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healyje
Trad climber
Portland, Oregon
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Jan 23, 2007 - 01:25am PT
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No results yet. The slings are in a box in a corner at the tester's office and it happens at their leisure so it may be a bit longer yet. The slings to be tested are variously two and three years old, well-frayed, and have all shrunk about an inch from the length of new ones. Last year's testing put them at 14k so it will be interesting to see what another year did to them.
But, with regard to the knotting issue, to some extent I think it's common sense to a degree - I mean just look at the damn things - if they don't look to you like they're really pushing the limits of plausibility then you must be pretty damn young or too used to all the new light gear. I have no problem accepting the idea that girth hitching them is a bad idea.
Also, over two years of replacing anchors I rapped with loads in a setup that included a Petzl Shunt and a figure-8 rigged with two girth-hitched, short Mammut dyneema slings that were then tightly taped in place with sport tape. These two slings are part of the batch being tested, and after removing the tape (see photo) they still looked brand new after two years - except, the inner one against the figure-8 was glazed to the point of the appearance of melted plastic about halfway through the sling (unfortunately no photo of the glazing). This inner sling was the one my haul bag was always on so between that and the Shunt it wasn't a safety problem beyond losing the bag; but it does point out again that they're not particularly burly.
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WBraun
climber
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Jan 23, 2007 - 01:32am PT
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"If two slings must be joined, the strongest way to do so is with a carabiner."
Well that's the been de facto standard for a long long time now. I can't believe people girth hitch slings on high potential loads. I couldn't even believe Sherman did that. You girth hitch slings together at anchors you're asking for trouble.
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craig mo
Trad climber
L.A. Ca.
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Jan 23, 2007 - 06:49pm PT
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I cant believe there is enough stretch action at the knot to cut it.It looks like it was cut with a knife.I dont want to believe that.Is that A posibility? Is this place visible from afar? Do people still hate rap bolting?
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knudeNoggin
climber
Falls Church, VA
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Jan 24, 2007 - 07:15pm PT
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The Mammut report confirms assessments of some of us of the cut sling
--i.e., that it was cut, not broken by any sort of loading or fatigure
from use or chemical degradation.
Now, we really should wonder how/why:
(1) Is the OP playing a hoax on us?
(2) Could this cut be made while loaded?
(3) ... or if not, then it was perhaps quite carefully cut only 98%
so as to hide that fact, with the part maybe pushed just behind
the collar of the Girth Hitch--pulled out a bit on loading.
(4) BUT the OP states he was on rappel, ... --i.e., weighting
the line! Could the 2% of HMPE uncut hold that weight for
the duration (i.e., could it have been pre-cut instead of cut WHILE
he was loading it)?
(5) OTOH, would a cut under his rapping loading be so straight?
--I guess a quick slice w/sharp knife would do so, but note how
un-frayed that end is (I'm wondering at whether one should
expect some evidence of it flying apart if cut loaded)!?
In short, though we should feel relieved about the scares advanced
re knotting HMPE dental floss etc., the fact is that this report was
made to the forums and to the vendor, at no insignificant concern
to us all; and if not an unfunny hoax, the guy on the sharp end
of this cordage must be wondering how unfunny the prank
of sling-cutting was, or ... ?!?!
But it seems that this sling couldn't be cut where it was in situ
w/o notice that there was a 2nd anchor point, which gives some
further things to wonder about.
*knudeNoggin*
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healyje
Trad climber
Portland, Oregon
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Apr 18, 2007 - 11:49am PT
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Got the results of the testing of a sampling of my now retired three year old Mammut 8mm Dyneema slings. These numbers are down from the two year old test average of about 14kn. These are normally rated 22kn new:
# 1) 8 mm Mammut girth hitched to 3/4" Nylon = 11.55 kN.
# 2) 3/4" Nylon girth hitched to 8 mm Mammut = 11.76 kN.
# 3) 8 mm Mammut girt hitched to 13 mm Dyneema = 8.32 kN.
# 4) 8 mm Mammut girth hitched to biner = 12.28 kN.
# 5) Ultimate tensile strength = 11.24 kN.
# 6) Ultimate tensile strength = 11.9 kN.
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scuffy b
climber
The town that Nature forgot to hate
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Apr 18, 2007 - 03:14pm PT
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Wow, Joe. I mean Wow.
3 years brings them down to slightly more than 50% of their
rated strength?
I guess I'm going to be sporting a bunch of new slings this year.
Thanks for the heads-up.
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Chiloe
Trad climber
Lee, NH
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Apr 18, 2007 - 03:19pm PT
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Joe, as I read your data they suggest that most of the strength reduction could be due to age, with relatively minor additional reduction due to the girth hitching itself. In fact, only the 8mm-to-Dyneema hitch looks weaker than the "ultimate tensile strength" alone. Is that your interpretation too?
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Jonny2vests
Trad climber
Nottingham, UK
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Dec 18, 2007 - 04:50am PT
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I know this post is past its sell by date, but I thought I'd offer a Brits perspective.
1. Larks footing (or as you call it Girth Hitching) slings together has always verged on the taboo in the UK. Firstly, the sawing action apparent here is well understood (yes, I know, I need a reference here), though admittedly, I would expect there to be some fusing or melting. I've noticed from several trips stateside that larks footing is commonplace which surprised me.
2. Any knot weakens rope or tape and this is proportional to the sharpness of the bend in the knot involved. Girth Hitches have very sharp bends.
3. Personally, I wouldn't have used a sling anyway, why not equalise using the rope and have less links in the belay chain to fail?
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Tom Hanson
Trad climber
Castle Rock, CO
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Dec 18, 2007 - 11:26am PT
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Personally, I hate these new 9.8 - 10.2 "single" ropes.
What ever happened to those good old 11mm's?
Spectra-sling? Forget that dental floss crap and use time tested 1" tubular.
Ultra-light biners? I'd use them for a keychain, but for actual climbing (even projecting sporty lines at my limit) I'd prefer to use a Stubai steel biner.
I weigh in at 200 lbs and don't mind hiking in an additional ten pounds of gear if it means that I can have total trust in my gear.
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knudeNoggin
climber
Falls Church, VA
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Jan 15, 2008 - 01:43pm PT
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Thanks to Healyje for this report:
> Got the results of the testing of a sampling of my now retired three year old Mammut 8mm Dyneema slings.
> These numbers are down from the two year old test average of about 14kn.
> These are normally rated 22kn new:
>
> # 1) 8 mm Mammut girth hitched to 3/4" Nylon = 11.55 kN.
> # 2) 3/4" Nylon girth hitched to 8 mm Mammut = 11.76 kN.
> # 3) 8 mm Mammut girt hitched to 13 mm Dyneema = 8.32 kN.
> # 4) 8 mm Mammut girth hitched to biner = 12.28 kN.
> # 5) Ultimate tensile strength = 11.24 kN.
> # 6) Ultimate tensile strength = 11.9 kN.
But this is incomplete in a few ways. Firstly, we don't know (except for #4-6) WHICH sling broke.
(Though the lowest value is for two made of HMPE.) Secondly, in the case of tape-to-tape, we
don't know the dressing of the knot--was it like the OP's (nearest to what obtains around a rigid
object, such as the 'biner), or like that shown in climerware's site, or the other form shown by
Kolin Powick ("strop bend")?
Chiloe smartly observes:
> Joe, as I read your data they suggest that most of the strength reduction could be due to age,
> with relatively minor additional reduction due to the girth hitching itself. In fact, only the
> 8mm-to-Dyneema hitch looks weaker than the "ultimate tensile strength" alone.
> Is that your interpretation too?
Ostensibly, one should conclude from this data exactly the OPPOSITE of the continued
ranting against "girth hitch"--i.e., that GHing has NO reduction in "ultimate strength",
both showing as 11kN above. But except for Chiloe's unanswered question, I don't see this,
but do see the continued nonsense.
--to wit, from a Brit:
Jonny2vests
> ... I thought I'd offer a Brits perspective.
>
> 1. Larks footing (or as you call it Girth Hitching) slings together has always verged on the taboo
> in the UK. Firstly, the sawing action apparent here is well understood ...
Firstly, but for Bill March's mistake, the historical name is "lark's HEAD"; the Brits seem
to have a lower estimate of this. (-;
As for this alleged "sawing action apparent" in J.Sherman's broken sling (the only rupture shown
in this thread), apparently J2v didn't bother much reading or comprehending Mammut's report on
the sling, and commonsense understanding of what a sawing action would do, in terms of the
resulting edge of the ruptured pieces (also testified to by those who've broken such material).
*kN*
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steelmnkey
climber
Vision man...ya gotta have vision...
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Jan 15, 2008 - 02:28pm PT
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Over on mountainproject, it was stated by those in the know that someone had intentionally cut the sling to cause an accident.
This was the statement:
"The conclusion of the manufacturer was that it had been intentionally cut. The testing was also unable to replicate the failure results. There was a thread about it on Rockclimbing.com I think. Unless somebody claims responsibility we will never know for sure."
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crunch
Social climber
CO
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Topic Author's Reply - Jan 15, 2008 - 03:32pm PT
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knudeNoggin, thanks for your analysis. And to Healyje. And the others who have wondered and posted about this.
knudeNoggin, you pondered about whether this was a hoax. As the OP, I can confirm that as far as I know, this is not a hoax.
Verm told me about this incident. Now, I've known Verm for maybe twenty five years; he seemed genuinely shocked about what had happened. He is well aware that a mechanical failure of climbing gear like this would be a very serious issue. He asked myself and a number of other folks to spread the word about this, because he was worried about someone else repeating this more or less body-weight break, but without the anchor redundancy that saved him. Hence my posting.
The sabotage theory is unlikely:
1. The location is extremely obscure. I've climbed there. Someone would have had to follow him, without alerting his dog, and then spend some time carefully cutting right inside the knot, to do this.
2. To deliberately stage this "accidental" and yet enigmatic breakage would be somewhat pointless. A disgruntled anti-Tamo/anti-Verm saboteur would surely make the damage obviously human-caused, to make some kind of warning. Or just cut the rope itself to, ahem, get the point across more strongly.
There might be a complex combination of factors, old worn webbing, bouncing repeatedly many many times, perhaps the same knot left tied for several rappel/cleaning sessions. Perhaps there was some kind of accidental cut already, and the new knot slid into place right there on the existing damage.....
The usage was not exactly regular climbing usage, almost industrial usage, and for this kind of usage, as I recall from the times I cleaned windows on rappel, it's customary to use really heavyweight versions of everything, because everything gets more beat up. Using ultra-skinny lightweight webbing would not seem a very good idea.
Evidently this failure is not easily reproduced. That is puzzling and frustrating. But on the bright side, if this failure is so difficult to reproduce, it's unlikely to be repeated.
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healyje
Trad climber
Portland, Oregon
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Jan 15, 2008 - 05:41pm PT
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I was having my Mammuts tested annually and the progression was basically:
22kn > 14kn > 11kn > 8kn > ?
My take on this informal but competetnt testing is that the stiff dyneema fibers break over time using them as alpine draws. Mammut's response to me was that these slings are designed as a consumable, ultra-lightweight sling for ascents which demand such optimizations. 'Consumable' being the key word. Today's material science isn't at a place yet to provide us with dramatic weight savings without something giving either in size, strength, or longevity. Trading away size (length) and strength isn't an option in slings so what has to 'give' is longevity.
The upshot? I wouldn't climb on skinny dyneema slings more than three moderate or two hard years at the outside max.
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Mimi
climber
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Jan 15, 2008 - 05:44pm PT
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I spoke with Verm when this thread started and he didn't believe anyone had cut the webbing when I asked if that was a possibility.
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knudeNoggin
climber
Falls Church, VA
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Jan 16, 2008 - 02:31pm PT
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> he did not believe ...
> The sabotage theory is unlikely:
Beliefs & likelihood are less durable grounds for a conclusion than the scientific
testing & analysis (microscopic, even) done by Mammut. Quite simply, the break
was a cut, and by a sharp enough object running perpendicular to the axis of
loading (so much for the supposed "sawing action" that might come from cyclic
loading). You can't just dismiss this because someone thinks it unlikely.
As for the ability for someone to find the sling etc., that maybe narrows the
suspects; re the dog, well, it wasn't there all the time, or it might have known
the sabateur and reacted quietly. What I think wasn't answered by Mammut is
how much force the few bits of uncut fibre could've supported, such that the
break didn't come on initial but only later-along loading.
I simply cannot understand how everyone is so quick to dismiss the absence of
ANY resemblance to breakage--no irregularity, no melted fibres, no adequate
force--resulting from normal circumstances, and the attested match to being cut
by a sharp object. And for the breakage to occur from knot action and yet the
cut lie just outside of the knot, which remained intact ... ?! Even some embedded
bit of sharp rock/sand/glass would have to work miracles to cross the strand and
cut it so evenly, and outside of the knot.
Now, re Healyje's tested slings, there is yet the oddity that, if Chiloe & I are reading
the results correctly, it made NO difference really whether the slings were GH'd or
not ("ultimate strength")? I don't believe this, but the test data has about 11kn for
both cases. Perhaps Healyje can reply something like "what I chose for Ultimate
testing were the worst, most ragged-looking slings, since I wanted to see how
badly ...", and we then have some reason to understand how they got the same
strength as some better-condition slings GH'd (which other testing & Mammut's
report suggest might be 50% of ultimate strength). ??!
*kN*
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