Dynamee Runner Failure

[fenderfour]

When you buy something, you need to know what it's for and how to use it. It's important for the end user to be educated. Responsibility lies on both sides- one side has to provide the info and one side has to absorb it.

 

CFF said it best, I think.

[layton]

Can anyone find how much girth hitching a sling to a nut or another sling reduces it's strength?

 

Are we saying now, "never girth hitch to runners together?"

Because I do it all the time when I've run out of biners.

[catbirdseat]

I'd say not to do it if you have the biners. If you run out of biners you don't have much choice.

[layton]

true, but it might influince (sp?) me carrying more biners

[underworld]

or...carry longer runners

[ClimbingPanther]

Don't forget that Mr. Sherman was rapelling on a single static line using a GriGri. The loads imparted using this method would be far in excess of what they would be using dynamic line and an ATC.

point repeated for emphasis

[G-spotter]

 

I don't think the loads generated rappelling would be significantly different for an ATC vs a GriGri, and not significantly different for a static vs dynamic rope unless you start jumping around all over the place.... rapping situation is close to a static load on the anchor.

[Blake]

Can anyone find how much girth hitching a sling to a nut or another sling reduces it's strength?

 

Are we saying now, "never girth hitch to runners together?"

Because I do it all the time when I've run out of biners.

 

Mike, without any facts to add, I'd suggest that if you do have to girth hitch runners (or do so when you run out of carabiners) that you girth hitch the widest ones you have left at the time.

 

On moderate alpine routes I often bring just enough carabiners to clip the wires on nuts, while girth hitching to cam sling and hex slings. I don't think I'll be doing that from now on.

[Cobra_Commander]

and what about girth hitching necks and constrictions? I've certainly done that with my spectra runners. I'd guess this is a bad idea too.

 

As for the rappelling I wonder just how fast mr largo was sailing down the line and stopping. Just dropping your knees while standing can generate 2kN.

[Farrgo]

Its true that you can generate some force while rapelling. And, since we weren't there we don't have really any idea of what he was doing. But we are talking about rapelling which still generates much much less force than a lead fall.

 

I don't know about everyone else but I girth hitch trees, knobs, flakes, tons of stuff when I alpine climb. I usually think that these features are pretty bomber pieces, now not so much. Mabey its time to just start bring lengths of cord and throw in a quick overhand instead of girth hitching runners that can't hold body weight plus a little tugging.

[Blake]

I think girth hitching flakes/trees etc is still ok.

 

Take that protruding pillar thing below the crux of Godzilla. Both times on that route I've girth hitched that with a 48" runner and felt confident running it up the flake a ways, because that pro is bomber. Hitching a skinny runner around a wide tree or block is different that hitching it around another really skinny sling. In the case of a lead fall, the runner wouldn't cut through itself (or another runner) but merely cinch down tightly on the block/tree trunk.

 

I think with this rap anchor failure that the half-dozen time-consuming rappels on the same anchor had in essence made one of these skinny slings saw cleanly through the other.

[underworld]

girth-hitching a tree or feature doesn't put the same radius on the sling as girthhitching another sling. just like the piano-wire analogy. knives are sharp because the radius approaches zero.

[JosephH]

Can anyone find how much girth hitching a sling to a nut or another sling reduces it's strength?

 

Are we saying now, "never girth hitch to runners together?"

Because I do it all the time when I've run out of biners.

 

I think as a rule you can just assume webbing-to-wire is a real losing proposition. For everything else I think you can make more or less make a blanket statement that soft-on-soft is a sub-optimal combo. But you really have to distinguish between webbing made of stiff high tech fibers like Dyneema, Kevlar, Spectra, etc and plain old nylon webbing. Soft-on-soft with any of the high tech stuff is pretty much completely out as would be using it to girth hitching anything with a small diameter like a biner. But, I and every other old guy here has girth hitched endless nylon slings over the years and we're all here. I don't know of any incidents with doing it among any peers my age. That said soft-on-soft of any material isn't the best of all possible ideas.

 

And not to rag on Sherman, but his rap anchor rigging completely sucked. Aside from having three cams minimum, the rope should have gone to two in-line, equalized cams in roughly the position of the one with the webbing that cut. He then could have put an alpine butterfly in the rope out from that and used the (slack) webbing on the cam to the left as a backup. In general that setup was a poster child for doing any of the "sliding-x" anchors or even just a cordelette.

[ClimbingPanther]

Google search: girth-hitch

 

There's very little good info out there about girth hitching slings to slings, but it seems like it's not a death-wish activity. Some of the more reliable testing indicated a 25% drop in strength, which isn't anything to think twice about. There is one type of girth hitch connection that possibly should be avoided ("linked girth hitch") ["possibly" because one sample is statistically stupid]

http://www.climerware.com/knot.shtml

 

 

Mike:

http://groups.google.com/group/rec.climbing/browse_thread/thread/3055c154ad4348bd?hl=en&rnum=1

This site shows results from testing sling-girth-hitched-to-wire combinations, but is a little hard to comprehend what's really going on. The wires themselves were tested over a tiny nut, then the wire-sling combo did not involve the tiny nut. So, the comparison is kinda stupid, but the absolute value of the breaking strength is still informational. Also, they do not indicate where the break occurred so we can't know if the sling stregth was reduced by 60-85% or if the wire was reduced by some unknown amount.

The one concrete result that you should take with you is that doubling the sling through the wire is better than girth-hitching it.

edit: oh yeah, I should mention that this was done with nylon 11/16

Edited October 26, 2006 by ClimbingPanther

[layton]

Thanks for the info. I'm adding a couple extra biner to the rack.

[kurthicks]

bluewater has done tests girth hitching spectra/nylon blend slings to stoppers. IIRC, usually the stopper wire broke. I can't find that data right now, but it does exist.

[dan_forester]

wow, I learned something from the internets today...I'm going to be using biners to connect 2 slings instead of girth hitching them from now on.

[catbirdseat]

Try tying the "Climer Sling Hitch". It's pretty cool. It is quite a bit more difficult to tie than an ordinary girth hitch, but in theory, it should be stronger, especially for 7 mm Spectra.

 

http://www.climerware.com/knot.shtml

 

I'd love to see a pull test done on the Mammut 7 mm using this hitch versus the conventional version.

[spotly]

As a newer climber who has not yet had the pleasure of needing to replace worn runners, I've been watching these threads pretty closely. I started trad last year and picked up 9 Mammut 8mm runners. They saw a little use last year (8 or 9) routes and quite a bit this year (dozens of climbs). They appear used but not what I'd call worn so I thought I might get another couple of years out of them. It appears that time, as much as wear should determine when they get replaced. Sounds like a few of you are saying 2 years and chuck em regardless of lack of visual wear. If that's the case and given the expense, I think I may go with nylon next time.

[kurthicks]

I took some time last night to try and repeat this failure.

 

Test procedure: We placed an anchor consisting of 2 cams into a concrete crack and equalized them. I then took 2 slings that have been on my rack, one mammut 8mm that is about 1.5 years old and one Metolius sling (that appears to be the same as Sherman's) that was found on the Stuart Glacier. The skinny sling was then girth hitched to the Metolius sling in the same configuration as the sling that failed. The Metolius sling was clipped to the master point while the skinny sling was clipped to my harness. I then conducted approximately 20 severe bounces on the sling by climbing the crack and dropping back down onto the sling. The force was much more than I can ever recall putting onto a rappel anchor. I weight about 145lbs and had no additional equipment on me during the test. The approximate FF was at most .5 onto a static system.

 

Results: The sling did not fail under these test conditions. Upon undoing the girth hitch, the 8mm Mammut sling had suffered from melting/fusing at the point of the girth hitch. This occurred on the inside of the hitch where the two slings had the greatest surface area. The skinny sling now has hard and soft spots where the girth hitch was tied AND where the biner clipped to my harness was. The Metolius had some shiny spectra fibers, indicating that it too had melted/fused during the test.

 

Analysis: While not a scientific test, this anecdotal evidence seems to reinforce the concerns regarding the low melting point of spectra/dyneema material. As always, be aware of the limitations of your equipment, inspect it closely on a regular basis, and retire it before you think it is necessary.

 

Mammut Sling Post-Test

click on the image to see circled areas of deformation though they didn't come out well in the photo.

[annyomous_coward]

Kurt~

Was this test done in a scientific lab?

[kurthicks]

no, but it should be. perhaps this will inspire the engineering types (i'm only an armchair engineer) to do more thorough testing.

[annyomous_coward]

maybe you will find a new career for next summer..... not working for the man anymore

[gary_hehn]

For what it's worth, I always carry a couple nylon sewn runners in my rack and save them for last. If I find the need to girth hitch something along the way I then use the nylon runners. Also, on moderate alpines I generally carry two or three double length nylon tied runners. This combination has worked pretty well for me.

Edited October 28, 2006 by gary_hehn

[David Trippett]

dunno if you've all seen this yet....but here's some pics with that runner failure.

 

notice I quoted and referenced the source!

 

Please feel free to forward this to your fellow climbers

 

Dyneema sling

failure under very low load when girth hitched 10-19-06 On Oct 19th I

experienced a partial rappel anchor failure when a Dyneema sling used

as part of the anchor broke at the point where it was girth hitched to

a wider Spectra sling. The anchor was set on Oct 15th, 30 feet back

from the top of the cliff and used only for rappels and was never

subject to any sudden impacts. The anchor was equalized for the

direction of pull with the girth hitched point of failure on one side.

In theory this part of the anchor should have only been subject to half

the loads, however because the equalization point was a clove hitch it

is possible that one side could have taken the full load (body weight

only) if the angle of the rope changed. The rappel line was a static

rope and I was using a Grigri as my rappel device.

Where

the rope ran over the lip of the cliff it was padded with a piece of

carpet.

Every morning the anchor was inspected for soundness (especially any

chewing by rodents) and seemed sound. When loaded, the Dyneema sling

was suspended in mid-air with absolutely no contact with the rock to

cause abrasion.

The

anchor was rappelled on a total of seven times (sling failed on 7th rap).

As

we were cleaning routes, the time of rappels varied from about 10

minutes to one hour. There was a small amount of rain on the 17th and

possibly some showers on the 18th, however the rappel line felt dry on

the 19th. The failed sling was in use less than one year and showed

no signs of damage prior to this incident. The girth hitch feels quite

tight after the break. When the sling finally failed I was partway

down a slab with multiple points of contact between the rope and the

rock to reduce the force on the anchor. I was stationary at the time

and suddenly dropped a foot when the sling broke.

The point

where the Dyneema failed was Dyneema pinching Dyneema and not in

contact with the Spectra (see photos). The Dyneema sling that broke

was an 8mm Mammut runner. The sling it was girth hitched to was a

5/8� Misty Mountain Spectra runner. The broken ends of the Dyneema

feel soft, not fused.

What factors might have increased the load beyond body weight?

* Pendulums across the face – 10 foot lateral swing at most, 30

feet

below the point the rope ran over the top of face.

* Extra force applied when prying loose blocks of with a prybar. In

theory this force could not exceed the amount I could deadlift. In

this situation I don’t beleive I ever exerted more than 100 pounds

of additional downward force on the rope.

* Sudden drops onto rappel line after it was unweighted when

standing

on ledges. At times the rap line was partially unweighted, but because I

am

nervous/careful when it comes to ropework I always sucked up the rope

through

the Grigri before reweighting it.

* Extra weight of bolting gear, prybar, etc – 40 pounds at most.

I don’t believe any of the above factors is significant, especially

since all of these take place below the lip where the friction of the

rope on the lip would reduce the load on the anchor.

At times the sling may have been stored in the same pack as a Bosch

battery.

Is there any evidence that NiCad cells emit anything that can damage

Dyneema?

At present my best guess as to why the sling failed is that when girth

hitched tightly such a small diameter sling can cut through itself (the

sling suffered a very clean break). In this incident I can imagine

that the girth hitch received numerous small tugs under low load (body

weight and less) and this might have caused a repeated microscopic

nipping or sawing action that eventually cut through the whole sling

(the wider Spectra sling it was girth hitched to also had some fibers

cut at the point of contact with the Dyneema). I am trying to contact

the equipment manager from Mammut to have this sling failure expertly

analyzed. Until then I suggest that Dyneema slings should never be

girth hitched or otherwise knotted.

John Sherman