16" 316.
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Old 10-18-2009
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I also have the external chainplates on my Morgan. I've replaced one chainplate and am satisfied with the current condition of the others; however, I do have some bleeding corosion that stains my hull. This is easily cleaned with a mild acid wash, but I don't know what would be the best treatment of the SS to stop the bleeding stain. ...Any thoughts?
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I certainly want to echo a thanks to those who contributed to this thread. It's great to hear from those who have been there, done that.

Pete
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Rust isn't necessarily a problem. You ought to pull the chainplates and bolts and inspect them. There shouldn't be anything that isn't stainless steel.
Stainless steel crevice corrosion doesn't cause rust stains. Staining comes from the iron that is still in the stainless steel. When EPA rules clamped down on metal processing solutions there was less removal of trace iron from stainless steel products. This iron is what causes rust stains in stainless steel. This is a cosmetic not structural problem.
The way to check for crevice corrosion/cracking issues is to inspect for cracking and do a dye penetrant check. You can should use a maginfying glass for inspection. Radio Shack had a cheap monocular I (think it is 50X) that works well for inspecting for cracks. It's especially handy for checking you other rigging tangs.
The way dye penetrant works is to wipe the area with penetrating oil with red dye in it. Then you wipe it off clean. Afterwards you dust the area with talcum power. If there's cracking, the powder will draw the dye from the cracks to the surface and stain the powder. You can get kits to do this or make up yout own.
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Contrary to what you might think, stainless bar is pretty cheap. It is not rocket science to make up a chainplate, either. I think if you took off the existing ones, ordered up the metal, and did most of the work yourself, you could get a machine shop to do the bends for pretty cheap.
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Old 10-19-2009
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chainplate source's

Perhaps we should put in a bulk order to Pacific Seacraft; keep them in business, and reduce our price? I would be open to a set for our 1987 Crealcok 34.

Larry
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