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lynne
Feb 28, 2003, 7:44 PM
Post #26 of 43
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In reply to: A more common scenario is that you want to equalize two pieces that are less than ideal, but not as bad as above. You want the pieces to share the load, but if one piece fails, the other will still probably hold, provided it isn’t shock loaded. In this case, “no extension” is more important than perfect equalization, and you should equalize the pieces statically. The best way I know of to do this is to tie a double clove hitch in a sewn runner; that is, to tie a single clove hitch in both strands of the runner. This forms three points of attachment in the runner: the hitch itself plus two loops. The clove hitch is put on one of the pieces to be equalized, and one of the loops is attached to the other piece. The rope is clipped into the remaining loop. Adjust the clove hitch as needed to optimize the equalization. |
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jt512
Feb 28, 2003, 8:04 PM
Post #27 of 43
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In reply to: In reply to: A potentially more serious situation is when the first piece fails at the peak impact force of the fall. If it is at peak impact force, then it has already absorbed much of the force up to that point. If one fails, it will see less load... Get it.
Adam, you are confusing energy and force. Forces aren't absorbed; energy is. The impact force varies over time. On a severe fall, the maximum impact force occurs when the rope is fully stretched. At this point the impact force on the climber is theroetically equal to the rated impact force of the rope. The anchor feels about 1.6 times this force. Thus, if the first piece were to blow at maximum rope stretch, the second piece would be shock loaded with 1.6 times the rope's impact force rating.
In reply to: The point of the sliding X is that it multidirectionally equalizes, and is relatively quick to set while on lead, rather than having to tie knots and such... This is hard to do when leading at your level, right ???
Indeed, the sliding X can be done with one hand; the clove hitch can't, at least not by me.
In reply to: Jay, I know you are not a fan of this, so don't use it.
It's not that I'm not a fan of it. It has its place, and I've used it. I'm only pointing out that it is often not the best choice. If you have a good stance before the crux and want to equalize two pieces, then, unless the indivicual placements are terrible, the clove hitch is the safer choice.
-Jay
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jt512
Feb 28, 2003, 8:18 PM
Post #28 of 43
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In reply to: In reply to: The best way I know of to do this is to tie a double clove hitch in a sewn runner; that is, to tie a single clove hitch in both strands of the runner. This forms three points of attachment in the runner: the hitch itself plus two loops. The clove hitch is put on one of the pieces to be equalized, and one of the loops is attached to the other piece. The rope is clipped into the remaining loop. Adjust the clove hitch as needed to optimize the equalization. maybe I just need more coffee, but I'm having trouble visualizing this. Can you point me to a picture or perhaps type slower next time?
We all need more coffee. That goes without saying. Unfortunately, I don't know of a picture of this I can point you to, either. Let me try to explain the hitch another way:
An EDK is a double overhand in the sense that it is a single overhand tied in both strands of a rope. Well, the double clove hitch I'm describing is analogous to the EDK. It's a single clove hitch tied into both strands of a sewn runner.
Take a sewn runner, and instead of tying a clove hitch into one strand of it, tie one clove hitch into both strands of it simultaneously. Now you've got three points of attachment: the clove hitch, which you clip one piece of pro to, and two loops, one of which you clip into the other piece of pro to be equalized, and the other, which you clip the rope into. I think that if you actually get a runner and tie the hitch you'll see what I'm talking about.
-Jay
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rrrADAM
Feb 28, 2003, 8:18 PM
Post #29 of 43
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You are arguing somantics, but I quoted and used your words "impact force". Much of the energy of that force applied to the anchor would be absorbed if one piece failed at maximum load, therefore the 2nd piece would see a smaller load.
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lynne
Feb 28, 2003, 8:31 PM
Post #30 of 43
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In reply to: An EDK is a double overhand in the sense that it is a single overhand tied in both strands of a rope. Well, the double clove hitch I'm describing is analogous to the EDK. It's a single clove hitch tied into both strands of a sewn runner. |
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jt512
Feb 28, 2003, 8:34 PM
Post #31 of 43
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In reply to: You are arguing somantics, but I quoted and used your words "impact force". Much of the energy of that force applied to the anchor would be absorbed if one piece failed at maximum load, therefore the 2nd piece would see a smaller load.
No, I'm not Adam. You're missing the point. The problem is, as I understand it, that if the first piece fails at the maximum rope stretch, the second piece will feel the same peak force as it would have had the first piece not been there at all. However, the second piece will be shock loaded; that is, it will feel this force abruptly, which could cause it to fail, whereas it could hold if the same peak force were reached more gradually, as it would if the rope had some stretch left in it.
-Jay
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mountainmonkey
Feb 28, 2003, 8:46 PM
Post #32 of 43
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When the climber comes to a stop (before bunjiing back up (rope stretch is at a maximum)), all of the energy of the fall has been absorbed but the force is at a maximum. The danger of the one piece failing w/ the sliding x is that each piece will experience half the load, but if one fails at the maxiumum force then the remaining piece will have the hold the maximum load (not half of the load). If both pieces hold up to half the maximum load, then you are set.
I want to reiterate my comments from earlier: The sliding X is useful in lead situations or as a component of an anchor, but should not be used as the only anchor for multipitch climbs. The impace caused from one piece failing and the extension in the runner is only absorbed by the static runner and will cause very high forces on the remaining piece.
Also, from Petzl:
"When suspect anchors are linked with a sling to distribute the load, use a locking carabiner. This avoids accidental opening of the gate at the moment of impact if one of the anchors fails."
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boltdude
Feb 28, 2003, 9:08 PM
Post #33 of 43
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Listen to Dingus, he knows the deal. I just did a Sliding X off of a rusty RURP and an RP on a free climb - coupled with a Screamer of course...
The reason we have the Sliding X warning on the ASCA website is because a LOT of beginner climbers (like me for the first couple years) use the Sliding X as the MAIN anchor setup off of bolts and natural pro. You'll see this all the time, and then multiple sliding X's used to link multiple (often poorly placed) trad pieces together, etc.
Many guide services teach this still. In fact, every couple months we get a complaint from a guide somewhere or other about how the Sliding X is completely safe and we're full of it.
Sliding X's do have their uses, but NOT as THE major anchor setup off of two bolts, etc, as is taught by way too many folks. Just because something is "long established" and "time-tested" doesn't mean it's correct (especially when you consider just how often anchors are actually "tested" by a major fall...and how often the exact causes of the - thankfully very few - catastrophic anchor failure accidents are never resolved...).
Greg
PS Don't underestimate what can happen when a rope absorbs most of the force of a fall and THEN a piece blows - a friend fell a short ways, broke the wire on an old fixed nut, and then blew both rope-end carabiners on the next two pieces and knocked his wife off the belay ledge. She caught them both off the main anchor (that's called "good belaying"...).
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biff
Feb 28, 2003, 9:08 PM
Post #34 of 43
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In reply to: In reply to: You are arguing somantics, but I quoted and used your words "impact force". Much of the energy of that force applied to the anchor would be absorbed if one piece failed at maximum load, therefore the 2nd piece would see a smaller load. No, I'm not Adam. You're missing the point. The problem is, as I understand it, that if the first piece fails at the maximum rope stretch, the second piece will feel the same peak force as it would have had the first piece not been there at all. However, the second piece will be shock loaded; that is, it will feel this force abruptly, which could cause it to fail, whereas it could hold if the same peak force were reached more gradually, as it would if the rope had some stretch left in it.
I understand all that is being said here .. and both of you are correct, and both of you are wrong.
if the first peice fails at the peak of the force (maximum stretch) in the rope, the sling will extend 1 foot , giving the rope another 2 feet of strech, also at that point (the rope is at maximum stretch) most the energy of the fall should have been absorbed, the climber will be bouncing up, or prety darn close to it.
so if that is when the peice fails, the dynamics of the system change, the rope gets more strecth, the climbers inital fall should have almost come to a stop, then the next peice (that didn't fail and should be stronger than the first) will experiance a sudden drop in force (while the rope recoils the 2 feet gained) and then will feel a force that could be less than the one that caused the first peice to fail.
Under the worst circumstances the first peice will fail before the maximum force and the force on the second peice will be greater than 2 times the force that ripped the first peice (since when it ripped, it was only bearing half the force of the fall) and will probably pull the second peice if it were shock loaded or not. since the placement was marginal to begin with if you were using the sliding x system.
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jhwnewengland
Feb 28, 2003, 9:36 PM
Post #35 of 43
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Check this out, a one-handed clove hitch! Works for me.
http://www.climerware.com/clove.shtml
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yosemite
Feb 28, 2003, 9:49 PM
Post #36 of 43
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I haven’t read all the posts, so excuse me if this is redundant. It may even be stupid, but here’s my view.
The overhand knot in the Petzl sketch is there to limit the amount of extension if a piece blows. As the overhand knot gets closer to the clip in point, you lose much of the range of direction that the anchor equalize. If the overhand knot is further away from the clip in point, the amount of potential shock loading increases.
It seems to my feeble mind that the infamous sliding Xit is the only automatic equalizing technique out there. If you tie an overhand or figure-8 into your slings or cordalette, unless the system is absolutely perfectly balanced to less than a gnat’s ass of precision, you will load your pieces unevenly and/or incrementally. Which negates the self equalization properties. I personally believe that it is darn near impossible to tie a perfectly equalized cordalette that will load the anchors simultaneously and equally. I think the Death X does this.
That said, I believe there are only two situations when the sliding X is justified.
(1) Manky sucky pieces of pro or aid. You don’t trust either, but maybe, just maybe, two crappy pieces will work. In this case, you want both pieces absolutely equalized. With the understanding that if one blows, so does the other.
(2) Rapping off a route with brand new shiny (preferably ASCA [write your donation check now]) bolts. Using a tied runner with rap ring and the Petzl overhand knot seems reasonable to me. In a rap situation, you usually don’t need the anchor to support high stress loads from all points of the compass. Therefore, the Petzl overhand knot ain’t bad. Furthermore, when rappelling, the forces on the anchor are essentially body weight plus change. Nothing near a fall situation.
Whatcha all think?
Gene
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jt512
Feb 28, 2003, 10:26 PM
Post #37 of 43
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In reply to: I believe there are only two situations when the sliding X is justified. (1) Manky sucky pieces of pro or aid. You don’t trust either, but maybe, just maybe, two crappy pieces will work. In this case, you want both pieces absolutely equalized. With the understanding that if one blows, so does the other.
I agree.
In reply to: (2) Rapping off a route with brand new shiny (preferably ASCA [write your donation check now]) bolts. Using a tied runner with rap ring and the Petzl overhand knot seems reasonable to me. In a rap situation, you usually don’t need the anchor to support high stress loads from all points of the compass. Therefore, the Petzl overhand knot ain’t bad. Furthermore, when rappelling, the forces on the anchor are essentially body weight plus change. Nothing near a fall situation.
An anchor formed using a sliding X is only as good as the worse bolt, since if it blows, the remaining bolt gets shock loaded, and it's likely to be lights out. Again, the X provides optimal equalization at the expense of potential shock loading. If both bolts appear to be good, then there is no need for perfect equalization. Therefore, you should (in the rappel situation) approximately equalize by using two slings, one on each bolt, with a rap ring through both of them. Then, if your judgment turns out to be wrong, and one bolt does fail, the remaining bolt will not be shock loaded.
-Jay
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venezuela
Feb 28, 2003, 11:27 PM
Post #38 of 43
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I use th sliding X almost always. I don't use it, only, when the pieces are weak, so what I do, is clip in to each of the anchor points directly: one locker - to sling - to locker - to anchor. (to avoid shock loading the whole anchor).
Why do I use the X?
1). because, many times, when I'm are belaying on a multi-pitch, I tend (as many of you, I suppose) to move/swing from side to side: to get a better view of the second cliber coming up, or to let him in to the anchor, or because I'm uncomfortable, or to eliminate rope drag, etc...
2). when belaying directly from the anchor (which I rarely do, anyways), with a reverso, or munter hitch, or a casin logic, or an ABS, you need to set up the device on a equalized anchor
3). many of you say: if the bolts are bombproof, why X them, they are not going to blow, so what's the use?.....answer: to preserve, and extend the functional life of the bolt!!!. If the second falls and there was to much slack (due to rope drag, or the belayer wasn't paying attention), or the first one falls before setting up the first pro, the anchor will recive an 1.x (insert high number where the x is) factor fall.....it's not the same for ONE bolt to receive such an impact, than TWO, or maybe THREE, bolts, with the foreces distributed through out them. (that's if you're belaying from the harness, imagine if you're belaying the second directly from the anchor, and there was to much slack, or he swings to a side because it was a traverse).
4). John Long's & Craig Leubben Advanced Rock Climbig......they show many ways to mix and match the use of the sliding X, with other equalizing methods....
5). when top roping: SLIDING X ....it keeps the forces distributed equally (and minimizes the force also, if you use a longer sling) when the climber falls, and swings to the side, or is hand-dogging
6)try always to set up the sliding X with 3 points. if you do it, and clove hitch the sling to each anchor point, and one piece blows, the anchor will not extend. although you will end up with a very precarious form of the american triangle, which, maybe, almost surely, will not stand another blow (note, when clove hitching the sling, it will minimize the radius in which you can swing from one side to another). (note 2: when clove hitching, it will reduce the strength of the sling, but not enough to not suport a small to medium blow: the clove hitch holds up 650 Kn....and use ONLY nylon webbing when clove hitchig, NOT SPECTRA).
6). to avoid extension, you can do an overhand knot to the sling...althoug it will also minimized the radius of "swinging". YES it will reduce the strength of the sling, but not enough to break easily.
if you where able to reading it all, without moving on...props to you :wink: ..
Diego.
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fitz
Mar 1, 2003, 2:20 AM
Post #39 of 43
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In reply to: Now read this... The sliding X is to multidirectional equalize two pieces. If you tie an overhand in it, it is no longer multidirectional. You have defeated the purpose. Regarding shockloading... If you have a sliding X on two pieces, ytou shockload both pieces with only 1/2 the force. If one fails, the piece left will only be shockloaded by the length of sling used. (This is much less force that the original fall, since it was higher, and much of the force was absorbed by the 2 pieces before one failed.) Do the math... You are better off.
I'm not sure if this was intended at my post or not. The overhand(s) I referred to limit the amount of sliding that can occur. Sort of like putting stops on the end of a track. They have no effect on the equalization that occurs, they just limit the amount of directional change that can be accomodated. I generally have no qualms about limiting up travel, because gravity has not failed to appear during one of my falls yet.
Do the math this way, forget the exact amount, shock loading is a proven killer (aka it's presence in RENE). So, if you tie an overhand between the biner and the top piece, equalization is not compromised (provided you fall down and both pieces hold). But, if the top piece fails, you've cut the drop (extension) about in half, dramatically lowering the shock load on the lower piece.
I personally think your math misses a few key points, but I'll let others play the physics hair splitting game.
-jjf
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blazesod
Mar 1, 2003, 3:05 AM
Post #40 of 43
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:?:
I have never used a sliding X to equilize pro. I have used a self equilizing figure 8 which I think works the same way. It has never failed me.
Has anyone had a sliding x fail them?
-curious
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jt512
Mar 3, 2003, 10:26 PM
Post #42 of 43
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In reply to: In reply to: An anchor formed using a sliding X is only as good as the worse bolt... Not true, as it only puts half the load on the "worst bolt"... Therefore it is twice as good as the worst bolt.
Now who is arguing semantics?
With a sliding X, if the weak piece fails, the entire anchor is likely to fail, so, in general, static equalization is preferrable.
-Jay
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janiszewski11
Apr 16, 2003, 2:16 AM
Post #43 of 43
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So why hasn't a cord, runner etc. been develeloped that's extra dynamic so that the sliding x can be used safely. Use two to be redundant and the dynamic quality of it to avoid shock loading if one anchor fails.
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