Author Topic: Wet rope  (Read 907 times)

Offline mikem

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Wet rope
« on: November 23, 2018, 10:16:29 am »
Previous discussions seem to have concentrated on abseiling - there is "only" a 30% loss of strength in static situations, so less than most knots (don't know if any testing of wet knots has been done) & unlikely to cause a problem (provided an anchor doesn't fail):
https://ukcaving.com/board/index.php?topic=11886.0

However, dynamic strength can reduce by 70%, even when just damp! & number of falls before failure reduces. So, cowstails & lead climbing ropes, or failed anchors are much more of a issue & the rope should be retired after holding a major fall in the wet. Fortunately the strength returns once dried sensibly:
https://www.climbing.com/skills/wet-rope-myths-debunked/

Mike

Offline andrewmc

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Re: Wet rope
« Reply #1 on: November 23, 2018, 11:34:46 am »
Fortunately major falls are extremely rare... I've never seen a big fall climbing (and by big I mean FF>1, not a harmless 10m whipper on a big sport route). Probably happens more often to cowstails when people fall off rigging, but I'm sure those people know about it...
I believe it still remains true that ropes have (almost) never failed due to overloading in normal circumstances, so I'm not too bothered.

Presumably the issue is that a wet rope has less springiness
(something to do with internal friction maybe?) so a higher impact force for the same fall.

And most likely the force to break the rope is still enough to break you (so the issue isn't necessarily the rope failing but that the impact force is greater). Are there tests comparing peak impact force for cowstails fall type drops with wet vs dry ropes?
« Last Edit: November 23, 2018, 11:43:12 am by andrewmc »

Offline Mark Wright

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Re: Wet rope
« Reply #2 on: November 23, 2018, 01:02:44 pm »
I remember being told the issue was one of the water inside the knotted rope not being able to extract itself quick enough when a dynamic force was applied thus significantly reducing the ropes ultimate strength.

I thought the information was in the attached HSE document but having looked at it again it isn't. It's an interesting document nonetheless. 

http://www.hse.gov.uk/research/crr_pdf/2001/crr01364.pdf

Im working away from home at the moment but will see if I have the information when I get home next week and post it here.

Mark

Offline Bob Mehew

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Re: Wet rope
« Reply #3 on: November 23, 2018, 07:54:45 pm »
I have done very little research into wet v dry ropes, save to note that wet ropes are less strong in terms of number of drops survived compared to dry.  I don't have to hand but vaguely recall a paper on the topic presented at a conference in Turin in the early 2000's to that effect. 

However, what is clear to me is the caver's wetting (and more so the post trip wash) does tend to remove the oils used in the manufacture of the rope.  I suspect these oils do help lubricate the yarn within the rope and thus reduce the tendency for some yarns to be overloaded rather than share their load out.  There was also an esoteric paper by Steve King on the impact of using detergent fabric conditioners on rope.  (This followed up on an American practice when using a washing machine to clean rope.)

What I have found is that even small usage of a rope down a cave reduces the number of drops survived.  So I am suspicious of the cited Climbing reference.  Where is the evidence?

Static work on knotted ropes (i.e. a slow pull rather than the dynamic 'hit' of arresting a falling test mass) does show knots much reduce strength.  The HSE reference Mark cites is very good on a wide range of topics including this one, see page 18.  The HSE paper only touches on wetness when considering the effect of rust on rope strength (minimal if at all, see page 20).
 


Offline ChrisJC

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Re: Wet rope
« Reply #4 on: November 23, 2018, 08:22:53 pm »
Of course a dry rope melts if you abseil too fast or are too fat. Not sure if that's worse than the strength reduction caused by water...

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Offline PeteHall

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Re: Wet rope
« Reply #5 on: November 23, 2018, 08:58:35 pm »
I always wet my ropes for this reason and shall continue to do so.

If, as has been suggested, it is reduced slip between fibres that causes the weakening, occasional use of fabric conditioner would surely outweigh any effect of wet vs fry?
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Offline mikem

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Re: Wet rope
« Reply #6 on: November 23, 2018, 09:01:01 pm »
It only melts if you stop part way. The opening statement actually says abseiling on wet ropes isn't the issue...

Bob, could it be the mud that causes permanent damage & thus not such a problem for climbers?

Mike
« Last Edit: November 23, 2018, 09:11:18 pm by mikem »

Offline droid

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Re: Wet rope
« Reply #7 on: November 23, 2018, 09:12:10 pm »
Back to ladders  :lol: :lol:
No longer 'Exceptionally antagonistic' 'Deliberately inflammatory'

Offline Bob Mehew

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Re: Wet rope
« Reply #8 on: November 23, 2018, 10:09:31 pm »
Bob, could it be the mud that causes permanent damage & thus not such a problem for climbers?
The only information I have is that the interior of many ropes I have seen don't look dirty (nor do their sheaths).  So I don't really have any evidence to base an opinion on.  I suppose one might be able to take a new and a used rope, open it up and do some energy-dispersive X-ray spectroscopy to see if one can see the presence of silicon or calcium (from micro grit) in the used but not in the new sample.  Done in conjunction with a scanning electron microscope, one might then see the bits of grit in their locations which would support your conjecture.  Perhaps an off the wall idea for someone who has access to the kit?

Offline PeteHall

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Re: Wet rope
« Reply #9 on: November 23, 2018, 10:14:38 pm »
Perhaps an off the wall idea for someone who has access to the kit?

I'll ask my wife what she thinks... Certainly no shortage of muddy old rope to spare and I even have a length of new in the garage...

Would this sort of thing be best combined with drop tests on the samples from the same bit of rope?
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Offline Bob Mehew

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Re: Wet rope
« Reply #10 on: November 24, 2018, 07:53:46 pm »
I'll ask my wife what she thinks... Certainly no shortage of muddy old rope to spare and I even have a length of new in the garage...

Would this sort of thing be best combined with drop tests on the samples from the same bit of rope?

It would be a 'starter for 10' if we could do a new rope, 'untouched', new rope 'conditioned', new rope post condition and aftr use in muddy state set of drop tests to show differences (I guess say 15m required of each state of rope to give us 5 samples for the statistics) plus an analysis of new, conditioned and muddy.  However the results would only show a correlation, not causation.

But in the first instance just confirming that new rope does not has calcium or silicon present in lumps would be a useful precursor.

Slight cautionary note - I am tied up with other matters for a while.

Offline mikem

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Re: Wet rope
« Reply #11 on: November 25, 2018, 07:44:34 am »
I guess there are also more minerals in cave water that may crystallise out within the rope when drying.

Mike

Online Kenilworth

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Re: Wet rope
« Reply #12 on: November 25, 2018, 01:51:35 pm »
Maybe it's fun to argue technicalities, but this another of those practically inconsequential matters. Work through every test, every paper, every scenario, and come out yonside, it'll still be that wet, dry, slimed, encrusted... unimportant.





Offline Bob Mehew

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Re: Wet rope
« Reply #13 on: November 25, 2018, 04:03:00 pm »
I guess there are also more minerals in cave water that may crystallise out within the rope when drying.

Mike
My thought was a Scaning Electron Microscope would show up the bits of grit where as crystallised out minerals would be more evenly spread.  Think of peanut butter over a nutty bread.

Offline mikem

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Re: Wet rope
« Reply #14 on: November 25, 2018, 04:34:26 pm »
I agree that in abseiling it makes very little difference, however, during fall arrest cavers should be aware that shock loadings on their body may be considerably higher than in a comparable outdoor climbing scenario...

Research showing that dried climbing rope recovers its properties - suggesting something else is affecting those used by cavers (plus, understanding what's going on could help lead to better rope designs):
http://www.singingrock.com/wet-and-icy-ropes-may-be-dangerous

Mike

Online Kenilworth

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Re: Wet rope
« Reply #15 on: November 25, 2018, 10:36:35 pm »
Research showing that dried climbing rope recovers its properties - suggesting something else is affecting those used by cavers (plus, understanding what's going on could help lead to better rope designs).

There is no need for better rope designs.


Offline Ian Ball

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Re: Wet rope
« Reply #16 on: November 25, 2018, 11:29:15 pm »
but is there desire?

Offline alastairgott

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Re: Wet rope
« Reply #17 on: November 26, 2018, 01:41:00 am »
suggesting something else is affecting those used by cavers (plus, understanding what's going on could help lead to better rope designs):

The answers probably as clear as mud.  :coffee:

Offline mikem

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Re: Wet rope
« Reply #18 on: November 26, 2018, 08:35:55 am »
There is no need for better rope designs.
Manufacturers will always look for something they can sell over other companies.

Answer may well be mud, but as Bob says he's never noticed any inside the sheath it could also be crystallisation, or could be because they are testing dynamic ropes, whilst we are looking at static (static aren't affected as much, so similar loss of performance will be more noticeable than in dynamics).

Mike
« Last Edit: November 26, 2018, 08:49:30 am by mikem »