"New-style" cows tails – comments/criticism/remarks welcome

[ChrisB]

Chris - not sure that single overhand will perform very well in drop tests (Americans call them European death knots as they tend to roll when used to join two ropes)...

In this context, it doesn't matter. I wouldn't think of using one on the end of a cowstail, but mid-rope, the krab can't escape. In a fall, the most that could happen would be that it rolled up the cowstail a bit, which would be advantageous.

The loading on the knot in the EDK is also quite different to a single overhand in the same rope.

 

[mikem]

But probably similar when attached to a krab - but midrope is trapped as you say.

Biggest danger with cowstail would be the anchor failing whilst you are clipped in.

 

[Bob Mehew]

Bob, I suspect that your drop tests were from a fixed anchor? If so the results in terms of ranking will be correct , but the generated force figures meaningless.

You need to test from a traverse line, anchors say 2m apart, with two alpine butterfly knots, or from a Y hang clipped to both loops in order to replicate down-cave conditions. And these days, with 9mm rope.

I have fallen twice on traverse lines when carrying big loads. I use Petzl Jane lanyards which are sewn dynamic rope [and blissfully the correct length for me ]. Shock loading to the body wasn't even noticeable.

I regularly clip direct to anchors when rigging, but I hang below, not climb above.

There are several scenarios around using cows tails and obviously clipped into a traverse line would normally give you a smaller force in the event of a fall. But that ignores the scenario of one anchor failing. (And there is no simple answer to that case.) Yes our drop tests did equate to a cows tail clipped into an anchor. I would expect the majority of cases where one clips into an anchor, one is below it so restraining the potential fall to under FF1.0, but not all cases.

There is also the point that one's crabs add to the potential fall distance without supplying much (if any) shock relief possibly converting a so called under FF1.0 drop into an over FF1.0 for situations involving cows tails. Quoting the 2006 FFS report:

The length of the lanyard = 36 cm + The length of the lanyard karabiner = 9 cm + 2 x the length of the harness karabiner = 18 cm
=63 cm which gives us a Fall Factor of : 63/36 = 1.75. For a 60cm lanyard this Fall Factor is : 87/60 = 1.45.

You may be aware of it but how many other cavers are?

 

[JoshW]

I think we should all start to rig on dynamic rope.. oh and do those abalakov things but on bungee.. and would a harness made out of stretchy elastic help?

 

[MarkS]

I'd add to the recommendation of at least 1 adjustable cowstail. I use a Kong Slyde.

Maybe request a pull/drop test from someone like HowNot2

I'd be interested to know if there is an example anywhere of anyone being badly hurt by the impact force of falling on a cowstail whilst caving...

 

[Chocolate fireguard]

I don't know of anybody being seriously hurt, but for the whole of my srt caving career people have been using knotted cowstails.

The Slyde is a world away from a lanyard sewn at both ends.
It does slide under heavy load and there is a knot at the other end.
I would be happy to use it.
But not the sewn lanyards.

 

[topcat]

Bob, an anchor failing on a travese will only introduce more stretching absorbing rope. An anchor failing on a Y hang will induce a small pendulum with? no significant increase of impact.
A single point rebelay failing would increase a fall length but would have lots of absorbing rope above it, and knots.

Folks can make their own informed decision on what to use for CTs but the information needs to reflect reality and not just lab conditions test results. Which I find very interesting to read and ponder.......your work and efforts over the years is much appreciated.!

 

[Chocolate fireguard]

I think we should all start to rig on dynamic rope.. oh and do those abalakov things but on bungee.. and would a harness made out of stretchy elastic help?

I feel your pain Josh, but this is a technical subject and numbers must come into it - we can't spend the whole 99.1% of the time just describing what happens.

 

[MarkS]

Can we start with the number of people that have ever been injured by the impact of falling on to cowstails in a cave?

 

[JoshW]

I feel your pain Josh, but this is a technical subject and numbers must come into it - we can't spend the whole 99.1% of the time just describing what happens.

it’s a technical subject, which needs an understand of actual real life application to make a judgement call on the numbers.

Also, if you can’t work out that there might be situations in the grey area between my described 99% (nil risk) and 0.1% (somewhat of a risk) I’m not sure you’re the person to be making a judgement call

 

[Chocolate fireguard]

it’s a technical subject, which needs an understand of actual real life application to make a judgement call on the numbers.

Also, if you can’t work out that there might be situations in the grey area between my described 99% (nil risk) and 0.1% (somewhat of a risk) I’m not sure you’re the person to be making a judgement call

Ah yes, I obviously misunderstood your meaning when you gave those numbers.
And it was wicked of me to mock anyway.

 

[Fulk]

Here are a couple of snaps of the 'krab keepers' I mentioned:

 

[JoshW]

Here are a couple of snaps of the 'krab keepers' I mentioned:

Interestingly there have been major incidents involving these keepers (or similar) on quickdraws and they’d created a false loop.

Obviously if they’d checked their kit properly prior to use they wouldn’t have got injured or died

 

[Leclused]

Kong has the "TRILONGE" in their product list

Trilonge

 

[Chocolate fireguard]

Can we start with the number of people that have ever been injured by the impact of falling on to cowstails in a cave?

I don’t know anybody who has been injured falling onto cows tails.

I wouldn’t be all that surprised if nobody ever has been injured.

I would be surprised if nobody has ever had a greater than FF1 fall onto them because, although people on this forum know that certain things shouldn’t be done underground, when people are tired, in a rush etc. those things are sometimes done. The various CROs get much of their custom from people making silly mistakes. And the FF theory is quite difficult compared with the idea that you should put a knot in the end of your rope, or that you shouldn’t ab a pitch without the ability to get back up.

The peak force on an average weight caver suffering a clean FF2 fall onto a typical knotted long cows tail will be around 5kN. The solid steel caver gets about 7kN.

Unless you are unlucky 5kN is survivable without serious injury, though perhaps not pleasant.

Taking out the knots and substituting sewn loops will push that up a lot.

I can’t imagine why people would want to risk that for the sake of being able to adjust the length, when a knot at the bottom and something like a Kong Slyde at the top will do the job just as well and retain the energy absorbing capacity.

Individuals are free to do as they like in this respect, but I do hope that sewn rope lanyards are never formally recommended as suitable for use as cows tails.

That Lyon Equipment report from 2001 that Bob referenced above is a long read, but on P81 it says:



"The tests show that the best material for cow’s tails is knotted dynamic rope. Of the knots tested, the Barrel knot produced the lowest impact forces, followed by the figure-of-eight.

As well as having the benefits of easy adaptation to the user it is currently the only way in which acceptable impact forces can be achieved.

…………………………………………………………………………………………………………………….

There are sewn termination rope cow’s tails on the market made from both dynamic and static rope: while these may be applicable to low fall factor situations, neither are suitable for use as cow’s tails.

Sewn dynamic rope cow’s tails should be restricted to uses where the maximum possible fall is fall factor 1".

 

[topcat]

......but the tests are flawed...see above.
In the real world sewn CTs have been good for me, and have saved by bacon a few times without any drama.
The added bonus is a compact system which I really appreciate , being rather fond on tight grotty holes

 

[Chocolate fireguard]

I’m not sure what you mean by flawed.

If you mean that the force on a real person will be less than that on the 80kg (or whatever) steel mass being used then that is certainly true.

But there is no other way of doing it, unless some very dedicated volunteers come forward.

I did once see a report (which I have tried unsuccessfully to find on Google this afternoon) on drop test measurements on people, but my memory is that the volunteers made their excuses and left when the tests reached a point where the force was going to exceed about 4kN.

IIRC the conclusion up to that point was that the body reduces the peak force by between a quarter and a third, but I could be wrong about all of that.

The Lyon report (admittedly for industrial rope access purposes not caving) came to the conclusion it did and it’s probably the best that can be done. It is a conclusion that was readily accepted by cavers for years.



If you are referring to your earlier post about traverse lines I was just preparing something about that.

We have never tested drops on traverse lines because it would be even more difficult to set up than a straight drop, and we are struggling at the moment to find somewhere to do even that.

But once we had some detailed data from our static tests on the relationship between force and things like rope stretch, rope given up by different knots, energy absorbed per metre of rope, energy absorbed by the knots it became fairly easy to predict peak forces in cows tails of different lengths with different knots, masses and fall factors. Always with the caveats that a steel mass was involved and the assumption that static tests could be read over directly to a fall.

It also became possible, if less easy, to predict what happens if a traverse line is involved, and I did that for my own amusement about a year ago. At that time we had no data on 9mm semi static or Alpine Butterfly knots because our focus is on cows tails, so the line is 10mm dynamic with no knots(!) and I convinced myself that those might cancel each other to give about the right answer.

We do have the data now and if I can motivate myself I shall include it.

There is a reduction in peak load if you move from FF1 on a bolt to FF1 in the middle of a traverse line, but it’s very small. Typically it’s less than 0.5kN in 5kN as you move from the bolt to the middle of a 3.5m traverse line.

The reason is the much greater distance fallen, a bit more than double, and so a bit more than double the energy to be absorbed.

It takes longer of course, which might be the reason for the more restful ride.

The same applies to different knots on cows tails – replacing a fig8 at the krab end by a barrel knot doesn’t result in the very big reduction in peak load you would expect from the very much greater energy absorbed by the knot, because it achieves that by producing much more rope so you fall further.

I suppose one of the advantages of the sewn rope lanyards is that while you are dislocating various bits of your body you can reflect that you aren’t falling as far.

If you or anyone else is interested they are welcome to a copy of the thing – it’s an Excel file of about 350kB. In fact there are several files as it proved impossible (for me) to include a big range of traverse line lengths in one file, although you can change mass, cows tail length, type of knots (or no knot at all).

Apologies for boring people with technical stuff again.

 

[Ian Ball]

Impossible, I very much appreciate the work you're doing.
I'm out of touch, what happened with the BPC setup?

 

[topcat]

I’m not sure what you mean by flawed.

Just that whilst the ranking of the various styles of CTs is certainly valid, the impact figures are inflated compared to down cave real life situations. Therefore they look scary but are likely to be well within what the body can take. And it does take a lot before it breaks......

The last time I had cause to use my CTs to save my ass was in Brownhill when I was 'falling' at the pitch head. More of a gradual diminishing really........the friction of the rock took all the force out of it ).

 

[alanw]

I'm out of touch, what happened with the BPC setup?

The old "Nissen Hut" style garage where it was located was demolished and has now been replaced with a new building.