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Crag Q
Trad climber
Louisville, Colorado
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Topic Author's Original Post - Jan 13, 2008 - 12:03am PT
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The lastest Climbing Anchors book caused me to rethink a lot of things about anchors that I held as sacrosanct. This last year I used the equalette extensively. The ability to adjust the clove hitches to make things just right and the equalization seems to add a margin of safety for unexpected directions of pull not present in the cordolette.
However, for mulitpitch climbing I have some issues with the master point. Having to use two carabiners to avoid binding seems a little extravagant and does not leave a good place to attach a reverso. If you want to get around the 2 biners using a magic x doesn't leave much room if you want to clip in multiple things such as the rope, a daisy chain and a reverso type belay device. Either way the master point is not as spiffy as with the quad anchor or the cordolette. Also I have a hard time imagining the equalette working well in a big wall anchor scenario since the over hand knots could easily get welded and because of these short comings with the master point.
So, I set out to come up with a way to merge the quad style master point and the equallette. In the end the solution was pretty simple, but it took me a couple of months with fussing with my cord to figure it out.
SOLUTION: the triplette. Triple up your cord and tie two overhands near the middle, then configure like the equalette using clove hitches.
PROS over equalette:
improved master point
no clutch effect/binding
only requires single carabiner at master point (instead of 2 for equalette)
bigger over hand knots are easier to untie
equalization/load bearing should be similar to equalette
additional anchoring possibilities with tails
CONS
same as equalette in terms of load bearing
requires untying your cord which may require a knife if your knots are welded.
the long ends may cause some confusion if not integrated into anchor
Some pictures of anchors all tied with 14ft of 7mm perlon...
Figure 1: The QUAD for reference (doubled up loop of cord with 2 over hand knots):
Figure 2: The EQUALETTE for reference (2 overhands and 4 clove hitches):
Figure 3: The TRIPLETTE (2 overhands and 4 clove hitches)in same scenario as EQUALETTE above:
Figure 4: Tying the TRIPLETTE
step 1...
Figure 5: step 2...
Figure 6: step 3...
Figure 7: TRIPLETTE in 3 anchor scenario. It's important to leave quite a bit of tail to be able to move the big overhands left or right to do this:
Now for the encore. The tails seem to be pretty handy if you tie figure eights in them rather than leaving them dangling.
Figure 8: advanced usage with figure eight knots
This seems to simplify tying the rig because you can "cordolette" one side and then tie the other side and throw in clove hitches (or not) on the individual piece. Here's 3 pictures describing this...
Figure 9: step one, set up tripled cord on left side (16ft piece of cord)
Figure 10: step two, cordolette left side
Figure 11: step three, tie another overhand and finish right side using clove hitch to take up slack
Figure 12: Real usage in an ice anchor with 3 cams. It was kind of weird trusting my life to something that had only existed in my brain and in my basement. It seems to work really well and I didn't die.
Whatever anchor setup you use, happy and safe climbing! I appreciate any feed back you may have.
-Craig
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Scrunch
Trad climber
Provo, Ut
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Jan 13, 2008 - 12:14am PT
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cool! I think that would be a good solution to some of the problems I've had with the equalette. That being said, I usually only use something like that in a wall situation, where you can use complicated procedures. I still build multi-pitch anchors with the rope, because I'm lazy and only use bomber anchors.
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WBraun
climber
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Jan 13, 2008 - 12:22am PT
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That's pretty eloquent.
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Tom
Big Wall climber
San Luis Obispo CA
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Jan 13, 2008 - 02:39am PT
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You want the anchors to be loaded mostly vertical, and not at all horizontal. At 45 degrees, you have about a 1.5 times-the-load force on the anchor, because the load is pulling sideways, as well as down, and the total force on the anchor is higher.
Keep the slings long, and the angle mostly vertical. Don't multiply the forces on the anchors with an unnecessary/unwanted mechanical advantage.
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Crag Q
Trad climber
Louisville, Colorado
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Topic Author's Reply - Jan 13, 2008 - 09:54am PT
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Scrunch,
I was actually trying to solve the big wall dilemma of "where am I going to clip everything" when I came up with this idea. I think a webolette like Metolius and Mountain Tools sell might work nicely with this setup.
Tom,
That's a good point about horizontal vs. vertical orientation. For a vertical setup the over hand knots need to move quite a bit to one side instead of the middle, but other than the setup is the same. For purposes of show and tell, it's much easy to photograph and see in the horizontal setup. Also, that is a little shorter (14ft)than the standard length (16-18ft), so that's probably distorting the angles a little bit. Obviously, in the real world you have to work with whatever you got. It's interesting that 99% of all bolt anchors are setup horizontally in total disregard to the mathematics of physics.
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marty(r)
climber
beneath the valley of ultravegans
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Jan 13, 2008 - 03:27pm PT
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Meanwhile, a storm has rolled in, your partner is mumbling to him/herself, and Croft has lapped you...twice. Safe? For sure. Time consuming? No doubt. I'm guessing that most folks are passing on so much work, but who knows.
Thanks for the instructions.
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JohnRoe
Trad climber
State College, PA
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Jan 13, 2008 - 09:26pm PT
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I made that thing in my basement last month too! (But two strikes against me: (a) I have not taken it outside yet and (b) I did not think of the name).
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Crag Q
Trad climber
Louisville, Colorado
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Topic Author's Reply - Jan 13, 2008 - 10:12pm PT
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I never said it was faster. I should have listed that in the cons. The ease / complexity of setup is comparable to the equalette. Truth be told Croft is going to pass me twice before I even finish the first pitch and get my cordolette out.
None the less, the complexity of any anchor system can be evaluated using the Western Anchor Numerical Knot Scale the foundations of which are laid down in the introduction to Ashely's Book of Knots. Essentially, the complexity of any anchor system can be evaluated as the number of links plus the number of knots.
Huber's NIAD ascent clove hitching one bolt = 1 knot + 1 biner = 2W
quad on 2 bolts = 3 knots + 3 biners = 6W
2 quickdraws on 2 bolts = 4W
cordolette with 3 pieces = 2 knots + 4 crabs = 6W
equalette with 3 pieces and 2 lockers on master point = 5 knots + 5 biners = 10W
triplette with 3 pieces and 1 locker using figure eights on the tails = 5 knots + 4 biners = 9W
mooselette with 3 pieces = 6 + 3 = 9W (lower than I thought)
clovehitching 3 pieces = 3 + 3 = 6W (higher than I thought)
utlrabiker figure 8 with 3 pieces = 1 + 4 = 5W
A noob or less than mechanically inclined person can't assemble anything higher than a 5W unless they were a Tenderfoot in the Scouts according to my friend in the AMGA.
It's also worth nothing that for alpine climbing the scale must be adjusted for air temperature, wind velocity and cord length, but that's beyond the scope of this post.
John it doesn't count unless you post it first! I here by declare that I am the first person to tie two overhand knots in a tripled up piece of cord (ever).
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Largo
Sport climber
Venice, Ca
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Jan 13, 2008 - 10:26pm PT
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I think if you kept the master point (essentially the quad power point set up between two overhands) tied, then riging might be pretty quick - just tying off the placements. You'd have to have pretty lengthy arms to cover most all anchoring arrays, but I could see how this system could be quick and efficient in the right hands. The main thing is for people to keep fiddling around with the basic concept and refining it over time, letting practical experience be the guide.
JL
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Crag Q
Trad climber
Louisville, Colorado
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Topic Author's Reply - Jan 14, 2008 - 09:16pm PT
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Largo,
Thanks for the comment. I was curious what you might think. So far I'm finding it works best with the figure 8's in the tails and moving the overhands to balance out reaching the placements. No doubt I'll keep playing around with it since it shows promise.
P.S. Last post is tongue in cheek.
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Clint Cummins
Trad climber
SF Bay area, CA
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Feb 22, 2008 - 04:04pm PT
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This is my favorite method:
No extra gear needed, fast, and reaches between widely spaced anchor points when necessary. (red rope = lead line)
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GDavis
Trad climber
SoCal
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Feb 22, 2008 - 06:11pm PT
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Interesting idea, definitely seems like something that I would like to use. As for me though, I don't think I would have the time to set that up, even if I had the thing wired. If there are bolts I usually just do the cheap n easy overhand o'lette, which takes about 10 seconds total.
If your set up could be done easily and as fast as any others, I would think it would be one of the best out there. However for bigger routes, just too much time.... think simple :D
i dont climb by the way i just post on internet and have argument.
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Mighty Hiker
Social climber
Vancouver, B.C.
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Feb 22, 2008 - 06:47pm PT
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I enjoy and learn from these discussions - it almost makes me reach for my copy of "Belaying the Leader", which was one of the earliest engineering/physics analyses of these things.
The concern I have is that a solution like the triplette (not to be confused with the Triplets of Belleville) may be a bit complex for real world situations. That is, climbers used solely to bolts and bolt belays, seeing a triplette (or indeed some other belay anchor systems that are promoted), would either get confused and screw it up, or say "Why don't we just put some belay bolts in?" There's enough convenience bolting already IMHO. Likewise, climbers have an intuitive grasp of physics, but that's as far as many want to go. Their eyes glaze over fairly quickly. And finally, climbers tend not to practice what is preached at them - an example is the passive resistance to suggestions that they not belay/lower through rappel rings or such. (Not to mention littering...)
I'm also not sure it is wise to suggest that belays MUST be 100% bombproof. The real world isn't like that, as others have mentioned upthread, and all climbing involves risks, trade offs, and judgment. But some at least will draw the conclusion from this that belay = bolts.
As the saying goes, KISS. The first principles are that people have to know how to place, and do place, reliable redundant belay anchors. The second is that they have to be attached to them. The other aspects of setting up a good belay may be less important. Peoples' belay anchors usually fail (so far as can be told) because they pull out, or the climbers weren't well attached. Unequalized anchors and other factors may play a part, but the bottom line is:
1. Have two (or more) reliable multidirectional anchors, equalized if time and circumstances allow.
2. Make sure you're tied securely to them.
3. Belay carefully.
After that it may be details - the rate of return (stronger, safer belay) quickly diminishes in terms of the time and equipment required to do the work, and considerable judgment is required to do it well.
Certainly the triplette, and similar solutions, are the sort of thing that experienced, skilled climbers should know about - although they may not always have the time or equipment to employ them, or simply will judge that a simpler solution is acceptable in the circumstances. It may be less applicable for novice and intermediate climbers.
I've used innumerable belays over the years that didn't meet the SERENE standard, but were still quite safe. (Not all - some were terrifying.) Many of those on SuperTopo can probably say the same. We know better now, and the quality of belays has improved. But if the goal is safer climbing, education and training, and experience, may be more effective than more complex, albeit perhaps stronger/safer, belays.
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Ragz
climber
Tartarus, black hole of the internet
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Feb 22, 2008 - 07:36pm PT
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Hiker, I agree.
climbers used solely to bolts and bolt belays, seeing a triplet (or indeed some other belay anchor systems that are promoted), would either get confused and screw it up, or say "Why don't we just put some belay bolts in?" There's enough convenience bolting already IMHO. Likewise, climbers have an intuitive grasp of physics, but that's as far as many want to go. And finally, climbers tend not to practice what is preached at them...
And egos prevent even the best ideas from getting thru. I will say that there is a comfort working with what you know, but that's limiting yourself. Learning to do something automatically in a crisis jsut takes practice (Oh, there's that boring word). In regards to the length of time it takes/complexity, that's bull IMHO. A couple hours practice will have it dialed, and although I have never used it I'm sure it could be tied in less than the time it takes to place three good pieces. Folks want to rely on bolts, fine. Only climb routes with bolts. It's about being resourceful. The more tricks I know the better equipped I am. Running out of options on a climb can be a real screw in your day.
The setup looks pretty straight forward, and worth a good look.
Thanx
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Crag Q
Trad climber
Louisville, Colorado
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Topic Author's Reply - Feb 22, 2008 - 10:09pm PT
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Yo trenchdigger. Awesome! I don't really follow rockclimbing.com, just supertopo and parts of mountain project. It looks we hit upon the same concerns and then a similar idea. Very cool. I look forward to reading the whole thread. I think you may get win "prior art" award.
I think putting the figure 8's on a bite on the tails makes this triplette idea really fly and expands the possibilities of what this rig can do.
I agree with a couple of the posts here that it's important to keep your mind open and keep learning and thinking. There's no one system that works for everything. Some people seem to get confused about that in these anchor discussions. A big bag of tricks is a good thing to have even if you have your favorite.
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Crag Q
Trad climber
Louisville, Colorado
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Topic Author's Reply - Feb 22, 2008 - 10:12pm PT
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Clint, I hardly ever use that anchor. True, it's on of the most spartan and bomber and retro. But if one person is doing all the leading you can't swap out easily, there's no place for the reverso and no easy way to escape the belay in case of accidents. :-(
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Clint Cummins
Trad climber
SF Bay area, CA
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Feb 22, 2008 - 11:09pm PT
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> I hardly ever use that anchor. True, it's on of the most spartan and bomber and retro.
Well, like you said, people have different reasons for using different methods. Your method is plenty good, and I would have no problem if you belayed me on it.
> But if one person is doing all the leading you can't swap out easily,
To handle that, you can add a free biner on each anchor piece (3 in my example), and clove hitch the follower into those, with their end of the rope.
> there's no place for the reverso
I don't use one, but how about on your belay loop?
> and no easy way to escape the belay in case of accidents. :-(
I've never needed to do that in 35 years. Have you ever needed to do it?
I suppose it could be done with some effort, like adding 3 biners. That might be good enough to handle once in 40 years? If you are doing all the leading, is escaping the belay less likely to be needed?
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Crag Q
Trad climber
Louisville, Colorado
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Topic Author's Reply - Feb 22, 2008 - 11:43pm PT
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Clint, you make good points. However, some of my partners like to hang when following. Having a reverso setup on the anchor makes that very easy to deal with.
As for needing to escape the belay with accidents, I prefer to deck on the belay ledge and then let my partner evacuate me. That simplifies self rescue quite a bit even on a multipitch climb.
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mike
climber
I have no clue
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Feb 22, 2008 - 11:59pm PT
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Nice setup. I supose setup and breakdown speed is subjective to your available placements. Commments?
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johnboy
Trad climber
Can't get here from there
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Feb 23, 2008 - 12:05am PT
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In your second to last pic (4 point anchor) only one leg on each side bears weight as you slide your anchor point one way or the other. If these two weight bearing legs are the ends with the figure eight in them, then the total weight of the anchor is bearing all the weight on only two strands of perlon. They are backed up on each side. If the backup is a clove hitch, then if the figure 8 leg fails, all the weight is again transferred (shock loaded to a degree) to a single strand of perlon.
Something to think about when setting it up.
another note edit: This is also one of the short comings of the equalette.
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WBraun
climber
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Feb 23, 2008 - 12:10am PT
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"no easy way to escape the belay in case of accidents"
That's not true.
You just untie from the rope. And yes I've had to do this many times for various reasons not necessarily due to accidents.
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Crag Q
Trad climber
Louisville, Colorado
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Topic Author's Reply - Feb 23, 2008 - 12:22am PT
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Werner, I had you figured for more of "cut the rope" kind of guy. But alas, you found the simpler path once again.
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ChrisW
Trad climber
boulder, co
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Feb 26, 2008 - 11:23am PT
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Hey Craig!!! You are such the thinker. But remember more steps, more complicated, more chances of something going wrong. Remember our anchors at "CAMP" Those where BOMBER.
Man, haven't seen you for years. I am getting knee surgery this week. But, ready to go again in September. Been doing in big Walling?????
HOw's the kids?
Chris.
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Crag Q
Trad climber
Louisville, Colorado
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Topic Author's Reply - Feb 27, 2008 - 10:05pm PT
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I'm doing great Chris although the girls and work have been keeping me busy. Climbing has taken some set backs the last couple of years. I broke my arm last spring as a follow up to my accident the year before. Hoping to get back on track this spring.
Neil Worden came through this winter. It was good to see him.
Where are you hanging these days?
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Brentg
climber
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Craig, great rigging. Just a few ideas to add & see what people think. I don't think I would personally use the setup in the first few pics where overhands were tied with the strands hanging. This leaves you having to clove hitch to pieces, which along with the powerpoint are reasons that have kept me from using the equalette. The clove hitch may be fast & easy but it's still a knot and requires adj. However, when I saw your rabbit runner setup it got me thinking. For most people that think this is to much work or to complicated, after maybe 10 min. of messing with this rigging I could consistantly set it up in no more than 10-20sec longer that a cordolette & much quicker than an equalette. Basically 2 overhands instead of 1 overhand with cordelette. I don't clove to any pieces, just clip bights and ends of rabbit runner as if rigging cordelette. In a 3-4 piece anchor, equalize your powerpoint as you would with cordelette, release the outermost arm or arms, tie your 2 overhands in proper location, and clip arm back in. I'm not adding anything new to Craigs great idea, but perhaps further expressing the simplicity of it. I'm basically doing what Craig is showing in figure 9-11. Instead of equalizing the 2 left bolts & cloving to the right, I'm rigging the whole thing, finding the powerpoint & then tying overhands.
My main ? for everyone after playing with this idea is why not just carry a couple rabbit runners instead of tied cordelettes or equalettes? Does anyone already do this? Any ideas? $8 for 7mm cord & you can buy sewn rabbit runners for the spectra lovers. I found using a 14ft. rabbit runner I could rig an equalette(triplette) to 2-4 pieces, or a cordelette to 2-4 pieces in about the same amount of time. Further you could double it over to sling trees, boulders, etc. Seems pretty versatile to me. Also, using the equalette with 4 pieces=4 single strands tied to each piece. With a rabbit runner you end up with 2 loops & 2 single strand. Don't know how much that matters. I think I have way over thought this. I need to go climbing.
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Crag Q
Trad climber
Louisville, Colorado
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Topic Author's Reply - Mar 21, 2008 - 10:07pm PT
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Hey Brentg,
I think that's a nice simplification! Shazam! Basically doing a mini cordolette on the left and right. I gave it a quick go and seemed to work very well in the horizontal configuration. I sort of did my figure 9 & 10 on the left and then again on the right. I suspect you could also string it all together, unclip a couple strands and tie the two knots sort of like tying a cordolette with two overhads. It sounds like maybe that's what you did.
You could throw in a clove hitch on any leg after if you needed to take up some slack or make an adjustment. I agree, it's a pretty simple rig once you do it a few times and not really all that complicated.
I haven't tried it out with a rabbit runner, but I suspect the metolius and moutain tools webolette things would rock if you eliminated the clove hitches. However, regular 7mm works nicely and is much cheaper.
Sorry, I missed your reply earlier. Mundane climbing topics like tying knots don't survive long on the front page. :-)
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JAK
climber
The Souf
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Apr 12, 2008 - 11:20am PT
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Hmmm...
Not sure how I feel about this. The potential to equalize 6 pieces is interesting. However, I wonder about situations where I might need a *six* piece anchor. Few and far between in good rock.
It does seem like it'd be faster than a regular three-strand-powerpoint equalette to rig less than four pieces.
However, it's definitely always going to be bulkier and result in a more complex anchor rigging.
I think I prefer the method I've been using, which is essentially the same, but without the fig8 legs. I just tied the tails into a double OH check knot behind the overhand limiter knots, and trimmed them.
It's pretty much what Trenchdigger described last May here:
http://www.rockclimbing.com/cgi-bin/forum/gforum.cgi?do=post_view_flat;post=1595156;page=1;sb=post_latest_reply;so=ASC;mh=25;guest=29388045
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Karl Baba
Trad climber
Yosemite, Ca
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Apr 12, 2008 - 12:16pm PT
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Any system where you have to untie the knots joining the cord is a deal-killer in my book. Perhaps you could make that part of the system modular and attach the legs.
Basically though, in almost any decent rock, anchors should never be so sketchy that perfect equalization should be needed.
The lack of shock-loading afforded by a regular cordalette may be better protection that perfect equalization.
Also, the time savings afforded by any system that's significantly faster to employ might afford more safety than a slower, better equalized system. Time is safety on longer climbs.
Here's my idea, if you REALLY need the best anchor protection on some sketch rock, just clip a shorty screamer to each piece (or at least one or two of them) and rig a regular cordalette anchor to the screamers.
If the system gets stressed enough to be an issue, the screamers will extend, leading to perfect equalization with no shock load, and also absorb energy from the situation at the same time.
How's that sound Largo?
Peace
karl
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Gobie
Trad climber
Northern, Ca.
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Apr 12, 2008 - 12:38pm PT
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I agree with ragz. Adding another tool to your arsenal is wise. I prefer to use a simple anchor much like the one Clint has shown up thread, but you should be able to look at the situation and quickly analyze what may work best for you at the given moment. If you insist on one type of configuration for every belay that requires passive protection you could spend unnecassary time configuring something that is not needed. When I first started climbing I took for ganted that anchors came easily for me. After teaching and guiding it became quite obvious that there are very talented people that struggle with anchor configurations. Ive always inisted to them that they take whatever time is necassary to first build a sufficient anchor, then worry about time. Ultimately the goal is to live to climb another day. I have actually climbed with a guy once that told me as I started to clean his pitch that I probably didnt want to trust his anchor. When I got to the belay i could tell he was gripped and his anchor consisted basically of a magenta camalot laying in the crack equalized to a small stopper. He had plenty of gear to rig a belay but for whatever reason he got freaked out and was unable to think straight. As someone mentioned above, stress can affect your posture so having rehearsed many scenarios is key to survival. I think we should do the basement scenario standinbg in a bucket of icewater, with the sprinkler on, in your underwear, with some one yelling your gonna die over and over again in your ear.:]
BTW, when I got to my buddies belay, I calmly reassured him that his belay was crap, clipped throug a couple of pieces I added and then suggested that I lead out the remainder of the day. No sense in overreacting and ruining a nice day in The Meadows.
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johnboy
Trad climber
Can't get here from there
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Apr 12, 2008 - 01:48pm PT
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The potential to equalize 6 pieces is interesting.
Could you explain how this is done?
In my estimation you might get an approximate equalization (if your cloves are precise) at one position. If your PP moves left or right with this, your left with equalization on 2 points that are backed up by the other points of protection.
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apogee
climber
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Apr 12, 2008 - 03:35pm PT
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Anybody aware of a significant pattern of anchor failure using the traditional cordelette method of rigging? Not just anecdotal evidence ('I know a guy who...', 'I heard this somewhere...'), but a clearly demonstrated and documented pattern?
The theoretical advantages of these variations all sound plausible and reasonable, but at some point theories can elevate beyond practical reality. That is to say, if we were seeing a significant number of anchor failures due to the traditional cordelette method, then the goal of additional equalization (and added complexity of building) would be justified.
I'm all for exploring new applications and theories, as long as there is a clear, realistic application and need. The most beautiful, effective mechanical systems are simple ones.
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Tahoe climber
Trad climber
a dark-green forester out west
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Apr 12, 2008 - 05:27pm PT
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I like the simple ones, too.
Nice reply above, Clint Cummins.
Good to discuss. Good to have tools in the old toolbox.
Use what works best for you, but for me, cordelette works best all around, with clove hitches to gear coming in close second.
TC
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Ed Hartouni
Trad climber
Livermore, CA
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Apr 12, 2008 - 05:55pm PT
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There are no statistics for belay anchor failure as there are relatively few accidents involving anchor failure, especially anything well documented, for obvious reasons.
For the most part, testing various anchor scenarios is limited to "the lab" which has some limitations. The work that was done to investigate the equalization properties of the cordelette was done in controlled conditions in the lab. Those tests showed the superior equalization properties of the "sliding-X." These sorts of tests are useful when thinking through a belay anchor system like tying your rope to one piece with a clove hitch and then putting a couple of more pieces in, connected with the sliding-X, and equalizing the length or the rope. That's the system I prefer, but I also believe that you should get anchor pieces in such that any one of them would hold a severe fall.
I think there are many possible, excellent anchor systems. But these haven't been tested by many severe falls. There are no systematic studies of belay anchor failure. That is good, we seemed to have addressed this issue with redundant safety systems.
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apogee
climber
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Apr 12, 2008 - 06:18pm PT
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Ed-
I posed that rhetorical question (apologies if it was misleading) as an attempt to bring perspective to the question of the 'triplette' system- unless I've been missing something, I've not heard of a multitude of anchor failures (documented or anecdotal) due to the use of the 'traditional' cordelette system.
The theoretical and lab-studied advantages of the triplette or many of the other variations seem to be attempting to create a solution to a problem (anchor failure) that doesn't seem to exist. The speed and simplicity of traditional cordelette system seems to far outweigh any minor lab-discovered equalization issues.
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Largo
Sport climber
Venice, Ca
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Apr 12, 2008 - 06:34pm PT
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Karl wrote: The lack of shock-loading afforded by a regular cordalette may be better protection that perfect equalization.
Except that lab testing strongly suggested that shock loading does not occur in the way we once thought - that the dreaded "cascade" zipper would happen if one piece ripped, and that the total force of the fall would be transmitted from one failed placement to the next one. There are many variables involved, but providing that the first placement (to fail) has some decent holding power, it actually REDUCES the loading forces onto the next piece in the chain. But there's some pretty fancy physics (especially once dynamic cord/sling is introduced) involved here and I'd better leave it at that.
That much said, I truly believe that the emphasis on the absolute holding power of the anchor is largely misplaced. When belaying a second up, unless there is a chance for a huge swinging fall, the load on the anchor is comparatively small, unsually in the low hundreds of pounds. The emphasis should always be on making sure that the top piece ("Jesus nut"), the piece that will actually arrest the leader fall, is bomber so you never fall directly onto the belay anchor - something that is exceptionally rare on everything but slab routes.
JL
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rgold
Trad climber
Poughkeepsie, NY
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Apr 13, 2008 - 09:10pm PT
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Apogee wrote: "...unless I've been missing something, I've not heard of a multitude of anchor failures (documented or anecdotal) due to the use of the 'traditional' cordelette system.
The theoretical and lab-studied advantages of the triplette or many of the other variations seem to be attempting to create a solution to a problem (anchor failure) that doesn't seem to exist."
The thing about anchors, as Ed points out, is that we have virtually no idea how good belay anchors are. And as we soldier on in this state of almost complete ignorance, it is convenient and comforting to mistake the fact that belay anchors are almost never tested for evidence that they almost never fail. We don't know if the anchor failure problem "that doesn't seem to exist" is a reflection on the basic soundness of climbing anchors or an artifact of the extreme paucity of factor-2 falls.
In fifty years of climbing (as of this summer), I've come across about five documented cases of anchor failure in the U.S., a rate of about one every ten years. (I have no idea what numbers the rest of the world has experienced.) Without even a hint of knowledge of how many anchors in the U.S. in the last fifty years have been subjected to factor 2 falls, we have absolutely no idea what the anchor failure rate is and so have absolutely no idea whether or not an anchor failure problem exists.
Let me add that when it comes to anchors, what we consider "experience" in the climbing world is a process that contains virtually no reality feedback, because hardly anyone who builds an anchor and makes a judgement about its soundness is ever confronted with a test that would enable them to understand (and possibly modify) how sound their judgement is. "Experienced" people whose anchors have never been tested teach other people to build anchors, and those other people build lots of untested anchors and eventually themselves become "experienced." I might add that, if memory serves, all but one of the anchor failures I referred to happened to "experienced" parties.
I'm not suggesting that we have any realistic alternatives at the moment, nor am I suggesting that we abandon our faith-based practices and instead wallow in paralyzing fear and dread. I do think the climbing world could pay more attention to Largo's exhortations about protecting the belay It is possible that discussions about equalization are distracting people from a far more important imperative.
Finally, I think that it is appropriate, considering the actual state of ignorance we live in, to adopt, first of all, a humble attitude about our so-called "expertise," and second of all, to cut those who wish to experiment with more effective procedures a little more slack then they seem to be getting, even if we do not yet find ourselves pursuaded to adopt solutions that, at this very early stage, seem too cumbersome and time-consuming.
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Crag Q
Trad climber
Louisville, Colorado
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Topic Author's Reply - Apr 13, 2008 - 09:34pm PT
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Rgold that is one of the most articulate and spot on replies I've seen to anything on this forum.
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morse
Trad climber
CT
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Apr 13, 2008 - 11:05pm PT
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Interesting,
How about a "quad" configuration with a Frost knot on one side and an overhand knot on the other side (tied with 10' or 12' of 7mm or 8mm). Should be pretty clean.
Originally, I was playing around with the Frost knot as a way of eliminating the double fisherman's knot (one knot instead of two/and full strength strands) for a two-bolt powerpoint like you would find on a wall climb.
The only way to adjust it though is to take wraps around the carabiners at the bolts.
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Karl Baba
Trad climber
Yosemite, Ca
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Apr 13, 2008 - 11:18pm PT
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Rgold wrote
" Without even a hint of knowledge of how many anchors in the U.S. in the last fifty years have been subjected to factor 2 falls, we have absolutely no idea what the anchor failure rate is and so have absolutely no idea whether or not an anchor failure problem exists. "
It's an exaggeration to say we have "Absolutely" no idea about what kind of problem anchor failure is. We find out when somebody dies from it and we're a small enough community to hear stories as well. If it were an endemic problem, we'd know.
but here's another thing we don't know, How much of an extra window of security does perfect equalization afford? For instance, in how broad a range of forces would a Equalette hold when a regular cordalette would fail. If you drop a truck on parachute cord, it's going to fail no matter how it's tied, and if you drop a sport climber on either anchor clipped to modern bolts in good rock, it's going to hold no matter how it's tied. So how wide is the grey area where it might make a difference.
Where are testing geeks when you need them?
PS Largo, are you talking about pieces of the anchor failing and not causing shockloading or pieces in the climbing protection system? I talking about the anchor. if it's an extending system, and an anchor piece fails, how do you not get shock-loading? It's pretty similar to cleaning pieces with Funkness, eh? If there's no shock-loading, why not just use a sliding X and call it good?
Peace
karl
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Ed Hartouni
Trad climber
Livermore, CA
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Apr 13, 2008 - 11:39pm PT
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We don't know how many times anchors have been tested.
We can guess that anchors have been tested by high force falls.
Most of us have probably held some sort of weight on our anchors, say 500 lbs (two beefy climbers with gear) and the anchors hold routinely.
Many of us have probably held a fall on our anchors, likely at low fall factors and with gear between us and the leader. Here the force is likely to be up, lifting us and using that weight as a counter balance with little involvement with the anchor.
Few of us have held serious falls without gear between us and the leader onto an anchor. This is the most stressing test. The infrequency of this happening could be because we know not to allow this particular situation to occur, we put gear in to "protect the belay." Routes on which this is likely to be difficult to protect, bolted face and slab routes, the anchors are generally bolts. If the bolts are in good shape then we're golden.
I suspect that in most cases a Cordelette is sufficient protection, even though it does not equalize. It is no worse than a sequential tie off using clove hitches, a system still used by many, and probably safely.
Statistically it is difficult to determine what the failure rate is, though I believe you can get a good idea, and it is greater than we think. However, modern practice is hugely redundant, and that redundancy does a good job keeping us safe. We just can't put a number on how good a job that is...
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WBraun
climber
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Apr 13, 2008 - 11:53pm PT
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Nice analysis Ed.
There was an anchor failure years ago during a SAR Training in the Bay Area on a sea cliff. The instructor set the anchors.
One anchor was the main line and the second was the belay line for a standard raising and lowering system.
Somehow the instructor had the brilliant idea to show his students what happens when the main line fails and how the belay line takes the load and saves the day.
He goes to the edge and cuts the main line with a knife and falls onto the belay line.
The belay anchor then fails as the students watch in horror as their instructor pummels to the sea rocks below.
A real rescue body recovery then came to follow in order.
Hummmmmnnnn?
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rgold
Trad climber
Poughkeepsie, NY
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Apr 14, 2008 - 08:31am PT
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Karl wrote: "It's an exaggeration to say we have "Absolutely" no idea about what kind of problem anchor failure is. We find out when somebody dies from it and we're a small enough community to hear stories as well. If it were an endemic problem, we'd know.
You haven't understood my point, Karl, and as part of that misunderstanding, you changed my language. Perhaps a rereading is in order.
"but here's another thing we don't know, How much of an extra window of security does perfect equalization afford? For instance, in how broad a range of forces would a Equalette hold when a regular cordalette would fail."
An excellent point. One thing that seems to be emerging, from various tests, is that with a tied cordelette three-piece anchor, one piece tends to get half the load. With perfect equalization it would be a third. Would a piece that could withstand a 3 kN load blow at 4.5 kN? Possibly, and then the question is what happens to the rest of the anchor. But the issue is moot, because in spite of the pages and pages of posts on the subject, no one has come up with a way to rig a three-piece anchor that seems likely provide, in practice as opposed to in theory, a load distribution that avoids the 50% to one piece scenario, because all the complex load-equalizing systems are either likely to be sabotaged by internal friction or are based on an equalette on two of the three pieces and end up delivering half the load to one piece, even theoretically.
So what to do in practice? If you find yourself forced to use a crappy two-piece anchor, an equalette (or some variant of it that you can stand to tie) seems to be the best option. If you are forced to construct a really poor trad anchor, you should at least consider four pieces and a cascade of equalettes. For the three-piece anchors that form the vast majority of our set-ups, fixed-arm rigging (cordelette or various direct tie-in methods) appear to be as good in practice as anything more complicated.
There is a simple thing one can do to improve load distribution when the arms are of fixed length, and that is to equalize the cordelette or rope tie-in arm lengths by adding low-stretch slings to anchor points that are further away than the closest anchor point. This is neither complicated nor complex, but it could use up biners that the leader might be happier to have later on.
"if it's an extending system, and an anchor piece fails, how do you not get shock-loading?"
There have been long discussions about this, but clarity does not seem to be a byproduct. The first thing to recognize is that "shock-loading" is an undefined term that means whatever each person in the discussion wants it to mean. I think Karl is part of the majority who would say that shock-loading happens by definition in an extending system, and if that is your position, then of course shockloading cannot be prevented in such a system.
Largo's point is different. He knows there is some sort of impact on the remaining piece(es) if a component of an extending anchor fails, but he asks whether that impact is significantly greater than the transfer of load that would occur in a non-extending anchor. His conclusion, based on drop tests conducted by Jim Ewing of Sterling, is that for small extensions, the impact to the rest of the system is not substantially higher than the load transfer that would happen with fixed rigging.
Unfortunately, I think there is a problem with the test protocol used for this result, and so I am not sure we can yet say with certainty that small extensions are not problematic. I suspect the severity of the load to the remaining pieces depends on the ratio of the extension to the length of the belayer's tie-in, and that if the belayer is tied in short or, much worse, uses slings rather than the rope, apparently small extensions might still produce large effects.
The SAR instructor whose anchor failed is one of the five anchor failures I've heard about, and I think this tragedy underlines my point about the fragility of our so-called expertise. The reason to continue the search for better anchoring techniques is precisely because we don't know how good our anchors are. Largo has made a start. Others have taken up the cause, but so far without effective results that are practical in the field. Rather than sneering at their failures, perhaps we should celebrate their willingness to fiddle and hope, for all of our sakes, that something practical ultimately comes of it.
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raymond phule
climber
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Apr 14, 2008 - 09:44am PT
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"Unfortunately, I think there is a problem with the test protocol used for this result, and so I am not sure we can yet say with certainty that small extensions are not problematic. I suspect the severity of the load to the remaining pieces depends on the ratio of the extension to the length of the belayer's tie-in, and that if the belayer is tied in short or, much worse, uses slings rather than the rope, apparently small extensions might still produce large effects."
AFAIK
The tests where performed with a dynamic rope connected to the anchor. One of the arms broke during the fall and the forces was measured.
There are no theoretical reasons that this is going to result in a huge shock load due to the fact that we have a dynamic rope in the connection. The fall merely get longer.
The test results agree with this.
A more realistic case is to connect a belayer to the belay. We can even ignore the rope and other climber in this scenario for simplicity. So a belayer connected with a rigid connection (or short rope) to the belay. One arm in the belay break and the belayer is falling. This is a stiff system due to the lack og dynamic rope and the forces might be high.
This scenario was not tested.
The important things are the stiffnes in the chain and where the masses in the system are.
One example.
Single rope rappeling from 1 m long sliding x and a dynamic rope. One side break and the top rope connection fall 1 m. The sling and biner are very light is going to result in a very low force so we can ignore them. The force can be calculated by the help of fall factors.
Scenario 1. The rappeller is 10 m belov the sling. Thus a 1 m fall with 10 meters of rope -> low forces. The sling can be considered stiff.
Scenario 2. The rappeller is at the belay with 0 m of dynamic rope between him and the belay. One side break and we have a 1 m fall an 2 m static sling. This is going to result in much higher forces and we can talk about a shock load.
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the Fet
Knackered climber
A bivy sack in the secret campground
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Apr 14, 2008 - 12:58pm PT
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Rgold that is one of the most articulate and spot on replies I've seen to anything on this forum.
Ditto. Rgold seems to be one of the rare breed of super smart engineers who can also articulate so well that even us lay people can understand.
with a tied cordelette three-piece anchor, one piece tends to get half the load.
I only read about the initial testing of the cordelette, and I thought the piece with the shortest arm of the cordelette got 'most' of the load. If one piece gets half the load, then I'm back to thinking the cordelette is fine for 99% of anchors.
no one has come up with a way to rig a three-piece anchor that seems likely provide, in practice as opposed to in theory, a load distribution that avoids the 50% to one piece scenario, because all the complex load-equalizing systems are either likely to be sabotaged by internal friction or are based on an equalette on two of the three pieces and end up delivering half the load to one piece, even theoretically.
I came up with this design which 'could' equalize 3 pieces. Basically it requires a Z-pulley on each side to theoretically put the same load on 3 pieces. I never tested it with load cells, but from empirical testing I think it would do a pretty good job of equalizing. I don't think the friction from a single strand of cord (especially the slippery cord I used) over each caribiner would negate it's equalizing properties. It probably wouldn't put an equivalent load on each piece, but I think they would all share the load to some degree (I'd be more concerned about the overall length of cord on each side affecting the equalization than the friction). After building and playing with this design for a while I came to the conclusion that any design that could equalize 3 pieces and reduce extension is going to be just too complex for practical use. Edit: So I don't use it, I'm posting it here to illustrate a point.
Another alternative is the sliding W, i.e. a sliding X with three arms. However that can't be made to not extend. But you could tie it with a 24" sling, then use other slings to extend to your pieces.
I would guess the primary cause of friction in sliding X designs is the binding caused by webbing on webbing contact at the powerpoint. So the sliding W, may equalize even less than my design above.
I have just gone back to a prettied sliding X with limiter knots. I tie it so one of the strands that goes around the powerpoint is a little loose so there is no or limited binding. Getting close to 50/50 equalization is really all I need; it's within my acceptable safety margin for the forces generated in even a factor two fall on the belay. Sometimes I'll throw in a 3rd piece with another sling tied slightly loose to the powerpoint. If I did end up at an anchor where the pieces weren't bomber (very, very, rare on the climbs I do) I could just setup cascading sliding Xs or something else.
A great benefit of a prettied sliding X is that there are no knots to tie, so you don't have to untie, pull in the direction of force, and retie at every anchor like the cordelette. Just slap it on and you're done.
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Karl Baba
Trad climber
Yosemite, Ca
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Apr 14, 2008 - 02:09pm PT
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Karl wrote
"but here's another thing we don't know, How much of an extra window of security does perfect equalization afford? For instance, in how broad a range of forces would a Equalette hold when a regular cordalette would fail."
Rgold wrote
An excellent point. One thing that seems to be emerging, from various tests, is that with a tied cordelette three-piece anchor, one piece tends to get half the load. With perfect equalization it would be a third. Would a piece that could withstand a 3 kN load blow at 4.5 kN? Possibly, and then the question is what happens to the rest of the anchor. But the issue is moot, because in spite of the pages and pages of posts on the subject, no one has come up with a way to rig a three-piece anchor that seems likely provide, in practice as opposed to in theory, a load distribution that avoids the 50% to one piece scenario, because all the complex load-equalizing systems are either likely to be sabotaged by internal friction or are based on an equalette on two of the three pieces and end up delivering half the load to one piece, even theoretically.
Now I write
What about my idea for shorty screamers on the pieces. Seems to me that would avoid the 50% on one piece problem at loads big enough to pull pieces
Peace
Karl
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hafilax
Trad climber
East Van
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Apr 14, 2008 - 02:56pm PT
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I think that an important situation where reducing extension is a good idea is if the belayer will get hauled into an awkward position should one piece blow.
From what I understand, the friction between strands of a sliding-W under load negates any possible dynamic equalization should the load direction change.
Being a physics student I really enjoy these discussions and look forward to more empirical studies.
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Ed Hartouni
Trad climber
Livermore, CA
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Apr 14, 2008 - 03:38pm PT
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Karl,
shorty screamers would be a good idea, but I'd build another product rather than using what exists... basically with a smaller incremental blow-force and more tacks... a special "equalizer screamer" for belay anchors. Karl, not sure I agree with your lack of interest in "theory" but I hope to provide some better visuals later in the week...
Friction? Look at:
http://www.supertopo.com/climbing/thread.html?topic_id=307091
this thread hashes over a lot of this, and has some physical data on friction.
My observations on friction is that the configuration of the webbing at the "X" intersection makes a difference. Some sling material sits side-by-side and has less effective frictional force than material that sits one-atop-the-other.
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Karl Baba
Trad climber
Yosemite, Ca
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Apr 14, 2008 - 05:01pm PT
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Ed wrote
" Karl, not sure I agree with your lack of interest in "theory" but I hope to provide some better visuals later in the week... "
I have found that a vast amount of climbing physics theory has little to no application in actual practice. Somebody did a study that found that climbing rubber had the same friction equally on wet rock and dry rock. Do I buy that in practice? Sorry, my experience proves otherwise.
What difference does it make if anchor webbing sits side by side or on top of each other? In actual practice it's almost impossible to arrange that kind of control of how things lay.
So I think the theory has it's place and leave it to folks with the math to work it out. I'm just the guy who needs to jump in and say "wait a minute, this is a cluster f*#k solution to a problem we don't seem to have. (maybe ice climbers do)
And then when I post a simple solution that is both non-extending and equalized, nobody cares to analyze it . Sure it means carrying a couple small extra pieces but compare that to Fet's system above.
Peace
karl
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couchmaster
climber
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Apr 14, 2008 - 05:14pm PT
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* I'm with Clint. He'd be done with a 10 pitch route before you could rig that anchor twice. Bet he can do that in 15 seconds and it's bomber. Your triplet, equalette, quatralette gets you stuck in the chimney 1st pitch off the deck.
* What Rgold says is true.
* Another note: Comparing European anchor failure statistics to the US is a bad idea. In the Alps they have big long (often technically easier) routes that they are trying to scream up before the weather turns to sh#t, and they routinely clove a single piece on each belay station to crank out and finish a route as opposed to being benighted and freezing to death in the cold-assed alpine evening.
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the Fet
Knackered climber
A bivy sack in the secret campground
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Apr 14, 2008 - 05:40pm PT
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Karl, I think your idea for screamers incorporated into the anchor is a good idea, but (like my photo) it is overkill for 99% of anchors. Why carry 2-3 screamers and have to rig them into the anchor when you don't need them. On an scary aid climb with dicey anchors that you will climb above without a 'jesus nut' your idea is probably the best thing you could do, and you'd probably have screamers with you on a climb like that anyway.
The anchor I have above I could rig on most anchors in less than 1 minute (I just need to adjust the two overhand knots). But training someone else to build it showed me it's just too complex. And it's the simplest (perhaps only) way I've seen to build an anchor with one cord that equalizes and reduces extension on 3 pieces. So my conclusion is that any anchor system that can equalize and reduce extension on 3 pieces is too complex and usually overkill for most anchors.
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Ed Hartouni
Trad climber
Livermore, CA
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Apr 14, 2008 - 06:57pm PT
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Fet,
you anchor may not do what you think it does. It is the same thing as with John's initial advocacy for the Cordelette. There is a simple way to look at these anchor schemes... I'm working on it for later in the week... and it is based on a theoretical analysis which is supported by Wootles test and would inform suggestions like Karl's.
The advantage of a theoretical understanding is that you know the realm of validity, and can predict the behavior of the system in situations that you cannot test them, but in situations which might happen.
Karl,
the dynema slings (sp?) actually like to sit next to each other rather than over/under each other.. it is their aspect ratio, so in all likely hood you don't have to intentionally set up a system configuration, the sling does it for you. As for friction, the best place to see this is in Wootles test... the differences in the expected behavior and the actual test performance can be explained.
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tolman_paul
Trad climber
Anchorage, AK
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Apr 14, 2008 - 07:15pm PT
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There is something to be said for simplicity in anchoring systems as well. I typically put 2-3 pieces with a sliding X, and doubled biners through the X, and an additional piece of pro in opposition to keep the leader from pulling the belayer and anchor out in a fall on the subsequent pitch.
Alot of factors go into building an anchor, and it's best not to get totally caught up on the "best" or "only" method of setting up an anchor and equalizing the gear.
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rgold
Trad climber
Poughkeepsie, NY
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Apr 14, 2008 - 07:30pm PT
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Karl wrote: "And then when I post a simple solution that is both non-extending and equalized, nobody cares to analyze it . Sure it means carrying a couple small extra pieces but compare that to Fet's system above."
Karl, I'm afraid you understand neither theory nor theoreticians, especially folks who have other things to do at work and also like to climb every now and then. When someone proposes an idea, I think those of us who are prepared to give some of our time to thinking about it will say, that's interesting, I'll have to think about that when I get a chance. We can't respond immediately because we simply don't know, and offering a totally unexamined response is against our religion.
Then, with something like your proposal, additional questions enter. The dynamics of such an anchor will be complicated at first, with the first screamer extension shifting the load to other pieces which then produce extensions in their screamers, shifting the load back...this ain't gonna be easy to analyze, Jack, and whatever analysis is done will depend on the specific geometry chosen for the anchor too.
If and when all the screamers deploy, the anchor will be equalized during that phase of communal deployment. If the fall onto the anchor is greater than about twenty feet, then there is the possibility that the screamers will fully deploy, at which point the anchor returns to being unequalized.
So the silence you experienced was not the sound of nobody caring to analyze it. Rather it was the initial silent whirring of the gears, accompanied by the feeling that this will not be easy to understand, followed by thoughts about whether the question would be worth the price in intellectual effort. Physical testing, which we don't seem to have the interest and resources in this country to pursue, might be a better way to understand your proposal.
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labrat
Trad climber
Nevada
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Apr 14, 2008 - 09:19pm PT
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No need for sit ups tonight. thanks rgold
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Karl Baba
Trad climber
Yosemite, Ca
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Apr 14, 2008 - 09:23pm PT
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Thanks for the reply. Since I live in the land of flint hard granite, it's easy not to care but I appreciate your time.
Peace
karl
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Ed Hartouni
Trad climber
Livermore, CA
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Apr 15, 2008 - 12:17am PT
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raymond phule
climber
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Apr 15, 2008 - 04:22am PT
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I think one thing is missing when analysing the cordalette and that is the configuration.
The configuration tested are vertical arms of different lengths and same length arms with the same angle to the power point.
I have done calculations of a third simple configuration. One arm is twice the length of the other arm but the angle to vertical is 30 degrees for both arms.
The calculations assumes a static case with a large force of 1000 kg (ok, not really a force...). I believe the dynamics forces are similar.
The result change with how dynamic the slings are (how long the extension are for a given force.
case 1. stiff sling. 1 % extenstion at 1000 kg.
Arm 1 is the shortest.
Force arm 1 F1 := 580.6445919
Force arm 2 F2 := 570.7888740
Angle arm 1 alpha1= 29.43846760
Angle arm 2 alpha2= 29.99834705
extenstion arm 1 in % 0.5806445919
extenstion arm 2 in % 1.141577748
The difference are small.
10% extension
F1 := 606.5663814
F2 := 520.5541220
25.28076135
29.84249003
6.065663814
10.41108244
A difference but still not large.
100% extension
F1 := 678.5600661
F2 := 371.3079062
12.95601019
24.18665277
67.85600661
74.26158124
A difference in forces but still not huge.
The conclusion is that the forces not only depends on the arm length but also much on the configuration. We can also see that the stiffnes of the arms matter and I think this is true except in the vertical case.
The forces depends much on the angles between the slings and the angles depends and change with the stiffnes of the slings.
The calculations was done with the use of maple. Maple behaved strange and sometimes gave a solution that wasn't a solution to the equations but I hope this are the correct solutions.
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Ed Hartouni
Trad climber
Livermore, CA
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Apr 15, 2008 - 10:23am PT
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The standard rigging rules apply in 2 Dimensions, basically resolving the forces into "vertical" and "horizontal" for the case of two arms.... three or more arms needs to go into 3 Dimensions, but there are no additional physics features in higher dimensionality.
The essential point for this discussion was to describe how the "master point" distributes the load on the sling(s) attached to the anchors.
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Largo
Sport climber
Venice, Ca
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Apr 15, 2008 - 11:56am PT
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Per Ed's note, the fact that the anchor tie in biner can slide at the master point makes all the difference, but said biner is also prone to bind (the so-called "clitch" effect) on the sliings if things are not set up correctrly. Testing showed that an anodized, pear-shaped biner laregly overcame any binding.
JL
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rgold
Trad climber
Poughkeepsie, NY
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Apr 15, 2008 - 01:43pm PT
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Ed's calculations are basically the same as ones I posted several years ago on rc.com, back when people still thought a cordelette would genuinely equalize if you could just tie it right. In particular, I mentioned, as the ultimate test case for equalizing, the three-point anchor with all three pieces in a vertical line, and that example eventually made its way into Largo's book.
As for systems with more than two arms being just combinations of the two-arm system, well, yes and no. Starting with three arms, the system becomes, in engineering terms, "statically indeterminate," which means, in the case of three arms, that there are three unknown tensions but only two equations relating them derived from force decomposition, meaning that there are infinitely many different solutions. Of course, the physical system doesn't have all those solutions, because there are additional constraining equations that come from Hooke's Law. (The engineers are usually more interested in beams, in which case they can get additional equations from the necessary equilibrium of torques.)
So it turns out that the elongation of the strands, which can be ignored when there are two arms of equal length, becomes essential to the solution when there are more than two arms, and of course then calculations become quite a bit harder.
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the Fet
Knackered climber
A bivy sack in the secret campground
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Apr 15, 2008 - 02:21pm PT
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Ed, thanks for the diagrams, they really help clarify what's going on.
I think Raymond's point is that as the angle of the arms to a vertical line above the power point increases the force on the piece increases. (e.g. if the piece is 60 degrees off vertical then that piece is getting a force equal to the total load at the powepoint).
I just saw this for this first time, good stuff:
http://www.caves.org/section/vertical/nh/51/Multi-point%20pre-equal%20anchors.pdf
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Chiloe
Trad climber
Lee, NH
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Apr 15, 2008 - 05:01pm PT
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I should be doing something more constructive, but instead ... for your edification, here's a different view of some key findings from Jim E's original test data, which involved 2-anchor rigs with either equal-length or unequal-length arms.
Two findings are that (1) well-tied cordelettes don't seem to equalize forces at all, if both arms are not the same length (or even if they are the same length); (2) the sliding-X does better than a cordelette but in the unequal-length case, due to binding, the short arm still feels significantly more force.
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Ed Hartouni
Trad climber
Livermore, CA
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Apr 16, 2008 - 12:17am PT
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Port
Trad climber
San Diego
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Apr 16, 2008 - 12:37am PT
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Thanks Ed, great info.
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raymond phule
climber
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Apr 16, 2008 - 03:13am PT
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"Two findings are that (1) well-tied cordelettes don't seem to equalize forces at all, if both arms are not the same length (or even if they are the same length); (2) the sliding-X does better than a cordelette but in the unequal-length case, due to binding, the short arm still feels significantly more force."
The point I tried to make is that the two tested cases are very special, atleast the vertical one, and I dont believe we can draw some of the conclusions that people have drawn because of that.
Unequal arm lengths might in theory result in ok equalisation in some cases. See my example above.
The testing was done in two different configurations, no angle (vertical) and an angle between the slings. I believe that a large part of the test results are a result of this instead of only a result from the difference in arm lengths.
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Ed Hartouni
Trad climber
Livermore, CA
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Apr 17, 2008 - 01:16am PT
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