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Strange rope question

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Wee Man View Drop Down
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Post Options Post Options   Quote Wee Man Quote  Post ReplyReply Direct Link To This Post Topic: Strange rope question
    Posted: 18 Mar 09 at 8:14pm

We have a job coming up in work using a lot of 6mm Dyneema.....3000m to be exact.

Does anyone know how much this is likely to stretch when loaded up to about a tonne & a half?

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Peaky View Drop Down
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Post Options Post Options   Quote Peaky Quote  Post ReplyReply Direct Link To This Post Posted: 18 Mar 09 at 8:25pm
About 1% (30m) I think, at those loads.  But don't take my word for it - check with the rope supplier.
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craiggo View Drop Down
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Post Options Post Options   Quote craiggo Quote  Post ReplyReply Direct Link To This Post Posted: 18 Mar 09 at 9:16pm
Peaky is right but be careful. What the supplier will quote is stretch but you must also consider the creep.

The individual strands will stretch STRETCH
The overall rope is made of many woven strands and as they straighten the rope appears to get longer CREEP

We fell foul of this when we used a hell of a lot of vectran in the Invictus C-class cat. The vectran hardly stretched but it crept a huge amount over the long lengths used to the point that we couldnt deflect the trailing edge when under load even though we'd pulled about 4ft through the cleat!

Edited by craiggo
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Roy Race View Drop Down
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Post Options Post Options   Quote Roy Race Quote  Post ReplyReply Direct Link To This Post Posted: 19 Mar 09 at 8:48am
There's an easy way to demonstrate this: Pull the core
out of a piece of spectra rope, go into your garage and
use it to suspend your lawnmower / road base / dumbells
or some other such heavy item from the garage ceiling
and about 1" off the ground. Come back the next day and
the item in question will be resting on the floor due to
creep in the rope.

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mike ellis View Drop Down
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Post Options Post Options   Quote mike ellis Quote  Post ReplyReply Direct Link To This Post Posted: 20 Mar 09 at 7:15pm
so which is the one that doesnt creep? and is it not easier just to use wire?
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craiggo View Drop Down
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Post Options Post Options   Quote craiggo Quote  Post ReplyReply Direct Link To This Post Posted: 20 Mar 09 at 8:36pm
They all creep including wire you just need to know how much, and this figure isnt always available.

Wetting rope then loading it up and leaving it to dry is often a good way of getting the creep out.
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Peter Rhodes View Drop Down
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Post Options Post Options   Quote Peter Rhodes Quote  Post ReplyReply Direct Link To This Post Posted: 04 Oct 09 at 6:11pm
I'm intreeged into what he wants a 3000 metre piece of high tech rope for!
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asterix View Drop Down
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Post Options Post Options   Quote asterix Quote  Post ReplyReply Direct Link To This Post Posted: 04 Oct 09 at 6:31pm
I imagine he's setting up a river ferry crossing using a winch
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bert View Drop Down
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Post Options Post Options   Quote bert Quote  Post ReplyReply Direct Link To This Post Posted: 05 Oct 09 at 12:19am

Originally posted by asterix

I imagine he's setting up a river ferry crossing using a winch

I`m having trouble now,why would you imagine that?

I for instance imagined a well attended group bondage party!



Edited by bert
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Lukepiewalker View Drop Down
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Post Options Post Options   Quote Lukepiewalker Quote  Post ReplyReply Direct Link To This Post Posted: 05 Oct 09 at 7:56am
Fundamental misunderstanding of Stretch and Creep I fear. These are both fundamental properties at a molecular level independent of rope construction. I digress...
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