/ use rope or sling to make cows tails?

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traderdb - on 09 May 2013
quick question about cows tails. When looking to ascend a slope on a fixed line in winter conditions such as with sections of Everest or Amadablam, is there any reason why you couldn't use a sling to make the cows tail? or 2 slings - one for the ascender and the other for the backup crab?
Jamie Simpson on 15 May 2013
In reply to traderdb:

Many people have for a long time used a sling(s) to attach themselves from the harness to a belay / jumar. Recently some companies have been pushing people to shift from slings to a rope. Beal make a dedicated rope attachment, with protective sheath at both ends.

DMM made a really good mini movie about what happens when you fall above, for example a belay while using a sling attached to your harness. Well worth watching. Quite sobering.

Both have advantages / disadvantages.
Dr Toph on 15 May 2013
In reply to traderdb:

The standard practice in rigging is to use dynamic rope for cow's tails to lessen shock loading in the case of a fall. (if you are clipping in below waist level, then fall arrest shock absorbers are also used but that would be excessive for your purpose).
Looking at the results of the DMM sling drop test, all the FF1-2 results show shock loading of over 10kn, which would risk internal injury, even if the sling doesnt fail. You are in a very short system when using cows tails, so high fall factors are quite possible.
Guess its a calculated risk - an increased safety margin on easy ground vs not carrying extra gear up there when a sling would suffice...
Milesy - on 15 May 2013
Surely if the OP is talking about ascending fixed ropes then you are connected to a dynamic or at least semi dynamic system anyway? so the use forces on a sling would not be anywhere near what it would be if we are talking about clipping straight from harness into a bit of gear?
The Ex-Engineer - on 15 May 2013
In reply to traderdb: For expedition use I'd suggest it is a bit better, easier and cheaper to use rope (or thinner 6/7/8mm cord). You will generally want more than just a simple single cowstails to deal with passing anchors and you will want to adjust it to the perfect length. A single length of cord/rope is normally tidier and hence easier to use than the 'double' strands you generally get if using slings. Finally, using rope/cord results in a slightly more dymanic system if you do fall/slip when passing an anchor.

I just can't see any reasons in favour of using slings.
The Ex-Engineer - on 15 May 2013
In reply to Milesy:
> so the use forces on a sling would not be anywhere near what it would be if we are talking about clipping straight from harness into a bit of gear?

You may be forgetting that you will need to pass anchors every 50m or so and that you will also often need to stop and wait for other climbers to exit the next section.

As such it is very hard to guarantee that you will always be in a low fall-factor scenario. It is very likely mountaineers will occasionally end up either clipped directly to anchors or attached via only 10s of cm of rope. As such the extra shock absorption of rope/cord cowstails over slings is almost certainly still worth having.
AlH - on 15 May 2013
In reply to traderdb: 2 good articles from experienced users here: http://www.mountainz.co.uk/fixed-lines.php and here: http://www.everestexpedition.co.uk/everest_south_col/fixed_ropes_on_everest.htm
Using rope is cheap, dynamic (more important perhaps on traverses) and allows you to get things at exactly the right length for you which can make a big difference during extended use at altitude. Enough of a difference to outweigh and perceived weight difference in carrying just slings that you might use for something else as well.
In reply to traderdb:

We recommend 8mm cord. We had a workshop on this a couple of years ago at our annual Expedition Leaders Forum. Streaky from DMM did a presentation.

Following the workshop we produced this booklet:

http://www.jagged-globe.co.uk/exp/Jagged_Globe_Fixed_Line%20Systems.pdf [3.6Mb]

Also see the DMM video mentioned above http://dmmclimbing.com/knowledge/how-to-break-nylon-dyneema-slings/
AlH - on 15 May 2013
In reply to Tom Briggs - Jagged Globe: ooh, nice little resource that Tom!
needvert on 15 May 2013
http://www.petzl.com/us/outdoor/verticality/accessories/sewn-slings-and-lanyards/spelegyca .
FF2 w/ 80kg we get 12kN, which isn't so different from a rope cows tail, though obviously blows your stitching.

From here:
FF2 w/ 80kg on a camp rope based sewn cows tail yields ~12kN.
Knotted instead of sewn are better, energy absorbing wise.

From DMM:
FF2 w/ 80kg on their nylon sling yields 16.5kN

Though your ascender will cease to be such around 4-6.5kN
( http://www.petzl.com/us/outdoor/ascenders-2/ascension )

Don't really have a point, I was hoping I'd find one.
cannichoutdoors - on 15 May 2013
In reply to traderdb: No reason why you can't use 2 slings - i did on Ama Dablam. But, my experience was that (a) they were a pain to get the right length (you don't want both strands to be at the same height), (b) the knots you put in are a bugger to undo once you've loaded them, and (c) in reality you are not carrying the slings for anything else anyway.

Our guide used a rope system that was set to exactly the right lengths derived from years of experience and multiple trips. I would use a 7-8mm length of cord adjusted to suit on any future trips.
Vance2038 on 15 May 2013
In reply to traderdb:
Please, please use something dynamic in your cows tail.
A quick appreciation of the fall factors you can expose yourself to when using them shows that they are the main part of the system absorbing energy.
Cavers use cows tails all the time with SRT and have spent time analysing this area. Standard practice is to use approx 2 metres of 8mm dynamic rope to make the cows tails from. Cheaper then a sling and light.
cannichoutdoors - on 15 May 2013
In reply to Vance2038: Sorry, you're quite right. I meant dynamic rope not accessory cord.
Stuart (aka brt) - on 15 May 2013
Where are people getting 8mm dynamic, off the reel from (as opposed to accessory cord)?
WJV0912 on 15 May 2013
Interesting read.

Currently I use a nylon/dyneema sling larks footed to my belay loop, with an overhand about 7" up so I can abseil off it.

Would I be better using a cut section of dynamic rope with an alpine butterfly 7" as a separate abseil loop?
WJV0912 on 15 May 2013
Also, this is in the context of arriving at belays and clipping in; would it be acceptable to have the rope fig 8'd round your belay loop?
jon59 - on 15 May 2013
In reply to traderdb: I was looking at using a grivel daisy chain instead of rope this year, this set up is rated to 23kn, adjustable but on the down side expensive.


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