[Update] I have written a lot about Dyneema standing rigging so I now have a guide to it all in: Dyneema / Synthetic Rigging Summary[End Update]
Following my posts Chainplates. We are going for a radical dyneema option and Termination of Dyneema Shrouds. The most contentious issue? I’ve just watched a new video from Free Range Sailing “Our sailboat REBUILD begins ⛵💪 – Episode 157“
They are also fitting dyneema chainplates (so far, just for their backstays).
Their solution is a little different to ours. In part, that is because their backstay chainplates don’t have to be waterproof, as they go through the stern from outside to outside. So their solution of two holes and 3 loops of a lighter lashing line isn’t quite right for us. Our use of the softshackle overhand knot to create a loop is better for us as we only need one hole to fill and there is no need to balance the lengths of multiple loops of a lighter line.
However, their use of a HDPE tube to run the Dyneema through is very interesting in one obvious and one less obvious way.
In our Dyneema chainplate design we are making the hole through the deck by creating a thickened epoxy section of deck, drilling through it and then smoothing the epoxy to avoid chafe. If instead we fit a HDPE or possibly a UHMWPE tube though the thickened epoxy then it should reduce chafe even further. We could also have it stick up above the deck a little to avoid as much water running into it (and no danger of gravel on the deck getting into the Dyneema and cutting it. Having an up-stand will make it easier to seal and provide an attachment point for our chafe protection to fit to.
That got me thinking about some strips of RG1000 (basically recycled UHMWPE) that we bought to allow our solar panels to slide on a solar arch (which is currently on hold until we have launched and got a Hydrovane self steering fitted). Anyway RG1000/UHMWPE has some brilliant properties:
This engineering plastic can be machined into virtually anything, from small (low load)gears and bearings to huge sprockets-shapes that until recently were only possible with metals. It not only outperforms metal in abrasion applications, it’s also easier to machine and therefore cheaper. This versatile plastic can be milled, planed, sawed, drilled, and turned to create a huge variety of parts at a very competitive price. It possesses outstanding abrasion resistance, superior impact resistance, non-sticking and self-lubricating and excellent mechanical properties, even in cryogenic conditions.UHMWPE Rod
I’m therefore thinking that this would be a great way to make the our DIY cheeky tangs. If we started with a metre long length of 70mm diameter rod (costing under £60) we could make plenty of tangs for both masts and some spares. All we would need to fit them would be longer replacement bolts. I’m sure we could use the dremel to cut smooth guides for the shrouds. If we drill the hole for the bolt above the centre then they will stay the right way up (making some form of retention possible). We are currently leaning towards either 11 or 12mm Dyneema for the standing rigging (the Colligo Marine recommendation to replace 8mm 1×19 Stainless Wire is 11mm). Using a 70mm rod would allow us to create nice guides while keeping a bend ratio of more than 5:1 for maximum dyneema strength. It would also allow us to figure out way of doing line retention (maybe as simple as a light dyneema line across the top of the tang?). We would not need thimbles (a significant cost saving) and we could fit chafe/UV protection to the eye splices as we can size the groove guides to fit (finding closed thimbles for 12mm Dyneema that has a chafe sleeve is proving very hard and the only option I’ve found is 16mm which very oversized and very heavy (and that does mean that despite my misgivings we might need to use low friction rings at the lower end of the shrouds due to availability and weight).
Again, just like the chainplate solution these DIY tangs give us something we can easily inspect for wear and we can carry replacements that we can fit ourselves anywhere in the world.
I’m also suddenly realising that these rods might also be the solution we need for our bow roller. 🙂
So very, very happy with this.
Update, having read more I’m not entirely convinced that HDPE or UHMWPE will resist the static loads that a tang fitted to the mast needs to handle. I’m now thinking that 2 or 3 circles of G10 epoxied together might be a better option.