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bwancy1
Trad climber
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Jan 15, 2007 - 11:53am PT
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I have been using a webolette for a few years now. I equalize as best I can, and tie a figure 8. By leaving the figure 8 a little "loose", there is enough give in the knot to compensate for slightly imperfect lengths on the three legs. I think that an anchor like this would auto-equalize fairly well when loaded.
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rgold
Trad climber
Poughkeepsie, NY
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Jan 15, 2007 - 01:28pm PT
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The analysis of the cordolette forces shows that if each of the arms of the cordolette are the same length, then it works to equalize
...if the cordelette has been tied exactly right. Any errors would have to be partially compensated by give in the knot (completely unpredictable) or stretch in the material (which is one reason why nylon is preferable to spectra).
The so-called "equal arm" situation is essentially three pieces in a horizontal crack. If either the left or right piece fails, the entire load is transferred to the middle piece with no load at all distributed to the other piece. This sets up the "cascade failure" scenario in which each piece in succession is required to bear the entire load.
The other problem with fixed-arm rigging is that it only distributes when the load is applied directly downward (or in whatever direction the rigging has been tied for). If the leader falls on one side or the other of the belayer, then when the rope comes taut the downward fall will be turned into a pendulum. This change of direction comes with a very high acceleration and so it is very reasonable to expect that such a fall will impose a high load on the belay that is not straight down, the direction the anchor was tied for. This load will have to be born by one of the outer single pieces of the anchor, and so will also set up the cascade failure scenario.
The usual response to these observations is that if things are really this bad, why aren't parties regularly plunging to their death? The answer, in my view, is that it is very rare that an anchor is tested.
Here is another way to look at the situation. Suppose there was a way to achieve practical equalization with directional tolerance, a way that was as easy to deploy as a cordelette. Wouldn't it be sensible to adopt such a method and thereby eliminate or at least significantly reduce potential scenarios such as the ones above?
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wootles
climber
Gamma Quadrant
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Jan 15, 2007 - 02:20pm PT
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The analysis of the cordolette forces shows that if each of the arms of the cordolette are the same length, then it works to equalize
Actually... no.
I did the drop tests for Largo's book and it may be pointed out in there that even when the legs of the cordelette were tied as near to perfectly equal as I could get them there was still significant differences in the force to each anchor. It should also be noted that it was easy to judge the direction of pull for each drop because I was using a guided mass where the pull, obviously, was in the same spot every time.
It's all in the book and as much as you all love to bust on rc.com everything is pretty well covered over there, that is if you can wade through the 1000 or so impertinent posts.
Constructing a safe anchor is not impossible, and cordolette or not, constructing a safe anchor always required careful attention.
I think this is a point that may have been missing in the discussion on rc.com. There seemed to be too much black and white thinking and that will only limit your 'bag of tricks' to building a safe anchor.
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Thom
Trad climber
South Orange County, CA
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Jan 15, 2007 - 06:17pm PT
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Man, this topic HAS been beaten to death 10x over...
I do believe the argument AGAINST the "sliding W" or any self-equalizing anchor set-up goes something like this:
If any single piece fails, the remaining pieces are shock-loaded as the anchor re-equalizes itself, thus requiring the remaining pieces to be "bomb-proof" to prevent their failure also. Since one does not know which of the pieces will fail, when using any self-equalizing system, we must be certain that EVERY piece is "bomb-proof" thus negating the need to use a self-equalizing system to begin with.
Someone needs to do some testing:
Rig up a tied-off, 3-piece cordelette anchor with the appropriate angles to promote equalization throughout the system; then, release one of the pieces and record how the weight transfers to the remaining pieces via the cordelette. I doubt there is much difference between the two.
Maybe hang 3 scales from a beam, rig the cordelette, hang a weight on the power-point, and record the weight on each scale; then, cut one of the cords and watch how the weight transfers.
I'd do it myself but don't have the equipment.
Cheers,
T.
Edit: haven't read the book, just saw the above posts and apparently somone has done some testing (finally) with the cordelette system. Guess I'll have to obtain said book to see the results. t.
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healyje
Trad climber
Portland, Oregon
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Jan 15, 2007 - 06:44pm PT
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It's a testament to the new RC forum software that you can do a "show all" on that thread. The pictures have been replaced with links to them and I'd recommend you right-click on those links and do "Open in a new window" so you keep your place in the thread easier. I'd also recommend you consider all the ideas more from a component perspective versus accepting or rejecting whole anchor designs. There are a lot of interesting ideas presented and many good ones are not necessarily in the best anchor proposals (imho). On the whole it was a pretty worthy exploration of the space even if later in the thread the conversation suffers a bit here and there...
RockClimbing.com: [url="http://www.rockclimbing.com/cgi-bin/forum/gforum.cgi?do=post_view_flat;post=1306133;page=1;sb=post_latest_reply;so=ASC;mh=25;guest=3555152" target="new"]Improved sliding x: Is it really safer?[/url]
P.S. Please do not rouse the sleeping beast that is that thread. Let that poor damn horse rest in peace - it went through hell for the cause...
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rhyang
Ice climber
SJC
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Jan 15, 2007 - 07:05pm PT
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I read JL's new book over the holiday, and was quite amazed. I'd like to experiment with the equalette more, since it seems like a useful technique.
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WBraun
climber
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Jan 15, 2007 - 08:26pm PT
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So Cjones
Still sliding on that W?
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rgold
Trad climber
Poughkeepsie, NY
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Jan 15, 2007 - 08:55pm PT
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Man, this topic HAS been beaten to death 10x over...Someone needs to do some testing
The trick now is to keep up with the beatings...which is why, Joe's urgent pleas not withstanding, there still appears to be some use in these discussions. And although the rc.com thread is gargantuan, there are a number of fundamental questions still unanswered and perhaps even unposed, primarily because that thread was, perhaps prematurely, about solutions.
So I'm gonna take up my club and administer another some more whacks for time number 11. In partial justification, the points made here have not been made in the rc.com thread. [Edit: This claim is overblown. In particular, GoClimb repeatedly raised the question about the effect of the belayer falling during anchor extension in the rc.com thread.] Nonetheless, they're probably of interest to only a few folks out there; to the rest I apologize for blabbering on so, but suggest that there may be something worth considering in the final two points.
In the case at hand, testing has been performed for a two-anchor equalized system (the equalette) with a drop of a bit under 5". The results, reported in the rc.com thread---which almost no one can bear to read---and reiterated in JL's anchor book, pp 190--191, are that the extension makes little difference in the peak loads.
I'm not exactly sure what question one should be asking for this situation, but I think it is this: If a fixed-arm system (e.g. cordelette) has one arm fail and all the load is transferred to the other anchor(s), how does the peak load in that situation compare to what happens if a sliding system fails and transfers the load to the same anchor(s)? I don't think this question has been answered yet. JL? Wootles?
Moreover, I think result reported by JL has to be understood properly. Those tests were conducted by dropping a weight directly onto the anchor. In such a test, the length of rope involved becomes important for understanding the results.
As is now well-known, the load on the anchor depends on the fall factor. When the anchor blows, the length of rope remains the same (I'm assuming an equalette made up of extremely low-stretch material that doesn't contribute to energy absorbtion) but the length of the fall increases by the amount of anchor extension. If this extension is very small compared to the amount of rope, then the fall factor barely changes and we wouldn't expect to see much difference in the loads on the anchor. I suspect this is what happened in the tests JL reported; perhaps Wootles could clarify this point.
If, however, the extension in the anchor is significant compared to the length of rope involved, then there could be a big increase in fall factor leading to a much higher anchor load.
In a climbing situation, the load on the anchor is delivered by the tension in the belayer's tie-in, which is usually relatively short. The dynamics of the situation are those of coupled harmonic oscillators (two sections of rope, one section between falling leader and belayer, the other section the belayer's tie-in), and I haven't worked out what would, in theory, happen to the tension in the belayer's tie-in. But it is possible to make some rough estimates by treating the leader's fall and the belayer's fall as if they were not coupled events.
The leader's fall energy is absorbed by the full length of rope involved, and a small extension from the anchor would have a negligible effect on the fall factor and so on the anchor load. But, assuming the fall pulls the belayer off and the anchor extends, the belayer's fall energy has to be absorbed by the short tie-in.
If an 80 kg belayer tied in with two feet of rope with 9 kN impact rating falls 4 inches because of anchor extension, then there is a fall factor of 1/6 with consequent load of about 3.2 kN, a bit less than 720 lbf. So given the showdown I proposed above between the cordelette and the sliding anchor, I'd expect the remaining anchor to have to withstand a somewhat higher load---it is hard to know how good an estimate 720 lbf is.
This effect might be mitigated by the fact extension might allow the extraction of the piece to absorb some fall energy. This point has been argued a lot too; it depends on whether the falling leader's rope can recover during the brief interval when it is unweighted. There are some theoretical reasons to believe this, and I think the data from the drop tests with arm failure suggest it too.
So there is reason to believe that an extension that is small compared to the tie-in length, although it will increase the load on the remaining anchors, has benefits that outweigh the deficits. [Edited.] But there are some caveats worth observing too:
(1) All bets are off if you tie in with slings or daisies. You will then have thrown out the belayer's energy absorber and a small extension might provoke a big load increase. Anyone using an extendible system must tie in with the climbing rope (and indeed this is true for all tie-ins in my opinion.)
(2) If there's a choice of belay positions, The longer your tie-in the better, since you want to minimize the ratio (extension) / (tie-in length).
Sorry Joe, I know you begged me not to do this.
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healyje
Trad climber
Portland, Oregon
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Jan 15, 2007 - 09:00pm PT
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Well, you're far braver than I and it will be interesting to see if it goes (ends) better over here. At least you can post pictures here - I'll grant you that much...
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cintune
climber
Penn's Woods
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Jan 15, 2007 - 09:05pm PT
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There is a way to view the embedded images in the rc thread if you use Firefox. It's a java script posted by melekzek that can't be posted here because the ST server reads it as instructions instead of as text, but for the details see here:
http://www.rockclimbing.com/cgi-bin/forum/gforum.cgi?post=1489870
The how-to is in the fifth post down, but the most recent version of the bookmarklet is in the sixth post.
Anyone who can equalize an anchor should be able to follow these directions.
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healyje
Trad climber
Portland, Oregon
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Jan 15, 2007 - 09:10pm PT
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"So there is reason to believe that extension, although it will increase the load on the remaining anchors, has benefits that outweigh the deficits."
As a blanket statement I'd probably disagree with that. Most of the effort on the RC thread was about exploring ways to resolve the competing and mutually exclusive requirements of equalization and extension when building anchors. I thought the result was a bunch of designs that sacrificed one for the sake of the other, or attempted to 'firewall' one from the other to provide a controlled amount of each. After going down those various paths together I haven't seen anything that would lead me to wholeheartedly embrace your proposition...
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rgold
Trad climber
Poughkeepsie, NY
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Jan 15, 2007 - 09:19pm PT
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Joe, I wouldn't agree with my statement as is either. I've edited it to add that the extension has to be small compared to the tie-in length. How small is a matter for experiments if there is anyone around who can do them. How about 1/10?
The smallness requirement means that the system must, as you say, incorporate a way to keep extension low (which is one of the reasons why an ordinary sliding W is not satisfactory). The new point is that the belayer's tie-in should be significantly larger than the extension and should be made with the climbing rope.
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GOclimb
Trad climber
Boston, MA
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Jan 15, 2007 - 10:02pm PT
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There were several excellent solutions proposed on that thread which, while untested by JL's crew, showed slightly more promise than the "accepted" method proposed by JL. Of course, they won't sell any books - which must be why they're considered impertinent. Apparantly the fact that they just might save lives seems not to be as important.
I've been using two of the methods from that thread exclusively since then. I've hauled off 'em, and slept on 'em, too - two people with all our gear, pig, ledge, etc. Slept easy. Neither method has caught a factor two fall. Hope that stays that way. But if one does, I'm as sure that it'll perform admirably as I can be without seeing any hard test data.
GO
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healyje
Trad climber
Portland, Oregon
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Jan 15, 2007 - 10:14pm PT
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Wanna share which ones? Preferrably with a pic of each (if you can find them). And if you were posting over on the rc thread were you doing it under GoClimb there as well (sorry, my memory isn't what it used to be...)?
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climbingjones
Trad climber
grass valley,ca
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Topic Author's Reply - Jan 15, 2007 - 10:33pm PT
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I do like the "W" Werner. But I am not so stuck on it that I will not give other ways a try. I dont "always" use it, but most of the time. Usually for 3 bomber pieces. I still think tying a knot into the same 3 pieces loads it unevenly. If I am faced with a sketchy belay I usually incorporate a mix and match approach. I have been accused of using too much gear on an anchor if I think it is sketchy. But so what? I like to carry lots of weight around anyway. Never been so concerned with saving that 8.34546623 'crucial' ounces. But I dig the discussion that it generated. Even though there are alot who seemed bent that it was being discussed. If you are so bent, or so over it, why did you post? Again.
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David Nelson
climber
San Francisco
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Jan 15, 2007 - 11:17pm PT
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Climbingjones asked a real question, let's not stray off topic for the poor guy, OK?
Listen to Werner B, he knows what he is talking about.
I haven't read the literature, but like the fig 8 because if one anchor pulls, the others are still equally loaded and there should be no shifting. Make sure you believe in the security of each one, don't start telling yourself "Oh, the others will hold." Make sure each one is good.
They may not be equally loaded with an off-angle load, but usually you know where the load will be coming from, and it is usually straight down. If the approach to the belay is from the side, there are some anchors from there, and the load might come from the side if the fall comes lower down, you might add another point that helps to resist a pull from the side.
Keep talking to climbers and listening.
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healyje
Trad climber
Portland, Oregon
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Jan 15, 2007 - 11:28pm PT
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Largo, are you up for starting on the third edition...?
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rgold
Trad climber
Poughkeepsie, NY
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Jan 15, 2007 - 11:46pm PT
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haven't read the literature, but like the fig 8 because if one anchor pulls, the others are still equally loaded and there should be no shifting.
Perhaps there would be some value in reading the literature. Your statement here is false in general.
They may not be equally loaded with an off-angle load, but usually you know where the load will be coming from, and it is usually straight down.
Again, the literature has something to say about this, although not as definitive as in the first case. I think there's a decent chance that there will be a off-angle impact in most cases. Only testing could tell us for sure.
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WBraun
climber
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Jan 16, 2007 - 12:16am PT
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Cjones
Why are people bent about the sliding W? Me don't know. Sometimes in certain situations it will be the way to go. Other times it will not be the way to go.
Totally depends on the type of situation. If there are a lot of dynamic variables in the angles of the power point (way to go) or when the power point angle remains perfectly static (not the way to go).
Gee whiz man it's not so hard to figure this stuff out.
Or is it? That is the first big decision, to accurately "visualize" your power points. Sometimes it also helps considerably to pretension your power points to get the angle/angles of your load/loads.
Let's beat it to death, hahaha
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rgold
Trad climber
Poughkeepsie, NY
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Jan 16, 2007 - 12:23am PT
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There were several excellent solutions proposed on that thread which, while untested by JL's crew, showed slightly more promise than the "accepted" method proposed by JL. Of course, they won't sell any books - which must be why they're considered impertinent. Apparantly the fact that they just might save lives seems not to be as important.
Perhaps this is what Joe was warning about when he suggested not opening this can of worms again. I'm always astonished when people pretend to know other people's motives, especially when they are ready to ascribe the basest motivations to people they don't know for actions they have no basis for judging. I hope you find yourself able to apologize for this one Gabe, it is way out of line, and contributes nothing but rancor to a discussion that might otherwise be useful.
It would be nice if an entity like the American Alpine Club could find a way to either fund or encourage research into anchoring solutions. This would be a substantial undertaking far beyond what could be expected from the author of a climbing book. In the meantime, it should be noted that JL acknowledges the rc.com thread in his book and expresses the view that better methods will ultimately come from the efforts of individual climbers.
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