Where to buy a short length of DM20 dyneema

Whitelighter

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I need a short (1.5 - 2m) length of DM20 dyneema.
DM20 as I understand that is the product with the lease stretch.

6mm ideally.

I’ve googked around and I can find loads of info but no stockists, just people who want to do all my rigging.

eBay full of SK78 but that has more stretch which I really want to avoid.
 

GHA

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Whitelighter

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What is creep?

It’s a connector between my tender crane and the rib
I need something I can connect to the Rib with some slack then shorten as I lower the crane into the lift position before locking off and lifting the Rib

Rib is 220kg so sonething thin, with high breaking limit and as close to zero stretch is called for.
I just don’t need very much of it
 

lw395

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Dinghy chandlers sell most things by the metre.
You could look at Vectran?

The 'stretch' you get in many applications with these ropes is more than the fibre spec suggests, because as you tension the rope, the fibres move around to fnd the shortest path.
So you seem to get some stretch with not much load, then the actual fibre modulus kicks in.
6mm is fairly stout, don't forget that whatever the rope is pulling against will compress or bend.
 

GHA

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What is creep?

It’s a connector between my tender crane and the rib
I need something I can connect to the Rib with some slack then shorten as I lower the crane into the lift position before locking off and lifting the Rib

Rib is 220kg so sonething thin, with high breaking limit and as close to zero stretch is called for.
I just don’t need very much of it

Creep is like very slow stretch, but dyneema is such crazy strong stuff you couldn't actually measure either stretch or creep on a 2m length. d12 max or d20 look way over the top for what you're after, though d12 max is really chafe resistant so might be worth the few extra quid. Easy to splice as well. 5mm is 3800Kg average breaking load from memory. Buy a few metres and treat yourself to some soft shackles :cool:

Don't quite understand "then shorten" ? - you want something adjustable?
 

lw395

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What is creep?

It’s a connector between my tender crane and the rib
I need something I can connect to the Rib with some slack then shorten as I lower the crane into the lift position before locking off and lifting the Rib

Rib is 220kg so sonething thin, with high breaking limit and as close to zero stretch is called for.
I just don’t need very much of it

I can't quite picture it. It sounds like the stretch you'd expect from 'any old dyneema' of say 6mm, which will have plenty of safety fatcor, shoud not be a problem?
 

Whitelighter

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It’s difficult to explain.
Basically I need to attach the end of the line to the Rib lift point with it running through the crane.
As the crane is then lowered the line is pulled through with no tension on
The line is then locked off (probably with a clutch)
The crane then lifts bringing the Rib with it.

The reason we need it this way is recovering the Rib from moving water without a slack line (ie metal to metal) is not easy with even small movement in the rib.
 

dunedin

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What is creep?

It’s a connector between my tender crane and the rib
I need something I can connect to the Rib with some slack then shorten as I lower the crane into the lift position before locking off and lifting the Rib

Rib is 220kg so sonething thin, with high breaking limit and as close to zero stretch is called for.
I just don’t need very much of it

For that application I don’t think ultra low stretch rope would be ideal. The load is quite low, but with no stretch the shock loads will be higher on the dinghy lift points.
Also for shortening and putting in a clutch stopper, you probably want as thick as the other fittings will permit to allow ease of handling and best grip in the clutch.
We use a basic dynema for the the Y-strops permanently attached to the dinghy - primarily as more leg friendly than wire, and the dyneema was a cast off end from a dinghy racer. But we use standard braid rope for the hoists.
 

lw395

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I would suspect that a bit of give from a nice bit of pre-stretch polyester might be a good thing when the rib is bouncing a bit and you're taking up the slack?
Dyneema and kevlar etc can feel an awful lot like 'metal to metal' when a wave drops something like RIB a few inches onto a line that goes tight with a bang.
 

Whitelighter

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There won’t be any hauling on the dyneema to lift the rib
The crane lowers enough, but I don’t want to do it with hands in the way.
Plenty of bounce in the lift strips the dyneema will attach to.

I’ll give the suppliers a call tomorrow - maybe just order some SK78 from eBay and see if that works
 

Daydream believer

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It must be worrying for yacht chandlers trying to survive when they see questions like the one that the OP has posted.
The obvious answer has to be -" Well walk into a yacht chandlers"
But it seems that the internet has become the norm that it probably has clouded the OP's mind to the fact that such places actually exist- or did once!!!
The fact that one can walk into such places is the reason that I try my utmost NOT to use the internet for some items so that i can continue to use the facility- Ancient concept that it may be
 

Ingwe

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I am not really sure that you want DM20 - or any form of uncovered dyneema for the application you are looking at as it is extremely difficult to tie knots in it so you will need it to be spliced and the other issue is that I have serious doubts about any clutch or jammer reliably holding uncovered dyneema long term as it is just so slippery.

For what you want to do I would get a clutch that can hold 6 to 8mm line and for now buy yourself a few metres of 8mm covered DSK99 dyneema (eg LIROS 8mm Control XTR) which will probably stretch about the same as the 6mm you were after but you will be able to tie normal knots in it and it will work perfectly in the clutches. You can then go out to the boat and play around with setting it up how you want to being sure that it will definitely work, if you then decide that you still really want the thinner line you can measure everything accurately so that when you come home you can order a piece of uncovered 6mm with an eye splice in one end to attach tot the tender and an area of cover spliced over it so that it holds well in the clutch.
 

andypag

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DM20 is actually slightly more elastic than sk78, but it creeps less. In either case, while I still don't really understand your application, it seems to me that either would be over engineering. Nothing wrong with that mind.

1591586113958.png

Unfortunately it doesn't show DM20. But it does give you an idea of the percentage elasticity you can expect from any of the Dyneemas. 0.6% over a 2m length will be 1.2cm. I don't remember what this load was but probably much more than 6mm line picking up a ~300kg dinghy.
 

zoidberg

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I'm advised that specialist rigger Katie at 'Rope Locker' is the go-to person for this kind of task, and is likely to have SK99 and other specialist fibres on hand. They have premises at Dawlish and Exeter. Buy Rope Online, UK rope supplier

It's my understanding that 'Creep' is a form of permanent elongation experienced in HDPE and other high-tech ropes when loaded PERMANENTLY.... as in standing rigging.

'Stretch', by comparison, occurs when a rope is loaded - as in halyards, mainsheets, guys - then unloaded, when it returns to its original length-dimension.
 
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