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naked A-thread rappel anchor

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 Pay Attention 18 Jan 2018

I was watching the Steve House video on naked A-thread rappel anchor.

Is it called the A-thread because the Americans haven't figured a wrong way to spell Abalakov?

It's led to other articles on the American Death Triangle and the Stone Dog Hitch.

Just speculation, but in the video it looks like he's on Cathedral Ledge.  Can anyone confirm?

 

 

 Wee Davie 18 Jan 2018
In reply to Pay Attention:

If you're meaning Cathedral Ledge New Hampshire then I'd say it doesn't look like it to me. There's too much uphill in the foreground from my fuzzy 1990's recollection. The ski hills seemed about 5km back from the crag.

 

 Pete Houghton 18 Jan 2018
In reply to Pay Attention:

My basic understanding is that a V-thread is horizontal and an A-thread is vertical, and the letter A was chosen not as a simplification for Abalakov, but because it's the only other letter that makes the correct shape. Using, for example, an F or a G, would be time consuming, and ultimately rather dangerous.


I believe a better name for a naked V- or A-thread is an O-thread, or nO-thread.

In reply to Pete Houghton:

Correct!

 

 Logs06 21 Jan 2018
In reply to Pay Attention:

I think something worth highlighting for anyone watching that Steve House vid on 'naked A-threads' is his use of two dyneema slings larks footed together (and also larks-footed through his belay loop) as his connection into the belay while building the v-thread.

Connecting to the belay with a dyneema sling while building v-threads is a fairly common set-up for all of us who ice climb. But the forces that can be generated in a simple slip on the ice can be high enough to break the dyneema sling connection to the belay, or the belay itself for some ice-screw placements.

See Petzl's and other's videos for drop-tests on screws, and compare the failure forces with the forces generated in DMM's video below on sling drop-tests. Various tests show an average of 10kN to rip out a 16cm screw in good ice. The force required varies depending on ice quality.

Watch DMM's video on how to break dyneema slings here: vimeo.com/27293337, then re-watch House's video with it in mind.. 

Any knot introduced into a dyneema sling (overhand, fig8, larksfoot) immediately reduces its failure strength to below the force that you can realistically generate in a small slip while faffing around at an anchor with a small amount of slack in the sling.

The House video shows him on low-angled ice where a slip would most likely be corrected before creating high forces, however it's an instructional video which demonstrates less than ideal practice without mentioning the risk of a practice which has led to anchor failures and fatalities in the past. Well worth reminding ourselves of the risk.

Apols for the essay, just a long-winded way of saying don't be complacent about faffing around at anchors while connected by a dyneema (or nylon) sling.

Post edited at 14:47
 John Kelly 21 Jan 2018
In reply to Logs06:

House has done a bit!

Post edited at 14:56
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 Logs06 21 Jan 2018
In reply to John Kelly:

He's certainly done a bit; no dispute over his experience! But having 'done a bit' doesn't preclude making everyday errors which lead to dying or being seriously mangled in simple climbing accidents. House himself attests to that, having seriously mangled himself by falling on a relatively straightforward alpine climb which led to near death and the end of his career as a leading alpinist.

I prefer to trust objective pull-test figures than trusting something because someone's experienced.

OP Pay Attention 21 Jan 2018
In reply to Logs06:

Thanks Logs!

That is an interesting and sobering assessment.

 John Kelly 21 Jan 2018
In reply to Logs06:

< a practice that has led to anchor failures and fatalities>

Is that true, I don't know of an instance

the risk as far as  I'm aware  appears to be theoretical and only if you misuse the essentially static (dyneema) sling, though I wouldn't like to fall on a belay even using skinny rope 

House fall unrelated to this issue

His accident was caused by flake snapping, I understand

 

Post edited at 17:10
 lithos 21 Jan 2018
In reply to Logs06:

> Watch DMM's video on how to break dyneema slings here: vimeo.com/27293337, then re-watch House's video with it in mind.. 

when you re-watch the video you'll see his centre of gravity is always well below the anchor.  the FF he'll be generating will be low. From my estimates most of the time  well below .25,  looked like at worst .5, on a gentle slope not vertical. compare to dmm excellent videos these are very different scenarios

I agree its worth pointing out but at the same time his practice of keeping well below the anchor is worth pointing out rather than a blanket condemnation.

1
 GHawksworth 21 Jan 2018
In reply to Pay Attention:

I'm pretty sure he explains in the video why its called an A-thread. Also, at 1:40 he uses the second screw across the ice to measure the distance, giving the cross of the A.

 Logs06 21 Jan 2018
In reply to John Kelly:

> < a practice that has led to anchor failures and fatalities>

> Is that true, I don't know of an instance

> the risk as far as  I'm aware  appears to be theoretical..

 

Unfortunately yes, there have been fatalities due to this. https://www.ukclimbing.com/forums/expedition+alpine/fatal_accident_-_shock_...

I'm aware of one other, in Canada, where the anchor sling failed under a FF2. If you search the journals of the various European and North American alpone federations you may find more.

Near misses also. http://www.neclimbs.com/SMF_2/index.php?topic=2565.0

That one involving John Sherman - another one who you could point out has 'done a bit'!

Following that incident Black Diamond ran tests on slings girth-hitched to slings.

https://eu.blackdiamondequipment.com/en_GB/qc-lab-connecting-two-slings-tog... 

Result of girthing an 8mm dyneema to an 8mm dyneema sling - 57% reduction of ultimate strength from 22kN (brand new sling) to 10kN.

 

My point about House falling IS irrelevant to the topic, as you say. I made it to illustrate how your raising his experience level is an irrelevant response to me pointing out that slings are a weak link worth highlighting in House's anchor video. Hoped that would be obvious.

 

It's interesting if you analyse the video for the weakest link in the chain and the most probable point of failure:

  1. Ice screw belay - each around 10kN assuming good ice. Less in poor ice and hard to know for sure. The video shows the norm of 2 screws equalised as a minimum for a belay.
  2. V-thread anchor - again around 10kN ultimate strength depending on ice quality. The vid shows the v-thread being backed up with a screw, again the norm you'd expect.
  3. Sling girthhitched connection. Maximum strength of 10kN if brand new. Good probability of this being lower than 10kN if a couple of years old, wet, frozen etc. No back-up. Slack in the system and the potential - not in this video perhaps but certainly in the real world involving the hundreds-thousands of people who will do this exact same thing - for a shock load in excess of the weakest link. 

 

He has to show the ice-screw belay and the v-thread anchor, as these are what you do when ice-climbing. He doesn't 'have' to show girth-hitched slings, which is less than good practice and many people aren't aware of the strength limitations (combined with potential for high shock-load) it introduces.

Not blanket condemnation is it? Just saying it isn't always clear what the biggest risks are in the mountains and there are lots of ways to kill yourself that aren't immediately obvious. The video overlooks (in a way encourages) a big one.

Post edited at 21:07
 John Kelly 21 Jan 2018
In reply to Logs06:

https://www.ukclimbing.com/forums/expedition+alpine/fatal_accident_-_shock_...

In situ tat failed not the sling, tragic but the weakness was within the fixed gear.

http://www.neclimbs.com/SMF_2/index.php?topic=2565.0

Top roping situation, semi permanent, very confusing, no idea what the cause is

 

Fair to say, given you trawled back to 2007 for a non example of a sling snapping, it's very rare but given DMM video not impossible

10kn - I'm pretty good with that figure, loads of gear and placements are less than that that so girth hitch not likely to be weakest spot, redundancy is the key for me

Always try desperately to avoid FF2

 

 

Post edited at 21:33
1
 Logs06 21 Jan 2018
In reply to John Kelly:

Hehe, 10kN sounds a lot yes, and in normal situations with a dynamic element (e.g. rope) it is. But you're overlooking two factors:

The 10Kn figure is for a brand new sling.

The use of a sling as a direct connection, especially a dyneema one, allows 10kN of force to quite easily be generated in a very short fall - less than a FF1 could generate enough force to break your (used) sling.

This is sometimes poorly understood especially with newer clibmers as it's common to have a grasp of the forces generated using a dynamic system, but less common to think in terms of forces generated in a static system.

How many of us carry brand new slings? I know I don't. So how about researching what the ultimate strength of a used sling might be. Here, did it for you:

10mm Dyneema Sling

New

26.1kN (4946 lbf)

Old

17.1kN (3846 lbf )

 

12cm Dyneema Dogbone

New

26.1kN (4946 lbf)

Old

10.5kN (2366 lbf )

From http://www.blackdiamondequipment.com/en/experience-story?cid=qc-lab-old-vs-...

 

Then take off 57% of that figure by introducing the girth-hitch.

So with used slings, found on a typical keen climber's rack as per the example above, you might be looking at 7.3kN ultimate strength when girth-hitched. And going off some of mine and my friend's slings, possibly less..

I'm just saying, be aware.

Post edited at 22:33
 John Kelly 21 Jan 2018
In reply to Logs06:

I've read that stuff and apart from the dog bone (you can't girth hitch a dog bone) the losses are in my view acceptable, I use a lot of 6mm beal slings and I do change them regularly 

There are simply not loads of examples of slings failing in the real world

Understanding the materials and the physics to some degree is, I agree with you, helpful

 

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 drsdave 30 Jan 2018
In reply to Pay Attention:

As I understand it both variations work fine. However (and I’m very happy to be advised on this), then making pick placement in Alpine very cold ice, isn’t it better to put one placement above the other as opposed to side by side because of ice fracturing. Hence the vertical thread placement may be the preferred option??

OP Pay Attention 31 Jan 2018
In reply to drsdave:

Yes, I read that somewhere but can't find the source reference just now.

 GarethSL 31 Jan 2018
In reply to drsdave:

> then making pick placement in Alpine very cold ice, isn’t it better to put one placement above the other as opposed to side by side because of ice fracturing

Placing picks side by side is a pretty out-dated technique with axe over axe being the norm. It's more for efficiency of movement, stability and balance, but has the caveat of limiting horizontal fracturing.

Ice typically breaks horizontally as a result of loading or expansion and contraction as the ice responds to variations in temperature. Cracks in low angle ice, bulges or slabs will follow perpendicular to whatever direction the internal stress in the ice has. This I find is most typically outwards, as laminated sheets, due to progressive layering of cold and warm ice in (again as a result of air temperature variations). Hence 'dinner plates' are usually conical or irregular in their fracture pattern, like glass. Gravity is always there and I'm sure many people have experienced the joy of watching a long horizontal crack propagate away from an axe placement, even on low angled ice, I know I certainly have.

Personally, I would say that building threads in a vertical orientation should be preferred. In stable homogeneous ice the orientation doesn't really matter, whilst in very tense ice, or ice under load, a vertical orientation should be considered as the most ideal. Obviously, threads shouldn't be built on bulges due to the risk of laminated ice.

As for naked or not, that I think is personal preference. I find that in good, dry ice a naked thread is quicker, safer whilst retrieving far smoother and more easily than one with cord. In wet ice cord is essential.

 drsdave 31 Jan 2018
In reply to GarethSL:

What a welcome informed response thanks. Ice really is a science. As I suspected vertical threads win out. Thanks 


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