There are essaintaly 3 ways to go about dealing with the shortcomings of the tayana 37 knee design. First you could remove the plates, check for water intrusion into the knee and inspect the bolts. The problem with this is you can’t actually see where the bolt enters the knee. This is where the corrosion will happen. The only way to be sure is to dig them out and check them. If the wood in the knee is dry, its unlikely the all the bolts are heavily corroded.
The second way to fix the chainplate issue is to remove the old knee and build a new one in its place, using an external backing plate and stainless carriage bolts to hold the chainplate to the knee. This will result in an assembly that can be removed and checked, which was the main fault of the original design.
However the other main drawback to the original tayana design is it creates 7 holes in the deck where materials of different expansion coeficants are close to one another. Theres also a ton of stess and fex acting on this small joint. All of this serves to make sealing the chainplates where they pass through the decks quite a chore. This is the reason the chainplates corrod in the first place.
Inorder to avoid sending the chainplates through the deck at all, they must be moved outboard. This fixes all the shortcomings of the original design and actually adds about 4” to each side deck. Gone are the days of swinging around the shrouds on the way to the bow.
This approach can and has been done with all stainless and all bronze. I will be talking about bronze as that is the matineral that i employed on Satori.
Pete at porttownsend foundry is who manufactured the chainplates. The cost per chainplate was about $170 each. These arrive beautifully finished and ready to mount. The customer can specify the bolt pattern.
The external plates hit the caprail, which protrudes about an inch outboard. I guess i could have cut the cap rail but that would look kinda hacked up. To avoid this I made 6 teak shims that hold the plates off the hull and caprail. They all get the shrouds even farther outboard, allowing more room on the side decks.
Widening the shroud attachment points:
Whenever I’m messing with the design of a major component of the boat I like to have confirmation that what I’m doing is not weakening the rig. Here’s an exchange I found on the TOG site regarding concerns about widening the chainplate attachment points.
I asked the same question about spreader length of a respected
professor of naval architecture. He said that the wider shroud base
will reduce rigging loads and enhance rig stability with no down
This email confirms my own logic that widening the chainplates will benefit the rig and not detract from it.
Rebuilding the chainplates:
Even though I elected to keep the original yard design, I think this exchange with perry is important enough to include:
“Here is an email exchange with Bob Perry regarding chainplate
replacement on the Tayana 37. My text is cut down a little for brevity
but Mr. Perry’s responses are in full.
Q: When the (chainplate) knees get replaced, as the designer of this
boat, after all these years, would you reconstruct the knees in a different
way than originally done by Tayana?
BP: Yes, most probably. I would go for plywood knees perpendicular
to the hull, as knees are normally, and covered with several layers of
glass bonded onto the hull and deck. This is the typical way I do knees.
Q: Would this entail turning the chain plates 90 degrees from the
May I share your response with the TOG association on Google Groups?
BP: Yes. My normal system of attaching chainplates has them 90 degrees to
The birth process of the TY 37 was a bit unusual and many of the
details that became standard were developed by the builder prior to my
involvement with the structure.
Sure you can share this information. Half the stuff you read as “Bob
Perry says” is not what I said anyway.
Thanks Mr. Perry for the exchange.