Embedded Chain plate maint/replacement - Page 16 - SailNet Community
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post #151 of 185 Old 01-29-2014
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Re: Embedded Chain plate maint/replacement

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3. The glassed in chain plate is oxygen starved, this combined with moisture is what allows galvanic corrosion to occur on the plate.
They don't suffer from galvanic in that situation, they get crevice corrosion - a completely different process.
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Woops yes crevice corrosion... Ty

Sloop Jon -Exactly so why would anyone want to reglass a new set into the hull, you're just setting the next owner up for the same mess.

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Re: Embedded Chain plate maint/replacement

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Sloop Jon -Exactly so why would anyone want to reglass a new set into the hull, you're just setting the next owner up for the same mess.
Usually it's the cheapest way to go, often by a lot.

There is a legitimate debate about internal vs external chainplates,personally I don't see any advantage to external since they just change where the corrosion occurs. But let's table this for a moment.


The real answer is one of two options.

1) move to non-penetrating chainplates. This is becoming more common on new boats and is very welcome. Basically a metal ring is glassed into place and the turnbuckle attaches directly to that ring. No need for deck penetrations at all, not only eliminating the chainplate problem but also two holes in the deck.

2) switch to titanium instead of stainless. This is also being done more and more, and is a much better option for retrofit boats. The upside is that once replaced it is a permanent fix. They will never need to be replaced or even inspected in the future absent physical damage (someone hits it with a sledge hammer). The downside is they are a little more expensive than stainless, figure about 25% more for the parts.

This is an example of 1)
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Re: Embedded Chain plate maint/replacement

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Sloop Jon -Exactly so why would anyone want to reglass a new set into the hull, you're just setting the next owner up for the same mess.
You've got me. If you read back through this thread you'll see that I am totally against the process - new or rebuild. In fact I am against ANY sort of metal being buried in glass - chains, floors, deck fasteners - you name it.

If one is replacing some chains done that way, as the OP is, I think they should go back in the same place they came out of, but bolted through the hull. Moving them to the outside does provide a slight benefit by putting the fasteners in compression instead of tension but since they are primarily in shear, that theoretical benefit does not begin to offset all the other negative aspects of the move.

Clean up the old glass and remount the new chains in the same old place with bolts through the hull.

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Re: Embedded Chain plate maint/replacement

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Moving them to the outside does provide a slight benefit by putting the fasteners in compression instead of tension but since they are primarily in shear, that theoretical benefit does not begin to offset all the other negative aspects of the move.
It also increases the lever arm relative to the bolt attachment points, which increases the torque on the bolt head.

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Re: Embedded Chain plate maint/replacement

When you bolt through the hull, are you placing a backing plate on the outside of the hull then? The head of the bolt is on the outside of the hull with the nut inside?
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Re: Embedded Chain plate maint/replacement

I've never seen a backing plate used on the outside in that situation.

Remember, the primary force on a chainplate is UP, which puts the fasteners in shear, so a backing plate is of limited usefulness. Building up the hull laminate in the localized area would be more effective.
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Re: Embedded Chain plate maint/replacement

Well I tell ya this has certainly given me food for thought. We are going to replace our chain plates this year and I was dead set on moving them to the outside of the hull and through bolting, I have seen it done on several 65's and I don't dislike the look. I have to say though I am going to re-consider my options. I may well go with the external plates, but I am looking hard at the idea of bolting through new plates from the inside. I will have a lot of interior work to do as a result of this anyway. Why this wasn't done when the deck/ hull joint was bolted and reinforced during refit I will never know.

THANK YOU!!, to all the posters, none the least of which the OP. I can't say that I am to exited about this project, but it must be done.
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Re: Embedded Chain plate maint/replacement

The new plates will be in the exact same positions and angles as the old plates. Through bolted and not glassed in.
I've worked out various redesigns on the interior to make it so they can be inspected without tearing out the side walls/joinery again.

At some point, maybe, just maybe there will need to be external backing plates on the hull. My riggers tell me no, I'm not so sure.
The primary reason I went for internal vs external was the cost - electro plated plates are x5 the cost - and not having to get a NA involved regarding angles of the plates, as well as not mucking up the (to me) rather lovely teak cap rail I JUST finished rehabbing and varnishing (down to bare wood and built back up).
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Re: Embedded Chain plate maint/replacement

BTW, I love the discussion on this.

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