Chainplate popped out when sailing - what's next?

[petered]

Hi all,

Novice sailboat owner here, so forgive me if I'm using some wrong terminology.

Bought the boat (Columbia 1967 38') knowing there was some leaking and possible core-issues around the sides. On her second sail, there was a sudden CRACK, and the starboard middle chainplate (the one holding the cap shroud) popped right out. We quickly took down the sails and fortunately the other chainplates held and the mast didn't topple or anything. See image below. And full album here.

So, I'm getting that I have some major work to do. My current thinking is that I should cut out a section of deck that extends about 1 foot around all the chainplates (maybe more depending on how the core looks), replace the core, and re-fiberglass the whole thing. Anyone who's been in the same boat, so to speak - does that sound reasonable? Any gotchas that I should be aware of before starting this project?

[gmakhs]

Is that a cap shroud or a lower shroud ???
The chain plate design is insufficient and weak , you will need to fix the issue with the deck as you propose , check the rigging tensions and ALL the chain plates but.most important chain plates should not stop on deck , they should be anchored on a bulkhead or at the hull something that is missing from.yours .
I give you a photo example of mine .

[Cheechako]

I believe that chainplate was intended to be attached more to the hull sides than the deck. (?) Based on the T bottom. So... the deck may not actually be your biggest problem. Rather, the old fiberglass that attaches the T shaped plate to the hull has given out. I would remove all chainplates including the stern, inspect the SS plates, Grind to fresh glass and re glass them to the hull.
Or make new chainplates and devise bolting them through the hull.

[rbk]

Originally Posted by gmakhs

Is that a cap shroud or a lower shroud ???
The chain plate design is insufficient and weak , you will need to fix the issue with the deck as you propose , check the rigging tensions and ALL the chain plates but.most important chain plates should not stop on deck , they should be anchored on a bulkhead or at the hull something that is missing from.yours .
I give you a photo example of mine .

Looks like rotten knees and the t bolts pulled out and took the top coat of glass off the inside of your hull. Do them one at at time to avoid dropping the mast. As cheechako said grind out the old backing (prob ply, teak or someother wood) glass in new backing and through bolt new 316 chain plates while you’re at it. Might look into the option of moving the cp outboard but that has its pros and cons. You’re lucky the stick didn’t come down.

[TrentePieds]

Chainplates outboard on the hull are IMO superior from every point of view to the pretty-pretty ones that pass through the deck. Easier to inspect, easier to replace. A less obvious advantage is that they must of necessity by through-bolted to one of the strongest parts of the hull, and the bolts will be in sheer. Correctly dimensioned bolts in sheer with shanks of correct length fitted in bores of correct diameter (press fit to the bolts) has to be better than any other means of fastening.

TrentePieds

[MartinR]

Originally Posted by TrentePieds

Chainplates outboard on the hull are IMO superior from every point of view to the pretty-pretty ones that pass through the deck. Easier to inspect, easier to replace. A less obvious advantage is that they must of necessity by through-bolted to one of the strongest parts of the hull, and the bolts will be in sheer. Correctly dimensioned bolts in sheer with shanks of correct length fitted in bores of correct diameter (press fit to the bolts) has to be better than any other means of fastening.

TrentePieds

Yes, that is the way to do this. new external chain plates. Easier to fix, easier to maintain, probably cheaper.

[Cheechako]

Originally Posted by TrentePieds

Chainplates outboard on the hull are IMO superior from every point of view to the pretty-pretty ones that pass through the deck. Easier to inspect, easier to replace. A less obvious advantage is that they must of necessity by through-bolted to one of the strongest parts of the hull, and the bolts will be in sheer. Correctly dimensioned bolts in sheer with shanks of correct length fitted in bores of correct diameter (press fit to the bolts) has to be better than any other means of fastening.

TrentePieds

Yeah, I lean that way on this too. Part of it is whether he can access the interior in the right spots for backing board and bolts etc.

[Hesti]

It has happened on other boats before and some of them were much younger.

So far, it was glassed to the inside of the hull, correct? And that gave way after 52 years, correct? Do you have photos from the inside of the hull in that place? Putting new chainplates on the outside of the hull might be an option, but bringing it back to the status that has lasted 52 years, perhaps with some "improvements" might be closer to the intent of the original designer. It might well be, that the problem started with water seeping in and then either some wood involved in holding it rotting away or perhaps frozen water pressing the fiberglass apart. Whatever. But it can be repaired. The deck would then hold it in place horizontally while the glassing to hull or whatever would take the vertical force. An improved design could for example have not just one T-bar but several and possibly be longer. Even some drilled holes in the T-bar would increase vertical holding power.


And yes - do the others as well.


If it helps you: Chainplate trouble is on the yard list of our boat as well ... They didn't pop out, but they were already loose.

[Sailmonkey]

It’s not your deck being soft that allowed this failure. This is a chainplate that was glasses to the hull and became detached.

I concur with others that suggest bolting external chainplates to the hull.

[petered]

Thank you all for the advice, I appreciate your answers and I'm really glad I posted here now.

To answer questions,

- Yes it was a cap shroud.
- Yes, it was previously glassed onto the inside of the hull. It looks like it was maybe reinforced more recently than 52 years ago (See Picture 2 of a surviving chainplate attachment).
- Yes I can access the interior where where the chainplate would be fixed. (see Picture 1)

After hearing your answers I'm going to look into doing external chainplates now.

I guess my follow up question is: For the remaining chainplates (See Picture 2) rather than removing them and re-glassing I was thinking of maybe just reinforcing them by drilling some holes horizontally through the "I" and bolting to an external stainless steel plate outside of the hull - that seems less labour intensive. Does this sound like a bad idea?

[a64pilot]

Actually the less labor intensive thing is replacing them they way they were originally installed, and you know most likely there is sufficient strength that way, as it lasted what, 50+ years?

The bond obviously is what failed.
Assuming the others can be accessed as easily as this picture illustrates.
What usually drives people with encapsulated chain plates to external plates, is the extreme amount of work required to access them to replace them, not that it is an inferior design strength wise.

When you replace them, they should be installed with directional fiber glass draped over the T in the plate and spread out over the hull.
I’ll see if I can find a picture.

This is mine being replaced on my boat, the strange color is because they are Titanium and not polished.


Red dye was added to the resin to make wet out more easily seen

[Cheechako]

Yes you could bolt them, and put the failed one back in position and do that also so they match.. 2 -3 big bolts likely enough, 4 or 5 better but I imagine 2 or 3 is as strong as original installation.
75% of the yield strength of a 3/8" bolt is about 24000 lbs. Shear strength is likely less and other things matter, But two of them will lift your entire boat in theory!

[a64pilot]

Strength of the bolts is not in question, strength of the hull is.
If you don’t spread out the load, bolts could just tear through the hull.

[TrentePieds]

As I read the last two pics you provided, the failed chainplate (and its mate presumably) were fixed to a thwartships bulkhead. Is that correct?

As Don sez, there is no trick to providing sufficient bolt strength. The trick is to make the anchoring points strong enuff. There is a consideration that is easily overlooked unless you are familiar with this sort of work - providing sufficient BEARING SURFACE where the sheerload of the bolts transfers to the boat's structure. Assuming six bolts, I would think that 3/8" dia would be sufficient PROVIDED the structure is solid enuff. As I said before, the bolts holes have to be a TIGHT fit in the holes in the supporting structure, and because AREA of the faying surfaces is important here, the DEPTH of the bores is also important. There is a material called "G10" that is excellent for building up a "sandwich" of material where the bolts have to pass, and these backing blocks of G10 can be given sufficient surface area to give a good adhesive bond twixt the "doublers" and the underlying structure. Note that the SHANKS of the bolts have to be as long as the holes are deep, minus "three threads" (the distance the nut advances in three full turns). This is to utilize the full bearing surface within the holes in order to avoid local stress points.

While in the general case I prefer chainplates on the exterior of the hull, it may be that your repair job will be easier by putting the chainplate back where it came from, even if that means making repairs to the bulkhead. Once the chainplate is solidly back in position, there are numerous ways to repair the deck where the tang sticks out.

TrentePieds


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[cal40john]

One issue is the chainplates are possibly in a wet low oxygen area so they potentially could be corroded and ready to fail.