Build My Own FeedQC LAB: Do ropes need to rest between falls?
Before any piece of Black Diamond gear makes it on to the shelves, it spends months, sometimes years getting put through the wringer by our Director of Quality, Kolin Powick, and his team of Quality Assurance engineers. Through extensive and meticulous testing, both in the lab and in the field, KP and his team help ensure that you can count on your BD gear to be as durable, reliable and as strong as possible every time you head into the mountains or out to the crags. Our QC Lab posts aim to answer some of climbing's most common gear-related questions.
A few weeks ago I was at a local sport climbing cliff when one of my buddies came up and asked if I would mind him posing a "technical-sciency-engineering-like-type-question." He wanted to know why each fall he took while working his "proj" felt progressively more painful. I mentioned the old adage from Freedom of the Hills as well as numerous climbing magazines about letting your rope 'rest' between harsh falls, or even switching ends before trying that crux move again. This of course is to reduce the loads experienced, which can become especially critical when climbing on sketchy gear. The rope is the number-one piece that helps absorb energy in the system by elongating—and like stretching an elastic, it needs time to relax between loading scenarios so that it can absorb the maximum amount of energy the next time. My friend looked at me, obviously not having a clue what I was talking about.
He went on to ask if there was anything else he could do to reduce the pain his kidneys feel, and minimize the load the gear sees. My smartass answer was don't fall. No fall equals no load. But on top of that: ensure a dynamic belay, use a cord with high elongation, loosen your knot slightly after each fall (as the knot absorbs energy by tightening during a fall), let the rope rest between attempts, and use nylon slings and quickdraws which absorb a bit more energy than spectra/Dyneema (which doesn't stretch).
To try to put some numbers to it, myself and a few of the QA engineering guys and gals dreamt up a quick test plan and headed down to the drop tower for an afternoon. We figured we'd try to see what the difference in loads seen on the top piece of protection were when:
- performing successive drops as quickly as possible on the same rope
- resting the rope for 30 minutes between whippers
- loosening your knot between whippers
- letting the rope rest for 2 hours between whippers
- letting the rope rest for a full day between whippers
Typical disclaimer: This is not intended to be a full-blown, PhD-level thesis; rather it's a mini science experiment. There is obviously much much more that one could do to expand on this. These limited data points and one page summary are intended just to give climbers some food for thought. That's all.
Test Setup:
- BD drop tower (not UIAA legit)
- 80kg rigid steel mass
- STATIC belay (this is critical because though not typical or realistic, it is repeatable and allows us to isolate the variables we're interested in)
- 10.5mm rope (new)
- Chain used as quickdraw
- Typical lead fall setup scenario
- Fall factor: 0.26
Baseline Testing (rope resting 5 minutes between drops)
- Using one section of rope in the test setup described above, the mass was dropped, and load (at the top piece of gear) recorded.
- The mass was subsequently lifted back to the same height and dropped again at the 5 minute mark.
- This was repeated for 10 drops.
Loosening Knot
- As the loads are relatively harsh during this test setup, we found that we could not easily untie the knot, therefore we decided to place a carabiner within the figure-8 knot on the mass. This allowed the knot to be untied after each fall.
- As above, the mass was subsequently lifted back to the same height and dropped again at the 5 minute mark
- This was repeated for 10 drops
Rope resting 30 minutes between drops
- Same as the baseline testing above however the rope was allowed to rest 30 minutes between drops
- This was repeated for 10 drops
Rope resting 2 hours between drops
- Same as the baseline testing above however the rope was allowed to rest 2 hours between drops
- This was only repeated for one drop
Rope resting 24 hours between drops
- Same as the baseline testing above however the rope was allowed to rest 24 hours between drops
- This was only repeated for one drop
Results
Observations
- As expected, progressive drops resulted in increasing forces
- The largest increase was from the 1st to the 2nd drop as expected
- Loosening the knot after each fall reduced the load a bit, but not much
- Letting the rope rest 30 min between drops had a bigger effect at lowering loads than loosening the knot, but still not much
- Allowing the rope to rest for 2 hours and 24 hours had an even greater effect at reducing the loads on the 2nd drop, as expected
- Allowing the rope to rest 24 hours still resulted in a 2nd drop load of 11% greater than the first drop
Conclusion
Loosening your knot, or letting the rope rest prior to a fall reduces the impact load on the top piece of gear by a small amount. However, using a different rope for each burn or switching ends of the rope would provide a greater benefit. And of course the best way to keep the forces on the top piece of gear to a minimum is to not fall in the first place. As stated above, this is not an exhaustive study and there are many more tests and experiments we could perform if we weren't busy making the best climbing gear in the world. Such as:
"How long does it take the rope to relax to as-new condition, or will it ever?"
"What is the difference if you used a realistic, dynamic, belay instead of a static belay?"
"How about doing all of these tests with a skinnier rope?"
"What about using double ropes, or twins?"
"What if the rope is wet or frozen?"
"Does the effect of loosening your knot or letting the rope rest get greater in a more real world loading scenario?"
Maybe some day...
Climb safe,
KP
United States / English 
22 Apr 2012, 3:52PM
It seems to me that a problem with this test is THE USE OF A **NEW** ROPE for the baseline. Consider the (only one) 24hr rest impact force --not so far below that of a 2hr and even 1/2-hr rest. It seems to me that there is some initial, new elasticity that is lost upon a fall (even one this mild), and that for a better indication of practical results one should have as a baseline USED ropes (if "used" only means "new ropes conditioned by taking a few low-FF falls (and maybe a rappel or two?) in order to simulate typical in-use ropes"). I would add to this a mere 2min? rest --isn't that likely, as a practical duration (5min seems a little long)?
It would also be nice to see the same tests (given this basis, maybe do only a few more, with *conditioned* ropes) done for a lesser falling mass --to simulate the female and other lighter climbers, say, of 120#?
Thanks, *kN*
10 Feb 2012, 3:25PM
Very interesting, excellent testing.
I would be very interested in the concept of the initial break in, mentioned above.
As to the testing, is there a reason you don't connect the other end to a 100 kg lump of metel. That would absorbe a descent amount of the shock and simulate some of the dynamic impact, thus getting more realistic results that are repeatable.
6 Jan 2012, 8:41PM
Another great post! Thanks!
And one more 'such as' question would be if used ropes (not brand knew ones, but in good condition) would behave the same way as new ones in terms of recovery. Since they've already stretched a bit could they, potentially, loose some of their recovering ability? It would be interesting to compare the 2nd drop data between a brand new rope and a used one in good condition.
Cheers!
6 Jan 2012, 10:46AM
All these tests and comments seem related to sport climbing. As for bigwall climbing, how much effect does a second jugging on a rope have on its ability to absorb fall forces?
5 Jan 2012, 11:57AM
Another thing worth testing is shaking out the rope to see if that helps the strands "relax" back toward their original state.
Great stuff. You guys have cool jobs.
4 Jan 2012, 7:55PM
would a washing (for the rope not you) and proper drying put more dynamic qualities back into the rope?
4 Jan 2012, 7:27PM
Interesting to see some numbers from testing. Thanks for the post!
I've made a practice of "taking the stretch out" of a long toprope
with a bad landing where a low fall could result in ground impact due
to rope stretch. It does seem to make a notable difference in top-rope
fall distance simply by having the belayer and climber weight the rope
prior to beginning the climb. I suspect this initial low-load stretch
takes a bit more time to recover than the stretch that occurs during a
lead fall like you're testing here.
I question the validity and safety of actually recommending
"loosening" a knot post-fall (most of us realize what you mean, but
future Darwin Award winners are out there lurking). In this test
scenario which involves rigid bodies and a locked "belay", the
influence of this slippage appears to be measurable, but only
marginally. In the real world, things like rope slippage through the
belay device, lifting of the belayer, and the fact that a climber is
not a rigid steel mass all likely contribute much more significantly
to load reduction in the system.
4 Jan 2012, 7:11PM
I'm also curious to see if the rope ever fully recovers... since you were using a brand new rope, it seems possible that there is an initial 'break-in' that occurs after your first fall that is never recovered, but maybe once the rope is broken in, it recovers to its baseline level more quickly than 24 hours
4 Jan 2012, 2:19PM
I'd be willing to bet that in addition to rest time between falls, flexing the rope would soften future falls. If the mechanism for absorbing the fall energy includes the fibers of the rope sliding past each other a bit, then flexing might encourage the fibers to 'reset' back to their unstretched state. Of course, it's possible that if the fibers bond to each other in the stretched state, then the rope may never fully recover.
PS. I am a physicist who also rock climbs.
4 Jan 2012, 1:13PM
As others have said, the real question is does the rope ever recover ? One would think that after a 24 hour rest it would have recovered as much as possible. How about an N day test scenario... Not that it really matters but still, it would be interesting to see how the 8 fall UIAA test measures against the kidney load.... (hey, this anti-spam unlock is the ticket, kicks butt over the stupid typing in of worthless words that you can't read to begin with)
28 Dec 2011, 6:39PM
Super interesting read. Thanks for the writeup!
27 Dec 2011, 6:47AM
Stefan this might answer your question...or it may not.
http://dmmclimbing.com/knowledge/carabiners-and-potential-rope-damage/
25 Dec 2011, 3:30PM
I would also like to know if the rope ever fully recovers. That is the most important question. Please do a follow up.
22 Dec 2011, 9:56PM
I'm surprised -- the data seems to suggest that after a fall, the rope will still be affected after 24hrs? I'd be curious to see how long it takes the rope to fully recover. Thanks, this was interesting.
21 Dec 2011, 9:34PM
Excellent writeup; thank you very much.
Just to post another technical type follow-up question if you don't mind:
does the amount of time spent hanging on the rope after a drop effect the ropes recovery time?
21 Dec 2011, 1:44PM
I had an interesting circumstance this past summer taking repetitive whippers with no rest in between on a 9.4 rope with no dead spots. The the falls were only from about three or four feet above the bolt and with a very dynamic belay and a very clean fall, so my body didn't take any impact and I experienced no pain. The interesting thing was after about 6 or 7 whippers in 5 minutes the sheath of my rope completely ripped leaving a 6 foot section of just the core exposed. I suspect that was due to the heat of the quickdraw caused by the friction of the repetitive falls and summer heat (I was, however, climbing in the shade). I am curious if there are any studies you guys have done on this sort of situation?
Thanks
Stefan
21 Dec 2011, 9:12AM
Amazing. Yeah. The whole time I was wondering about your first "such as" question: relax to as-new condition, if ever - that would be a really cool question to ask - like do the drop once a week, or once a month. Good job.