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 Post subject: Re: New Chainplates for my T37 #49 HELP PLEASE!
PostPosted: 08 Jul 2021 18:40 
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Joined: 29 Dec 2006 09:38
Posts: 656
airedog wrote:
It is my understanding stainless corrodes from inside out, therefore visual inspection tells you nothing. And the way to be sure is to have them x-rayed.

https://digitalcommons.uri.edu/cgi/view ... ext=theses

I was curious about your statement and read this paper and I do not see where they are claiming that SS oxidizes "from the inside out". Actually, if there is a crevice, I suppose one could contend that surface hidden is "inside", but this report seems to suggest that most ss and titanium corrosion is surface and does not reorganize the internal structure. My view is that cracks are serious on stainless and can harbor and enable corrosion. But thinking that your SS is corroding while all the surfaces look fine? I am still not convinced. I had a failure of a forward lower shroud once: it was almost new and the failure turned out to be from a crack I had not seen that was made when the rigger rolled it. This also convinced me that new rigging is not automatically better or that it obviates the need for careful, regular inspection.


 
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 Post subject: Re: New Chainplates for my T37 #49 HELP PLEASE!
PostPosted: 08 Jul 2021 22:18 
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Skipper

Joined: 13 Feb 2011 21:19
Posts: 337
Location: Canyon Lake, TX
Both of my aft lowers were cracked when we removed them. The cracks were inside the deck and not visible from above or below. The crevice corrosion on the mainstays was also inside the deck but nowhere as bad as the aft lowers. In an abundance of caution, the Admiral and I decided to replace all the side stays and the aft stay chainplates. $2k well spent, we think.

_________________
Wayne
Master and Commander of the Sailing Vessel Impetuous
I'm not a complete idiot, some parts are missing.
Subservient to no man except SWMBO
Any day without dock lines is a GOOD day!


 
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 Post subject: Re: New Chainplates for my T37 #49 HELP PLEASE!
PostPosted: 09 Jul 2021 20:59 
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Skipper

Joined: 29 Dec 2006 09:38
Posts: 656
I get it. If you can't see the crevices, that is a problem. I guess if I was taking another 2 year cruise, I would take mine out and inspect them. Has anyone actually had a failure of a chainplate itself? On my boat, the weak point is the starboard rod and weld to the hull knee which I can readily inspect. It should have had a turnbuckle on it, but it is simply welded to a fitting and bolts to a knee. My boat is a deep fin keel version and may differ from the centerboard construction. FWIW.

Ray Durkee
#373


 
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 Post subject: Re: New Chainplates for my T37 #49 HELP PLEASE!
PostPosted: 10 Jul 2021 23:19 
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Navigator

Joined: 06 Sep 2020 10:08
Posts: 99
OK. We're doing the chainplates with the mast up.

Today:
* we removed the head cabinet. Thanks for the helpful instructions. The one difference we encountered was needing to cut off some bits of the masonite headliner and the face frame of the cabinet to get it out.
* took out trim and the headliner of the pilot berth. This was straightforward as described on this forum. One shortcut we made for future flexibility was cutting the trim strip that's behind the grab rails at the bulkhead between the pilot berth and the galley. Now our boat will be a tiny bit uglier, but we can take apart either the pilot berth or the galley area independently.
* pulled the four lower chainplates. The mast is supported by the headstay, backstay, cap shrouds, and a halyard to either side.

Total time (for two of us) was about 4 hours.

After cleaning and scotchbright, the chainplates have some scoring and pitting from crevice corrosion, but look serviceable for a few more years. The bolts, however, are all trash. Several of them were bent and most have damaged threads that were destroyed during removal.

Two questions:
1. The worst thing we found was the bottom "bolt" for the starboard aft lower isn't a bolt. It's a long rod that goes through the pilot berth footwell and is secured with a nut inside the hanging locker (where the water tank deck fills are). That rod was corroded and broken inside the thick plywood bulkhead. Has anyone replaced that long rod with a regular bolt? Any reason the long rod is needed?

2. In the saloon our port side looks different from what I've seen in some posted photos. The chainplates are mounted to a teak plywood surface that's flush with the angled trim pieces. (see attached photo) The plywood seems kinda soft. You can see it's been wet in the past. The aft lower chainplate looks like it was sliding a bit and has worn away some of the wood (light patch halfway down the outboard side). Should we remove this piece of wood and replace it with a G10 spacer because it will be stiffer and more rot resistant?


Attachments:
File comment: Port side saloon: chainplates mount to a flush wood surface. This seems different and not so good.
PXL_20210710_203516980.jpg
PXL_20210710_203516980.jpg [ 1.83 MB | Viewed 0 times ]
 
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 Post subject: Re: New Chainplates for my T37 #49 HELP PLEASE!
PostPosted: 11 Jul 2021 16:39 
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Skipper

Joined: 13 Feb 2011 21:19
Posts: 337
Location: Canyon Lake, TX
On the port side, I would just get a piece of 1/8" AB plywood and stain it to match the rest of the wood. The big problem as far as I'm concerned is that Tartan didn't use butyl tape on the chainplate perforations. They lined the entire hull/deck joint with it but left this off. So the chainplates leak. Stop the water intrusion at the deck level and prevent the rot from the start. If that piece of wood is soft, have you checked the coring under the deck?

Just my opinion and worth everything you paid for it.

I just got a roll of tape to rebed my ports and the chainplates when we reinstall them.
https://shop.marinehowto.com/products/bed-it-tape

_________________
Wayne
Master and Commander of the Sailing Vessel Impetuous
I'm not a complete idiot, some parts are missing.
Subservient to no man except SWMBO
Any day without dock lines is a GOOD day!


 
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 Post subject: Re: New Chainplates for my T37 #49 HELP PLEASE!
PostPosted: 15 Jul 2021 10:40 
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Navigator

Joined: 06 Sep 2020 10:08
Posts: 99
So our chainplates are different from the drawings Maineiac posted. I've seen photos from another post on this board that look the same as ours. The biggest difference is the forward lowers which are two plates welded together with 4 holes in a diamond.

Attached are PDF drawings based on measurements of our four lower chainplates. We'll be pulling and checking the cap shroud plates this weekend.

When we reassemble, we're adopting the 1/4" fiberglass on deck suggestion. For sealant, I'm more comfortable with 4200 than butyl. From everything I've read it seems like either can work, and either can fail, depending on whether it's installed correctly. So I'm going with the material I know better.


Attachments:
chainplate starboard forward.pdf [48.37 KB]
Downloaded 30 times
chainplate starboard aft.pdf [59.13 KB]
Downloaded 15 times
chainplate port forward.pdf [49.32 KB]
Downloaded 12 times
chainplate port aft.pdf [58.6 KB]
Downloaded 14 times
 
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 Post subject: Re: New Chainplates for my T37 #49 HELP PLEASE!
PostPosted: 15 Jul 2021 14:41 
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Skipper

Joined: 09 Aug 2017 15:35
Posts: 725
Location: Maine/USVI
When I get a minute, I'll look at the differences, but I don't think there's much difference except for a front side backing plate or two. I think all the hardware holes go in the same places, same angles, different approach. Matter of fact, I think my existing have the extra plates not shown on Tartan's drawings.


 
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 Post subject: Re: New Chainplates for my T37 #49 HELP PLEASE!
PostPosted: 16 Jul 2021 09:11 
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Skipper

Joined: 09 Aug 2017 15:35
Posts: 725
Location: Maine/USVI
It's nice to have the drawings, but the tool shop should have the actual chainplates in hand to assure consistency. But I suspected they were all pretty close. If I were doing a do-over, and a big refit, I'd figure out a way to get rid of the welded aft lowers. Dumb idea.


 
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 Post subject: Re: New Chainplates for my T37 #49 HELP PLEASE!
PostPosted: 24 Jul 2021 20:08 
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Navigator

Joined: 06 Sep 2020 10:08
Posts: 99
Here are some photos of our chainplates after cleanup. All four of the welded ones were not flat on the mounting side. So I goobed them up with epoxy, and clamped them to a flat board (coated with mold release) to make a flat mounting surface. We epoxied 1/4" fiberglass "islands" to the deck in hopes of keeping some of the water away from the 4200 sealant.

We installed all new 316 hardware. For the aft lowers, we put all the bolts on the forward side of the bulkhead and the nuts "in the triangle." That makes getting the bolts through the holes a lot easier. We concluded that almost all the load from the aft lower is supported by the single bolt at the bottom. On our starboard side, that bolt was corroded and broken. That let the vertical plate bend when the shroud was tight.

I agree that building new chainplates to match the old ones would be better than following the drawing. Not all the holes are straight, so tolerances on where the holes are located are about +/- 1/16" (+/-1.5 mm).

Putting everything back together we're certainly going to leave some better access for inspection and future repairs.


Attachments:
File comment: installed with 1/4" fiberglass spacers
PXL_20210723_165147803.jpg
PXL_20210723_165147803.jpg [ 3.91 MB | Viewed 0 times ]
File comment: cap shroud chainplates are the same as the drawing PDF
PXL_20210717_202401257.jpg
PXL_20210717_202401257.jpg [ 4.91 MB | Viewed 0 times ]
File comment: cleaned up lowers
PXL_20210711_010711475.jpg
PXL_20210711_010711475.jpg [ 4.42 MB | Viewed 0 times ]
 
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 Post subject: Re: New Chainplates for my T37 #49 HELP PLEASE!
PostPosted: 21 Aug 2021 07:35 
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Skipper

Joined: 09 Aug 2017 15:35
Posts: 725
Location: Maine/USVI
Yup, I got a set too.


 
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