The Sliding X

Brandon R wrote: http://www.mountainproject.com/v/rock-fall-results-in-chopped-anchor/110088639 A pretty good reason to not use the sliding x for a bolted anchor.

Happy to be here to share my 2 cents. I would be dead if I had chosen a sliding X on bolted anchors.

The sliding X is an option that is best used if the last piece of pro prior to the anchor is way off the fall line. If this causes the direction of pull to change dramatically as the climber traverses into the anchor it is a good tool if used with limiter knots. 

Other than that, if used without limiter knots, it is neither redundant or non-extending. Both cornerstones of any stupid acronym that has ever been dreamed up to teach anchors.

The question is if there is no change in the direction of pull what do you gain by using the magic X vs. a pre equalized anchor? Better equalization? Maybe but I'd take redundancy ( cause it saved me) and no extension any day.

On another note. There is a growing movement away from equalization happening within the euro guiding circles. Slightly different, but lead belaying from a single fixed point is a thing and it's coming this way.

https://youtu.be/eqZQnCGl24A

gf9318 wrote: http://www.safeclimbing.org/education/slidingx.htm When there is an option to avoid shock and increase redundancy, take it.

I have much respect for the ASCA, but that page is horribly written.

"Death X", lol

cdec wrote:

On another note. There is a growing movement away from equalization happening within the euro guiding circles. Slightly different, but lead belaying from a single fixed point is a thing and it's coming this way.

Can yet more via ferratas, bolted cracks, and other assorted euro nonsense be far behind...

P.S. Maybe read the 133 pages of sliding-X[cess] over on RC before rehashing it all again here.

No one is dying from load limiter knots (unless you are taking static falls on a dyneema tether, but thats a different thread).  I agree that people get far too caught up in the idea of knots weakening slings. 

If a piece blew on my anchor, I would want it to be on a sling with load limiter knots, and not a sliding x.  Not all bolts are good and not all climbers can evaluate them appropriately. 

The sliding-x may be fine in some situations, but i don't think its ever the best option.  There are other "self equalizing" anchors that won't extend and shock load the only remaining component of an anchor.

As a climbing instructor, I have been following the discussion on sliding-X, shock loads and delimiter knots for ages. It is clear that the question of shock loading is NOT an easy one. Even the underlying physics is very complicated.

I have yet to see compelling evidence (experimental or theoretical) that a significantly higher load will be placed on a remaining piece when one piece in a sliding-X fails in a FF 2 situation. It is hard to ignore the fact that the rope is still dynamic and capable of absorbing the small extra amount of energy introduced by the extension.

However, there is a more obvious reason why extension matters. If the belayer is hanging directly off the sliding-X anchor, and one piece fails (due to a leader fall, rock fall, failed piece, or whatever), then we do have a fall on static material (assuming the belayer is connected to the anchor using static material or very little rope). If the sliding-X is a 60 cm (2 ft) sling, then the extension is probably small enough that the sling does not break, but the shock may well cause pain, distraction, and loss of control. This in itself is reason enough to use delimiter knots, or to use a different anchor design.

The question about the shock-loading effect of the falling leader is still an open issue, but the question of a static fall by the belayer is not.

johnliungman wrote:
As a climbing instructor,

Hmmmmm....

johnliungman wrote: Even the underlying physics is very complicated.

It isn't really that complicated.

johnliungman wrote:I have yet to see compelling evidence (experimental or theoretical) that a significantly higher load will be placed on a remaining piece when one piece in a sliding-X fails in a FF 2 situation. It is hard to ignore the fact that the rope is still dynamic and capable of absorbing the small extra amount of energy introduced by the extension.

There is compelling evidence experimental and theoretical.  If there is weight at the anchor (AKA) the belayer then that is the weight "shock loading" the system with no dynamic rope in place.
(I have looked for some good test videos but my google foo isn't working.)

johnliungman wrote:The question about the shock-loading effect of the falling leader is still an open issue, but the question of a static fall by the belayer is not.

It isn't really.  The physics is all there and not too complicated.

EDIT:
https://dmmclimbing.com/Knowledge/September-2013/Slings-at-Anchors

Shows the issue of "shock-loading" with the sliding-x.  Note this is applicable if there is a belayer weighting the anchor.  Not particularly relevant if there is no weight at the anchor.

johnliungman wrote: As a climbing instructor

We're still talking about two bolts, right?  What is the actual original argument for a sliding X?  That the anchor was off to the side.  First, it has long since been established that shockloading is a thing so that's a nonsense argument.  Even if you are cloved into a rope, how much does 2 feet give you in terms of force dissipation?  So the load shifts to the side when you're bringing a second up.  So what?  One bolt is plenty to take that weight, and the second is there for redundancy.  Given how much people like to use dyneema connections, and given the amount of testing that's out on it from DMM, BD and others about how sudden loads and down to a FF1 can break the material, clearly a sliding X isn't the best choice, especially on 2 bomber bolts.

Let's make sure we can potentially break a dyneema sling, which is the only attachment point, because we need to share the load on two bomber bolts for someone top roping up to an anchor.

Jesus.

johnliungman wrote: As a climbing instructor, I have been following the discussion on sliding-X, shock loads and delimiter knots for ages. It is clear that the question of shock loading is NOT an easy one. Even the underlying physics is very complicated.

I have yet to see compelling evidence (experimental or theoretical) that a significantly higher load will be placed on a remaining piece when one piece in a sliding-X fails in a FF 2 situation. It is hard to ignore the fact that the rope is still dynamic and capable of absorbing the small extra amount of energy introduced by the extension.

However, there is a more obvious reason why extension matters. If the belayer is hanging directly off the sliding-X anchor, and one piece fails (due to a leader fall, rock fall, failed piece, or whatever), then we do have a fall on static material (assuming the belayer is connected to the anchor using static material or very little rope). If the sliding-X is a 60 cm (2 ft) sling, then the extension is probably small enough that the sling does not break, but the shock may well cause pain, distraction, and loss of control. This in itself is reason enough to use delimiter knots, or to use a different anchor design.

The question about the shock-loading effect of the falling leader is still an open issue, but the question of a static fall by the belayer is not.

That you haven´t seen the evidence is immaterial, I haven´t seen the evidence for gravitational waves nor would I understand it if I did but that doesn´t mean they don´t exist.

The physics is, as Patto says, easy. The difficult parts are obtaining the data to plug into the theory and clearly the biggest difficulty for many is actually performing the required though experiments as a starting point for either theory or experimentation.
For example your concerns over FF2 falls; there are two main scenarios we should consider and in both the dynamic behaviour of the rope is of no practical importance. In the first scenario the leader is directly belayed off the anchor with an Italian Hitch or whatever and the belayer standing, not loading the belay at all. The limiting factor regarding the force on the belay at any time, whether or not a piece fails and there is extension or not is the force applied through the belay device. Considering the normal impact forces produced by climbing ropes and the usual braking force from most normal belay devices it is highly unlikely the rope plays any role in the situation and any extension will be irrelevant.
 The second sitution is more problematic; when the belayer is weighting the belay AND belays off their harness/belay loop. Then the limitaion of the force on the belay is still the belay device BUT if one piece fails then the belayer is accelerated downwards, not by gravity but by the force applied by the belay device and this can easily mean the apparent weight of the belayer is three of four hundred kilograms as they hit the extension. This destroys everything in the belay. I´ve seen impact forces of over 37 times the "belayer" weight in testing and I along with others have abandoned drop testing at this stage as the slings break.
I assume your opinion that a 60cm sling won´t break is just a guess?

Brandon R wrote: mountainproject.com/v/rock-… A pretty good reason to not use the sliding x for a bolted anchor.

From earlier in the thread.  This damn thing should be stickied.  Redundancy + limited extension > “equalization.”

Ted Pinson wrote:

From earlier in the thread.  This damn thing should be stickied.  Redundancy + limited extension > “equalization.”

But that's all solved with limiting knots, right? The way I learned it, at least, there's no situation for an X without knots. Maybe as part of two pieces sistered as one leg of an anchor, maybe.

jg

I shall await your explanation as to how far apart your limiter knots can be and still be safe with interest  

Josh Gates wrote:

But that's all solved with limiting knots, right? The way I learned it, at least, there's no situation for an X without knots. Maybe as part of two pieces sistered as one leg of an anchor, maybe.

jg

Yes and no.  If you use limiter knots in a manner that drastically reduces extension, then you've also equally limited the lateral range of that sliding X- which is the primary purpose for it to begin with.  So if you're going to do that, why not just tie a regular masterpoint in the anticipated direction of pull to begin with, and skip the extra knot tying and needless "equalization" on two good bolts?  I know the argument to this is going to be "but then when the follower arrives, the anchor is still oriented in that direction".  That's quick and easy to fix and not really that big of a deal if you don't considering we're still talking about two bolts.

don'tchuffonme wrote:

Yes and no.  If you use limiter knots in a manner that drastically reduces extension, then you've also equally limited the lateral range of that sliding X- which is the primary purpose for it to begin with.  So if you're going to do that, why not just tie a regular masterpoint in the anticipated direction of pull to begin with, and skip the extra knot tying and needless "equalization" on two good bolts?  I know the argument to this is going to be "but then when the follower arrives, the anchor is still oriented in that direction".  That's quick and easy to fix and not really that big of a deal if you don't considering we're still talking about two bolts.

The two ways that I set up two-bolt stations (and I've never built a two-bolt anchor for anything but TRing, so this may be the issue w my understanding - anytime I've done multipitch, it's been gear anchors) are with a sliding x with limiters and a quad. What's the method you're thinking of? Doing it with the rope? That wouldn't help with setting TR anchors, though. Did you have something else in mind?

jg

Cordellette/figure 8.  Simple, redundant, non-extending.

Josh Gates wrote:

The two ways that I set up two-bolt stations (and I've never built a two-bolt anchor for anything but TRing, so this may be the issue w my understanding - anytime I've done multipitch, it's been gear anchors) are with a sliding x with limiters and a quad. What's the method you're thinking of? Doing it with the rope? That wouldn't help with setting TR anchors, though. Did you have something else in mind?

jg

Are you referring to top roping single pitch routes and belaying from the ground?

don'tchuffonme wrote:

Are you referring to top roping single pitch routes and belaying from the ground?

Yes. 

Josh Gates wrote:

Yes. 

Why would you ever need a sliding X there?  When top-roping it's hard to put even 4kn on an anchor with a dynamic rope, even if there's a lot of slack in the line when the climber falls- which there should not be.  If both bolts are bomber, and you want to be super safe, then put a locker on each bolt and have two lockers opposed and just tie a masterpoint.  Even if the last piece isn't below the anchor and is off to the side, the same principle applies.  You don't need to try to distribute a load equally on two bomber bolts.  You could belay an elephant on one bolt and just have the other one incorporated as a backup/redundancy.  IMO the sliding X serves only a very limited purpose in very select circumstances.  Anything involving a 2 bolt anchor where both bolts are solid isn't remotely in any of those circumstances.