Sliding X: Too Much Extension?
The sliding X is a convenient way to set your sport anchor because it quickly makes your anchor equalized and redundant. But, if you know yourbasic anchor principles, you know that there is more to a good anchor than just equalization and redundancy (SARENE-SA). The sliding X covers small angles (SA), redundancy (R), equalization (E) and small angles (SA), BUT it comes up short when you consider no extension (NE).
Picture for yourself what would happen if one of your bolts fail. The anchor will extend the distance between the failed bolt and the original apex of your X, thus shock loading the remaining bolt - not good. For this reason, many climbers choose to never use the sliding X and instead rely on the Figure 8 on a Bight, which has no extension in the event of a failed piece of pro. The downside of the Figure 8 on a Bight, however, is that it does not constantly equalize as the Sliding X does. The Sliding X has the ability to micro-adjust and equalize throughout the climb so that both bolts are constantly equally weighted. The Figure 8 on a Bight, however, is static and cannot micro-adjust once tied. This means that as the anchor gets weighted differently, the bolts are not taking an equal amount of weight. There are pros and cons to both the Sliding X and the Figure 8 on a Bight. Make an informed decision when setting your anchor based on the conditions of the bolts (if one looks more suspect than the other, avoid the Sliding X and go with the Figure 8 on a Bight) and the nature of the route below (if it is a wandering route, use the Sliding X so the anchor can micro-adjust and equalize). |
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There is an interesting thread on this topic on TradGirl.com. We've taken some of the most compelling arguments for and against the Sliding X and pasted them below. To read the whole thread, click here.
Mike Garrison, 8/16/2001 It's like everything else involving anchors. There are times to use it and times when something else is better.
When you don't need dynamic equalization, don't use it. The dynamic equalization comes at direct cost of extension risk. When you do need dynamic equalization, use it. There are techniques (such as knotting the slings) that reduce the extension risk in direct proportion to how much they limit the range of dynamic equalization.
Hans Lehmann, 8/16/2001 Let's not forget that the sliding X pretty evenly balances the load between the two bolts, so the chance of either one breaking is much less...It just seems to me that a sliding X is perfectly safe. IF one peice does rip then the 2nd peice would be shock loaded due to the 6-12 in of extension caused by the X. However that amount of force is still significantly less than that cuased by a lead fall. And we trust one bolt to hold during a lead fall, and IF it does not than, as you state, we expect the bolt below to hold, in spite of the now more than doubled force(compared to that of the first bolt) has to absorb. Which is equivelant to one bolt on the X giving out, only the second bolt only has to deal with 6-12 inches of force created, vs. 6-12 feet on the second bolt during the lead fall.
the ASCA Many climbers use a "sliding X" to equalize two pieces - ususally beginner climbers with bolt anchors. You should NEVER use this except in...specialized cases. While the sliding X does equalize the pieces, it assumes that neither could break, since if one does break, there is severe extension in the system - enough that it would likely cause the carabiners to break. Since it assumes neither piece would break, it's a stupid system - if neither would break, there's no need for equalization. If one might break, then there is WAY too much extension. This is why many call it the "death X." Instead, use one sling off of each bolt or piece. You can tie one shorter to approximately equalize the pieces if needed.
Greg Barnes, 7/8/2001 As I'm sure has been beat to death here in the past, you really shouldn't ever use the sliding X, except as a component of an anchor with no extension should one of the sliding X pieces fail (e.g. equalizing two poor nuts with the X, and then the X is one of three points of a cordalette) - or for equalizing dicey aid pieces. While the X equalizes better, it should only be used where both pieces are completely bomber, since if one breaks there is severe extension. Since you're using it with two bomber pieces, why worry about great equalization in the first place?
Anyway, just use separate slings on the different bolts (you can tie one shorter to approximately equalize if needed), and back up with another sling on the good bolt, all going to 2 or 3 biners, and you don't have to worry about it. But for a 2-piece anchor, dump the sliding X regardless. If you need to use it, it's too dangerous to use. If you don't need to use it, why make things complicated when one sling off of each bolt is better?
aT, 11/5/2001 This is actually recomended in John Long's "Climbing Anchors" book. You have to be careful though- there is a possibility of the overhand knot coming to rest at the tie in point in the event of one piece failing. don't want the knot *on* the biner..
Mike Garrison, 8/16/2001 It's like everything else involving anchors. There are times to use it and times when something else is better.
When you don't need dynamic equalization, don't use it. The dynamic equalization comes at direct cost of extension risk. When you do need dynamic equalization, use it. There are techniques (such as knotting the slings) that reduce the extension risk in direct proportion to how much they limit the range of dynamic equalization.
Hans Lehmann, 8/16/2001 Let's not forget that the sliding X pretty evenly balances the load between the two bolts, so the chance of either one breaking is much less...It just seems to me that a sliding X is perfectly safe. IF one peice does rip then the 2nd peice would be shock loaded due to the 6-12 in of extension caused by the X. However that amount of force is still significantly less than that cuased by a lead fall. And we trust one bolt to hold during a lead fall, and IF it does not than, as you state, we expect the bolt below to hold, in spite of the now more than doubled force(compared to that of the first bolt) has to absorb. Which is equivelant to one bolt on the X giving out, only the second bolt only has to deal with 6-12 inches of force created, vs. 6-12 feet on the second bolt during the lead fall.
the ASCA Many climbers use a "sliding X" to equalize two pieces - ususally beginner climbers with bolt anchors. You should NEVER use this except in...specialized cases. While the sliding X does equalize the pieces, it assumes that neither could break, since if one does break, there is severe extension in the system - enough that it would likely cause the carabiners to break. Since it assumes neither piece would break, it's a stupid system - if neither would break, there's no need for equalization. If one might break, then there is WAY too much extension. This is why many call it the "death X." Instead, use one sling off of each bolt or piece. You can tie one shorter to approximately equalize the pieces if needed.
Greg Barnes, 7/8/2001 As I'm sure has been beat to death here in the past, you really shouldn't ever use the sliding X, except as a component of an anchor with no extension should one of the sliding X pieces fail (e.g. equalizing two poor nuts with the X, and then the X is one of three points of a cordalette) - or for equalizing dicey aid pieces. While the X equalizes better, it should only be used where both pieces are completely bomber, since if one breaks there is severe extension. Since you're using it with two bomber pieces, why worry about great equalization in the first place?
Anyway, just use separate slings on the different bolts (you can tie one shorter to approximately equalize if needed), and back up with another sling on the good bolt, all going to 2 or 3 biners, and you don't have to worry about it. But for a 2-piece anchor, dump the sliding X regardless. If you need to use it, it's too dangerous to use. If you don't need to use it, why make things complicated when one sling off of each bolt is better?
aT, 11/5/2001 This is actually recomended in John Long's "Climbing Anchors" book. You have to be careful though- there is a possibility of the overhand knot coming to rest at the tie in point in the event of one piece failing. don't want the knot *on* the biner..
