Chainplate replacement question

[Drinky Crow]

My C&C 27 Mk V has aluminium chainplates roughly configured as in example pic below.
16" vertical - 3" width - 3/8" thick w/3/16" thick horizontal piece.
6 bulkhead through bolts each and 6 through bolts or screws in horizontal piece.
Port side so severely corroded as to be unsafe so will replace both, but using 316L stainless instead.
My question is regarding the need to weld horizontal piece. Doing so increases the complexity and cost of project.
Is a welded horizontal needed for structural strength?
It does simplify the task of sealing the chainplate during install. I guess.
How much could the deck "work" in relation to vertical piece and does the horizontal piece do anything at all other than to create more opportunities for moisture ingress?
Bulkhead is 3/4" ply, glassed on chainplate side.

[coopec43]

I'd be putting the horizontal strip in for sure as it is vital that you keep salt water off the chain plate so they are not permanently wet with saltwater.


Will salt water corrode stainless steel?

Stainless steel can, in fact, rust and corrode if continuously exposed to saltwater or other corrosive conditions over time.14 Oct 2020


https://www.ulbrich.com/blog/overcom...ainless-steel/

[GordMay]

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In particular their “DIY Projects”
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C&C 27 Chainplate /w [welded horizonta] deck plate.
IMO, the deck plate wasn't intended to take any load - just to provide a large surface, for sealing.
IMO, I think the welded deck plate is a better solution [more leak-resistant], than on my C&C29, where the deck plate was a separate [loose] piece.

[Joe28532]

The answer to your question is no, the cover plate does not need to be welded to the chainplate. Lots of boats have separate plates with a slot that slips over the chainplate instead. Some boats don't use cover plates at all. If using butyl tape to bed the new chainplate then a separate cover plate with its own screws will help compress the butyl.

[coopec43]

Originally Posted by GordMay

Check out the “THE C&C PHOTO ALBUM & RESOURCE CENTER”
In particular their “DIY Projects”
➥ C&C Yachts - C&C Photo Album & Resource Center

C&C 27 Chainplate /w [welded horizonta] deck plate.
IMO, the deck plate wasn't intended to take any load - just to provide a large surface, for sealing.
IMO, I think the welded deck plate is a better solution [more leak-resistant], than on my C&C29, where the deck plate was a separate [loose] piece.

My chain plates are very similar to the one pictured. You are correct when you say the deck plate is not intended to take any load.

[Breaking Waves]

Originally Posted by Joe28532

The answer to your question is no, the cover plate does not need to be welded to the chainplate. Lots of boats have separate plates with a slot that slips over the chainplate instead. Some boats don't use cover plates at all. If using butyl tape to bed the new chainplate then a separate cover plate with its own screws will help compress the butyl.

This is the correct answer to OP's question. The welded cover may be a good idea for additional leak protection. But lots of boats live just perfectly fine with separate (not welded) plate covers. The cover plate is not at all structural. It is there for leak protection.

[GordMay]

Originally Posted by Breaking Waves

This is the correct answer to OP's question. The welded cover may be a good idea for additional leak protection. But lots of boats live just perfectly fine with separate (not welded) plate covers. The cover plate is not at all structural. It is there for leak protection.

Although I suggested the welded plate might be better [for water-tightness], I [now] wonder if it might transmit some of the chainplate forces to the deck, through the 6 bolts?
I also wonder what useful purpose the 6 bolts, in the welded deck plate, serve?
I also note that the deck plate would have to be welded to the chainplate at a very precise height.
IDK, anymore.

[AKA-None]

My c&c uses separate plates
Easy peasy

[Drinky Crow]

So my rigger, who owns a '79 C&C, thinks it should be welded as the deck molding may not have been glassed to the top of the bulkhead as in his boat. Need to get a big guy to bounce up and down while I examine from below. There is no way to tell otherwise because, liner.
Thing is deck core is rotten around both chainplates especially port side so deck plate couldn't have been doing much as it was. Maybe fasteners in horizontal piece were "working" the deck in heavy weather or from backstay application which breached sealent and allowed water ingress?

deck plate would have to be welded to the chainplate at a very precise height.

They have actuals to work from but will have to fit both while "tacked up" and then take them back for welding after angle is confirmed.

My c&c uses separate plates

Interesting. Can you tell if the bulkhead is tabbed on top?

[Drinky Crow]

Originally Posted by Drinky Crow

deck plate couldn't have been doing much as it was.

Except maybe holding deck down?

[coopec43]

"Shiny on the outside, rotten in the middle, is a pretty accurate summation of older stainless. As the top side is getting oxygen, occasional polish and fresh water rinse from time to time, it will look better and last longer than the parts you can’t see. Unfortunately, where it penetrates the deck or is glassed into the hull, it is degrading day by day. A good example which you can see first hand is in the video on this page. There are several materials that have been and continue to be used today, but the most common are 304 grade stainless, 316 grade stainless and Titanium.


In



the 1970s and ’80s, 304 Stainless was the most common material as a replacement for Bronze; which was heavy, soft and had a habit of turning green. In its day, 304 was a great option although, history would prove otherwise. It’s strong, easy to work and polishes up nicely. The problem with 304 is its susceptibility to corrosion and oxygen deprivation. Generally, 304 grade stainless is good for about 20-25 years. Longer life spans are seen, upwards of 30-35 years, in freshwater


https://theriggingco.com/2015/02/02/chainplates/

[Ballsnall]

Originally Posted by Drinky Crow

Is a welded horizontal needed for structural strength?
It does simplify the task of sealing the chainplate during install. I guess.
How much could the deck "work" in relation to vertical piece and does the horizontal piece do anything at all other than to create more opportunities for moisture ingress?

I would suggest that welding longitudinally is structurally unsound by causing a stress concentrator and also changing the metallurgical structure of the stainless. The separate cover plate is a far better design and also the shroud tension is not acting on the deck directly. I would have no trouble changing to single piece chain plate with cover plates. It will certainly not be less sound.

[coopec43]

I think we all agree it is essential to keep saltwater off the chain plate below the decki.e where it is deprived of oxygen.

"While stainless steel won't rust the way regular steel will, it does corrode in a distinct fashion: Crevice Corrosion. Crevice corrosion occurs in areas where the chromium oxide layer has broken down, usually in areas that are deprived of oxygen or very moist or exposed to acidic vapors"


https://www.riggingdoctor.com/life-a...vice-corrosion

[Toccata]

I have replaced several sets of chainplates on old yachts.
My take is: Don't forget to replace the bolts as they too suffer crevice corrosion, particularly if there has been any leaking through the deck.
I chose to weld the cover plate. I fitted the chainplates, then scribed a mark at deck level, I then set the plate 2mm above the deck, to allow for a decent layer of sealant. No screws through the horizontal pate so force transfer to the deck probably nil. The weld was of minimal penetration.

[GordMay]

Originally Posted by Toccata

I have replaced several sets of chainplates on old yachts.
My take is: Don't forget to replace the bolts as they too suffer crevice corrosion, particularly if there has been any leaking through the deck.
I chose to weld the cover plate. I fitted the chainplates, then scribed a mark at deck level, I then set the plate 2mm above the deck, to allow for a decent layer of sealant. No screws through the horizontal pate so force transfer to the deck probably nil. The weld was of minimal penetration.

Good idea.