Limiter Knots on Sliding X

When you use a sliding x anchor, do you use limiter knots on the legs to reduce shock load potential? If so how close together do you tie them? Obviously the closer they are, the less self equalizing, but it seems safer if one of the pieces blow.

While I understand the argument for using limiter knots with sliding x, personally I never tie them. I don't use the sliding x that often, but when I do, I'm usually using a single length runner and trying to be quick.

Pierre, I see some limiter knots but no sliding x in that anchor, doesn’t really address OP’s question...

Have to admit, now I'm curious if anyone ties limiter knots in their sliding x. I suppose it's possible to do with a single length, particularly a skinny dyneema sling, but I would have a pretty hard time fiddling with limiter knots in a thicker nylon single length. And if I'm using a double length or longer cord, I would probably make a different type of anchor than sliding x.

Beckett Aizeki wrote:

When you use a sliding x anchor, do you use limiter knots on the legs to reduce shock load potential? If so how close together do you tie them? Obviously the closer they are, the less self equalizing, but it seems safer if one of the pieces blow.

Yes and No.

Yes: I use limiter knots to make the system redundant.
No: I do not use the limiter knots for the purpose of reducing the shock load, but it is an added benefit.

How often would we be better off without having the sliding action? Or, in other words, how often do we really need load sharing?

The best sliding action would be to tie the limiter knots, skip the sliding x, and clip one strand between the limiter knots. I might do this if I’m really worried about each piece individually.

If one piece fails, a limiter knot is not very strong in the way it gets shock loaded. Would it be better to instead individually sling the two pieces so that the two rope-side biners are not so far apart in direction of fall loads?

I don’t have the definitive answers.   I do find that as the years have gone by, I’m using the sliding X less and less on lead. 

Edit:  One way to get exquisite load sharing is to climb with doubles and clip the two pieces to different rope strands..

You guys should really read the quad thread.  

https://www.mountainproject.com/forum/topic/120831728/quad-anchor-is-not-redundant-at-the-clip-in-point

another vote for sliding x with two slings and no limiter knots

Yoda Jedi Knight wrote:

another vote for sliding x with two slings and no limiter knots

I don't think this really creates the desired security being sought from using 2 slings. A single sling is strong enough for the task on its own, so the additional sling is presumably only there to mitigate some kind of failure mechanism. These are:

1. A carabiner comes unclipped, in which case extension occurs and the sliding x catches as designed. 

2. An anchor component fails, in which case extension occurs and the sliding x still catches as designed.

3. The sliding x sling gets cut. Two realistic possible cases here (things such as gremlins and murderous partners aside).

a. A sharp edge cuts the sling. Since the sliding x slides *by design*, presumably no one is building it over a sharp edge since they probably want to live.

b. The sling is cut by rockfall (or maybe ice fall?). In that case, whatever rock fell and struck with enough force to sever one strand of material has a very good chance of severing two strands of material. If it somehow doesn't, then you're incredibly lucky and [your favorite deity here] clearly thinks you're better off being alive at least a little while longer. 

Consequently, I don't think the second sling is particularly beneficial. The second sling also probably adds friction at the focal point, reducing the ability of the sliding x to slide, and therefore reducing the value of choosing it in the first place. Also, extension upon failure of a single component could fail the entire anchor catastrophically. (As Mark suggests, see: https://www.mountainproject.com/forum/topic/120831728/quad-anchor-is-not-redundant-at-the-clip-in-point?page=4#ForumMessage-120859851). 

If the sliding x is for speed/convenience, I'd offer the swamp/wishbone knot suggested upthread, a girth hitch masterpoint, or banshee belay variation as substitutes.

Gumby King wrote:

Yes and No.

Yes: I use limiter knots to make the system redundant.
No: I do not use the limiter knots for the purpose of reducing the shock load, but it is an added benefit.

What redundancy does this add?  If one piece were to blow, the anchor still holds.  It would save you from a cut if it happened to happen above the knot, but that’s very unlikely.

Anyways, I usually use Xs as part of anchor (not the whole thing) and so do not bother.  I ended up having to rig an X as my anchor yesterday though (didn’t have the gear for anything else) and did tie limiter knots.

I only use a sliding x on 2 bomber bolts. And not that often anyway. I use a clove hitch master point most of the time.

None of the shock/redundancy issues of the x, none of the hard to untie problems of a quad or pre equalized options, can be done with single length slings. Great for 3 piece trad anchors as well (either as the master point or linking 2 of the 3 pieces). 

Derek DeBruin wrote:

I don't think this really creates the desired security being sought from using 2 slings. A single sling is strong enough for the task on its own, so the additional sling is presumably only there to mitigate some kind of failure mechanism. These are:

1. A carabiner comes unclipped, in which case extension occurs and the sliding x catches as designed. 

2. An anchor component fails, in which case extension occurs and the sliding x still catches as designed.

3. The sliding x sling gets cut. Two realistic possible cases here (things such as gremlins and murderous partners aside).

a. A sharp edge cuts the sling. Since the sliding x slides *by design*, presumably no one is building it over a sharp edge since they probably want to live.

b. The sling is cut by rockfall (or maybe ice fall?). In that case, whatever rock fell and struck with enough force to sever one strand of material has a very good chance of severing two strands of material. If it somehow doesn't, then you're incredibly lucky and [your favorite deity here] clearly thinks you're better off being alive at least a little while longer. 

Consequently, I don't think the second sling is particularly beneficial. The second sling also probably adds friction at the focal point, reducing the ability of the sliding x to slide, and therefore reducing the value of choosing it in the first place. Also, extension upon failure of a single component could fail the entire anchor catastrophically. (As Mark suggests, see: https://www.mountainproject.com/forum/topic/120831728/quad-anchor-is-not-redundant-at-the-clip-in-point?page=4#ForumMessage-120859851). 

If the sliding x is for speed/convenience, I'd offer the swamp/wishbone knot suggested upthread, a girth hitch masterpoint, or banshee belay variation as substitutes.

A sliding X is with one sling.

Beckett Aizeki wrote:

When you use a sliding x anchor, do you use limiter knots on the legs to reduce shock load potential? If so how close together do you tie them? Obviously the closer they are, the less self equalizing, but it seems safer if one of the pieces blow.

I would say close enough to limit your extension in case of one leg failing. The knots are to limit extension and they must be tied to prevent extension or could result in shock loading the other leg which enough shock could cause failure of anchor completely. Personal preference dictated, but knots closer together will limit extension as compared to farther apart. Practice before you get outside and have to do it in the moment. 

Ted Pinson wrote:

What redundancy does this add?  If one piece were to blow, the anchor still holds.  It would save you from a cut if it happened to happen above the knot, but that’s very unlikely.

Limiter knots on a sliding-x add the redundancy if any part of the sling or gear/bolt is cut/fails.

The twist in the Sliding-X allows for one of the strands between the knots to be cut and the other (should) hold.

Tradiban wrote:

A sliding X is with one sling.

Indeed. But I was replying to the suggestions to construct one with two slings, as you can see in the comment that I quoted. 

Derek DeBruin wrote:

Indeed. But I was replying to the suggestions to construct one with two slings, as you can see in the comment that I quoted. 

Ah, I see now. Two is always better than one!

abandon moderation wrote:

As another failure scenario: I've had a sling get cut 90% of the way in a lead fall already; there is some chance I could have gotten to an anchor and not noticed, and used that sling as my only sling in the sliding X. Arriving at the anchor with an already weakened sling (you know, the one you keep beside the car battery or the one you hit with your ice axe) is probably the most likely failure case.

I make it a point not to carry things on my harness that I wouldn't whip on, so no worries about the car battery ;) As for the axe, certainly a possibility, though I think you'd have to be pretty damn motivated to affect the strength or the security of the sling in a consequential manner within the context of a single climb. 

As for the 90% sling cut, I don't know what was underneath that piece, but glad to hear it still did it's job when it was called upon.

I'd argue that the second sling is about as useful as the second bolt. You could probably go your entire climbing career belaying off a single bolt and never have an accident. Seriously, when's the last time you were belaying off a two bolt anchor and one unexpectedly fell out? You could probably get by with a single sling on a sliding X as well.

I've never had a bolt pull, but I know of a fatality in Moab where precisely that happened when the climber was clipped to a single bolt while rappelling. (Unfortunately, I have no further details.)

But we all know that weird things happen in climbing.

I agree that weird things happen (seen my share), but I'm not actually sure we all know and/or care to admit it, whether owing to little experience, hubris, poor understanding of the systems involved, etc.

 In a case where redundancy is so easy to achieve (ie the second bolt is already there, or adding a second sling takes maybe an extra second) I think it makes sense to use it. That, or as you mention use some other anchor system that provides redundancy and preferably reduces extension.

I suppose this is where we differ. I can save material by using a different configuration for no additional time cost. Despite your close call (and I mean no disrespect to it), this seems to be a sufficient edge case that I'd place it within my scope of acceptable risks as opposed to doubling up all my anchor rigging; I'd instead just build something redundant in the first place.

Simple answer: don't use a sliding X.  There is, essentially no situation where a sliding X is the right choice.  More explicitly, there is no situation below the expert level (e.g. a desert sand-stone tower that is as much mud as rock, and basically a do-not-fall environment) where a sliding X is the right choice.

If you are building an anchor on a pair of bolts, you care about 1) redundancy, and 2) possibly minimizing extension.  There is no point in trying to "share" the load between two 20 kN bolts.  If one bolt is in bad rock, and you are attached with a tether, you care at that point about minimizing extension -- a sliding X adds extension.

If you are building a gear anchor, place solid gear.  Again, you care about 1) redundancy, and 2) minimizing extension if a piece isn't good.  But each piece should be good enough, on its own, to take the full load to be applied to the anchor.

Tradiban wrote:

Ah, I see now. Two is always better than one!

When you showed up by wife disagreed... 

Gumby King wrote:

Limiter knots on a sliding-x add the redundancy if any part of the sling or gear/bolt is cut/fails.

The twist in the Sliding-X allows for one of the strands between the knots to be cut and the other (should) hold.

Ah, I see.  Hadn’t thought of that as I rarely use them.  Honestly that makes a very strong case for using limiter knots if you’re going to use an X.  

The main thing you should limit is the use of “limiter knots”.