This is it. The final (at least the latest) design of our Dyneema, synthetic chainplate.
A short recap on the background.
- This is a Rival 38 Centre Cockpit Ketch (possibly the only one)
- Currently we have the original Superstron (Bronze) chainplates
- The chainplates are essentially an eyebolt with a flange that is bolted through the deck and the hull shelf that the deck rests on. Below the deck there is a small backing plate and two nuts. The backing plate is made up of two strips of stainless steel.
- The chainplate for the main mast cap shrouds is tied into a bulkhead. A stainless strip has been bolted to the bulkhead and the top bent over to right angles (flush with the underside of the hull shelf), this has a hole which the chainplate comes through.
- We have cracking in the deck around one of the mizzen chainplates (the backing plate is made of 2 sheets of stainless steel and they have slipped so no longer aligned and therefore have bent and not spread the load correctly)
- Several Rivals have had chainplates fail. This has happened to both original Superstron and replacement stainless steel chainplates. Other Stainless Steel versions have been inspected and found to have corrosion where the thread meets the flange at the top of the deck.
- Other Rivals have had some deck cracking around chainplates. Some have installed larger backing plates.
We have some constraints (and remember we need chainplates of 4 sizes for 12 shrouds, 2 main mast backstays and 2 mizzen running backstays so 16 in total)
- For a wide variety of reasons we want to switch to Dyneema Rigging
- Replacing the Chainplates with new and longer versions (and ideally slightly increased diameter) so that they can be used with thicker, larger backing plates would cost several thousand pounds.
- New metal chainplates will need a means to connect to a tensioning lashing for the shrouds. Colligo make suitable products and we would also need toggles to ensure alignment. This would cost several thousand pounds.
So we have decided to make our own.
We have been through a number of designs. All of them look similar above deck. A low friction ring is held in one of more dyneema loops that disappear into the deck. The shroud or stay will end with a low friction ring and a lashing will be used to join these and tension the shroud/stay.
Below decks our ideas have varied. The key difference for this design is that we have decided not to create any extra connection between the hull and deck. Whilst modern design would want to see a solid tie between the chainplate at the deck and the hull (preferably extending a long way down the hull) we reason that Rivals were not built that way and none of the failures that we have heard of include separating the deck from the hull. Amongst other factors to create such a link would require the removal of the inner plywood lining that is fitted to the inside of the stringers approx 3cm from the hull.
Here then is our design for our chainplates. Note that for the main mast Cap Shrouds we will still create a “knee” to tie the chainplate to the bulkhead (not the hull) – this is not illustrated.
We welcome your thoughts.