Chainplate Replacement Questions

[Winf]

Hi All

Our boat is 35 years old. To the best of my knowledge, chainplates have never been done.

I noticed rust weeping from the bolts for the two backstay chainplates which are attached to the inside of the transom inside the lazarette and are fibreglassed over.

So I bit the bullet and started to cut away the covering fibreglass to have a looksee. There was water inside behind the fibreglass both top and bottom. -Main corrosion was around the top of the plate and the water was quite black looking.

So have now totally removed one plate and am working on the other.

The plate is approx 9.8mm thick and the two holding bolts on each plate are approx 9.1mm diameter. Plates were only polished for the exposed top. The rigging is 5/16 wire with ⅝ pin toggles on the turnbuckles. The transom is a good ½ inch thick.

My question is to do with the appropriate replacement. I am going to get two new 316 plates made up.

1. Is the existing plate thickness sufficient? I read if you have a ⅝ toggle pin you should be looking at ½ inch thick chainplate?

I don't like the idea of enclosing the new ones like the previous design and want to get away from that. Locating them on the outside of the transom will mean some mods around the toe rail which I am not keen on either.

So I was going to locate them back where they were, just not encase in fibreglass. Would put butyl tape between the plates and the transom to seal and butyl tape to seal at deck with seal covers.

2. Should I have the new plates made up with the two "cross plates" as before or do as as a single flat bar piece?

I am thinking these cross pieces are there to either add surface area in contact with the transom and add extra holding but if not encased, am wondering if really necessary.

3. Should I add a couple or three more chainplate bolts?

The two bolts seems a bit light on to me. Would probably go up a size also for the bolts

4. Any comments or problems I should watch for with this job and am i doing the right thing to replace?


Thx in advance.

Winf

[DougR]

1. 10 mm plate is thick enough but the cost for 12mm isn't too much more. My Cal 39 has 3/8 thick by 2" wide plate with 5/16 wire and 5/8 pins. No problem...

2. The cross plates will do nothing if the plates are not encapsulated.

3. Use at least 6 bolts per side 1/2 " diameter to spread the load in the fiberglass.

4. To me it looks like they need to be replaced, and don't encapsulate.

DougR

[Stu Jackson]

Originally Posted by Winf

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Would put butyl tape between the plates and the transom to seal and butyl tape to seal at deck with seal covers.
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While mine aren't encapsulated, I used butyl tape successfully.

Chainplate Rebedding 101 - with Bed It with Butyl from Maine Sail

C34 mark 2 chain plates leaking - Chainplate flix

[Paul L]

If you want a chain plate you can encapsulate without corrosion issues, do a search on CF for titanium.

[Winf]

Thanks for the responses guys.

One more I forgot - should i polish full length of the plate?

Winf

[Suijin]

Originally Posted by Winf

Thanks for the responses guys.

One more I forgot - should i polish full length of the plate?

Winf

If you can have them electropolished, that would likely be less expensive and more effective than polishing. If I had them polished, I would pickle them afterwards as well.

Polishing is the most labor intensive part of the fabrication process...likely 50%+ of the labor required.

Short answer...do something, either electro or mechanical polishing, to the whole plate. And make sure you check the deck seal periodically and reseal as necessary.

I agree with DougR that you need to add more bolts if don't include cross pieces and encapsulate. I would also try and stagger them in a zig-zag pattern down the chainplate if possible.

[Boatguy30]

As you noted, the only area originally polished was the area that was seen. I would suggest the fundamental lifespan is more dependentant on quality stainless used and not the quality of the polishing.

[DougR]

One other thing....When laying out the location of the 5/8" pin hole in the upper end of the plate you should lower the center of the pin hole about 3/16" or 5 mm below the center point of the radius that you use to scribe the arc for the top of the plate.

The reason for this is that steel is stronger in tension than it is in shear. By lowering the hole slightly there will be more steel above the pin ( shear stress location) than on the sides of the pin (tensile stress location) and the chain plate will be equally strong in all directions.

DougR

[Jim Cate]

You might consider using 2205 duplex s/s instead of 316. Not all that much more expensive and much stronger and less susceptible to crevice corrosion. Well worth the extra expense...

Jim

[Winf]

Originally Posted by Jim Cate

You might consider using 2205 duplex s/s instead of 316. Not all that much more expensive and much stronger and less susceptible to crevice corrosion. Well worth the extra expense...

Jim

Thx Jim. Wasn't aware of that s/s. Always learning. Will see if I can source.

Thx to all for the info.

Winf

[1boat2many]

Hi All,
My boat was new to me last spring - I saw some weeping and a little rust around the bottom of the chainplate in the lazarette - planned to rebed all of them over the winter. My chainplates are 2 pieces; 1 buried under a solid layer of 3/8" thick fiberglass, 1 on top of the glass through bolted to the other, sort of a chainplate sandwich. When I pulled the upper bolts they felt wet, the second from the bottom wept, the last required bolt hole required a shot form the heat gun to dry. After reading this post I realized I had to bite the bullet and do some surgery - I cut through the glass with a mini-grinder I was glad to see the underlying stainless looked good, not sure how this plate is fastened into the hull, but it wouldn't budge after gentle persuasion with a small pry bar.

Next steps? I know I'm doing some glass work, but I'm wondering if I should also add some additional reinforcement across the plate that will be buried in glass again once all is said and done, similar to Win's cross tee'd chainplate. All input greatly appreciated (BTW starboard side is just as bad, but I don't think I need to cut it open based on what I found here - maybe just weep holes at the base of the chainplate cavity?)

Here's what I'm looking at: