Dyneema Rigging

[Daverw]

Been watching guide a few changing from wire to dyneema standing rigging. Just wondered how they are sizing it. As it’s so much stronger if you calculated based on the steel wire would you not have quite thin dyneema for example if your wire was 6mm etc

 

[Stemar]

Free Range Sailing on Youtube are doing this. Their dyneema looks to be a fair bit thicker than wire would be. Personally, I'd want it to be a fair bit stronger than wire because, as I understand it, dyneema is less elastic, so any peak shock loads are going to be higher.

There's also the question of abrasion resistance. You won't abrade steel with much less than a hacksaw. Dyneema's a bit different, so reserve strength would seem useful; it'd be a bit awkward if the genny sheets sawed through the shrouds tacking up a river.

 

[Daverw]

Yes I’d seen Free Range Sailing and Rigging Doctor and others but none seem to explain how they had sized the dyneema, I’ve seen some have outer covers on lower level of outer shroud, I assume for the genny sheets

 

[Topcat47]

I'm not a great fan of using exotic materials on cruising yachts. Replacing wire with Dyneema is not straightforward. Rigs are designed with a measure of compliance built in. The elasticity of the standing rigging is a consideration from the off. Replacing wire with Dyneema will place an additional bending moment on the mast during tacks and, more importantly, gibes. In a modern racing yacht designed with rigid standing rigging in mind, it's probably no big deal, but in cruising yachts, the replacement of an elastic rope with an inelastic one without re-calculating the rig loads is probably not a good idea.

 

[V1701]

A guy along the pontoon from me has just done this on his Albin Vega, looks somewhere between 8 & 10mm so yes bigger than SS wire would be. He's done it in such a way that it's possible to adjust tension, some of them have bottle screws, others done a few different ways to see what works best, it's impressive work and I think you have to give some credit to the early adopters...

 

[Daverw]

I do think the use of low friction rings and cord to tension is ironic as it’s going back in time but is simple, not seen anyone keep the ringing screws but sounds obvious to do so.

 

[Daverw]

Also not see anyone detail how they measured the tension, do rig gauges still work. They all seem to do it by feel or correct twang

 

[TernVI]

I've had dinghies with rope tackles adjusting the shrouds.
Dyneema really is generally not very good. It creeps, it takes ages to settle to its eventual length.
Mostly, we gave up on dyneema and use Vectran, which has performed well over the last 10 years or so.
I appreciate there are many different variants of 'dyneema' and 'spectra'. Maybe there is one better for shrouds.....

As for oversizing the rigging, you might want to think carefully about that, if a rig has been designed and developed with the elasticity of s/s, then reducing the stretch using thick dyneema might have unforeseen consequences. As well as the drag factor of the proverbial bingo hall....

Also be careful about chafe. Dyneema is 'chafe resistant' not 'chafe proof'.

 

[Daverw]

I suspect all the boats I’ve seen looking at this and converting have all been originally designed for ss wire so would interesting to see over a little time what happens, also how do the insurance companies view this upgrade path.

 

[Bobc]

Personally I think it's a very bad idea on a cruising yacht.

 

[DoubleEnder]

My boat had wire running back stays which I changed initially to Vectran but now dyneema. Vectran is susceptible to UV. I oversize the dyneema because the 4mm which would be amply strong just looks frighteningly thin. And to take account of chafe.
good stuff. Easy to splice, light weight and doesn’t gouge the boom or wear holes in the sail

 

[thinwater]

I suggest visiting the Colligo web site. There is a lot more to know and more differences than will be sorted out in a thread.
Colligo Marine

Perhaps the biggest difference is that Dyneema is sized for creep, not strength. This approach allows for UV . It will still be lighter and far more fatiuge resistant. But ONLY if you get the details right.

No, a standard tension gauge will not be quite accurate, but you can measure tension by deflection. Again, the spec points will be different, because the stretch is different.

 

[Daverw]

Thinwater, brilliant loads of info

 

[rgarside]

Free Range Sailing on Youtube are doing this. Their dyneema looks to be a fair bit thicker than wire would be. Personally, I'd want it to be a fair bit stronger than wire because, as I understand it, dyneema is less elastic, so any peak shock loads are going to be higher.

There's also the question of abrasion resistance. You won't abrade steel with much less than a hacksaw. Dyneema's a bit different, so reserve strength would seem useful; it'd be a bit awkward if the genny sheets sawed through the shrouds tacking up a river.

For the same diameter, Dyneema is MORE elastic than wire rope. It is less elastic than many other fibre ropes. To get similar elasticity to a wire rope, a larger diameter dyneema rope would be required.

 

[TernVI]

For the same diameter, Dyneema is MORE elastic than wire rope. It is less elastic than many other fibre ropes. To get similar elasticity to a wire rope, a larger diameter dyneema rope would be required.

But not hugely larger.
Tensile modulus of stainless steel is in the 180GPa region. Dyneema SK75 113GPa.
But that's ss as a material, not a wire rope which will stretch more as the strands move.
Likewise ropes of dyneema and other fibres initially seem to stretch a lot as the strands take up position.

High tech rigs may have straight metal rod rigging, or parallel filament fibre which changes this behaviour.

 

[mattp]

Does anyone know of any professional rigger here in the U.K. that can install Dyneema?
From what I understand it’s best to use Dyneema Dux which is pre stretched and then use a chafe cover over the top. There is a couple on YouTube who replaced theirs about a year ago, Tula’s endless summer

pretty in depth and also used Coligo Marine as mentioned earlier...I’m pretty sold on it if not just loosing all the weight up top.

 

[mattp]

..

 

[mattp]

Personally I think it's a very bad idea on a cruising yacht.

I’m sure people said the exact same thing when fibre glass appeared in the 60’s...people are suspicious of change. what about when they started using SS rope instead of the old fashioned rope with block and tackle?