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bloodyhands


Feb 5, 2006, 9:08 PM
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Ok, there’ve been a lot of threads discussing the safety of a “sliding x” anchor equalizing system. Everybody knows the big problem with the “sliding x”; if one anchor fails, the remaining anchor will be severely shock loaded.

The most common way to reduce the possible shock load (other than using a different equalizing system) is to tie an overhand knot in both legs. If one anchor blows, the rope bearing biner will drop only a short distance onto the overhand knot.

My question: Has anyone given thought to how much relative strength the sling has with the biner loaded onto the overhand knot in this configuration? It seems to me like it might be significantly weaker, but I hesitate to abandon my favorite equalizing system.

Your thoughts, please.


landgolier


Feb 5, 2006, 10:05 PM
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it's pretty generally agreed that you can't do much to a standard sling with knots that can reduce its strength by more than 50%, which still leaves you well north of 10kN


pico23


Feb 9, 2006, 10:36 PM
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Ok, there’ve been a lot of threads discussing the safety of a “sliding x” anchor equalizing system. Everybody knows the big problem with the “sliding x”; if one anchor fails, the remaining anchor will be severely shock loaded.

The most common way to reduce the possible shock load (other than using a different equalizing system) is to tie an overhand knot in both legs. If one anchor blows, the rope bearing biner will drop only a short distance onto the overhand knot.

My question: Has anyone given thought to how much relative strength the sling has with the biner loaded onto the overhand knot in this configuration? It seems to me like it might be significantly weaker, but I hesitate to abandon my favorite equalizing system.

Your thoughts, please.

IMO, if I was building an anchor and I thought that one of the two pieces was bound to fail I would not use the sliding X.

I use the sliding X when attached to bomber pieces because it is simple and fast.

Any tied knot reduces rope and sling strenght but the shock load on your gear from an already extended sling even with the overhand would concern me more.


vivalargo


Feb 10, 2006, 8:32 AM
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Funny this should come along just now. I'm just finishing redoing the anchor books into one big anchor building omnibus. We're basically done --all that's left is a bit of editing, and incorporating a slew of drop tests we did with Sterling Ropes (conducted by America's leading drop/test dude, Jim Ewing, with statistical analysis by trad master Dr. Larry Hamilton and climber/fitness model/criminology professor, the esteemd "Crimpgirl," Dr. Callie Rennisson).

The tests were to determine, once and for all, which system was better at load sharing when sustaining a dynamic fall (Factor 1 for our testing)--the Cordelette, or the Sliding X. Both rigging systems were tested when rigged to vertical and horizontally oriented anchor points. In the vertical configuration--as you find in a crack--the rigging systems have unequal sized legs; in the horizontal configured anchor (as found, for instance, with bolts placed side to side on top of a sport climb), the legs are as close to equal as they could be tied.

Moreover, each set up was tested with several diameters of high tensile strength cord and webbing (Dyneema, Technora, Spectra, et al), as well as with old style nylon cord and webbing.

It is still too early to release the results, but I can say right now that there is a significant difference in load sharing performance between the two systems, and much that has been written about the cordelette's equalizing capacities is strictly untrue.

More later. I'm just eyeballing the graphs I got from Jim, Larry and Crimpy. At least now we finally know what's up with these systems, and that's a real good thing.

JL


trenchdigger


Feb 10, 2006, 8:53 AM
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Ok, there’ve been a lot of threads discussing the safety of a “sliding x” anchor equalizing system. Everybody knows the big problem with the “sliding x”; if one anchor fails, the remaining anchor will be severely shock loaded.

Shockloading the big problem? I was always bothered more by the lack of redundancy in the sling.


elvislegs


Feb 10, 2006, 8:54 AM
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Funny this should come along just now. I'm just finishing redoing the anchor books into one big anchor building omnibus. We're basically done --all that's left is a bit of editing, and incorporating a slew of drop tests we did with Sterling Ropes (conducted by America's leading drop/test dude, Jim Ewing, with statistical analysis by trad master Dr. Larry Hamilton and climber/fitness model/criminology professor, the esteemd "Crimpgirl," Dr. Callie Rennisson).

The tests were to determine, once and for all, which system was better at load sharing when sustaining a dynamic fall (Factor 1 for our testing)--the Cordelette, or the Sliding X. Both rigging systems were tested when rigged to vertical and horizontally oriented anchor points. In the vertical configuration--as you find in a crack--the rigging systems have unequal sized legs; in the horizontal configured anchor (as found, for instance, with bolts placed side to side on top of a sport climb), the legs are as close to equal as they could be tied.

Moreover, each set up was tested with several diameters of high tensile strength cord and webbing (Dyneema, Technora, Spectra, et al), as well as with old style nylon cord and webbing.

It is still too early to release the results, but I can say right now that there is a significant difference in load sharing performance between the two systems, and much that has been written about the cordelette's equalizing capacities is strictly untrue.

More later. I'm just eyeballing the graphs I got from Jim, Larry and Crimpy. At least now we finally know what's up with these systems, and that's a real good thing.

JL

well... THAT was one of the most useful things i've ever seen posted on the web. straight from the horses mouth. looking forward to the new publication.



shit. did i just call largo a horse?


bloodyhands


Feb 10, 2006, 9:11 AM
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Ok, there’ve been a lot of threads discussing the safety of a “sliding x” anchor equalizing system. Everybody knows the big problem with the “sliding x”; if one anchor fails, the remaining anchor will be severely shock loaded.

Shockloading the big problem? I was always bothered more by the lack of redundancy in the sling.

The improved sliding x does offer a bit of redundancy; even if part of the sling fails ( provided that it fails above the knot) the rope will still be caught. If the the sling fails below the knot, you are indeed, thoroughly f**ked. But this never bothered me; my anchor sling's in excellent condition.


trenchdigger


Feb 10, 2006, 9:22 AM
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Ok, there’ve been a lot of threads discussing the safety of a “sliding x” anchor equalizing system. Everybody knows the big problem with the “sliding x”; if one anchor fails, the remaining anchor will be severely shock loaded.

Shockloading the big problem? I was always bothered more by the lack of redundancy in the sling.

The improved sliding x does offer a bit of redundancy; even if part of the sling fails ( provided that it fails above the knot) the rope will still be caught. If the the sling fails below the knot, you are indeed, thoroughly f**ked. But this never bothered me; my anchor sling's in excellent condition.

True, and it depends a lot on the anchor and if abrasion/cut resistance is a factor.


healyje


Feb 10, 2006, 9:29 AM
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In our anchor replacement project all the anchors are the heavy Metolius Rap anchors with 3/8"x3 3/4" SS bolts and dressed out with tandem X slings threaded through two Fixe 50kn SS rap rings. We opted for both quality and redundancy to insure long term safety in spite of the costs given the amount of traffic this [trad] crag receives.


wings


Feb 10, 2006, 9:31 AM
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Ok, there’ve been a lot of threads discussing the safety of a “sliding x” anchor equalizing system. Everybody knows the big problem with the “sliding x”; if one anchor fails, the remaining anchor will be severely shock loaded.

Shockloading the big problem? I was always bothered more by the lack of redundancy in the sling.

Then use two slings.

- Seyil


greenketch


Feb 10, 2006, 9:40 AM
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Largo, thanks for a great post. I'm looking forward to the new book.

Just a bit of thinking out loud here. Did you do any testing where part of the anchor failed? The OP brings up a good point regarding the shockload potential vs the limited equalization. I'm trying to imagine a test rig that would have one bomber anchor point and one that could be rigged to fail at less than the applied force. Thus a test could be done that simulated a partial failure each trial. Have you done anything like that?


maldaly


Feb 10, 2006, 9:52 AM
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Most of the time I set up and EQ anchor I use a sliding x. I have ants in my pants and can't seem to stay in one place long enough to keep anthing with at "master" knot even remotely equalized. I do worry about lack of redundancy with a sliding x so I always tie directly into one of the anchors with my lead rope as well.
Mal


vivalargo


Feb 10, 2006, 10:05 AM
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Largo, thanks for a great post. I'm looking forward to the new book.

Just a bit of thinking out loud here. Did you do any testing where part of the anchor failed? The OP brings up a good point regarding the shockload potential vs the limited equalization. I'm trying to imagine a test rig that would have one bomber anchor point and one that could be rigged to fail at less than the applied force. Thus a test could be done that simulated a partial failure each trial. Have you done anything like that?

That sounds like an easy question to answer, but it's not. Yes, Jim started doing some tests like this just to see what figures came up. It's easy to rig: you just tie off one anchor with a piece of sling that gives out at, say, 1,000 pounds, and you do a drop that generates 1,200 pounds.

What makes this tricky is that so long as you are climbing with a dynamic rope that is belayed, true "shock loading" never really occurs owing to the stretch in the rope and, most importantly, rope slip through the belay device. In other words, when a Sliding X is configured with limiter knots, the few inches of extension will never produce a true shock load, or anything even approaching that kind of stress.

A genuine shock load will only occur in those instances reflected in Duane Raleigh's recent tests for Rock and Ice, say, when someone is tied off to an anchor with a short shank of high tensile cord. He climbs a few feet above the anchor and falls. Here, you have true shock loading, where biners blow apart and anchors rip out because there's no rope slip at the belay device, no stretch in the rope, no human body to absorb loading, et al.

This doesn't happen when a placement blows out on a Sliding X or a Cordelette, owing to flex and give in other parts of the system during loading.

JL


pastprime


Feb 10, 2006, 10:39 AM
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I have long suspected, but kept it to myself for lack of proof, that the concerns over shock loading when one leg of an equalized anchor failed, were not to be ignored, but were probably overblown.

My hunch has been that the realistic way to see this situation is that the extra force on the remaining good piece, when the piece it is paired with fails, is probably not hugely more than the extra force generated by whatever amount the fall distance is increased, which usually isn't much.

In other words, say you have 2 pieces sliding x'ed together with a 24" sling. A 10 foot fall occurs, loading the pieces, and one pulls, the other holds. Rather than this now becoming some huge catastrophe, this just means the leader has now taken an 11 foot fall, and the remaining good piece now feels that appropriate load.

There has been a lot of conjecture about how much the impact absorption abilities of the rope would have been used up in pulling out the first piece, and this is of course affected by whether the first piece pulled very easily, or almost held until pulling at the final few pounds of impact.
The remaining impact absorption of the rope is also going to be very dependent on how much rope of the ropes ultimate shock absorption ability was used up in the first hit. If the first hit almost stopped the climber, but that was still a low fall factor fall, the rope would, I expect, still have a lot more absorption left. If the first hit was a high fall factor, and the piece almost, but not quite, held, the rope's give is much more likely to have been used up.

In the case where the ropes ability to absorb was almost used up, that would also usually mean it had already come about as close to stopping the fall as it could in any case; then the faller continues 1 more foot than they would have had the X not failed.

I'm wide open here. Is this close to what the data shows, or is this wacked?


greenketch


Feb 10, 2006, 10:54 AM
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Largo, thanks for a great post. I'm looking forward to the new book.

Just a bit of thinking out loud here. Did you do any testing where part of the anchor failed? The OP brings up a good point regarding the shockload potential vs the limited equalization. I'm trying to imagine a test rig that would have one bomber anchor point and one that could be rigged to fail at less than the applied force. Thus a test could be done that simulated a partial failure each trial. Have you done anything like that?

That sounds like an easy question to answer, but it's not. Yes, Jim started doing some tests like this just to see what figures came up. It's easy to rig: you just tie off one anchor with a piece of sling that gives out at, say, 1,000 pounds, and you do a drop that generates 1,200 pounds.

What makes this tricky is that so long as you are climbing with a dynamic rope that is belayed, true "shock loading" never really occurs owing to the stretch in the rope and, most importantly, rope slip through the belay device. In other words, when a Sliding X is configured with limiter knots, the few inches of extension will never produce a true shock load, or anything even approaching that kind of stress.

A genuine shock load will only occur in those instances reflected in Duane Raleigh's recent tests for Rock and Ice, say, when someone is tied off to an anchor with a short shank of high tensile cord. He climbs a few feet above the anchor and falls. Here, you have true shock loading, where biners blow apart and anchors rip out because there's no rope slip at the belay device, no stretch in the rope, no human body to absorb loading, et al.

This doesn't happen when a placement blows out on a Sliding X or a Cordelette, owing to flex and give in other parts of the system during loading.

JL

Thanks again, You stated exactly what I would suspect and basically the test that I would propose as well. I was more interested to see if there was data to suport what the diagnostics would suggest. My belief is that there is a significant reduction in force prior to the piece pulling (unless it is really bad) and the that in the minor extension that occurs only minimal energy is regained.


Partner cracklover


Feb 10, 2006, 11:12 AM
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Largo, thanks for a great post. I'm looking forward to the new book.

Just a bit of thinking out loud here. Did you do any testing where part of the anchor failed? The OP brings up a good point regarding the shockload potential vs the limited equalization. I'm trying to imagine a test rig that would have one bomber anchor point and one that could be rigged to fail at less than the applied force. Thus a test could be done that simulated a partial failure each trial. Have you done anything like that?

I'm extremely interested in this question, too. Basically, there are two sides to this argument. Those who say:

1 - When a piece rips from a two-point anchor, and a sliding-x extends, the remaining piece will feel a huge force due to having to catch that foot-long fall on a rope that's already stretched out.

versus those who say:

2 - This "shock load" is nothing more than a one foot fall on however much rope is out. It is more or less equivalent to increasing the fall distance by a foot. Do your fall-factor calculation with one more foot of fall distance - that's all that's happening. Although it may feel less than this due to the fact that one foot's worth of tension in the rope is released first.

GO


vivalargo


Feb 10, 2006, 11:21 AM
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Largo, thanks for a great post. I'm looking forward to the new book.

Just a bit of thinking out loud here. Did you do any testing where part of the anchor failed? The OP brings up a good point regarding the shockload potential vs the limited equalization. I'm trying to imagine a test rig that would have one bomber anchor point and one that could be rigged to fail at less than the applied force. Thus a test could be done that simulated a partial failure each trial. Have you done anything like that?

That sounds like an easy question to answer, but it's not. Yes, Jim started doing some tests like this just to see what figures came up. It's easy to rig: you just tie off one anchor with a piece of sling that gives out at, say, 1,000 pounds, and you do a drop that generates 1,200 pounds.

What makes this tricky is that so long as you are climbing with a dynamic rope that is belayed, true "shock loading" never really occurs owing to the stretch in the rope and, most importantly, rope slip through the belay device. In other words, when a Sliding X is configured with limiter knots, the few inches of extension will never produce a true shock load, or anything even approaching that kind of stress.

A genuine shock load will only occur in those instances reflected in Duane Raleigh's recent tests for Rock and Ice, say, when someone is tied off to an anchor with a short shank of high tensile cord. He climbs a few feet above the anchor and falls. Here, you have true shock loading, where biners blow apart and anchors rip out because there's no rope slip at the belay device, no stretch in the rope, no human body to absorb loading, et al.

This doesn't happen when a placement blows out on a Sliding X or a Cordelette, owing to flex and give in other parts of the system during loading.

JL

Thanks again, You stated exactly what I would suspect and basically the test that I would propose as well. I was more interested to see if there was data to suport what the diagnostics would suggest. My belief is that there is a significant reduction in force prior to the piece pulling (unless it is really bad) and the that in the minor extension that occurs only minimal energy is regained.

I'm still putting all of this together--with a lot of help from the statistical experts--but understand that it's rope slippage through the belay device, and the absorbtion qualities of the human body, that provide the crucial flex and give in the system. That much said, the testing suggests that the difference in loading between a six and a seven foot fall are no significant because of several factors. One, mass doesn't accellerate that fast, and two, there is some initial (and very variable) load reduction with one piece rips out and the load is then caught on by the rest of the system--sort of like a Yates screamer. Of course the amount of reduction will vary according to the placemet, but again, when limiter knots are used on the Sliding X, the extension is mere inches, and the load increase here is almost nill.

In other words, the phobia about extension in the Sliding X (with limiter knots) producing "shock loading," or for that matter, ANY significant increase in loading, is looking almost certainly like another anchoring myth.

I promise more on this later.

JL


pastprime


Feb 10, 2006, 12:05 PM
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So I haven't really been alone in all the world in thinking the terrors of shockloading were exageratted in these situations?

Gee, I feel all warm and fuzzy.


Can we hug?


pastprime


Feb 10, 2006, 12:15 PM
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Vivalargo: Any idea when the book may be on the shelves? Is it a updated version of one of your existing books, or something new entirely?


healyje


Feb 10, 2006, 12:36 PM
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John,

I assume when you're talking about shockloading "myths" you are talking about run-of-the-mill multi-pitch climbs as opposed to the demands and accidental loads that can be placed on big wall anchors by blowing ledges, hauling, and flying pigs?


vivalargo


Feb 10, 2006, 1:47 PM
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What I'm saying here is that it was thought by some that the Sliding X (with limiter knots) was a poor choice because if one piece in the system failed the extension in the system would produce a "shock load" on the remaining piece(s). So far, testing says otherwise.

The business of what a true shock load is, and why, is a very long discussion.

JL


roy_hinkley_jr


Feb 10, 2006, 1:55 PM
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What I'm saying here is that it was thought by some that the Sliding X (with limiter knots) was a poor choice

Did you test without the limiter knots too? That's how the Sliding-X is most commonly used. How about when the load comes from a different angle than anticipated when using the 'lette?


bloodyhands


Feb 10, 2006, 1:57 PM
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but how strong are those limiter knots?


healyje


Feb 10, 2006, 1:57 PM
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So I can take from that you make no distinction about the use of the anchor relative to any reality of shock loading?


jklap


Feb 10, 2006, 2:02 PM
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Ok, it seems like there an assumption that the shockload of an anchor failing (sliding x, no extension limitiation) is identical to a fall of an additional foot? I don't think they are the same at all-- when the anchor fails the rope is already stretched out from the initial fall-- so instead of 30%ish of elongation it's more like 5%ish-- which means if the anchors were equalized in the first place the remaining anchor is going to take a shock larger then it did the first time (if not equalized, and assuming the failed anchor had taken the majority of the previous load, then the remaining anchor is taking a load much higher then previously). In addition, the directional load on the anchor is going to change (it's might have been fine with the previous direction of pull, but now you just wiggled it around). If you were using a longish sling (say 120cm) to get the best equalization angle, it also means the extension is two feet, not one.

Given that the directional change is going to happen no matter what, I think I would try to limit the amount of new load the single anchor is about to take--- especially since it's now the last piece protecting my butt.

Ok-- what am I missing or screwed up?

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