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.

12 comments:

supos said...

Quite frankly, I get a headache just looking at all those elaborate anchors. I don't even want to think about using them in a real world situation, where stress and other factors multiply the potential of getting it wrong. For that reason, I'm a pretty big believer in the cordelette. After all, I'd guess (with nothing to back it up, I admit) that most anchor failure accidents happen because of human error, not gear breaking/blowing and the like.

However, I do see the problem of bad equalization. I believe however, that this problem can be greatly reduced by one very simple improvement: Use dynamic rope for your cordelette.

Static as well as dynamic stretching would lead to much better equalization prior to failure. Even if one piece blows, the shock loading of the remaining pieces (which is already pretty low with the cordelette) would be greatly reduced.

Best of all worlds: Simplicity of the cordellete, with improved equalization and even lower shock loading in case of failure.

One problem: Where do we find thin, affordable dynamic rope? I believe the thinnest you can get is Mammut Twilight twin rope at 7.5 mm, but that's quite expensive.


Nb. I have a pretty strong gut feeling that I'm forgetting something terribly important here. After all, if this was as good as it seems, everybody would be doing it, right? So please do correct me, before I go out and spend my hard earned cash on a skinny twin rope that's gonna kill me :-)

Will Gadd said...

Supos--I like cordelletes for some anchors for sure and you're right about nylon cord being better for impact absorption (in general), but I think you're missing something. Dynamic cord will help with impact forces to some extent, but it won't help equalize those forces. There's a bunch of info on this out there, but basically unless each leg of the cordelette is exactly equal in length then the different legs will stretch different amounts, putting different loads on each anchor point. Counter-intuitive, but that's how it seems to work. Picture a 20-foot bungee and a five-foot bungee, although the principle is the same with anything that elongates at all.

supos said...

I guess I was mistakenly talking about equalization when what I really meant was load sharing, as described in the paper you linked to. Using highly dynamic cord, would greatly helps in this regard.

Think about a three piece cordelette anchor using perfectly static cord. If you are unable to adjust the length of the legs perfectly, one piece will be completely unweighted. Try this with bungee cord, and all pieces will be weighted. Maybe not equally, but at least they'll all contribute to some extent.

Add to that the improved dynamic properties, and I don't see why we don't use dynamic cord instead of semi-static accessory cord for our cordelettes. Except of course for it not being available in 7 mm thickness.

Will Gadd said...

The problem is in the stretch. If you have a five-foot bungee cord and a ten-foot bungee cord in your anchor which one is going to take the vast, vast majority of the load? That's right, the short one. Under high loads the relative stretch becomes extremely important, and basically puts all the force on one anchor.

And, theoretically, it doesn't matter what you use for anchor material, it's all about the relative length and then of course relative stretch under load. So, no, you're not going to get much load sharing due to stretch, just the opposite in fact...

Another way to think about it is this: An absolutely static and perfectly balanced anchor with the load coming in exactly the line that the anchor is organized for will produce very good load sharing/load equalization/load distrubution/whatever you want to call it; one with unequal elastic legs won't. Make sense? Took me a while to understand this. You might get 50 pounds or something like that of "load sharing," but the stretch factor is gonna ruin things pretty fast.

Will Gadd said...

But you definitely are right about using static cord for impact absorption as long as it's strong enough! Some people use Technora cord for belays, not something I'm keen on, but neither am I keen on 5mm nylon cord at belays, weak enough to fail. 7mm nylon is the min. for me, or use the rope if possible.

maldaly said...

So have anchor systems been failing at an alarming rate and I've missed something, or is all the cordalette/equalette/Alpine Equalizer stuff solving a problem that doesn't exist? Seems to me that when I look through the ANAM journal each year I see injuries happen from falling rock or ice, falling climbers hitting heads, falling climbers breaking other bones, rappelling, lead gear pulling, belay failures, getting lost/benighted/delayed and exposure. Unfortunately the ANAM statistics compilations don't have a specific category for belay anchor failure so it's impossible to quantify the number of these accidents. As an ANAM junkie, though, I recall few (2) accidents with injuries that occurred because someone's belay anchor failed. And both of these incidences happened to SERENE anchor setups. Can anyone enlighten me here?

What I do see out there all the time--and it scares the shit out of me--is a generation of SERENE/Cordalette anchor junkies obsessed with building exquisitely constructed 3-point equalized, master-knotted, shelfed, and non-extending anchors, and giving no thought, whatsoever, to making them multi-directional. Now I don't know about the readers of this blog, but I've caught a hell of a lot of hard leader falls and the force has always, ALWAYS, pulled me up or sideways. I have never, not once (okay... on snow a couple of times), caught an F2 fall where the force has pulled me down.

So, how do I recommend building an anchor when I conduct a clinic? I tell the students to remember 3 rules. Bomber, Bomber, Bomber and Multi-directional. (Yeah, I know. That's four, but it helps me figure out who's paying attention.) Nine out of ten anchors I place are rigged with 2 down and one up. I tie in and tension them together with the rope, then clip in to the top piece with a draw or runner. The second piece (bomber, remember) is where I re-direct or belay from. That's it.

Now, I don't climb in the CN rockies, so I can count on what's left of the fingers of one hand how many time's I've had to set up anchors in crappy rock. If I get to a belay and the anchors suck, I move. I'll anchor a pitch short because I know that I can move faster if I set up a quick and bomber anchor and don't have to fuck around with a cordalette. What crops up more often, in the bad anchor category, is when I get to the only available belay spot and there's only room for a single piece.

So do I use cordalettes? You bet. I got stuck in Donini's driveway last winter and it took a cordallette chain and a truck to get me out. Seriously, I use them all the time when I'm setting up TR and I won't be staring at the anchor a lot. That's a perfect use for them. I don't guide any more but had I mastered cordalette skills back them I certainly would have made good use of them when multi-pitching with clients.

So spend your time teaching them the importance of evaluating rock quality and the quality of the gear placements. If they can recognize when a setup is bomber, then they'll spend less time rigging stupid anchors. Teach them how to move efficiently. There are 100 times more rescues called out each year because of the consequences of moving slowly then there are from belay anchor failures. Look at what causes accidents to actually happen, not at where they "might" happen, and teach to avoid and mitigate those. Spend your valuable teaching time helping your students and clients solve real problems, not "what if" problems.

Climb safe,
Mal

Will Gadd said...

Mal--thanks for that, excellent points, and they paint a bigger picture than I'm focusing on.

I totally agree on understanding the physics of what's gonna happen if the leader falls, and setting the anchor for an upward pull as well. I do need to reinforce that with not only myself but other people I teach, thanks.

And yes on the belay failure too. That said, the same stuff goes for rap anchors, which have killed a lot of people over the years. Multiple junk blades strung together do not equal a good belay or rap anchor...

And the truth of the matter is that I'm a nerd, and obsess about this stuff way too much, gotta face facts sooner or later!

Got stump? Yeah! When are you going to come back up north and do some climbing? It's still ice season here!

maldaly said...

Probably no more ice for me this winter. Just got back from the desert and am in full lizard mode now.

What I had originally written, and had to delete because of blogger's character limit, was that the concept of equalization or load distribution is an absolutely critical component of being able to build safe anchors. What's missing from most of the dialog and distracting to the main point--having a safe day in the mountains--are the concepts of multi-directional and being able to evaluate when, not just how, to build an distributed anchor.

Still in awe of your 24 hr climb.

Mal

PS, If we plan it carefully, I might actually be able to pull off a 20 sport day sometime if you're game.

SImon NZ said...

I am glad there are people who have the energy to put into these things.

I have a similar view - the cordellette has been popular for quite a while now globally yet it has not been the cause of many deaths that I am aware of - personally I think it's simplicity makes up for it's supposed weaknesses. When the carnage mounts maybe I will look again but it is still the main anchor linking system taught worldwide I reckon.

juho.risku said...

This comment comes kind of late. I just bumped into this article and obviously I should read climbing blogs more often. :-) Anyways it got me thinking about the belays, forces involved, limiting the extensions and equalizing.

I usually do a belay anchor by equalizing with a 120 cm sling and sliding x with limiter knots between two bomber screws. It led me thinking if one could tackle both the extension as well as piece failure into some extent by using two screamers clipped between the sling and each screw?

It might be obvious, but here's my thinking: Let's say that the screamers starts ripping at 4.5kN, which means roughly 7.5-9kN of total force until screamers start ripping (provided that screws are positioned correctly). --> Should be enough for most climbing conditions. So if one screw fails prior 4.5kN (which clearly means it wasn't bobmer), the screamer in other screw still limits the forces caused by the extension. It should also limit the problems related to improper equalization, as well as limit the overall forces applied to screws in the most serious falls.

All this being said, carrying two extra screamers might be a bit over kill (i.e. there might be better use for em elsewhere).

Will Gadd said...

Juho--

Hmmm, I'll have to think that one through, but off the top of my head since things are seldom actually equalized unless using a sort of equallette system then one screamer will start ripping first. If it rips enough to equalize with the other one then maybe that will work out? I don't know. I think the base idea that one point must be bomber is really important, more important than anything else. But I like the thinking.

Generic Viagra said...

you need all the equipment to practice this, we have to remember that is not a child play, your life is in risk in this practice.