Rope Shrinkage

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Rope Shrinkage

Postby Scott McCrea » Nov 29, 2005 8:59 am

In the Bobbin bunches a sheath thread, the process for pre-shrinking ropes by soaking them in water before their first use is discussed. I would like to learn more about this. Anyone know how much one can expect a rope to shrink? I'm sure it depends on the rope type, construction and materials. Anyone got any data?

Anyone have any brand new rope they want to soak? If you do, let's do an experiment. Measure it before you soak and then after. Let's make our own data.
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Postby ian mckenzie » Nov 29, 2005 12:15 pm

Google says anywhere between 5 and 10%, which is consistent with my experience.
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Postby cob » Nov 29, 2005 8:42 pm

ian mckenzie wrote:Google says anywhere between 5 and 10%, which is consistent with my experience.


No offense Ian...

but I am not convinced that nylon shrinks in water alone (heat? yes)

Truly... I would like to see some data on this. Got a specific link?

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Postby caverdoc » Nov 29, 2005 9:39 pm

I seem to recall something in one of the "On Rope"editions about hydrophilic bonding between the nylon molecules. Of course, all this talk of water and shrinkage reminds me of a certain "Seinfeld"episode...
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Postby cob » Nov 29, 2005 10:27 pm

Yah.... I saw that one too... except he was talking about COLD water... I think I mentioned wet heat... which has the opposite affect...

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Postby RescueMan » Nov 29, 2005 10:28 pm

cob wrote:I am not convinced that nylon shrinks in water alone (heat? yes) Got a specific link?


A wet nylon rope acts much the same as a hot ( 140-175 F / 60-80 C) nylon rope, because water lowers the Tg or glass transition temperature dramatically.

Actually nylon rope lengthens by 3-5% when wet and then shortens to 4-8% less than new when it's dried.

For a very interesting study of the changes in strength and energy-absorption in wet and frozen ropes, see:

http://www.alpineclubofcanada.ca/services/safety/wet%20ropes%20text.rtf

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Postby potholer » Nov 30, 2005 7:00 am

An excellent link, RescueMan - thanks.

Do static ropes lengthen in a similar way to dynamic ropes when wet, or is some of the lengthening down to the construction as well as the material?
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Postby RescueMan » Nov 30, 2005 8:18 am

potholer wrote:Do static ropes lengthen in a similar way to dynamic ropes when wet, or is some of the lengthening down to the construction as well as the material?


Because it involves a change of the mechanical properties of the nylon at the molecular level, the effect would be the same with either dynamic or static ropes.

This is why it is often suggested to soak and dry any new rope before use - it "sets" the rope to its proper length and tightens the sheath onto the core.

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Postby itabot » Nov 30, 2005 8:46 am

RescueMan wrote:it "sets" the rope to its proper length and tightens the sheath onto the core.

- Robert


When I soaked one of my ropes...it seemed like the sheath seperated from the core. Its tight, now that its dry. Brand new rope!


I WAS IN THE POOL! :wink:
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soaking the rope

Postby Dangerjudy » Nov 30, 2005 8:52 am

well, that's a new one on me - I've never heard of people soaking new ropes. I've been thinking about getting some rope - do most of y'all soak your new ropes? :?:
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Re: soaking the rope

Postby Scott McCrea » Nov 30, 2005 11:16 am

Dangerjudy wrote:well, that's a new one on me - I've never heard of people soaking new ropes. I've been thinking about getting some rope - do most of y'all soak your new ropes? :?:

Hey Judy,

When you get some new rope, measure it before and after you soak it. See how much difference there is. 8)
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Postby RescueMan » Nov 30, 2005 11:17 am

itabot wrote:When I soaked one of my ropes...it seemed like the sheath seperated from the core. Its tight, now that its dry. Brand new rope!


Yes, as I said, nylon rope stretches (becomes more amorphous) when wet and then shrinks beyond its new state when dried.

This is why wet nylon ropes lose as much as 30% of their static strength, and dry treatments don't seem to make much difference (with the possible exception of Sterling "dry core" ropes).

For those worried about sheath slipppage, you might want to check out Petzl's new Vector lifeline, made by Samson Rope. It is a nylon core with a polyester sheath that is "fused" to the core.

"The Petzl Vectorâ„¢ Performance Lifeline and Rescue Cord sets new standard for rope. In a partnership with Samson Rope Technologies, Petzl and Samson have developed a new rope using a proprietary technique called Fusion Processâ„¢. This technique incorporates a polyester sheath over a nylon core that work together to provide supple handling, greatly reduced sheath slippage, ability to retain shape, and superior abrasion resistance. The core has continuous nylon fibres, which give the rope is amazing strength, while the 32 carrier polyester sheath fibres protect the core against abrasion and help to main the rounded shape. The Vector's shape retention helps provide amazingly consistent interface with all mechanical rope devices and prusiks."

http://store.karstsports.com/pevero7wh.html

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Postby itabot » Nov 30, 2005 8:44 pm

I see! :) Thanks for the info Rescue Man. It was my understanding that the sheath should never seperate from the core. That leads to my next question. Since its a natural thing for nylon to stretch and seperate from the core when wet, what if you're in a wet cave?
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Postby RescueMan » Nov 30, 2005 9:05 pm

itabot wrote:It was my understanding that the sheath should never seperate from the core. Since its a natural thing for nylon to stretch and seperate from the core when wet, what if you're in a wet cave?


There are a lot of "shoulds" that don't go with "never".

I didn't say that it's either "natural" or common for the sheath to slip, and slightly wet ropes don't behave the same as thoroughly saturated ropes.

In my experience, some ropes are more prone to sheath slippage than others. It seems to have to do with both the fineness of the sheath weave (thickness and number of carriers), and the tension settings on the weaving machine when the rope was fabricated.

My first experience with sheath slippage was with a Blue Water climbing rope with an extremely supple sheath - great handling and knotting, but one good rappel and the sheath bunched up. Blue Water, to their credit, sent me a new rope which seemed to perform better (in fact, I think I still have it 15 years later).

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Postby ian mckenzie » Nov 30, 2005 10:22 pm

cob wrote:No offense Ian...but I am not convinced that nylon shrinks in water alone ... I would like to see some data on this. Got a specific link?
None taken. Nylon does not shrink - but nylon rope does. http://www.bealplanet.com/notices/2005/ ... =1&lang=us
"before first use, soak the rope and leave to dry slowly. It will shrink by about 5 %. Take this into account when calculating required lengths."
http://web.ukonline.co.uk/andy.mccarron/cncc/cor.htm
"When first soaked all ropes, particularly nylon ropes, can be expected to shrink by various amounts up to 8 or 10%"
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