Stretching 12 strand dyneema

[Roberto]

Hello,
I am making an emergency stay/shroud out of 12strand dyneema, breaking load about 10k daN.
On one end it will have a double Precourt/Colligo lashing fitting, but I would like to remove as much as possible the initial constructional stretch by pretensioning the rope; with soft shackles, splices or other small lengths etc I simply use the boat winches (power ratio 52), in this case the rope will be more than 20m long, YouTube shows several methods often involving US cars/trucks so big I could load three or four of my little renault on them.
Any idea how to apply a couple of times a load of about 2 tons to such a long rope, possibly keeping it for a couple of hours?
tia r.

ps I already have the rope, so no pre-stretched or heat treated dyneema option.

 

[B27]

When I wanted to test some spliced rope, we used a 20:1 leverage from a scaffold pole., there were some handy posts concreted into the ground,

I think with 12 strand rope, you might be wasting your time, because as soon as you remove the load and coil the rope, the strands will move out of their loaded positions?

 

[Roberto]

I think with 12 strand rope, you might be wasting your time, because as soon as you remove the load and coil the rope, the strands will move out of their loaded positions?

Maybe, I do not know I would like to try, a number of videos show the rope really gaining in stiffness, if keeping the rope with the hand parallel to the soil the stretched rope makes a sector of circle 20-30-50cm+ in radius, depending on thickness. Being for emergency stuff, it would be preferable if after fitted one should not think to re-tighten it again and again every half hour.

 

[AntarcticPilot]

I presume the amount by which it will stretch is small, in which case a jack might do it, or a Spanish Windlass. A suitable jack should manage a load of 2 tons .

 

[Chiara’s slave]

I presume the amount by which it will stretch is small, in which case a jack might do it, or a Spanish Windlass. A suitable jack should manage a load of 2 tons .

2 tons is about as much use as a sparrows fart on 10 ton breaking load dyneema.

In any case, it’s not stretch, but creep that could be an issue. You do need some means of tensioning it later if it’s standing rigging.

 

[DownWest]

Not Dyneema, but fellow a/c engineer used to test new control cables after he had swaged them by using the RSJ base rail of the hanger. He fitted a sliding fitting at one end and a fixed 'L' shaped tensioner at the other. Cable was fixed to the sliding bit and locked at the correct distance. The other end was attached to the 'L' on the short leg and the load applied to the long leg. Given the test load specified (multiplied by the lever difference) It was good enough for the CAA local surveyor. As you can imagine, they had to right..

Local friend recently rigged his new self build. I was happy to swage up the rigging as I had for the last one. But when he went off to buy the cable, they suggest Dyneema, and it was cheaper... They include the 'needles' in the package. Very easy and looks good (if a bit odd..)

 

[ChromeDome]

I'm using a Gleitstein 8mm Titanx Dyneema in a place where no stretch at all is wanted. And it actually is just like steel wire without the ability to kill someone in case of breaking, and other nasty properties.

 

[B27]

2 tons is about as much use as a sparrows fart on 10 ton breaking load dyneema.

In any case, it’s not stretch, but creep that could be an issue. You do need some means of tensioning it later if it’s standing rigging.

20% of breaking load, I think you'll get somewhere between 0.5% and 1% stretch.
That's between 10 and 20cm for this 20m rope.

But that's elastic stretch of the fibres, over and above the rope settling into its loaded state.

Then, as you say there is creep.
I have a dinghy with adjustable shrouds. I got rid of the dyneema from the highly loaded parts of the adjustment tackles. Creep meant I was forever trying to get the two sides the same. It's stable now those parts are Vectran.

Dyneema is wonderful stuff, but we still generally use stainless for standing rigging for good reasons.

 

[AMOREST]

Isn’t there some good technique involving tying one end to the bumper of the car, throwing it over the roof and hanging off the other end. - oh yes and asking the wife not to go shopping.

Sorry

 

[Plum]

Hello,
I am making an emergency stay/shroud out of 12strand dyneema, breaking load about 10k daN.
On one end it will have a double Precourt/Colligo lashing fitting, but I would like to remove as much as possible the initial constructional stretch by pretensioning the rope; with soft shackles, splices or other small lengths etc I simply use the boat winches (power ratio 52), in this case the rope will be more than 20m long, YouTube shows several methods often involving US cars/trucks so big I could load three or four of my little renault on them.
Any idea how to apply a couple of times a load of about 2 tons to such a long rope, possibly keeping it for a couple of hours?
tia r.

ps I already have the rope, so no pre-stretched or heat treated dyneema option.

I've used two cleats on the marina pontoon and a rigging screw. There is probably a cleat every 4m.

 

[Chiara’s slave]

20% of breaking load, I think you'll get somewhere between 0.5% and 1% stretch.
That's between 10 and 20cm for this 20m rope.

But that's elastic stretch of the fibres, over and above the rope settling into its loaded state.

Then, as you say there is creep.
I have a dinghy with adjustable shrouds. I got rid of the dyneema from the highly loaded parts of the adjustment tackles. Creep meant I was forever trying to get the two sides the same. It's stable now those parts are Vectran.

Dyneema is wonderful stuff, but we still generally use stainless for standing rigging for good reasons.

The main one for me is the obviousness of damage. I could use dyneema easily, my shrouds are tensioned by the backstays each time we go out, there’d be no creep. But I don’t, I’d rather check for failure in the conventional way. However, this is an emergency, so he just needs it to work. A pre stretch isn’t a terrible idea, but a mere 2 tons really isn’t going to do much. It will still be fully elastic at that load I think.

 

[Chiara’s slave]

I've used two cleats on the marina pontoon and a rigging screw. There is probably a cleat every 4m.

A couple of tons on the pontoon cleats, better be sure the structure is up to it!

 

[AMOREST]

How about dock side cleats. I don’t mean pontoon cleats - but quay side bollards. and a muscle box or multi turn block arrangement.

 

[AntarcticPilot]

2 tons is about as much use as a sparrows fart on 10 ton breaking load dyneema.

In any case, it’s not stretch, but creep that could be an issue. You do need some means of tensioning it later if it’s standing rigging.

You may well be right, but 2 tons was the load specified by the OP.

 

[Chiara’s slave]

You may well be right, but 2 tons was the load specified by the OP.

Yes, I’m merely pointing out it’s not enough, and not for long enough. The manufacturers use simultaneous heat, and longer term tension up to about 50% of breaking load. Don’t try that at home, kids. Or at least not if it’s 8mm or so SK99 equivalent.

 

[Slowboat35]

10k daN
Seriously?
WTF is that in English?
I realise that you and maybe some others can probably read that sort of gobbledegook readily, and I too could figure it out could I be bothered, but is it really necessary to showcase your command of such ridiculously clever-clever esoteric flummel rather than telling us what the breaking strain actually is in terms understandable to normal people, ie Kg or tons (even in tonnes if you really are that pedantic).
After all, it's not as if this might need to be measured in space or on a planet with different gravity to ours...

 

[AntarcticPilot]

Yes, I’m merely pointing out it’s not enough, and not for long enough. The manufacturers use simultaneous heat, and longer term tension up to about 50% of breaking load. Don’t try that at home, kids. Or at least not if it’s 8mm or so SK99 equivalent.

I'd imagine the amount of energy stored under those conditions would lead to "interesting" events if anything broke!

 

[B27]

10k daN
Seriously?
WTF is that in English?
I realise that you and maybe some others can probably read that sort of gobbledegook readily, and I too could figure it out could I be bothered, but is it really necessary to showcase your command of such ridiculously clever-clever esoteric flummel rather than telling us what the breaking strain actually is in terms understandable to normal people, ie Kg or tons (even in tonnes if you really are that pedantic).
After all, it's not as if this might need to be measured in space or on a planet with different gravity to ours...

daN means 'deca Newton'.
It's a lot like a kgf . That's a 'kilogram force, meaning the weight of a 1 kilogram mass in the earth's gravity.
The difference between mass and force is taught in all good primary schools.
daN is used a lot in rope specs.
You might want to look up what 'strain' means too.

 

[B27]

I'd imagine the amount of energy stored under those conditions would lead to "interesting" events if anything broke!

The less stretchy the rope, the less energy stored. (for the same tension).
Which is why hi-tech ropes are favoured by land rover nuts for winches etc.

 

[Roberto]

is it really necessary to showcase your command of such ridiculously clever-clever esoteric flummel rather than telling us what the breaking strain actually is in terms understandable to normal people, ie Kg or tons

Please address this to people who wrote 99% of technical details for stuff that has come into the consumer market during the past maybe 20 years.