/ use rope or sling to make cows tails?
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.
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...
I just can't see any reasons in favour of using slings.
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.
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.
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:
Also see the DMM video mentioned above http://dmmclimbing.com/knowledge/how-to-break-nylon-dyneema-slings/
FF2 w/ 80kg we get 12kN, which isn't so different from a rope cows tail, though obviously blows your stitching.
FF2 w/ 80kg on a camp rope based sewn cows tail yields ~12kN.
Knotted instead of sewn are better, energy absorbing wise.
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.
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.
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.
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?
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