Chainplates. We are going for a radical dyneema option

In my last post “Chainplate update, more challenges” I linked to a whole bunch of YouTube channels where people have switched their rigging from Stainless Steel Wire to Dyneema Synthetic rope.

I’m going to write more on why we plan to switch to Dyneema, fully recognising that this is not yet seen as the norm. Also on the connections that are needed at the mast end of each shroud/stay.

Here though, I’m focusing (again) on the chainplates. I’ve detailed the problems we have with our chainplates, although it is worth noting that these problems are not typical of other designs. We don’t see many boats with bronze chainplates and we don’t see many boats where the chainplate is basically just a bronze eye bolt through the side deck with a backing plate (the chainplates for our main mast cap shrouds are bolted to right angle connection from a plate bolted to the bulkhead rather than just a backing plate).

Normally on boats this age, there is a long stainless steel plate that goes down into the cabin with multiple bolts either to the hull of the boat or to a main bulkhead. This plate sticks out of the deck for the shrouds to attach to it. With newer, higher performance boats the engineering of these has to be much more sophisticated as rig loads are greater and the general material in the hull much lighter and thinner.

What we have seen is that it is very normal to need to refurbish or replace the chainplates on boats that are over 40 years old especially when there are plans to cross oceans. So we have seen Tula’s Endless Summer, Beau and Brandy, Kittiwake, and others who have had to do this work. There have been a variety of solutions from upgrading to Titanium, direct replacements, or switching to through bolted external chainplates.

Going Dyneema.

We however, are not looking at a refurbishment (doesn’t solve the problem of the thread being too short for a thicker backing plate) or a replacement with similar (cost and not ideal attachment point for Dyneema shrouds).

When thinking about our chainplates while planning for Dyneema rigging one of the practical issues to sort is the attachment points. I will do a separate post about our plans for the ends at the mast. At the lower end you need a means to tension the shroud and a way to attach it to the chainplate.

As I have been reading about Dyneema rigging it has struck me that lots of people have multiple extra fittings to adapt the connections at the ends. It allows existing chainplates and mast fittings to be reused, essentially via adapters.

So if we have got to do work on our chainplates anyway I started wondering if it would be possible to end up with a chainplate which we could directly connect the tensioning lashing to. The only solution on the market is the Colligo one but that would cost hundreds of £ per shroud and would not solve any of the problems with the chainplates themselves.

Then as I was searching I found these Soft Padeyes

These are not generally being used as chainplates for shrouds, but for sheeting, temporary attachment points, removable inner forestays and the like. Most boats won’t be able to consider these for their chainplates because

  • they only make sense for dyneema shrouds
  • they only make sense if you are tensioning your rig with dyneema lashings, not turnbuckles
  • I’ve only worked out how they can be used to replace chainstays like ours that are in the side deck and that don’t have engineered ties to the boat

But for us, I have realised is that it should be simple for us to make these ourselves, using the backing plates we have already designed. Not only that, but they will be easy to inspect at sea and even replace at sea ourselves if needed.

Making and fitting the dyneema chainplate

I don’t think it is going to be very difficult – but don’t hold me to that 😉

  • Remove the existing chainplate and old backing plate.
  • Drill out a significantly larger hole where the chainplate bolt was. This is to make sure that we get to clean dry deck core. Later it will be filled with thickened epoxy and then a hole drilled in the epoxy for the dyneema loop. This way the deck core will be protected from damp by the epoxy. It also means we will have the option to angle the hole so that it is aligned with the shroud (currently they are not).
  • Now fit the backing plate using thickened epoxy so that the hole in the deck is in the centre. We might apply pressure from below or drill a small hole in the centre to allow a light line to pull it up tight through the deck hole.
  • If this is one of our more heavily loaded chainplates (eg main mast backstays or cap shrouds) then we will add the additional bracing to the hull.
  • With the backing plate fitted we can now fill the hole in the deck with thickened epoxy.
  • Drill from the deck through the thickened epoxy and through the backing plate. Hole should be big enough to thread a doubled dyneema line through from below. I’m going to use dyneema one size up from the size used for the shrouds and I’m going to cover it with a chafe sleeve.
  • Round and smooth the edges of the hole at both top and bottom to minimise chafe when the loop is tensioned.
  • Make a dyneema loop. I’m going to follow a simplified version from the video below. It uses a very simple overhand knot which can’t slip because the loop is passed through eye splices that stop the knot from slipping. It seems to have a lot of advantages for this (easy to create, large knot, very strong and tested). Mine doesn’t need the soft shackle eye which makes it even simpler. It will just be a loop, closed by the knot at the open end. This probably needs to be about as short as I can make it because we want to keep the loop above the deck as small as possible, just suitable for a low friction ring or stainless steel thimble.

At this point we could just thread the loop up through the backing plate and deck, then put the low friction loop in it (and if we wanted a padeye on top of the wheelhouse roof this would be fine).

However, it will leak.

Stopping Leaks

One option for a waterproof version is to buy this complete solution from Colligo for about $80 (for the waterproof version), but they only go up to 5mm with 5,000 lb breaking strength.

Alternatively we can make our version waterproof while still keeping it easy to replace ourselves.

For this we need a “washer” made from the same material as our backing plate. The outside diameter should made to just fit inside a short length of plastic pipe. Choose a pipe that is large enough for the knot to easily fit inside it, also a pipe that we can get a waterproof end cap for.

Epoxy the washer onto the backing plate so that the hole lines up. So that the knot fits well against the washer. I will make a large countersink around the hole in the washer (making sure it is nicely rounded and smooth). We are consideing lining the countersink with a thin hard rubber to spread the load a little more evenly over the knot.

Now we fit the length of pipe over the washer so that it is long enough to hide the knot (a marine sealant should be enough to attach it). Any water seeping down the dyneema will be caught in the pipe and you can remove the end cap whenever you wish to drain the water and inspect the knot or even replace the dyneema.

We will put some silicone sealant around the loop as it comes through the deck to reduce the amount of water that can seep down and stop debris slipping down and damaging the dyneema.

If the loop sticking out of the deck is quite long, I’ll put a whipping around it to hold the friction loop/thimble in place.

The results

We will now have a dyneema chainplate. It will be a lot stronger than the dyneema shroud connected to it (because it is made from the next size up dyneema). It will be a lot lighter than any other solution.

There is nothing to corrode, there is nothing we can’t keep spares for and nothing that we can’t replace at sea.

Compared to all the other ways of attaching a dyneema shroud there are fewer components so cheaper, lighter and keeps the lashing much lower to the deck for improved looks and less chance of chafe or snagging on anything.

For improved looks, UV protection and chafe protection we will make covers for the lashings. Probably rectangles of Sunbrella material held on with velcro and ties.

Tensioning

Both Rigging Doctor and Tula’s Endless Summer have videos on how to tension dyneema shrouds with just lashings. Colligo themselves don’t suggest that for boats over 30feet. However, both Wisdom and Adreneline are much longer than Vida and as we have a ketch rig our masts are a lot shorter. We might have a slight advantage as our low friction ring will be so close to the deck that we don’t have to worry so much about it being pulled out of alignment as we tension the lashing.

Summary

Compared to every other solution for improving our chainplates and connecting dyneema rigging this seems much cheaper and easier to fit. Plus it is lighter, stronger, tidier, and more functional than any other solution I’ve found. Finally, we can inspect it, maintain it and replace it ourselves, even at sea which is fantastic.

What do you think?

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