Friday, November 24, 2006

More Gear Commentary

Anchors: Cordelette, Sliding X, or? A brief history of anchor building (with lots left out...)

When I started seriously climbing in the early 80s most of us weren't thinking all that deeply about equalizing multiple pieces at belay anchors. A couple of slings of roughly the same length on each piece, good to go. Then we realized this wasn't optimal, and started using the "sliding X," basically a sling clipped in the middle to equalize two pieces at a belay or on-route (the X keeps the biner from sliding off the sling if one piece blows). Then some "smart" people figured out that if one pice blew with a "sliding X" that it would theoretically shock-load the remaining piece. Cordelettes, basically a long piece of 7mm cord, became all the rage 'cause you could clip multiple pieces together quite quickly, and with what was thought to be good equalization. The preferred material for cordelettes was first 7mm nylon, then 5mm Spectra, then Dyneema, then someone figured out that these types of fibers don't stretch much which is hard on the anchors in a factor two fall, so it was back to 7mm nylon cord...

Some recent research suggests that cordelettes actually don't do a very good job at equalizing multiple pieces. In fact, they do a lousy job, and for a reason that in retrospect seems, ah, pretty obvious: If the legs of the cordelette are at all different lengths then they will stretch differently. So if there are two pieces in an anchor, "A" and "B," with the amount of cord going to "A" twice that of "B" then B will take almost all the force when loaded: less cord to B, less stretch, more load, especially as the cord or anchor point comes close to failing. The cord to A will come into play a tiny bit, but because there is so much more cord going to A the load on A will be relatively minimal... This seems very obvious when thinking it through, but I just took the whole cordelette concept for granted 'cause that's what the "experts" said to use on belays. Less stretchy webbing isn't any better, as it's the relative amount of stretch that matters--if webbing only stretches two percent at load then the short leg will just stetch at 2 percent of it's length vs. 2 percent of the long leg, same non-equalized loading situation. A cordellete will work great when all the legs are exactly the same length and the load comes from exactly the "planned" direction. My belays generally don't work like that when climbing (some top-rope or rescue anchors do).

Now there's also some new research that suggests the shock-loading problems with the "sliding X" aren't a big problem; in fact, the main problem with the sliding X system is that there can be a lot of friction at the "X," which reduces the effectiveness of the equalization system. Using a big anodized biner basically solves this. I really have to laugh about this whole subject, I can remember the epic arguments about the sliding X vs. the Cordelette; we were all arguing about the "wrong" factors. The problem with the sliding X wasn't the shock loading, and the problem with the Cordellete wasn't the 7mm cord... I actually thought the stretch in the cord would help equalize the various pieces, when in fact it does the opposite. This is why I'm a climber and not working on the space shuttle.

The solution to all of this is something called a "Duo glide." This a rat's nest of a knotted cordelette strung together in such a complicated manner that I am really likely to do it wrong in any but the most optimal of conditions. I played with it on my hallway coat rack and could get it right most of the time, but slowly. I don't like it. Trango makes something called the Alpine Equalizer, which seems promising, but when I alpine climb I want gear that does multiple functions and is easy to deal with. It also requires an overhand knot to work to it's full potential, and anyone who has tried to untie an overhand in webbing after it's been loaded, especially in winter, well, good luck...

I'm going back to a sliding X with a big biner, backed up with a sling of about the right length to a third piece. If the belay is so shitty that I feel perfect equalization is in order then I might go for the duo-glide option, but realize I'm basically being an idiot for trusting my life and that of my partner to a dubious belay.

There are several epic discussion on in the internet about this, about the best is here.

I thought Donald Rumsefield was an idiot for talking about "unknown unknowns" and such. He's still an idiot for other reasons, but in climbing there are a lot of "unknown unknowns." Anchors should have solid gear tied together in such a way that even if everything in the anchor blows but one piece the system will still hold....

Training: Went climbing yesterday, the elbow is not happy today. I am thinking of cutting the arm off. Bit extreme, might try more physio first.

3 comments:

Andy Arts said...

Hey Will,

Thanks for bring this up and re-educating us. I hope people think about changing with the times...

cragrat said...
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cragrat said...
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