Discussion Topic |
|
This thread has been locked |
maldaly
Trad climber
Boulder, CO
|
|
|
Jun 30, 2008 - 05:39pm PT
|
tolman_paul,
The last sentence in your post is now my rule #5.
Mal
|
|
bluering
Trad climber
Santa Clara, Ca.
|
|
|
Jun 30, 2008 - 05:47pm PT
|
Since piqua was talking about using the sx to equalize two pieces of LEAD PROTECTION for redundancy, clove hitching the two pieces would work also instead of a sx. I've done it, seems to work fine. Of course you gotta get the hitches just right for it to work effectively.
Of course, the hitches are probably better when setting two OPPOSING pieces.
|
|
rgold
Trad climber
Poughkeepsie, NY
|
|
|
Jun 30, 2008 - 09:38pm PT
|
Mal (and Paul), I've enrolled in Over Anal - yzers Anonymous and have been through their 12-step program and...still...can't...help...geekish...posting...eeeaaaahhhhHHHH!
In my opinion, Jim's testing does show that extension in a sliding system used to equalize pro is of little concern, because in the case of pro the extension will almost always be tiny compared to the amount of rope absorbing energy. So the pro situation is very different from the anchoring situation, and this makes the sliding X or, better, an equalette, a good choice for two questionable pieces. The equalette will, in many cases, be too tricky to tie while leading, while the sliding X, although more subject to binding, is easily installed with one hand.
An issue I've never seen discussed with the sliding X is what happens to the power-point biner if one of the anchors fails. A turn of webbing holding the failed anchor is going to tighten around the power point biner, with significant potential for opening the gate or cross-loading the biner. Because of this, I'd say that the power point in a sliding X set-up on pro should always consist of two biners with the gates opposed.
|
|
Jaybro
Social climber
wuz real!
|
|
|
Jun 30, 2008 - 09:45pm PT
|
of course not... trick question?
|
|
Lost Arrow
Trad climber
The North Ridge of the San Fernando
|
|
|
Jun 30, 2008 - 10:10pm PT
|
I no longer use a sliding x. I tie in to a bomber with the rope and than back that piece up with more pieces and webbing to a single locker.
JDF
|
|
Ed Hartouni
Trad climber
Livermore, CA
|
|
|
Jun 30, 2008 - 10:13pm PT
|
Answer the question:
I use the sliding-x sometimes, usually in a 3 piece anchor where it equalizes two pieces and the the rope goes to the third piece by a clove-hitch.
Sometimes I use the cordelette in the same manner, depends on the distance of the pieces.
Sometimes I use the cordelette with three pieces, especially if the legs are pretty much equal in length.
I always try to to follow Mal's first three rules...
The accident on the DNB will never be definitively analyzed. However it is possible that a flake blew and that all the pieces were behind the same flake. Note that that arrangement violates Mal's rules 1 through 3, and those people were experienced.
Read the accident report...
http://www.supertopo.com/climbing/thread.html?topic_id=554557&msg=557937#msg557937
I did try to measure the coefficient of friction in the "sliding x" configuration, the "clutching" can be significant, but it depends on how the sling sits, on top of each other or next to each other... so not a reliable setup, but less of a force differential than the cordelette in a very "asymmetric" configuration (one leg much longer than another).
As for "shock loading" analysis would say that it has to be a factor... so it would be interesting to push the analysis difference of the tests and the calculations... there is some good wisdom hiding in there that a concerted effort at understanding would reveal.
|
|
k-man
Gym climber
SCruz
|
|
|
Jun 30, 2008 - 11:26pm PT
|
... OT from the OP ...
Using the lead rope to anchor, a friend showed me how to "equalize" with a bowline-on-a-bite.
FOLLOW RULE #3!
I now use this at all two-bolt belays.
A single biner on each bolt. Fast, and the least amount of gear
you can possibly use. You can adjust the bowline, if needed, to
assimilate a degree of "equalization."
|
|
tom woods
Gym climber
Bishop, CA
|
|
The thing with anchors is that we build them fro two purposes. For the follower and for the leader. For the folllower, barring an extreme swing, you could body belay the person from a good ledge.
For the leader, (that's what got the DNB folks a couple of years back) you're building a an upward or mulit directional anchor, but you have body weight on your side.
Things get interesting until you get back to the old schoolers and the leader must not fall mentality. I don't like falling either so problem solved, QED.
Tom
|
|
Gobie
Trad climber
Northern, Ca.
|
|
Did anyone read the OP??
Karl is obviously the only one that did.
It doesnt say anything about belays. Do rules 1-4 apply to protection as well? I wish all my pro was bomber, sometimes I settle for what I get. Hopefully it will slow me down before I get to rules 1-3 and its strong enough to apply force to rule 4.
Answer to question. I would prefer to extend my (dubious) pro to be as close to equal to each other as possible even if this results in a little bit longer of a fall. I did this once with a small brass hb and a loweball. I thought it was cute at the time and then I got higher and realized that it was my pro. I fell and pulled the hb and the loweball held. I cant be convinced this would of happened if they were on an X. I didnt have a calculator, or time to think about it, my brain just works that way.
"Have you ever been experienced...well I have."
|
|
Ed Hartouni
Trad climber
Livermore, CA
|
|
well, the link follows, and it does refer to anchors... I assumed these could be belay anchors...
and I do use the sliding x occasionally to equalize two marginal placements, judging that the distributed force would be held by the combination where both, one at a time, would not. I can't tell if this is one of the exceptions or not...
Sliding X (aka Death X)
by Editor
March 18, 2003
Republished with permission of the American Safe Climbing Association.
Many climbers use a "sliding X" to equalize two pieces - ususally beginner climbers with bolt anchors. You should NEVER use this except in two specialized cases (see below). While the sliding X does equalize the pieces, it assumes that neither could break, since if one does break, there is severe extension in the system - enough that it would likely cause the carabiners to break. Since it assumes neither piece would break, it's a stupid system - if neither would break, there's no need for equalization. If one might break, then there is WAY too much extension. This is why many call it the "death X." Instead, use one sling off of each bolt or piece. You can tie one shorter to approximately equalize the pieces if needed.
The two cases where the sliding X is used:
-Equalizing tenuous pieces in a larger anchor - for instance, two poor nuts in a large natural pro anchor. The nuts are equalized, then the sliding X is equalized with other pieces through a cordelette, webolette, or other non-extending method.
-Equalizing two very tenuous pieces in extreme aid - for instance, a hook and a bashie on A4 terrain.
Camp4 Editors Note- If you do have to use this system, make sure you make the twist in the sling before clipping the caribiner (see image above). If you don't and one of the anchors fail, the WHOLE SYSTEM WILL FAIL.
|
|
k-man
Gym climber
SCruz
|
|
I don't know Ed, I think I'll go with the updated info from JL.
|
|
Ed Hartouni
Trad climber
Livermore, CA
|
|
the dynamic behavior of the "clutch effect" has not been explored, as the physics of friction are somewhat complex, and the engineering (which is what the tests are all about) probably do not fully explore the issue.
There are two frictions, as it were, static and dynamic friction, and each has a coefficient associated with them, the dynamic coefficient usually being smaller than the static coefficient.
In our case, the power-point 'biner (which acts as a pulley) slides freely until the normal forces of the webbing produce enough frictional force to prevent the slings from sliding. Whatever the configuration of the webbing is at that time, it acts like a two-legged cordelette, that is, the the forces on the pieces connected to the webbing are inversely proportional to the length of the legs.
As long as the force on the sling is less than the generated static frictional force, the sling will remain static in the possibly unequal force configuration.
However, if the forces are larger than the frictional force, the sling will begin to slide again and equalize. The sliding will be "sticky" because of the dynamic coeff. but it is possible that the equalization will be complete.
One way to reduce the friction is to use a 'biner with a larger diameter aluminum shaft, effectively reducing the "wrapping angle" and thus greatly reducing the frictional forces. I think this is demonstrated empirically in John's recollection of the tests, reducing the coefficient of friction has the same effect, and doing both would greatly reduce the tendency of this system "to clutch".
I'll get back to my dissertation on the calculational details soon... but you can look here (look at several posts in this general area and hey dirtineye, check this for me! please... and cleo too).
|
|
Elcapinyoazz
Social climber
Joshua Tree
|
|
obvious implication is that you would want to use spectra slings with little nylon in them for a decreased friction coefficient?
|
|
the Fet
Knackered climber
A bivy sack in the secret campground
|
|
I'd say with about 99% certainty that the "clutch effect" on a sliding X is not due to friction of a sling on the biner, but is due to having two wraps of webbing going around the biner (one with a twist in it) and the two wraps of webbing binding on themselves and the biner. Try it with a sliding X; pull down on the powerpoint biner and move it side to side, if the X binds you can feel the clutch effect. Then try a biner on a single strand of webbing, the friction is negligible.
Using a large diameter biner mitigates this effect substantially. Or you can pretty much eliminate the clutch effect if you have a sliding X with limiter knots and you make the strand with the twist in it a little loose. I keep saying this but no one is getting it, so maybe it's too complex for general use.
As for the original question I have used a 12" sling to make a sliding X to equalize 2 pieces, but really it's only needed on hard aid. If I put 2 pieces in because it's a long way down to the next piece, or I'm pulling a hard move and I can't have that piece fail I'll just put them in series.
|
|
Ed Hartouni
Trad climber
Livermore, CA
|
|
a sliding-x with limiter knots is not a sliding-x...
also, the coef-of-frict for nylon on nylon is not that dissimilar to that of nylon on aluminum...
Elcap... I think spectra is interesting not so much for the reduced coef, but because the slings tend to be square, rather than ribbons, and the squares sit next to each other rather than over/under... this reduces the normal force considerably as one sling does not trap the other against the 'biner. You cannot guarantee this configuration in an engineering sense with the 'biners that are available, but you could see how you might design a special 'biner.
|
|
ontheedgeandscaredtodeath
Trad climber
San Francisco, Ca
|
|
This not really a "real world" question, but if one piece blows, would some dynamic or static friction not be beneficial in that it would prevent a shockload to the second piece?
I don't see the point of the sliding-X cept on aid, beyond saving a runner and a biner.
|
|
maldaly
Trad climber
Boulder, CO
|
|
GEEK ALERT!!!!
You guys might want to think about moving this conversation over to rc.com. It's getting pretty thick...
;-)
Mal
|
|
Scrunch
Trad climber
Provo, Ut
|
|
Tools in a toolbox, like anything else in climbing.
Climbing in Big Cottonwood, Your only pro a #2 microstopper in a seam? Throw in two, equalize with a SX, and throw screamer on it. BOMBER!
In Little Cottonwood at a two-bolt anchor? Two clove hitches and your done. 3/8" by 3" bolt in granite arn't going anywhere.
Keep in mind that a modern dynamic rope, by UIAA standard, can't produce more than 12kn of force on any part of the system. In a factor 1.77 fall situation. With 180kg of weight on it. Most ropes now boast a sub-10kn rating (though one of my favorites, MAXIM, has a few 10.5's)
If you climb on crap gear, you roll the dice. But if thats all you got, you might as well stack the deck in your favor. At least the stuff will slow you down.
The point is that Almost every tool has it's place, especially a tool as light to carry as knowledge.
(I prefer my metaphors shaken, not stirred)
Adam
|
|
Matt
Trad climber
primordial soup
|
|
from the tread that ed linked to:
Their anchor -- which appears to have pulled in its entirety during the accident -- consisted of the following. One 3/8-inch Alien and one #4 Black Diamond Stopper were clove-hitched together to one of the lead ropes approximately three feet from Eldridge's tie-in point. Two double-stem Camelots, .5 and .75 were each independently clove-hitched about a foot and a half apart on the other lead rope with 15 inches separating the lower piece form Eldridge's tie-in point. There was no evidence that bolts or other fixed protection were involved in the anchor.
All of the anchor pieces were severely damaged, though it is impossible to know whether the damage occurred when they were pulled out or during the fall and final impact. Nevertheless, the two Camelots were each bent in a similar way suggestive of a severe downward force after being placed in a vertical crack.
A loose quick-draw and a few carabiners were also found at the base. Their original purpose could not be determined, and they may have simply unclipped from the falling climbers -- a common occurence.
Analysis
Both Dunwiddie and Eldridge were skilled climbers, and in the days prior to their deaths they had completed a number of challenging free and aid routes in the Valley. Based on the location of the bodies, and on the topo of the Direct North Buttress found in their possession, they were probably on the DNB at the time of their accident. Rated at 5.10c and known for both its length and route finding difficulty, the DNB includes several sections of "run out" climbing and loose rock.
What can we learn? This accident hits close to home for most climbers because the party involved was very experienced with difficult climbing and familiar with Valley rock -- as have been at least a third of Yosemite fatalities, historically. Other factors, such as rock fall from above, may have been involved, but the prime suspects are basic anchor and leading concepts that all of us are often tempted to ignore: avoiding anchors in suspect rock, sharing the load to an adequate degree, and stuffing in that first (and second) lead piece right off the belay. If you can't meet these criteria, continue on with the realization that your survival may depend only on your climbing skill and on the quality of the next handhold. At least five other cases of complete anchor failure (protection pulling out -- not breaking) have occurred in the Park in the last 30 years. (Source: Lincoln Else, Climbing Ranger, Yosemite National Park)"
just for clarification-
my point above was that (in the absence of a pair of 3/8" bolts in granite) i would prefer some sort of imperfect equalization that would at lest distribute the load to a degree, to a system where one can expect multiple pieces to be loaded sequentially.
|
|
k-man
Gym climber
SCruz
|
|
Scrunch,
In Little Cottonwood at a two-bolt anchor? Two clove hitches and your done.
Two binners and a bowline-on-a-bite! Mo bettah ...
|
|
|
SuperTopo on the Web
|
Let us know!