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Improved sliding x: Is it really safer?
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tradklime


Feb 10, 2006, 3:18 PM
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Ok-- what am I missing or screwed up?

Other dynamic properties of the system. Rope slipping through the belay device, belayers body absorbing some energy, etc. I'll add friction in the sliding-x itself as it equalizes, lots of variables.

Just using your numbers, if a 6 foot fall creates 30% elongation of the rope, what is the difference if an andditional 1 ft. fall only creates an additional 5% elongation? Its proportionally the same.

I think the real point is that a static (semi) fall of a few inches, as the sliding -x slides to the limiting knot, generates negligible force.

Couple that with the fact that cordelettes are rarely, if ever, equalized...

Thanks to John for initiating some testing to help dispell some of the myths.


jklap


Feb 10, 2006, 3:33 PM
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I'm guessing the initial fall would have taken up most of the slack (ie though the belay device) so that wouldn't reduce the shock much.

Sorry--- what I meant by the elongation of the rope is the initial fall causes a larger elongation than a soon after second fall-- ie the rope becomes stretched, doesn't have time to recover and won't stretch as much the second time--- hence a higher shockload on the remaining anchor.


In reply to:
I think the real point is that a static (semi) fall of a few inches, as the sliding -x slides to the limiting knot, generates negligible force.

Ah, this is my point--- what I was questioning was the statement that the shockload of an anchor failing without a limiting knot is no different then that of a fall + a foot (ie the length of the sling slipping)


roy_hinkley_jr


Feb 10, 2006, 3:37 PM
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belayers body absorbing some energy

The Italian Alpine Club disspelled that one a while ago at their drop tower. Same with tightening of the tie-in knot absorbing energy. Both are so minimal they're inconsequential.

In reply to:
Thanks to John for initiating some testing to help dispell some of the myths.

Yep, good effort! Though it's a shame our own alpine club is pretty worthless for things like this.


vivalargo


Feb 10, 2006, 3:40 PM
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Re: Improved sliding x: Is it really safer? [In reply to]
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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?

I'm not sure what you're asking, and my sense of it is that you already have an answer in your head--and you should simply state that answer and we can work from there.

To briefly answer the question of off angle loading on a cordelett, what happens (according to the testing) is that almost the entire load is taken by the shortest arm of the cordelette.

Also, the notion that an initial load, if it blows out one arm or a sliding x, will then quickly multiply to a higher weight when it drops onto the next arm--be it 4 inches or 1 foot--is something not happening in the actual drop tests. And these tests have load capturing devices accurate to one kilo.

That much said, the million dollar question was, and still is--what rigging strategy, the Cordelette, or the Sliding X, works best at achieving equalization between anchor points rigged in vertical, horizontal, and other axis'. And so far one of these rigs is losing by an overwhelming statistical margin. It's not even close.

JL

PS: Hi Ron. The I-talian tests were a little confusing if you look at them closely. For instance, when a load is straight down on a belayer lashed snug to a belay anchor, body flex/abosrbsion is minimal. But when a leader falls above, and the belayer is pulled UPWARDS, the body acts as a counter weight to the sudden loading and then it plays a role in load absorbtion, though not remotely as much as the rope slippage at the belay device.


jklap


Feb 10, 2006, 4:00 PM
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Also, the notion that an initial load, if it blows out one arm or a sliding x, will then quickly multiply to a higher weight when it drops onto the next arm--be it 4 inches or 1 foot--is something not happening in the actual drop tests. And these tests have load capturing devices accurate to one kilo.

Ok, I'm confused--- if you have two anchors, each joined together with a sling and say a 40 degree angle between them, then they each share a part of the initial load. Correct? How is it then that if one of those fails that the other anchor doesn't take the full load plus some for the initial shockloading part? I'm not questioning the results of the tests, just questioning if I'm understanding it correctly..

-J


healyje


Feb 10, 2006, 4:05 PM
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John,

Actually I don't at all!

I'm just curious if you consider shock loading a "myth" in general. That, along with normal multi-pitch, you don't need to worry about the X shocking in a hauling accident or in a case of a heavy bag slipping off a ledge, or maybe a portaledge getting slammed up and down in a storm. I can't tell whether, from your description of the role of belaying in all this, you mean just climbing as opposed to also including the forces involved with all the other various big wall activities.

I'm asking because you're the one that's spent endless hours on all those wall anchors of varying quality over the years - I haven't but would still like to and am trying to figure out if it's worth it to do all the Chongo/PTPP major construction projects with cordalette powerpoints, etc. or should you just throw in a couple of X's and call it good...


antiqued


Feb 10, 2006, 4:15 PM
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Re: Improved sliding x: Is it really safer? [In reply to]
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Ok, I'm confused--- if you have two anchors, each joined together with a sling and say a 40 degree angle between them, then they each share a part of the initial load. Correct? How is it then that if one of those fails that the other anchor doesn't take the full load plus some for the initial shockloading part? I'm not questioning the results of the tests, just questioning if I'm understanding it correctly..

-J

I think he means that the load on the remaining single anchor is approximately equal to the sum of the loads on the original two anchors, and is not significantly raised by the further extension or by the 'hardening' of the rope.

It follows from the equations of stiffness - if any leg of a structure connected in series is soft, then the whole series is soft - so as long as a significant length of the rope is included in the only linked structure between the falling object (leader) and the anchor, then the catch is soft. Alternatively, if there is a parallel connection (tied in with rope and a parallel steel cable of the same length), then the system is 'hard'.

So for aid falls on daisies, or belayer falls direcly on the anchor, the system is hard and 'shock loading' is possible, but for lead falls it is not, unless the nut tool catches on the slings as he flies by.


fracture


Feb 10, 2006, 4:17 PM
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Hey John; I recall a passage in Freedom of the Hills 7th ed. (I don't feel like looking up the quote, sorry) which claims that there is test data out there saying that the X doesn't really adjust instantly to sudden changes in the direction of the load, supposedly making the "dynamic equalization" aspect of it significantly less effective. They don't say where they got that information, though....

Does your data contradict this?


Partner cracklover


Feb 10, 2006, 4:23 PM
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Ok-- what am I missing or screwed up?

Question: What creates force on the anchor?
Answer: The tension in the rope.

A piece rips out of a two piece sliding-x anchor. The sling extends and all the force comes onto the other remaining piece.

Question: What is the maximum amount of force that can come onto that piece?
Answer: Exactly as much force as the tension in the rope is creating. No more. That's the only place where force is.

In fact, the immediate force will be slightly less, because a foot (or whatever) of tension will be taken *off* of the rope.

Does that help?

GO


Partner cracklover


Feb 10, 2006, 4:28 PM
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Sorry--- what I meant by the elongation of the rope is the initial fall causes a larger elongation than a soon after second fall-- ie the rope becomes stretched, doesn't have time to recover and won't stretch as much the second time--- hence a higher shockload on the remaining anchor.

Um, what do you think it means to add a foot to a fall. That extra foot *is* on a rope that's already stretched as much as it's stretched. Take a five foot fall on a given rope length, or a six foot fall on a given rope length - the six foot fall is like adding an extra foot of fall on an already stretched rope.

Sorry, it's late on a Friday and it's been a long week - my writing skills are not at their best. Am I helping?

GO


roy_hinkley_jr


Feb 10, 2006, 5:23 PM
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the six foot fall is like adding an extra foot of fall on an already stretched rope.

Except a dynamic rope doesn't stop stretching...till it breaks.


Partner cracklover


Feb 10, 2006, 5:47 PM
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In reply to:
In reply to:
the six foot fall is like adding an extra foot of fall on an already stretched rope.

Except a dynamic rope doesn't stop stretching...till it breaks.

That's my point.

GO


papounet


Feb 14, 2006, 4:20 PM
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Dear

I am eagerly waiting for the results to be published.

And yet I have a question:
did you have the opportunity to test a "ropalette" ( a cordalette/ anchor system made with rope or equally strechable material) ?

My poor attempts at physics have made suspect that the stiffer the material, the worst a manually-tied anchorpoint is.
Any deviation from the predicted angle would load only one protection.

(for example sake, one may try to build an anchor with 3 nuts with rigid steel cable; there may be a configuration for which a biner distribute the pull between the 3 nuts, but any deviation in the force direction would load only one nut)


roy_hinkley_jr


Feb 14, 2006, 5:18 PM
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the six foot fall is like adding an extra foot of fall on an already stretched rope.

Except a dynamic rope doesn't stop stretching...till it breaks.

That's my point.

Mine too...all those broken climbing ropes, tragic.

It really should be no surprise that death-o-lettes were over-sold and under-tested for trad climbs. Even with nylon instead of spectra, they've always been sketchy.


crotch


Feb 14, 2006, 5:51 PM
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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.

Does this hold up in the special situation where one is hauling loads off a sliding X setup with a static rope?


lofstromc


Feb 14, 2006, 6:28 PM
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Hey all,

Dumb question coming up...What is the limiter knot in the sliding X that was mentioned?
The more I know the better.

Thanks


Partner cracklover


Feb 14, 2006, 7:49 PM
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Hey all,

Dumb question coming up...What is the limiter knot in the sliding X that was mentioned?
The more I know the better.

Thanks

http://i26.photobucket.com/...triker/sliding_x.jpg

http://i26.photobucket.com/...liding_x_knotted.jpg

GO


vivalargo


Feb 14, 2006, 8:06 PM
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In reply to:
In reply to:
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.

Does this hold up in the special situation where one is hauling loads off a sliding X setup with a static rope?

All of our tests are with a shank of dynamic climbing rope featuring a dynamic fall. You'd have to do some tests to get that data. This is a question worth answering, but not one we went after in our tests, which were geared to show the performance differences (measured equalization under a dynamic load) between a cordelette, a sliding x, and a third rigging option known as the "Duo Glide" or simply, the Slider.

JL


curt


Feb 14, 2006, 8:40 PM
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In reply to:
So I can take from that you make no distinction about the use of the anchor relative to any reality of shock loading?

I'm not sure what you're asking, and my sense of it is that you already have an answer in your head--and you should simply state that answer and we can work from there.

To briefly answer the question of off angle loading on a cordelett, what happens (according to the testing) is that almost the entire load is taken by the shortest arm of the cordelette...

Actually, that should be obvious. This point has been made numerous times here on RC.com by rgold, myself and others. Still, it is good that your new book (that will, no doubt, be widely read and regarded in the climbing community) will make this point clear.

Curt


patto


Feb 14, 2006, 10:24 PM
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I was scepical at first about the dismissal of the dangers of shock loading in this thread. However being an avid fan of physics I gave it a bit of thought, and found that there is some basis claiming that the danger of shock loading is overstated.

To summerise: If there is little mass attached to the belay point then there is little danger of shock loading.

However if a piece blows and causes extension when the belay is off a harness then there is a severe risk of a large shock loading (we are talking a few multiples of the original force). This is because the falling climber has accelerated a mass (the belaying climbing), which is connected to an anchor via a static, non energy absorbing link. Luckily relative to the smallish extension distances a climber's mass deformation is not negligable, and so would likely prevent the forces multiplying to order 10x the total.

EDIT:
Of course if the extension was mere inches due to a knotted sliding-x as vivalargo suggested then shock loading would be negligable in both case. If the extension was a foot or greater with a climber attached then you would be getting into a danger zone.


healyje


Feb 14, 2006, 11:15 PM
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I'm just curious if you consider shock loading a "myth" in general. That, along with normal multi-pitch, you don't need to worry about the X shocking in a hauling accident or in a case of a heavy bag slipping off a ledge, or maybe a portaledge getting slammed up and down in a storm. I can't tell whether, from your description of the role of belaying in all this, you mean just climbing as opposed to also including the forces involved with all the other various big wall activities.

I'm asking because you're the one that's spent endless hours on all those wall anchors of varying quality over the years - I haven't but would still like to and am trying to figure out if it's worth it to do all the Chongo/PTPP major construction projects with cordalette powerpoints, etc. or should you just throw in a couple of X's and call it good...

John and Curt,

I guess I'm feeling incredibly stupid and dense on this because I'm not getting it at all. I think I've just been programming for way too many week/days/hours in a row now and am starting to lose it. Couldn't you guys show a little pity, put me out of my misery, and just answer this question for me because I really do want to know the answer?


patto


Feb 14, 2006, 11:32 PM
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In reply to:
In reply to:
I'm just curious if you consider shock loading a "myth" in general. That, along with normal multi-pitch, you don't need to worry about the X shocking in a hauling accident or in a case of a heavy bag slipping off a ledge, or maybe a portaledge getting slammed up and down in a storm. I can't tell whether, from your description of the role of belaying in all this, you mean just climbing as opposed to also including the forces involved with all the other various big wall activities.

I'm asking because you're the one that's spent endless hours on all those wall anchors of varying quality over the years - I haven't but would still like to and am trying to figure out if it's worth it to do all the Chongo/PTPP major construction projects with cordalette powerpoints, etc. or should you just throw in a couple of X's and call it good...

John and Curt,

I guess I'm feeling incredibly stupid and dense on this because I'm not getting it at all. I think I've just been programming for way too many week/days/hours in a row now and am starting to lose it. Couldn't you guys show a little pity, put me out of my misery, and just answer this question for me because I really do want to know the answer?

If anything of considerable mass is attached via static line only then any free movement will allow shock loading to occur. This shock loading will be present even before any possible protection piece failure so it is not restricted to the sliding-x setup.

Any mass falling on a static line at an achor can create a dangerous scenario. Thus a heavy bag falling off a ledge IS dangerous.


For example if I can drop a ridgid 50kg weight 4 feet on static sling, which extends on 1in then the force on the anchor and a the sling is 2400kg which is the rated strength of most biners and slings!


verticon


Feb 15, 2006, 1:20 AM
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So we have a bomber pro and a failing one equalized with a sliding X.

The good piece will take two yanks: the first one will be at the same force as the failure force of the poor piece. At this point, the fall is nearly consumed, and the rope still have (?) some stretching reserve.

The bad pro fails and the sliding X extends. Here occurs the second yank. Some of the energy of the fall is already dissipated by the rope stretch and the failure of the bad piece. The remaining energy will produce a load only on the good piece.

So, the total energy of the fall, which is a constant for a given fall, will be shared between the two yanks, instead of producing a single (shock ?)load on the system.

IMO, "how strong is the failing piece?" is an important aspect to think about. If it blows when you sneeze on it, the whole energy of the fall will load only the good anchor, which could produce it's failure as well. If the poor placement holds a fair amount of the force, it could work like a screamer by absorbing part of the energy of the fall before failing.

Could this be used as an emergency protection for a weak anchor or for belaying a leader on a little protection pitch ?
I mean that in extremis, one could intentionally place an additional weak piece of pro (say a 5 kN nut) which will lower the impact force on the system by braking if a shock occurs.
What do you think ?


patto


Feb 15, 2006, 4:11 AM
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So we have a bomber pro and a failing one equalized with a sliding X.

The good piece will take two yanks: the first one will be at the same force as the failure force of the poor piece. At this point, the fall is nearly consumed, and the rope still have (?) some stretching reserve.

The bad pro fails and the sliding X extends. Here occurs the second yank. Some of the energy of the fall is already dissipated by the rope stretch and the failure of the bad piece. The remaining energy will produce a load only on the good piece.

So, the total energy of the fall, which is a constant for a given fall, will be shared between the two yanks, instead of producing a single (shock ?)load on the system.

IMO, "how strong is the failing piece?" is an important aspect to think about. If it blows when you sneeze on it, the whole energy of the fall will load only the good anchor, which could produce it's failure as well. If the poor placement holds a fair amount of the force, it could work like a screamer by absorbing part of the energy of the fall before failing.

Could this be used as an emergency protection for a weak anchor or for belaying a leader on a little protection pitch ?
I mean that in extremis, one could intentionally place an additional weak piece of pro (say a 5 kN nut) which will lower the impact force on the system by braking if a shock occurs.
What do you think ?

There is little evidence in this post of any understanding of physics. Energy and force is being completely confused in this post, it makes hardly any sense at all.

To answer the final question, not it is unlikely to absorb much energy and would do more harm than good. Screamers work because they exert a force over a distance. Most of the time when a piece blows it blows suddenly and at a single point, thus very little energy is absorbed.

EDIT: Sorry I don't mean to be rude, I was just posting how I see it. I noticed your location is Bucharest, nice one! You english is good! :)


healyje


Feb 15, 2006, 4:43 AM
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Actually, a screamer equalized to a weak anchor is way better than no screamer at all, and one that has been pre-sliced at a steep angle to provide a kinder, gentler loading profile can be especially helpful. I have built several "spider webs" of 6-8 micro nuts in a circle all equalized to the center with a pre-sliced screamer and fallen on them to the tune of four different screamers worth of falls.

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