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Old 23-08-2015, 12:01   #1
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Chainplate saga part 2

Well nothing is as simple as it seems. There are too many pics to attach here so Chain Plates | Sailing Vessel Vigah

My problem isn't how to do the physical replacement of the chainplate support substrate, but should I attempt to use the same captive bolt arrangement the OEM did in 1979 or can I just re-build and instead bolt thru the hull? The top two bolts are like that.
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Old 23-08-2015, 12:15   #2
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Re: Chainplate saga part 2

I never see such a setup as yours, my 2 cents trough bolted outboard could do the trick.
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Old 23-08-2015, 13:16   #3
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Re: Chainplate saga part 2

I really hate thru bolted chainplates. It's one more exposure point for stainless, and adds holes to a boat. I always harp on this, but I would have new titanium plates made, and use captive titanium bolts bedded into G10 instead of plywood. It may cost a bit upfront, but it will never need to be done again. Nothing to rot, noting to corrode, and if you want you could completely seal it for the future.
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Old 23-08-2015, 13:46   #4
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Re: Chainplate saga part 2

Thru bolted I think. Clean and reinforce where the rot was.
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Old 23-08-2015, 16:09   #5
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Re: Chainplate saga part 2

Yah, I was thinking that with counter sunk holes and butyl tape , thru bolting would be an alternative. There is less chance of leaking that way than the chain plates through the deck because for butyl to work you have to have some compression. Even 4200 or 4000 doesn't seal for very long.

But then maybe the thin chain plate design allowed too much movement in the first place when the mast flexed.
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Old 24-08-2015, 09:41   #6
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Re: Chainplate saga part 2

Don't know what your top sides look like, but if I were to experience the same problems I would go all external chainplates. It would also make my deck more sailor friendly.
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Old 24-08-2015, 09:58   #7
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Re: Chainplate saga part 2

Quote:
Originally Posted by Stumble View Post
I really hate thru bolted chainplates. It's one more exposure point for stainless, and adds holes to a boat. I always harp on this, but I would have new titanium plates made, and use captive titanium bolts bedded into G10 instead of plywood. It may cost a bit upfront, but it will never need to be done again. Nothing to rot, noting to corrode, and if you want you could completely seal it for the future.
X2 G10 build out and some epoxy cloth coverage.. just for good measure.
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Old 24-08-2015, 11:25   #8
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Re: Chainplate saga part 2

I agree with Stumble and I don't like SS through bolts. Every boat is different so I won't bore you with too many details of the complete chai plate replacement I did 2 years ago.

There was slight distortion on the outside of my hull so I completely removed the origina chain plates which was the hardest part of the whole job. Then I pressed the distortion out with some timber and a screw system from the inside. I set that with some glass and epoxy.


I cleaned a large area inside the hull and layer up about 3 layers of double diagonal glass that were each about a foot shorter than the previous.


I designed my chainplates after looking at as many different boats as possible as well as googling. I drew up the various components full size in thin cardboard.


I filled any original chainplates holes with glass epoxy etc. Then I made many measurements especially from the fore stay chainplate back on each side. I didn't trust the original which was slightly non symmetrical.


I cut out all the 316 SS and got a welder to tack both lightly together. Then I cut a slot on each side of the deck and slid the long SS flange down the slot. The important part was that at this stage I had not attached an internal knee. I made the knee and used the flange as a guide as to its alignment just gluing it to the reinforced hull. Then I removed the chainplate assembly an while the final welding was being done I glassed in the knee using the standard fillets etc.


Having SS on either side of the knee ; one a backing plate and the other going outside through the deck adds considerable strength.


My plane is loading so gotta go


Good luck.
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Old 24-08-2015, 11:28   #9
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Re: Chainplate saga part 2

I too have chain plate issues. Cant wait for more good advice.
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Old 24-08-2015, 13:18   #10
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Re: Chainplate saga part 2

Through bolts aren't the big problem with chainplates, it's the deck chain plate interface. Bolts can usually be sealed, the deck/chainplate area is always a problem. Butyl may be better as it remains flexible and tacky so resistant to breaking the goo/metal bond.

Exterior chain plates are better than through deck types but still have crevice corrosion issues at the top hull/deck/chainplate interface. Surveyor flagged the external chain plates on our W32. Thought it was stupid till I pulled the 10 year old metal. There was corrosion pitting on them where they passed through the wood caprails. On your boat, would go with exterior chain plates as long as you can live with the cosmetics. SS chain plates will bleed rust down the hull but that's largely a cosmetic issue from run off from the wire. Oxalic acid is a quick and simple clean up of the stains.

If you can afford it, Titanium is definitely the Cadillac of materials, strong, light and no corrosion issues. Are titanium bolts available to fasten it, though?? When I replaced the chain plates on current boat, wanted to go with bronze, never thought of Titanium, but couldn't find silicon bronze flat stock. Only suitable bronze I could find was 954 Aluminum Bronze. Could find no information on Aluminum Bronze on a boat. If anyone has experience with it, the feedback would be nice. Went with SS. The original chainplates had survived 40+ years with minimal corrosion.
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Old 24-08-2015, 15:57   #11
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Re: Chainplate saga part 2

I was looking at the problem and it appears that I will able to re-construct the original easier than trying to do the thru-bolt approach. For the chain plate deck interface I am thinking 4000/4200 to give a base and then butyl on top compressed with the chain plate covers. Should last better than 4000 alone.

Just as an aside, Bailsout, what do you mean by making the deck more sailor friendly?
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Old 24-08-2015, 17:42   #12
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Re: Chainplate saga part 2

Rover,

Up to about 4" bolts titanium fasteners are available off the shelf. Fasten all carries it in stock at a lot of their stores, and if not Allied Titanium has a warehouse in Washington state with it boxed and ready to go. McMaster Carr also carried titanium bolts.

Unless you are in a hurry buy direct from AT. the prices will be about 10% the cost of McMaster.
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Old 25-08-2015, 06:19   #13
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Re: Chainplate saga part 2

Further to my chainplate replacement. I made them out of 75mm X 3 mm SS 316 with long plates going down maybe 450mm inside the hull and bolted through a new knee bonded to the hull. There is a matching plate on the other side off the knee which doesn't go through the deck.
My deck cover plate is welded to the long flange. Normally chain plates in similar style have a separate cover plate with a slot sealed with Sika or some such. That traditional method is much quicker for a builder to construct. It does though allow some working over time and potential leaks and corrosion.
My way required very precise work design and planning to fit properly and would have been expensive in time for a professional to carry out.
As I mentioned before the new internal knee was not installed first. A precise slot was cut in the deck first. The tack welded chain plate was inserted through the slot and aligned with temporary small screws and small screw holes in the coverplate into the deck. My prefabricated internal knee was G clamped to the long chainplate flange. That ensured perfect alignment of the knee to the plate. The knee at that stage was simply edge glued to the previously glass reinforced inside of the hull. Then the chainplate was removed proper filleting and glassing in place of the knee was carried out.

Because my coverplate is an integral part of the chainplate I firstly reinforced the deck area over about 600 mm length with a prefabricated balsa sandwich panel glued up under the deck in the chainplate area.

All this work took me about a month working most days on it. The hardest part was the deconstruction and removal of the old plates and knees. Then the sanding off of the paint inside a large area of the interior of the hull and new double disgonal glass epoxy over a large area.

The 316 SS cost over $600 then there was several hundred $s on resin, glass and bolts etc. Somehere just over $1,000 for me to do it all. The slots in the 4 mm cover plates were precisely milled by an engineer friend but paid for.

Because I drew everything out first full size on thin cardboard there was zero waste in the SS materials.

I'm sure it would have cost me $15/20,000 for a professional to do all that work and they wouldn't have done it as well. Not because I'm better but because I take more time to do the work precisely.
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Old 25-08-2015, 06:42   #14
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Re: Chainplate saga part 2

I would go with Cheechako an NeilPride on this one. I also agree with Neil that I have never seen such an arrangement previously. It looks like the marine ply had water ingress from above as the plates flexed, which is frequently the case. In the end all that was holding the rig up was the glass skin which was holding the "box" encasing the ply. It could be that the thinking was to have ply to absorb some of the shockloads by damping? In any case it is finished and I would check and cut any other suspect. I am not really a fan of encased ply like that as I have seen exactly this phenomenon fairly often, though not with this particular arrangement as stated. Since you ahve cut the box clean back to its edges and left, it would appear, little flange to rejoin a fresh skin, my instinct would be to tebuild the box with layered glass replacing the whole thickness of the ply as original, including the skin and then throughbolt to the hull. Simply throughbolting without a rebuild of the box around it may compromise the hull skin as it was not designed originally to take such loads, but with the rebuild plus throughbolt arrangement you may end up with a fix that is stronger than the original. I would love to have Minaret's opinion on this as well as any others who may have views on the actual function and reasoning (if any) behind the original use of marine ply in this encased method, and whether my suggestion would make too rigid a structure as may be the case therefore. Still, it is likely what I would do given what I can gather from your photos.
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Old 25-08-2015, 08:15   #15
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Re: Chainplate saga part 2

Well the hull thickness at the top chain plate thru bolt is right at 12mm. Thru bolting with an FRP spacer plate epoxied to the hull would be very easy to accomplish. It does have a nice box cover for the chain plate area. Thru bolting would also allow me to use a thicker chain plate, i.e. 1/2 in instead of 1/4 in, and cut down on any flexing. Leaks would also be easier to spot.
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