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Old 16-07-2023, 02:09   #1
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Glassed in deep

Hi all,

On a new to me 1980 Beneteau First 35... The internal chain plates are buried under glass, then internal cover panels, then cabinetry. Sidestays come to the one point at the deck (rather than for and aft lowers), then a deck fitting attaches to a section of rod down to the internal chain plate. Hopefully the drawing makes a little sense.

I had a boat builder take a look at these original buried chainplates. He observed no cracks above the clevis pin hole and said they are ok.

43 year old buried chain plate... all research advises against this being ok and I intend to travel to remote places.

Would it even be an option to dig out/off enough glass to inspect the first few (loadbearing) inches of the 1m long chainplate, then glass back over?

Otherwise, build something new...

Would a single large chainplate (for all three sidestays) bolted to the exterior hull be a straight forward solution? Or perhaps another way, build an interior bulkhead that doesnt change the rigging geometry.

Would to hear ideas/feedback.

Many thanks
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Old 16-07-2023, 03:17   #2
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Re: Glassed in deep

I may be missing something, but if you slip out the clevis pin at the top end of the tie-rod, will you be able to lift the chainplate out from above? Or is it bolted inside with out-of reach bolts?

If you really need to change it out, you may have to violently cut the deck away then build it up again after, like people do when replacing metal chainplates with composite.

If you change the chainplate location, you may need structure to support it, which would entail removing cabinetry and doing some heavy glassing, and you would want to have any changes carefully engineered. That tie rod transfers load to something strong down lower, because the deck and hull are too lightly built to take the load. So you'd have to figure that out as well.
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Old 16-07-2023, 05:30   #3
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Re: Glassed in deep

Hi Benz,

The internal photo is taken looking down at where the rod attaches to the glassed in chain plate. The rod goes up through the deck and deck fitting. The round head nut seen from outside screws on to the top of that rod.

Photos auto rotating

I think the simple/effective solution would be external bolt on chain plates, but I'm sure theres more to it than that.
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Old 16-07-2023, 06:04   #4
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Re: Glassed in deep

I've seen that set up on other boats too, seems like bad design to me. All three stays coming to one plate for one thing. Looks like they designed the interior before the exterior and rig, normally there's a bulkhead at that point and the chain plate is bolted to that. But there's no bulkhead there.
External chainplates would be the strongest way, they've been doing those since the old sailing ship days. Problem is you can't trim the Genoa in as closely, that's the whole point of moving the plates inboard no matter how they're secured. I had a boat with external plates, I actually rigged two separate jib sheets systems. The working jib sheeted inside the plates and the Genoa outside. Separate hank on sails. A little thought about advantage of exterior plates is they make walking forward along the side deck safer and easier, they don't impede the side decks. No toe stubbers either. I'd move then outboard if I had to replace them.
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Old 16-07-2023, 10:51   #5
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Re: Glassed in deep

Beneteau has kept that same basic design for a long time. On my 2004 Oceanis 423 the D1 forward goes to chain plate that is just thru-bolted to the cabin top. The D1 aft and V1/cap go to fitting similar to yours then have a tie rod down to the bar glassed in below. One the one hand given the general longevity of this design based on the number of boats and total miles sailed this way, including many circumnavigations, it seems to be a sound design. I do hear your concern about how to inspect the buried part of the setup. Sorry I don't have a good answer on that part.
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Old 16-07-2023, 10:53   #6
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Re: Glassed in deep

Oh, and regarding external chain plates. I have heard of others doing that sort of thing. For sure you will need new spreaders but you should enlist the services of an appropriate naval architect to advise. You also have to consider how your genoa sheets will lead.
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Old 16-07-2023, 11:11   #7
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Re: Glassed in deep

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Originally Posted by Surfshack View Post
Hi Benz,

The internal photo is taken looking down at where the rod attaches to the glassed in chain plate. The rod goes up through the deck and deck fitting. The round head nut seen from outside screws on to the top of that rod.

Photos auto rotating

I think the simple/effective solution would be external bolt on chain plates, but I'm sure theres more to it than that.
Oh that's actually a clever design I think (top part), very easy to inspect and understand.

For the buried part in the hull - if there is no signs of any significant water intrusion, what should have damaged it?

Your drawing skills are top notch by the way
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Old 16-07-2023, 11:37   #8
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Re: Glassed in deep

I wouldn’t change a thing, just inspect regularly.

But maybe it can be x-rayed in place?
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Old 16-07-2023, 15:04   #9
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Re: Glassed in deep

^^^^^^
Ditto, inspect regularly for water intrusion.
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Old 16-07-2023, 15:35   #10
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Re: Glassed in deep

Please don't take this personally, but consider that you are suggesting taking a design with years of dependable service in thousands of hulls and replacing it with one of unknown engineering and unknown materials that would detract from sailing performance and look clunky to boot.

Bennies are not known for stout construction, that's for sure, but neither are they known for rig failures. Rudder and keel issues abound and grid failures are known to happen, but masts seem to stay erect, so why so much worry? And then too, their hulls are pretty slim on scantlings. Changing to external chainplates would be putting a new and not accounted for stress on the hull, something that seems ill advised to me. A good deal of thoughtful reinforcement would be needed, preferably from a good NA and then execution by a good builder. None of that would be inexpensive!

To me, the changes you propose are not a good idea. YMMV.

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Old 16-07-2023, 16:00   #11
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Re: Glassed in deep

I agree with Jim, its been standing for 4 decades, leave it alone as its working.

The problem with chain plates is water leaking down between the deck and the steel. So crevice corrosion and wooden bulkheads going soggy. Since your chain plates are separate items with an air gap, that could be a real advantage.

The only thing I would do is next time the mast is down for new rigging, lift the deck plates and re-seal them just to be sure and then enjoy years of not having to worry about them.

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Old 17-07-2023, 02:47   #12
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Re: Glassed in deep

Thanks all for your input. Honestly, all helpful. Redesigning the boat is the second last thing I want to do.

Is the recommendation that they won't need replacement unless showing faults on the small section visible?

I see plenty of photos of chainplates corroded at the (wet) through-deck section, but I get this is different. Maybe a better question would be; when people unearth their glassed in chain plates, are they finding much corrosion/stress fractures?

Thanks
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Old 17-07-2023, 02:51   #13
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Re: Glassed in deep

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Originally Posted by Surfshack View Post
Maybe a better question would be; is stainless steel likely to corrode when sealed with fibreglass in this way?
As long as there hasn't been any water intrusion then your chain plates are likely as good as the day they were installed.
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Old 17-07-2023, 03:05   #14
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Re: Glassed in deep

I agree with Jim as far as no re-design, but I have to point out that crevice corrosion happens where you can't see it.
Forty years? Every day makes failure more likely. I'd find out how to replace with same, and do it ASAP.
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Old 31-07-2023, 21:44   #15
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Re: Glassed in deep

We are just finishing up this same project, though of a different design. Our 1976 Miller 44 is a very strong boat, and I'll add smart as well, except for the fact that the 6 massive tree-like chainplates were glassed into the hull. I'm sure that was a comprimise to create the space we enjoy below. When I purchased Giselle, I negotiated based on the fact she needed new rigging and sails. I failed to comprehend the gravity of the chainplates. I was pursuded by excellent shiprights and riggers in Port Townsend to replace them all. I'm glad I did. There was plenty of crevis corrosion and probably cracks, though we didn't spend the time or money to confirm. They looked awful. This was messy and expensive and time consuming - and worth it all for a good nights sleep in poor conditions offshore.
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