Magic X versus quickdraws

[eternalX]

The other day my partner got into a discussion about what to use for an anchor on sport routes. He uses 4 locking biners and one sling using the magic x and I use two qds with locking biners. He says the sling is better because it's equalized and I say the qds are better because everything is backed-up. It's probably 6 of one versus a half-dozen of the other, but how can the sling be safer?

[Dru]

why do you carry 4 locking biners on a sport route anyway? are you one of those guys who takes prussiks and tiblocks to the gym?

[eternalX]

No. I only take a couple pulleys to the gym. Actually, I would normally use 2 qds each with one locking and one non-locking, but i was trying to compare apples to apples.

[ken4ord]

Agreed. Two regular draws, in oposition is what I have always used. I have never had it come unclipped or broken them. With that said locking biners are safer, but in my opinion, overkill.

[iain]

Forget the x. Just clip the sling ends and tie a knot in the webbing to equalize. No reason for that x business on a sport route (or really almost anywhere else). Draws are just as good.

[Dru]

99% of the people anchoring on a sport route will just use 2 regular quickdraws.

 

but back to your question.... the two quickdraws will not equalize whereas the magic x will. if the climb traverses at all below the anchor instead of being straight up and down, then there may be a point where you have unequal weighting of the draws or even all the force on one draw. in this situation the sliding X would be stronger even though not as redundant. so yes it is 6 of one half dozen of other.

[ashw_justin]

Two quickdraws are the standard, locking biners if you want to be really safe. The self-equalizing action of the "magic X" also leads to extension should one anchor point fail, this is understood to be a bad thing. Of course if the anchors are as bomber as they should be, you'd expect your gear to fail first, and even this is highly unlikely in a toprope situation unless there is unusual crossloading or rock contact on your gear.

 

Specifically regarding your partner's setup, the problem with that is there is only one sling holding the setup together, so if anything goes wrong with that one sling, there is nothing backing it up. Due to the fact that is in the "magic X" configuration and not tied off at the attachment point, failure at any point in the sling will eliminate your anchor.

[cracked]

Whenever I use a sliding X I back the power point up to one of the pieces with another sling or QD, so the system doesn't rely on one sling.

[badvoodoo]

I'm with ashw_justin on this one. Seems to me like using a single sling removes the redundancy of your anchor, which I'd put higher on my personal list of priorities than equalization if made to choose.

[Dru]

If the anchors are poor it may be better to equalize and distribute force than to sequentially weight and pop. It was suggested that the accident resulting in 2 deaths earlier this year on Tahquitz would have been avoided if the belayer had been using a sliding X rather than individually anchored to each piece. Certainly this is less relevant when anchor is a nice sport bolt pair but still worth knowing.

[ashw_justin]

How is the magic X not sequentially weighting and popping? If one piece goes, the other piece(s) get shockloaded sequentially. Better to equalize by tying off correctly...

 

(edit: unless it's a meandering route or traverse, and you can't set up adequate directionals...)

Edited September 8, 2004 by ashw_justin

[Dru]

it distributes the force evenly so is less likely to max out any one piece and cause the first failure in the cascade of failing pieces

[ashw_justin]

But then in a way you're putting all of your faith in your weakest piece, because it will be the first to fail, and the rest of the pieces will be shockloaded. You risk putting greater forces on more important pieces just to strengthen a weak piece. Unless all of the pieces are obviously horrible...

Edited September 8, 2004 by ashw_justin

[Dru]

Lets say your individual sucky pieces will hold 6, 8 and 9 kn. Climber falls and exerts 15 Kn of force at an angle to the anchor. Three way sliding X puts 5 kn of force on each piece... you both live because nothing pulls. "Regular" equalized-with-a-big-knot cordelette loads asymmetrically and puts all the 15kN on one of your three pieces...which blows...then the next...which blows...then the third... RIP you. This is more or less the purported scenario from the Tahquitz accident. Sliding X is not perfect for the resons you note, but does have its place as in the scenario I just described. A blanket condemnation of a belay anchor technique which under some circumstances is the safest thing to use, serves no one well.

[ashw_justin]

"Regular" equalized-with-a-big-knot cordelette loads asymmetrically

 

If it was properly equalized, it wouldn't load assymetrically. Then again I'm not familiar with the climb.

[ashw_justin]

The counterexample (because math is fun ) is three pieces, 5, 9, and 9 kN, with a fall force of 18 kN. If all pieces are equalized statically, the 5 fails but the fall is held by the two 9's. Equalized dynamically (magic X) the 5 fails, and the two 9's take 18 kN plus whatever extra force is generated when the magic X extends, possibly overloading the 9's and RIP.

 

Does anybody know how much extra force is actually generated when a magic X extends?

[Dru]

screamers on each piece man!

[ashw_justin]

My legs are rated to 873 kN!!

[catbirdseat]

Don't forget that the magic X is not perfect at instantly equalizing all the pieces. Due to friction, more load can go on one piece than on the other. I don't think there is any one perfect solution. If I were going to use the X is would probably only be on a pair of bolts.

[Greg_W]

Lets say your individual sucky pieces will hold 6, 8 and 9 kn. Climber falls and exerts 15 Kn of force at an angle to the anchor. Three way sliding X puts 5 kn of force on each piece... you both live because nothing pulls. "Regular" equalized-with-a-big-knot cordelette loads asymmetrically and puts all the 15kN on one of your three pieces...which blows...then the next...which blows...then the third... RIP you.

 

Just a question: In your scenario, once piece #1 fails, wouldn't piece #2 be subjected to somewhat less than 15 kN? The 15kN from the initial fall is generated partially due to the distance fallen through space. The distance of the fall due to piece #1 failing to impact on piece #2 is much less; therefore, less force is exerted on piece #2.

 

GregW

[Dru]

Don't go ruining my good hypothetical situation with some sort of weasel logic here!

[Greg_W]

I want to know if my line of thought is correct or not.

[Dru]

i think the shockload would partially compensate for the lower distance... but I think you are correct. When RP's came out they recommended using them in series as a shock absorber... sew a crack up with 6 of them, when you fell, the force would pull or break the first 4 or 5, then the force would be low enough that the 6th one would hold you

[Greg_W]

i think the shockload would partially compensate for the lower distance... but I think you are correct. When RP's came out they recommended using them in series as a shock absorber... sew a crack up with 6 of them, when you fell, the force would pull or break the first 4 or 5, then the force would be low enough that the 6th one would hold you

 

Gee, that sounds heartwarming...and pants-filling!!!

[iain]

Greg, that makes sense to me. It might not reduce the force by much though. I still don't like the sliding x. Using a cordolette, I think it is somewhat unlikely that a single piece will be loaded in such a manner at a belay anchor, unless the person who set it up completely blew it when determining the focal point of any forces involved. It won't be perfectly equalized, but such is life.