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Old 09-02-2020, 17:18   #1
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External Chainplate Thru-Holes: Best Approach?

Hi All,

I'm part way through a move to external chainplates, and I'm getting near the scary part: Drilling holes in the side of the hull.

Boat's a 1967 Columbia 38 (so should have a solid fiberglass hull). Previous chainplates were internal and glassed to inside of hull (until one popped out!). See picture summarizing project:



Two approaches come to mind:

(1) Drill a hole exactly the diameter of the bolt-shanks (3/8" in my case), and apply sealant (pictured) to inside of hole to prevent water penetration of fiberglass.

This approach confuses me a bit because if the hole is exactly the diameter of the shank (My understanding is that the shanks should fit tightly in the holes in order to properly transfer load to the hull), how is the bolt supposed to go in after I've applied sealant to the inside of the hole? Applying sealant only outside the hold (between chainplate and hull), seems like it's asking for water to work its way into the fiberglass hull via the hole.

(2) is drill a slightly larger hole, fill with thickened epoxy and let set, then drill a hole through the epoxy of exactly the diameter of the shank. What I'm wondering here is if that's going to be as strong - there's now a bolt passing through a ring of thickened epoxy which is glued to the hull - is there not a risk of the epoxy ring separating from the fiberglass hull over time and allowing water to penetrate?

Any advise on the matter is appreciated.
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Old 09-02-2020, 17:25   #2
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Re: External Chainplate Thru-Holes: Best Approach?

Your correct the hole and fastener need to be almost a press fit, I’d even ream the holes to the correct size, some may see that as excessive, but drill bits don’t make perfect smooth round holes like a reamer can, having said that, there is still room for a tiny bit of sealant.
For this kind of thing I prefer 5200, even though many swear against it, but I believe it’s stood the test of time, and it’s likely your chainplates will never be removed again.
I would put 5200 in the hole, on the bolt, under the chainplates and under the bolt head. Meaning everywhere, excess is easily cleaned up with acetone when it’s wet.

There may be a better way though, but you don’t want to oversized the holes to make space for sealant.
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Old 09-02-2020, 17:28   #3
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Re: External Chainplate Thru-Holes: Best Approach?

To drill the holes, I’d use a drill bushing to fit the hole in the chainplate, that allows a smaller pilot hole perfectly centered, then drill/ream to full size, install bolt temporarily, then repeat with each hole installing bolts as you go, these are temp fitting to ensure perfect hole placement, then remove and clean up, apply sealant and fit permenantly.
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Old 09-02-2020, 17:46   #4
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Re: External Chainplate Thru-Holes: Best Approach?

It seems to me you are worried about the wrong thing. You seem to be worried about water compromising your solid fiberglass hull. That doesn't happen. I mean, think about it... your hull floats in water 24/4/365.

Your bolts need to be a good snug fit in the holes, as you say to properly transfer loads and avoid point loading at the top of the bolt and movement in general. The sealant that prevents leaks through the bolt holes is actually under the chainplate, NOT in the holes.

If your holes are a good tight fit, the sealant in there is actually close to useless.

The best thing you can do, is to put a bit of a countersink on the chainplate side of the bolt hole to hold a bit of sealant around the shank of the bolt, and not turn the bolt as you torque it (turn only the nut).

A shame you chose stainless and not a good bronze for the plates, but oh well.
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Old 10-02-2020, 09:15   #5
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Re: External Chainplate Thru-Holes: Best Approach?

thanks for this post,illustrations pictures. I have this project on my wish list. I first agree with post that suggests marine bronze. I have looked for source for them. My internal chain plates are glassed in and without grinding down to survey there status is only know to be old. Your project what are you doing with old chain plates, I thought I would be using existing internal plates as backing and add additional backing per your illustration fairwinds
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Old 10-02-2020, 09:19   #6
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Re: External Chainplate Thru-Holes: Best Approach?

Check out Patrick Children's and his channel Where is Brickhouse. He had a chainplate failure. His mast broke but he made it back to Port.

His repair includes titanium chainplates. His website tells you where to get them. They are affordable and will last forever.
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Old 10-02-2020, 09:32   #7
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Re: External Chainplate Thru-Holes: Best Approach?

I think friction provides lack of slippage as much as anything, but it's good to have the holes close to the bolt size. Just rely on sealant outside the hole to seal it.
Drill one hole, stick a bolt in, tighten somewhat, then drill the rest. I'd be tempted to drill one hole, attach the rigging wire just hand snug. Drill the rest.
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Old 10-02-2020, 10:11   #8
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Re: External Chainplate Thru-Holes: Best Approach?

I think your internal fiberglass reinforcing patches could have been larger and built up with tapered layers to minimize any hard sports developing in the hull.
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Old 10-02-2020, 10:31   #9
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Re: External Chainplate Thru-Holes: Best Approach?

On my Westsail, drilled the holes with a same size drill as the fasteners, drilled the top hole and bolted it up, drilled the 2nd hole and repeated till all four were done, pulled the chain plate and radiused the holes at the outside of the hull with a counter sink, caulked with LifeCaulk and bolted the chain plate back, repeat for each chain plate, and was finished.

The 3rd owner replaced the chain plates because of crevice corrosion on a couple but that was way more than 10 years and two more trips to SoPac after I'd done the initial installation. I didn't and wouldn't worry about locating and drilling exact size holes or putting anything between the backing plate and the hull except caulk. Can guarantee the factory didn't take that much care in installing the chainplates. Did the installation on the hard six months before installing the mast.
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Old 10-02-2020, 10:48   #10
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Re: External Chainplate Thru-Holes: Best Approach?

I didn’t read all replies

You always oversized holes..alignment issue and waterproof Integrity

A tight hole scrapes off caulking and leaks

Caulking starved
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Old 10-02-2020, 10:55   #11
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Re: External Chainplate Thru-Holes: Best Approach?

Quote:
Originally Posted by billknny View Post
The best thing you can do, is to put a bit of a countersink on the chainplate side of the bolt hole to hold a bit of sealant around the shank of the bolt, and not turn the bolt as you torque it (turn only the nut).
One of the best things to do, after the holes are drilled, is to square the outside of the holes and use carriage bolts. In addition to preventing turning of the bolts, and making it much easier to snug up the nuts as a one man operation, mooring lines and drooping sheets will not hang up as they do on hex head bolts. I used carriage bolts on my (bronze) external chainplates, while a friend used hex heads and he was having to put a big blob of sealant under the heads to prevent the lines hanging up.

Instead of using a single backing plate I used discs and fender washers on the inside. On a boat of the vintage of the OP the hull is going to be very thick and shouldn't need as much spreading of the load. Still, the single plate is a better solution.

Converting to exterior chainplates simplifies and strengthens the rig - a really good thing to do.

Greg
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Old 10-02-2020, 10:59   #12
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Re: External Chainplate Thru-Holes: Best Approach?

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Originally Posted by CarinaPDX View Post
One of the best things to do, after the holes are drilled, is to square the outside of the holes and use carriage bolts. In addition to preventing turning of the bolts, and making it much easier to snug up the nuts as a one man operation, mooring lines and drooping sheets will not hang up as they do on hex head bolts. I used carriage bolts on my (bronze) external chainplates, while a friend used hex heads and he was having to put a big blob of sealant under the heads to prevent the lines hanging up.

Instead of using a single backing plate I used discs and fender washers on the inside. On a boat of the vintage of the OP the hull is going to be very thick and shouldn't need as much spreading of the load. Still, the single plate is a better solution.


Converting to exterior chainplates simplifies and strengthens the rig - a really good thing to do.

Greg
Exterior chain plates expose the rigging and structural chain plate To docking and collision damage
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Old 10-02-2020, 11:05   #13
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Re: External Chainplate Thru-Holes: Best Approach?

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Originally Posted by StoneCrab View Post
Check out Patrick Children's and his channel Where is Brickhouse. He had a chainplate failure. His mast broke but he made it back to Port.

His repair includes titanium chainplates. His website tells you where to get them. They are affordable and will last forever.
My chainplates are encapsulated in the hull, are a royal pain to replace and cannot realistically be inspected.
For this reason I got grade 5 Ti chainplates made for me by Allied Titanium, as you say the price really isn’t that much more, and grade 5 Ti plates will easily outlast the hull, no need to ever inspect them.

But for a much older boat, especially external plates that are easily removed and inspected, as long as it’s a good grade of SS, I think he will be fine.
Bronze may be more attractive, especially on an older boat, moreso if his port lights etc are bronze
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Old 10-02-2020, 11:14   #14
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Re: External Chainplate Thru-Holes: Best Approach?

Quote:
Originally Posted by CarinaPDX View Post
One of the best things to do, after the holes are drilled, is to square the outside of the holes and use carriage bolts. In addition to preventing turning of the bolts, and making it much easier to snug up the nuts as a one man operation, mooring lines and drooping sheets will not hang up as they do on hex head bolts. I used carriage bolts on my (bronze) external chainplates, while a friend used hex heads and he was having to put a big blob of sealant under the heads to prevent the lines hanging up.

Instead of using a single backing plate I used discs and fender washers on the inside. On a boat of the vintage of the OP the hull is going to be very thick and shouldn't need as much spreading of the load. Still, the single plate is a better solution.



Converting to exterior chainplates simplifies and strengthens the rig - a really good thing to do.

Greg

An issue with carriage bolts is the square corner, if you actually have square holes put into the chain plates, then those corners are stress risers and are where a crack will propagate from, if it the plate ever cracks.

If you have nice round holes and force a square peg into a round hole, then it’s a weak joint as the corners carry all of the load, where a nice fitting hole the load is distributed.

You really don’t want to oversize the hole to allow for sealant either, because you lose strength doing so, sealant under the bolt head and under the chainplate will be water tight as you can get.

Now assuming the chainplate is nice and thick, I personally see no problem with using internal wrenching countersunk bolts that will fit flush with the chain plate if you desire that. May look less “agricultural” as I’ve heard external plate described.
The machine shop that drills the holes for you ought it be able to countersink them easily.
I don’t have the correct tooling to drill proper holes in thick SS myself.
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Old 10-02-2020, 11:42   #15
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Re: External Chainplate Thru-Holes: Best Approach?

Hi All, CaptVR here.
Built 6 boats, refit hundreds in my 73 years, inspected thousands. External chain plates, can't beat them. Lot less chance of oxygenation (crevice corrosion). An earlier blogger mentioned it and I conquer, I would use silicon bronze, but you have the SS, go ahead and use it, that's my second choice, as long as it's 316.
Don't over engineer. Bolt holes, same size as bolts. You want 0 movement. Drill top hole, put bolt in place with backing plate in place. Align chain plate drill very bottom hole, install bolt. Slightly tight, drill all center holes. remove chain plate and backing, clean all surfaces. Do not, I repeat do not put sealant inside the holes, do not put sealant under the backing plate. Only put sealant around the holes on the back side of the chain plate, slide bolts into chain plate. Now align bolts and put ends into holes carefully and push the chain plate carefully against the hull, hold in place while someone else goes inside to put backing in place and put on nuts. You keep the bolts from spinning while the person inside tightens bolts. Your done.
1. Why would you want to use sealant on the inside, don't think water will leak out.
2. Sealing both side, can easily start crevice corrosion on your bolts. Very bad.....It
oxygen deprives the SS of oxygen and can cause corrosion. Before correcting me, all
you wanna be experts, look it up........You will say, I'll be damn, I didn't know that..
3. The exterior chain plates, properly sealed as I described will not leak to FRP core. They
should not corrode. One thing about external chain plates, easy to pull A bolt once a
year at haul out, just to check on bolt soundness.
4. I would countersink the chain plates, and use either flat head or oval head bolts. To
hold them use a very large screw driver with a crescent wrench. Your not turning, just
holding. Person inside turns the nut. That is the correct way to tighten bolts anyway.
5. After surveying in the area of 50 dis-mastings, most were caused from crevice
corrosion of chain plates through deck areas,chain plates looked like swiss cheese in
deck passage area. . Next where chain plates were bolted to bulkheads and the
bulkheads under chain plate passage had rotted from leaks. Other's were rigging
failures. Never seen a mast failure due to external mounted chain plates, because of
the chain plate failure. Rigging lesson Free.......
Happy sailing to all. Capt. Vince Rakstis, Ret.
PS: Use 3M 5200 sealant, non better for this purpose......
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