Wednesday, March 24, 2010

Belay forces and A look at the "Equallette"

Holy writing, I've spent too much time thinking about this stuff but I'm a climbing nerd...

First off, if you're following this whole discussion you'll likely enjoy the comments section of the last two posts, some really good ideas and thoughts without the usual "the internet makes you stupid) influence in forums. Thanks for that to all who wrote.

The main question I have with most of the research done on belay anchors that I've seen is that it doesn't take into account the weight of the belayer (belayers) on the anchor as pieces fail. The falling climber is attached to a big spring, but that force goes through the belayer and into the anchors. If a piece in the anchor blows then the belayer is being accelerated faster than just gravity; he may become a sort of human "funkness" cleaner device on the anchor (not really 'cause hopefully he tied in with his rope, but there's the idea). This is why there are some very high forces in the "J.M" study when a single point blows with a 500-pound weight suspend on the anchor (that's about three of me, but hey, the world is getting fatter!).

I don't think I'm going to use the equalette, Trango Alpine Equalizer (nice video Mal!) or any other form of "self-equalizing" anchor very much. The easiest to explain reason is that equalettes and other systems are a pain to deal with, doubly so in winter. Knots lock up under real loads at hanging belays, especially with thin slings and cord. Even a falling second on the power point will completely lock most knots for the day in modern thinner materials.

The second reason is that any anchor that allows the focal point carabiner to move enough to produce meaningful real-world equalization also allows that carabiner to move so much that some degree of shock loading is inevitable when a piece rips. If you're clipped into the focal point with the rope then this shock loading will be lower, but the study that started all this discussion (link here) has made me think more carefully about what happens when a piece fails in a multi-piece anchor system held together with a static material. I await more research from Mr. JimE (like he doesn't have enough to do already at Sterling!) when he gets a chance.

The third reason is that if you build an equalette or other system "correctly" so that each piece equalizes relatively well (and in the real world I'm not thinking this happens much at all) then you only have a 1/3 chance of the anchor not extending violently if one piece is relatively weak... So then you have a 2/3 chance of a violent extension (equalette cord to piece A, carabiner on focal point, cord to a carabiner, sliding X to pieces B and C). Half the load theoretically will go to the leg that goes to A, and half to the leg that goes to the sliding X on B and C, so only 1/4 load on each of those pieces...). The way I'd build this anchor is to put leg A on the absolute strongest piece in the anchor, and a sliding X on B and C as they should only have 1/4 load on each of them. Might be easier to diagram this if it's not making sense. Anyhow, in a non-lab fall the odds are high that the impact is going to be violent and off to the side, or at least far enough off the vertical axis directly below the focal point that the carabiner is going to hit the limiter knots, and then you're totally on either the strong piece or the two weaker pieces. If either of the weaker pieces blow then you've got horrendous extension. If the "strong" piece blows then you're on the two weaker pieces and the equalization isn't that great so if one of those blows you're potentially shocking the hell out of the remaining piece.

A cordalette (a relatively huge knot, especially when tied with a figure 9) doesn't tend to lock up so much even in winter if done with 7mm or larger cord or a couple of slings roughly equalized and either tied together or clipped into a burly focal point (use the rope for the focal point--chance of cross-loading a biner, be careful of that) probably does about as well. Maybe. You should figure it out for yourself, I'm just thinking this stuff through. The more I think about this all, read about it, talk about and work through the more I end up in the same place: have at least one and better two or more bomber pieces in the anchor or it's not a bomber anchor.

Tuesday, March 23, 2010

Equalization/Extension in anchors post #2

The post on anchors prompted a lot of comments (should be right below this one). Right-click (or control click for the Apple cultists) on this to download it, nicer to have the PDF than to be looking at the study in a browswer window.

I spent some more time geeking out on the data last night. Here are my conclusions:

1. All of this is equalization/extension theory is primarily relevant in only three situations: A factor-two fall directly onto a belay, catching a second who somehow takes a relatively hard fall onto the belay, and when building a two or more piece protection point (this happens a lot on sketchy trad climbs and also on ice). These are situations where it would be real nice if the anchor equalized well under load, and then didn't shock-load the other pieces if one failed.

2. Unfortunately, it's about impossible to get any sort of realistic equalization out of a multi-piece anchor (with the gear we commonly use as climbers). If you go to page 29 of the study there's a low-friction equalization situation (equalette) shown there. Even in this perfect situation the pre-drop load totals per piece are obviously different (and could be improved by adding another sliding X etc.,), but even looking at the total "per leg" it's clear it isn't anwhere near perfectly equalized. The rest of the sliding X stuff etc. are worse (with the exception of page 28, but the extension problem is horrendous). A big smooth anodized aluminium 'biner might improve things a little, but even with knots etc. the real problem is what happens when one piece fails and the anchor extends. Yes, you cold tie limiting knots etc., but it looks to me like any extension is violent, which makes sense if you think about it (relatively static webbing or limited cord on a sliding X--bang).

3. In this study, and this is only one study, extension in the anchor is more problematic than poor equalization in terms of the max forces generated on the anchor. That's a real big departure from previous studies I've read.

All of this may and likely will change with the higher forces involved in a factor two or other high-impact situation with a lighter belayer and a larger fall force...

My basic idea that one piece in the belay must be capable of handling very high forces hasn't changed. I want one absolutely for sure bomber nut, cam, screw, whatever. Two absolutely bomber pieces are better, hell throw a third one in for grins. Two or even three or ten "maybe" quality pieces just aren't good enough. If I'm "equalizing" a stubby, an icicle and a shit pin for a piece before punching it up a difficult bit of alpine terrain I'm going to assume that the entire piece is only as good as the strongest individual piece.

I remember a helicopter pilot explaining the term "Jesus nut" to me. He didn't mean a super-religious person, he meant the nut that held his main rotor on. If that broke the only thing left to do was pray to Jesus. In a belay I want one super-solid "Jesus nut" that will hopefully hold any impact I can foresee and then some. And, because I'm not into the whole one-god thing too much, I'll put in another Jesus nut... And still try to limit extension to some point, and even roughly equalize it all.

And this may all change again once JimE gets some more research done, or I see another study done differently. I doubt that the basic concept of having one "for sure!" piece and preferrably two is going to change. And if I can't get that level of security then I'm gambling with two lives.

Monday, March 22, 2010

Maybe better to limit anchor extension after all...

Warning: Serious climbing geekery ahead. Short version: use bomber pieces in yer anchors...

I was out climbing on the weekend (rock, not ice), and at one point had to build a sorta odd anchor. A bomber cam, a very good nut, and a small nut that would be bomber if it weren't in Rockies limestone, all basically in a vertical line but spread out over about ten feet. I tied it all together with the rope to limit extension and felt good about it. But I knew that the stretchy rope would load each piece close to individually, and next thing you know I'm up for most of the night looking for information...

This is the most difficult to understand, broad and ultimately useful study about what happens when a single point in a multi-point anchor fails that I've read. It took me about an hour to start to understand what the results mean, and I'm still not sure I totally get it. The first interesting numbers really show why it's a bad idea to rig your anchors with your gear widely spread out unless you also use very long legs to hold it all together... This is why the combined force on each piece at the start of the test is higher than the weight hanging below the anchor (500 pound weight, but commonly 700 or so pounds total on the pieces...). To put it another way, it's not a good idea to have short legs and widely spread gear on any anchor system. This is why the "American Triangle" belay system had force issues.

The more I dig into the data at the end of this paper the more interesting the results become. No system does a very good job at equalizing the forces when a piece blows in the anchor, and this study was done in a perfect lab setting with a perfectly suspended weight. Tying marginal pieces together and equalizing them is bad physics if you want a good anchor. At least one piece in the anchor must be truly bomber; two or more is better!

Interestingly, total length of extension does appear to matter; this is in contrast to JE's tests. It doesn't matter (from the anchor's point of view, from the load's point of view it does...)whether you use one inch webbing, static cord, or 8mm nylon cord, high loads result when there is serious extension after an anchor piece fails. This is really interesting to me. JE's test results always seemed slightly odd to me, this makes more intuitive sense. However, Mr. JimE is a very smart guy, he likely has some ideas about what's going on. For now, I think I'll do a little more in my anchor building to limit extension. Not to equalize, but to limit extension. A cordellete, the rope, a sling, whatever, clip it all together so if something blows the extension won't be too dramatic. However, know that in the real world there will be extension and general weirdness, so make sure at least one and better two or three pieces are truly bomber in any pull direction that can be foreseen.

This is what's cool about climbing; just when you think you've started to figure it out something new or at least different comes along... I didn't learn anything about what I actually set out to learn (why does that happen so much on the internet?), but here I am writing about it like the nerd I can be...

If anyone comes up with something else out of this study please let me know, thanks.

Edit March 23rd: Some good comments below, thanks for that, be sure to read them.