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climbaddic
Oct 24, 2006, 4:28 PM
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From http://www.supertopo.com/...html?topic_id=269434
Some pictures from the website.
http://i138.photobucket.com/.../Dyneemafailure1.jpg
http://i138.photobucket.com/...tt/dyneemaanchor.jpg
John Sherman just yesterday had a dyneema sling break, under bodyweight.
The Verm has been packing on a few pounds lately, but he never suspected he was at the rated breaking strain of dyneema.
He was on rappel, cleaning a new line, and, up above, one of his two rappel anchors failed, causing him to fall a couple feet before the other held. When he scrambled back to the top, it turned out that what broke was a dyneema sling girth hitched to another skinny Spectra-style sling. It looked like one skinny sling cut right through the other, right at the girth hitch knot.
The slings in question were not rubbing on anything. The dyneema appeared to break right at the girth hitch knot, with the break having a fairly sharp edge, indicating cutting rather than tearing/shearing. Verm was rappelling and cleaning using a static rope, which presumably was putting small ("chunky" bodyweight) but repeated shock loads on the webbing until, fiber by fiber, it broke/cut.
He will send the webbing for testing.
Consider using carabiners to connect Spectra/Dyneema slings to each other, especially for any fixing/rappelling/toproping purposes.
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sweetchuck
Oct 24, 2006, 5:10 PM
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I speculated that this could happen and started a thread over in the Lab a couple months ago exploring the possibility. New skinny slings are so thin, and, when compressed by a girth hitch, they are probably not any thicker than the wire stoppers that we all know we should not girth hitch to. I guess now we know. I am glad no one was hurt. We all should beware and not girth hitch with these skinny slings. And for cryin' out loud, listen to sweetchuck! Sure I have been too broke lately to send some skinny slings in for testing, but I tried to warn you all and maybe get one of you fat cat lotacamalot alien mofos to ponie up some slings for testing, but no... I guess the traditional wisdom has to be reconsidered in light of innovation.
sc
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thatnameisalreadychosen
Oct 24, 2006, 6:50 PM
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i will be glad to donate a couple of used mammut dynema slings
just pm me the addy to send it to
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braaaaaaaadley
Oct 24, 2006, 6:59 PM
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Woa, thats pretty interesting. I have always been kinda skeptical about those 8mm slings especially when paired with the new lighter, skinny biners. This is just another good example of why we should use very redundant anchors. I'm glad that nobody got hurt.
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sungam
Oct 24, 2006, 7:45 PM
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Hey, if anbyone wants to send me your thin slings, i'd be freaking happy to recieve them!
Who the hell puts nylon to nylon anyways?
If anyone ACTUALLY wants to get rid of their slings, I'd be happy to pay for shipping and an extra 5$ :D Let the PMs roll in!
-Magnus
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ridgeclimber
Oct 24, 2006, 8:38 PM
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Would doubling the sling through, rather than girth-hitching, yield similar effects? Can anyone explain the physics involved in cutting in girth hitches compared to how it might work if the sling is doubled?
Thanks.
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devkrev
Oct 24, 2006, 8:53 PM
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Isn't there something in the literature with this slings saying DON'T GIRTH HITCH THEM?
I remember reading that somewhere reputable.
dev
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konaboy
Oct 24, 2006, 9:10 PM
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I seem to recall reading elsewhere that girth hitching the mammut slings was a bad idea. . . is there any hard evidence out regarding clove hitching these slings to a biner?
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bri1682
Oct 24, 2006, 9:48 PM
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based on my limited experience and what i have read and been taught, Girth hitches in general are not very safe. When using slings or corfelletes, it is very easy for the girth hitch to cut through the rope when under significant pressure.
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musicman1586
Oct 24, 2006, 10:55 PM
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Girth hitchs on their own are not good for most climbing applications. All the force pulls onto a single point in the webbing (just look at a girth hitch and you'll see that point, where one side digs into the other). If pulled in the correct direction, this is usually not a problem, but by nature girth hitches move to where they are positioned in that stressful situation. Second, as others have already said, you shouldn't ever put webbing on webbing, a saying that I was taught is "soft on hard, hard on soft" or something along those lines. Excluding very few things (quickdraw on a wire) metal should never be on metal, webbing should never be on webbing, it should always be alternating.
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catbird_seat
Oct 25, 2006, 6:37 PM
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I refer you to some actual test data:
http://www.rockclimbing.com/....php?p=409478#409478
Somewhere on the net, I found a site that described a sort of improved girth hitch that was supposed to have greater strength. I would be interested to see that tested using 7 mm Spectra.
While I'm at it, I'd like to point out something about the actual incident above. John was using static rope and a GriGri with which to rappel. If the lever of the GriGri were suddenly closed while the rappeller was moving at a good clip, the static rope would be expected to put a rather high load on that anchor, far in excess of what one would get using dynamic rope and an ATC. If this action was repeated again and again as it would be by someone intent on cleaning a route, that could cause abrasion.
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sungam
Oct 25, 2006, 7:32 PM
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The offer stills stands, If anyone wants to get rid of these DEATH MACINE WIDOW MAKERS, then PM me and I'll give ya my adress, and pay for shipping ;)
-Magnus
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jimdavis
Oct 25, 2006, 8:37 PM
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edit: looks like there's more accuracte info than what I had, listed below...
Cheers,
Jim
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grimbo
Oct 27, 2006, 4:03 PM
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I own Misty Mountain Threadworks, the maker of the sling that the broken dyneema was girth hitched to. I just tested a bunch of 11/16" nylon and 5/8" spectra slings and found that when girth hitched together they broke at about 50% of their normal breaking strength, and always at the girth. Spectra to spectra broke at about 3600 lbs compared to 6,900 lbs as a normal sling. Nylon to nylon broke at about 2,800 lbs compared to 5,700 lbs as a normal sling. The rated strength of those 8mm Mammut dyneema slings is 22 KN (about 4,950 lbs) so at best, brand new and girth hitched together they would break at roughly 2,500 lbs.
I wonder if the setup could have caused a bit of a vector pull on that side of the anchor thus multiplying the force. Adding a little wear on the sling, the static setup, and the bounce of the prybar could all add up to just enough for failure. Luckily, no one got hurt.
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sweetchuck
Oct 27, 2006, 4:36 PM
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Hi Grimbo, it sounds like you are just the one to get to the bottom of this. I think the problem is that, since the 6mm and 8mm slings are so much skinnier, they will break at LESS than 50% strength. The reason that girth hitches are so weak is that they bend the sling at such a tight angle (think bending the sling over a knife edge vs. a coke can). Therefore, the skinnier the sling, the sharper the angle it turns in a girth hitch. The reason we have been told for all these years not to girth hitch slings to wire stoppers is because the wire is so thin it will cut the sling. It is because of the thinness of the wire, not because it is metal or sharp or anything like that. Now, take a 6 or 8mm sling, and compress it as much as you can (say, with a zip tie) and it will be no thicker than a good stout wire on a wire stopper. It's the same physics, and so the same disclaimer should apply. Don't girth hitch anything that thin! We need to test these skinny slings as they are and not try to extrapolate the tests from thicker slings. I hope you test this and share the results. I love the skinny slings, but I do believe that they are unsafe to girth hitch, and I'd hate to see an injury or worse because the tests have not been done, and or, the information has not gotten out. Thanks for the tests, I'll have to remember to buy some Misty Mt. Stuff! (and do the Misty Mt. Hop!)
sc
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grimbo
Oct 27, 2006, 6:29 PM
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Right on Sweetchuck, if I can get a hold of some of those 8mm Dyneema slings I'll be happy to test them and post the results.
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brutusofwyde
Oct 27, 2006, 8:03 PM
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PM me with your snail mail address and I'll be happy to provide a few... some with about 2 years' usage, some new. I am also interested in the strength of the double-shoulder length (48") slings of the same material...
when used in a "cordelette-style" configuration, i.e. used as a belay anchor to 2 pieces, with the lengths of the "legs" of the anchor fixed by tying a power point using either an overhand or a figure-eight.
Brutus
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knudenoggin
Oct 28, 2006, 4:47 AM
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In reply to: I own Misty Mountain Threadworks, the maker of the sling that the broken dyneema was girth hitched to. I just tested a bunch of 11/16" nylon and 5/8" spectra slings and found that when girth hitched together they broke at about 50% of their normal breaking strength, and always at the girth.
NB: your results are a whopping 20 %-points LOWER than those from Chris
Harmston's testing linked to by Catbirdseat & also at another site, http://www.climerware.com/knot5.htm
Your consistency in results is the point of rupture--in the sling making the Girth
Hitch.
Now, about "Girth Hitch": note that this name is ambiguous re knot form, as for the
hitch to something solid (like a 'biner or tree) brings the hitching material back around
itself (to make a sort of collar), whereas when made in webbing, it usually
goes around the hitched-to sling. BUT, in the case at hand, the collar makes
a compromise--it's neither here nor there but pretty inbetween!? So the testing
done is not entirely relevant to that structure (no more than it is to the case of
a hard object).
Frankly, that's a might sharp/neat break!? It's also right at or a little even
past the point of contact? --at least, the knot stayed tied, there was enough of
the broken side jammed by the collar to hold (as opposed to one part coming
out the front, and the other spilling around the opposite way, unwrapping the
collar. !?!?
Elsewhere it has been reported by the owner that the broken sling had been stored
near an acide source; but HMPE is supposedly pretty resistant to acid (and most
chemicals). Mammut is to examine/test it.
In doing further testing of slings, how about giving some further testing to the
sling-2-sling joint(s) proposed at the climberware site (actually, to the one given
there, and to the not-quite-the-same one shown in a link from Franz Bachmann
in the other RC.com thread on thin HMPE slings (see it). --rather than toss out
the idea of ever putting slings together, let's see about maybe a better way to
do so.
Oh, and on the slings you (Grimbo) did test, did the breaks look the same?
(like a cut) And did the Girth hitch stay intact? (break at similar point)
*kN*
(This post was edited by knudenoggin on Dec 5, 2006, 6:56 PM)
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curt
Oct 28, 2006, 5:15 AM
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In reply to: From http://www.supertopo.com/...html?topic_id=269434 Some pictures from the website. http://i138.photobucket.com/.../Dyneemafailure1.jpg http://i138.photobucket.com/...tt/dyneemaanchor.jpg John Sherman just yesterday had a dyneema sling break, under bodyweight. The Verm has been packing on a few pounds lately, but he never suspected he was at the rated breaking strain of dyneema. He was on rappel, cleaning a new line, and, up above, one of his two rappel anchors failed, causing him to fall a couple feet before the other held. When he scrambled back to the top, it turned out that what broke was a dyneema sling girth hitched to another skinny Spectra-style sling. It looked like one skinny sling cut right through the other, right at the girth hitch knot. The slings in question were not rubbing on anything. The dyneema appeared to break right at the girth hitch knot, with the break having a fairly sharp edge, indicating cutting rather than tearing/shearing. Verm was rappelling and cleaning using a static rope, which presumably was putting small ("chunky" bodyweight) but repeated shock loads on the webbing until, fiber by fiber, it broke/cut. He will send the webbing for testing. Consider using carabiners to connect Spectra/Dyneema slings to each other, especially for any fixing/rappelling/toproping purposes.
I was copied on the original e-mail that Verm sent out to a number of climbers on October 21st which included these pictures. It sure looks to me like the sling that failed was cut. Take a look at how straight and even the threads are where the sling has parted.
Curt
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majid_sabet
Oct 28, 2006, 6:00 AM
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That was I thought Curt and it does look unusual with such a sharp cut.
This may sound like a typical equalized anchor however when you closely look at the direction of tensions , you can clearly see that the direction of load (B) was inline with main rope (C ) and second anchor (A) was poorly placed for an equalizing job.
Also under tension and shock, I would worry about that sling been over a sharp edge as pointed in blue.
Another note, most failures are around the knot or sewing which in case did fall in to that category.
http://img99.imageshack.us/...emaanchorcopykz7.jpg
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dbarandiaran
Oct 30, 2006, 4:41 PM
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In reply to: I seem to recall reading elsewhere that girth hitching the mammut slings was a bad idea. . . is there any hard evidence out regarding clove hitching these slings to a biner?
i would like to add myself as an interested party as far as this question is concerned... i currently have my dyneema slings cloved to one of the biners in my quickdraws, it is so nice that way, very easy to extend when trick-tripled, but i really would like to know about any safety concerns with this setup
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maxdacat
Nov 2, 2006, 11:42 AM
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hi....reading this with interest.
2 related questions:
1) i've been using a Wild Country 60cm 8mm dyneema sling as a cow's tail for sports anchoring for a few years now....it's girth hitched to my petzl corax belay loop....should i be worried?
20 I've been using the same brand 120cm 8mm dyneema girthed to the same harness but with an overhand knot about half way for rapping....and using the end bit for anchoring....could the OH knot give rise to similar forces to the one in the original post?
cheers
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maxdacat
Nov 2, 2006, 11:43 AM
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hi....reading this with interest.
2 related questions:
1) i've been using a Wild Country 60cm 8mm dyneema sling as a cow's tail for sports anchoring for a few years now....it's girth hitched to my petzl corax belay loop....should i be worried?
20 I've been using the same brand 120cm 8mm dyneema girthed to the same harness but with an overhand knot about half way for rapping....and using the end bit for anchoring....could the OH knot give rise to similar forces to the one in the original post?
cheers
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timm
Nov 2, 2006, 2:19 PM
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In reply to: hi....reading this with interest. 2 related questions: 1) i've been using a Wild Country 60cm 8mm dyneema sling as a cow's tail for sports anchoring for a few years now....it's girth hitched to my petzl corax belay loop....should i be worried? 20 I've been using the same brand 120cm 8mm dyneema girthed to the same harness but with an overhand knot about half way for rapping....and using the end bit for anchoring....could the OH knot give rise to similar forces to the one in the original post? cheers
According to the WC website, they don't make a 8mm dyneema sling. They make 10mm versions of what you are describing.
Until we know the results of the testing in the case of the Mammut case, I would be hesitant to girth hitch these skinny slings to any nylon (belay loops included) and to tie any knots in them.
Generally, girth hitching nylon to nylon is not a good idea. Theoretically you should not generate enough forces when using them to statically support bodyweight to cause the slings to cut themselves. However, the incident with the Mammut slings may prove otherwise. I'm waiting to hear the results of the Mammut testing.
Cheers.
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