Rope shrinkage

[Over the Hill]

Having recently purchased a rope at 33 mts to allow for shrinkage to 30 mts (not measured in front of me) and then got it wet I decided to measure it that day on getting home. Came out at 28.8 Mts. I wonder how this stacks up with other cavers experiences? 

 

[Mark Wright]

Ropes will shrink at different levels depending on the manufacturer. Typically a rope will shrink by around 5% when it first gets wet. Before first use all ropes should be conditioned by soaking in water and then allowing to dry naturally. This process removes the lubricants used in manufacture and is usually clearly visible in the water container used for soaking by a milky solution. Further shrinkage will then take place through use. You can expect further shrinkage of <10% so +/- 15% shrinkage in total.

Mark

 

[ah147]

I use, almost exclusively, gleistein geostatic. I cut it expecting 10% shrinkage. In a year they're still the length I cut em, from 400m of rope total,  Id say that's pretty good.


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[Leclused]

10% shrinkage is average.

There is a how-to prepare your new rope video avaliable here : http://cavingnews.com/20150602-watch-how-to-prepare-a-new-rope-for-caving

 

[Huge]

Having recently sorted the clubs new ropes and allowing 10% for shrinkage, I found that the whole 10% was lost in the initial soaking  and pulling through a descended. I'll be allowing 15% for shrinkage in the future!

 

[Fulk]

I find that, depending on the type of rope it is, rope will typically shrink anything from 5 or 6% to 9 or 10% on initial soaking and drying, and will continue to shrink more slowly for years ? up to 12+%, so allowing more that 10% extra is probably a good idea.

(I think that this topic has been covered elsewhere on the forum, but I couldn't find it; it would be surprising if it hadn't.)

 

[Bottlebank]

I agree with the last comments, more or less. I've started allowing an initial 10% plus another 10% over time, so nearer 20%. Before a recent trip we measured a few of ours and they were all 10% down on marked lengths.

 

[paul]

I find that, depending on the type of rope it is, rope will typically shrink anything from 5 or 6% to 9 or 10% on initial soaking and drying, and will continue to shrink more slowly for years ? up to 12+%, so allowing more that 10% extra is probably a good idea.

(I think that this topic has been covered elsewhere on the forum, but I couldn't find it; it would be surprising if it hadn't.)

One of the many previous topics on the subject: http://ukcaving.com/board/index.php?topic=7234.0

 

[Over the Hill]

Thanks for your views so far. My PHD caving mate is thinking of carrying out a few tests of his own at his University.

 

[Maj]

Thanks for your views so far. My PHD caving mate is thinking of carrying out a few tests of his own at his University.

Can I also suggest measuring a length of rope as it comes off a drum for the first time. Then let the rope settle off the drum for few days and then re-measure.
I believe that at the end of the manufacturing process the rope is under tension when wound onto a drum and will remain slightly stretched on the drum until it is unwound (ie when purchased), at which point it relaxes and shrinks in length.
I'd be curious to know by how much, but not curious enough to buy another drum (200m) of rope.

Maj.

 

[Fulk]

I'd be curious to know by how much, but not curious enough to buy another drum (200m) of rope.

Maj.

Tight wad  :tease:

 

[Bob Mehew]

For what it is worth, I have found measuring rope accurately is quite difficult.  The standard places a 3m sample of the rope under a small tension (10kg) in order to get a set length.  But clearly the self weight makes this approach unusable for long lengths (plus finding some where to hang a 100m rope, other than the pitch you want to descend).  In theory the shop measuring system will give a reasonable value but I have been worried about how hard one pulls it through the machine and whether that might make a difference.  You could weigh the rope and use the manufacturer's quoted weight per metre value but as has been mentioned the first wash removes the manufacturing oils which will change the weight.  Plus the manufacturer's value is for a conditioned rope (24 hr at 10% humidity followed by 72 hr at 65% at 20C).  15% seems a better value to me.