Dyneema Shroud and Chainplate progress

We haven’t been able to get to the boat this week, Jane has been ill and I had a seminar on my day off.

But we have had a delivery from Jimmy Green Marine. That means I’ve been able to do some practice splicing. As a result we can see how the Shrouds and Chainplates are going to work.

The first image shows my very first Dyneema Eye Splice. It isn’t very good, but that isn’t a surprise. I’m going to make sure I practice lots before the first real splice 🙂 This is a Möbius Brummel splice (which means it is locked in two directions with a long straight bury. To see how to do this splice see this video from Rigging Doctor. As Dyneema is slippery you need to bury a tail that is 72 times the diameter of the line in length. Our Mizzen Shrouds are 9mm (for reasoning behind that choice see The mysteries of sizing Dyneema standing rigging). For simplicity and an overabundance of caution I decided on 720mm of bury (I think I ended up with about 680mm on this first attempt). The double locking stops the splice from slipping but another key to the strength is tapering the buried portion (so there are no kinks caused by sudden changes in direction for the fibres), my taper ended up being 360mm long. I’ve put a low friction ring in this eye splice which is what will be used at the bottom of the shroud. At the top another eye splice will be fitted to the custom tangs I’m going to make.

Now we have my first attempt to make a chainplate loop. This is also very simple. It is essentially a soft shackle with overhand knot (I tried this one without the soft shackle eye but will put that in the next one). A video on how to make this is here. As I didn’t make the soft shackle eye I’ve put a simple whipping to hold the low friction ring. This started as 3m (3000mm) of 9mm Dyneema and has ended up being about 300mm sticking out above the overhand knot. This uses 2 simple Brummel splices which the loop goes through so that they go around the overhand know,. As the buried tail reaches all the way upto the whipping it can’t slip as it is going all through the knot. Nor can the knot slip because the tails are these eye splices held by the main loop.

This one is only pulled hand tight at the moment. I’m going to have to make some kind of rig to properly tension these to get the knots tight before I install them.

To install them the chainplate is basically a big backing plate with a hole going through it and the deck. The loop (without the low friction ring) is push through the hole from below. The knot can’t fit through the hole in the backing plate. The low friction ring is inserted and now you have a secure point to attach the shroud to.

I’m guessing I can reduce the length of the original line to 2.5m and the buries to 600mm without any significant strength loss. That would place the low friction ring at about 200mm above the deck which is just about what I am looking for. Rremember that Dyneema rigging is sized for stretch not strength, so even with the splice it should be more than 3 times stronger than the stainless steel it replaces. I will do some strength testing but don’t think I can affordably or safely achieve a 10,000kg pull.

Here they are together. They get joined by a 6mm dyneema lashing, that loops between the two low friction rings. When you pull on the tail of the lashing it gives you a mechanical advantage (more will be needed to get enough tension),

Neither of these were difficult to make. I managed both in a couple of hours. I’ve ordered some extra splicing tools and special dyneema knife and scissors (it is very hard to cut!!). My next practices will be on 6mm Dyneema which is for the guardrails/lifelines and the shroud lashings.

We had another delivery today, some Mild Steel Angle Iron which I am hoping to use to repair the platform on my drill press. I have plans to use that to help make the tangs for the top end of the shrouds.

7 thoughts on “Dyneema Shroud and Chainplate progress

  1. Andy May 15, 2021 / 12:49 pm

    Hi David, enjoying watching your progress now lockdown has made things a bit easier. You may have seen this but an interesting blog on Dyneema rigging and this week they talked about cover loops. Using the Dyneema cover rather than the braided core for loops. https://info.upffront.com/blog/loop-cover-shackles-a-new-twist-on-soft-shackles

    I know what you mean about cutting Dyneema, interested to see what you purchase to cut it.

    Regards,

    Andy
    Rival 32 Corrival

    Liked by 1 person

    • dave42w May 15, 2021 / 3:09 pm

      Hi Andy,
      Yes I saw that article. At the moment, our plans need only 4 dyneema sizes (12mm main rigging; 9mm mizzen rigging; 6mm lifelines and rigging tension lashings; 2.5mm lifeline lashing, rigging seizing and frapping knots).
      I found my Selma Fids quite easily snagged the Dyneema strands (where the slot gap joint in the rolled tube is). As I have a lot of splices to do I think it worth experimenting to get good tools now rather than later. So I’ve ordered a set of D-Splicer needles and their Dyneema knife and scissors (I find a knife is easier for cutting the whole rope and scissors easier for the tapering). Ordered from RopesDirect.co.uk
      Dave

      Like

  2. Mike Norton June 16, 2021 / 11:08 pm

    Tensioning dead eye.
    What about pulling up with a halyard?
    Could be set up to pull inline with each stay.
    Multi part if needed.
    Would pull mast in same direction as tension possibly decreasing the amount of pull needed?

    Liked by 1 person

    • dave42w June 17, 2021 / 12:05 am

      My current plan is to hoist a block and tackle with the halyard. The tail will be lead to a primary winch.
      I agree this should make alignment simple.
      It should make it possible to work on two shrouds, one per side at the same time to even tension.

      Like

  3. Jocko July 3, 2021 / 6:31 pm

    I purchased a 4” Ceramic knife at the Dollar Store for haha 2 dollars, and it cuts the tough slippery stuff just fine.

    Try one on your ropes first, then pick up half a dozen for the Rigging Kit, & Galley, and you will never be without. ChaChing!

    Like

    • dave42w July 3, 2021 / 8:47 pm

      I’ve found the scissors a lot easier to use for strands. Not been browsing in shops for 17 months now.

      Like

Leave a Reply to Mike Norton Cancel reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s

This site uses Akismet to reduce spam. Learn how your comment data is processed.