Author Topic: Rope lengths in the dales....  (Read 1111 times)

Offline docfunk

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Rope lengths in the dales....
« on: October 15, 2019, 10:24:15 am »
Hi all, im returning to caving after a bit of a break in both time and body haha
anyhooo im looking at getting a spool of rope since what i have is 10 ish years old and my favourite caving is vertical! if i get 200m what lengths do you guys recommend me chopping it in to?
nominal lengths as ill work out shrinkage or pre shrink it before chopping.... 

Offline MJenkinson

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Re: Rope lengths in the dales....
« Reply #1 on: October 15, 2019, 10:25:52 am »

Offline MarkS

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Offline docfunk

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Re: Rope lengths in the dales....
« Reply #3 on: October 15, 2019, 10:54:36 am »
Ha! Cheers I couldn’t search on my phone for some reason.

Offline Maj

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Re: Rope lengths in the dales....
« Reply #4 on: October 15, 2019, 10:55:43 am »
......... if i get 200m....... 

I assume you will buy a complete drum of rope.
Something to also bear in mind is when the rope comes off the drum it will probably relax/shrink before you wash it.
 
I purchased a couple of drums a few years ago to split between various friends. I measured the whole drum before cutting expecting there to be a few extra metres, but alas no it measured 200m. I measured and marked (twice, if not three times) the whole 200m before cutting into the required lengths.
After distributing it became apparent the cut lengths were a little shorter from when they were cut. I can't recall by how much or how long it took.
I guess when rope comes of the production line it is under slight tension when wound onto the drum and hence will relax when taken off the drum.
If you have the time and space it would be interesting to know how much a 200m length shrinks over say a week or two after just removing from the drum. It would require measuring as it comes off the drum to get a definitive start length and then again a while later.

Maj.
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Offline Cave_Troll

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Re: Rope lengths in the dales....
« Reply #5 on: October 15, 2019, 11:39:27 am »
unreel it into a large bucket of water
soak
remove and dry
soak
remove and dry

think about cutting

If i do this to a 200m reel and chop 150m of shrunk rope off, i expect to have about 35-40m rope left.

Offline rhyst

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Re: Rope lengths in the dales....
« Reply #6 on: October 15, 2019, 12:00:17 pm »
I made this:

https://docs.google.com/spreadsheets/d/1aEoitnEc7UERcPYyW_PfxcQI1KjKsxdRSEDtf4HDBiI/edit?usp=sharing

The second sheet has all the rope lengths from NFTFH and some relatively recent edition of the CNCC rigging guides.

The first sheet has a histogram of the lengths and a calculation of the amount of rope you need to always have the correct lengths for a cave. If you want your ropes to never be more than 5m longer than the pitch then you need 1.3km of rope. If you can live with your ropes never being more than 10m longer than the pitch then you only need 800m of rope!

I think it's a harder problem to go from a length of rope and work out the optimal lengths to cut to, so clearly the solution is to buy another kilometre of rope!

Probably most useful is the histogram which gives you an idea that you may want a few 20s/30s and one or two big ropes.

Offline Chocolate fireguard

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Re: Rope lengths in the dales....
« Reply #7 on: October 15, 2019, 01:07:37 pm »
Hello docfunk.
Do you have plans for your old rope?
If not, and you want to get rid of it, I can offer some of it a new home.
Ideally there would be up to 100m of it and it would be 10 to 11mm diameter, stiff as a board and tying a knot in it would be hard work.
It would not be used as an abseil rope.

I am in Sheffield.

Offline alastairgott

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Re: Rope lengths in the dales....
« Reply #8 on: October 15, 2019, 06:39:08 pm »
Scraps and Maps, Scraps and Maps, Squawk, pretty polly...

Offline Maj

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Re: Rope lengths in the dales....
« Reply #9 on: October 15, 2019, 10:34:31 pm »
unreel it into a large bucket of water
soak
remove and dry
soak
remove and dry

think about cutting

If i do this to a 200m reel and chop 150m of shrunk rope off, i expect to have about 35-40m rope left.


Curious to know how much shrinkage there is after coming off the drum but before soaking.

Maj.
Confucius say "War does not determine who is right, war determine who is left."

Offline Leclused

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Re: Rope lengths in the dales....
« Reply #10 on: October 16, 2019, 09:44:16 am »
unreel it into a large bucket of water
soak
remove and dry
soak
remove and dry

think about cutting

If i do this to a 200m reel and chop 150m of shrunk rope off, i expect to have about 35-40m rope left.


Curious to know how much shrinkage there is after coming off the drum but before soaking.

Maj.

When you don't soak the rope and start using it it will shrink over time bit by bit.

I always soak new ropes before cutting, my experience is that I have the following shrinking

Edelrid : 8-5%
Petzl : 5%

I think the difference can be explained due to the fact that petzl is not delivered on a drum and is therefore not stretched during the upwinding on a drum what is well the case for edelrid.



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Offline andrewmc

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Re: Rope lengths in the dales....
« Reply #11 on: October 16, 2019, 10:01:03 am »
The rope will continue to shrink even after washing and drying (even after several cycles), so I always cut my ropes pre-soak and leave 10-15%. Once you have washed it, you don't know what fraction of the total shrinkage has occurred, whereas shrinkage is only sometimes over 10%.

Obviously on shorter ropes this is less important; for 5% unexpected shrinkage if your 10m rope ends up 50cm shorter than you expected you can probably still manage to get off the pitch but if your 100m rope is 5m short you are buggered! So I will happily cut shorter ropes for 10% shrinkage and try and get closer to 15% for longer ropes.

Offline Ian Ball

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Re: Rope lengths in the dales....
« Reply #12 on: October 16, 2019, 02:44:19 pm »
I've a feeling that a 95m rope used on a 100m pitch would be fine getting off at the bottom, but disappointingly difficulty to reach the rope after it is untensioned!


Offline mikem

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Re: Rope lengths in the dales....
« Reply #13 on: October 16, 2019, 04:56:22 pm »
I've a feeling that a 95m rope used on a 100m pitch would be fine getting off at the bottom, but disappointingly difficulty to reach the rope after it is untensioned!
Just clip it to a ground anchor, so nobody else can descend, but at least you can get back up!  ;)

Offline alastairgott

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Re: Rope lengths in the dales....
« Reply #14 on: October 17, 2019, 07:19:57 am »
carry 40kg of lead for tying to the bottom, more efficient than carrying 5m more rope.  :smartass:
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