We are very comfortable with our solution to the backing plates / under deck reinforcement: replace the inadequate stainless steel plates that have 4 problems
- too small (so the load is not spread far enough which can cause the deck to crack or even complete failure)
- made of two layers that can move out of alignment (then they can bend and cause cracking or complete failure)
- no tie in to the hull (so the deck can pull away from the hull or crack or fail)
- potential for corrosion due to mixed metals (bronze chainplate bolt with stainless steel rigging and stainless steel backing plates).
Note that while there seems to be a common view that Rival yachts have rather under engineered chainplates I have not heard of any actual failures. But the boats are getting older and we have deck cracking around one chainplate.
Our solution with 10mm FR4 board attached with thickened epoxy and the the option of FR4 ties to the hull is going to be a much better solution and one that is ideally suited to DIY. However, we have some remaining problems.
First, the thickness of the deck that the chainplate bolts go through varies. The deck rests on a shelf that is attached to the hull, as it would have been laid up by hand the thickness of the deck and shelf varies. That means a few of the chainplate bolts are barely long enough. So even with the inadequate backing plate the bolt doesn’t extend all the way through the 2nd nut which is used as a lock nut. With a thicker backing plate bedded onto thickened epoxy to ensure even load distribution it might not be possible to fit a lock nut. Any replacement is going to be very expensive (custom bronze fixtures). If they were stainless steel we could replace the double nuts used to lock them on with a nyloc nut and reduce the length of thread needed, but I don’t think these are available for bronze nuts.
Secondly, we have a long term plan to replace all the stainless steel rigging with Dyneema synthetic rope. We wrote about this back in October 2019 “Starting to sort out sailing“. More and more people are doing this (for example 4 YouTube channels have documented this: Rigging Doctor, Tula’s endless summer [my playlist of their videos], Free Range Sailing, Sailing Zingaro).
I’ll go through the dyneema rigging elsewhere, however, the relevant issue here is how to attach the dyneema to the chainplates. So far in the videos and reading we have done there are three options.
a) A toggle that allows a deadeye (see image below and how to make one by Rigging Doctor) to be attached via a clevis pin. We don’t have this sort of toggle (need Fork to Fork but we have Fork to Spade – examples of both here) at the moment (because of the style of rigging turnbuckle we have). This is the solution used by Rigging Doctor, Zinhgaro and some of Tula’s shrouds. However, none of them have bronze chainplates so there is no issue of mixed metals. So we have the expense of toggles, the risk of corrosion between dissimilar metals, and using a chainplate that has had 43 years of wear on the hole to which the toggle attaches. This solution is complex with so many different components (chainplate, toggle, deadeye, lashing to shroud) that have to be bought/made and fitted.
b) A Colligo marine female Chainplate distributor which Tula used on some of their shrouds. Again we have the cost of these (we would need 14 and the price ranges from over £60 each to hundreds depending on size).
c) A frictionless ring attached to the chainplate by lashing it to a shackle (see the Free Range Sailing video at 15 mins). This is a whole lot cheaper as it is just a shackle and a frictionless ring (so under £20 per shroud).
All 3 solutions don’t solve the dissimilar metals problem as all of them connect something not bronze to the bronze chainplate. All of them rely on there not being too much wear in the 43 year old hole in the bronze chainplate and they don’t help with the problem of the length of the chainplate threads.
But we have come up with a creative solution that is going to be much cheaper, lighter, easier to maintain and stronger. Wait for the next blog post 🙂
For reference here is a grainy image of how one of our chainplates looks on deck.
To attach the rigging turnbuckle (that is used to tension the stainless steel shroud/stay) a toggle is fitted like this. It provides articulation to handle the different alignments of the turnbuckle and chainplate.