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

[Fulk]

Here are a few comments:

LadyMud: I have seen that method, but thought that there might be too much 'stuff' in my central Omni.

Jason: The picture I posted, of the knots tied in a bit pf old 8-mm tat, was merely to indicate the concept – not for actual use.

thehungrytroglobite: No, I'm not really tall (in fact I have been referred to as a 'skinny little bastard'), and I don't cave with midgets. I do sometimes use my hand-jammer as a safety cord.

TheBitterEnd: Ask Jason if he managed the rebelays OK on our trip to Death's Head on Friday.

ChrisB: See reply to Jason above.

 

[Chocolate fireguard]

Personally I’ve transitioned to evolv adjust lanyards (dual Petzl connect adjusts basically) and so can have whatever length cowstail I want

The idea is good, but I would worry that the rope is the only energy absorber and would want at least one decent knot in there.

I have been involved in work to measure the energy absorbed by the different parts of a cows tail (rope and knots).
The work has been done on a static rig rather than a drop rig, but I can't see any reason why the same results aren't applicable in a fall, up to the sort of forces likely to be encountered in a fall onto cows tails. I appreciate that there is not universal agreement on that, but I am quite prepared to argue my case.

The results show that the knots absorb far more energy than the rope.

Applying the results to a 70kg (unyielding) mass falling (FF1) onto a 750mm cows tail, made up of a krab, barrel knot, fig8 knot plus about half a metre of 10mm dynamic rope gives a peak force of about 4.4kN.

The same mass falling onto a 650mm sewn lanyard of the same rope with a krab on the end gives 7.9kN.

The force on a person would be less due to the body also absorbing some energy, but in the second case I think that might be a part of the problem rather than part of the solution!

Did you consider tying a fig8 in the lanyard where it fastens to your maillon in the usual way? There looks to be plenty of rope.

Re the OP, I would be quite happy to use that, although I have used the loop and double knot system for many years.

 

[andrewmcleod]

I have, with no justification at all, assumed there would be a small amount of energy-absorbing slippage when falling on the adjustable end of my adjustable cowstails (and the other cowstail is a conventional barrel knot and the whole setup is attached by a Fig 8 on a bight to the central D-ring). I have replaced the rope (several times) even though you are not 'supposed' to do it.

The Evolv Adjust is made with twin rope and is therefore not rated as a personal attachment, but then neither is 8mm static rated as 'rope' and I'll happily use that.

 

[mikem]

I don't think it would have to be a barrel knot, just anything that is tight round the krab. Is there any reason why you can just tie an overhand knot and clip the krab through the middle of it? It will tighten hard on the krab once you load from the primary krab.

You'll never tie an overhand tight enough to stop the krab rotating through it (short of tying it on a smaller diameter, loading it, then putting intended krab through!)

 

[cap n chris]

You'll never tie an overhand tight enough to stop the krab rotating through it (short of tying it on a smaller diameter, loading it, then putting intended krab through!)

Clove hitch would probably do it.

 

[mikem]

Although you'd normally do a hitch on the wide end of the krab ... (Or did chrisB, not Chrispy, mean a single overhand, rather than a loop?)

 

[JoshW]

The idea is good, but I would worry that the rope is the only energy absorber and would want at least one decent knot in there.

99% of the time either I have a loaded cowstail (because I can tension them) and therefore I can’t fall OR I’m in a position where I won’t fall.

0.1% of the time am I in a position where I could fall/slip and I’d be getting anywhere near to forces that might have me concerned about not having a knot in place.

Yes having a knot will absorb more, yes certain knots are stronger, but if you’re that concerned about those you might need to look at the way you are using your cowstails.

 

[Chocolate fireguard]

If you're happy that's fine.

 

[Pitlamp]

What happens in the remaining 0.9% of the time JoshW?

(Sorry - someone had to say it!)

 

[Bob Mehew]

Well, thanks for all the feed-back so far . . . but it's late at night and I'll have a god look at it tomorrow. Bob – I tried to access Speleology 11 but it took me to a BCRA page . . . would it be possible to provide a short précis of it?

download from here .

 

[JoshW]

What happens in the remaining 0.9% of the time JoshW?

(Sorry - someone had to say it!)

other stuff

But I’d guess approximately that amount of time I’d be in a position that I might fall but I wouldn’t be concerned about the forces involved

 

[Fulk]

Thanks, Bob.

You'll never tie an overhand tight enough to stop the krab rotating through it (short of tying it on a smaller diameter, loading it, then putting intended krab through!)

You can get little 'keepers' that keep the Krab in place . . . I'll post a picture of one before I'm much oldeer.

 

[Bob Mehew]

I was meaning when comparing the different types of knots and their relative strengths, thought that was clear from the context.

Lyon Equipment Ltd's HSE report "Industrial rope access - Investigation into items of personal protective equipment" indicates at Figure 12 that the reduction in strength of rope by a knot varies between 15 and 45%. As the report seems to have been lost from the HSE web site, I have attached it.

 

[2xw]

Lyon Equipment Ltd's HSE report "Industrial rope access - Investigation into items of personal protective equipment" indicates at Figure 12 that the reduction in strength of rope by a knot varies between 15 and 45%. As the report seems to have been lost from the HSE web site, I have attached it.

You'd have to be proper yeeting yourself about to generate that amount of force for it to matter, surely? And there are already knots in the rope so does it really matter?

 

[Bob Mehew]

You'd have to be proper yeeting yourself about to generate that amount of force for it to matter, surely?

You can certainly generate forces which will seriously hurt you by falling on a cows tail. Especially if you don't relax your knots and are in an above belay point situation (so the FF is larger than 1). I have yet to sort out if one might be able to generate enough energy from a fall onto a cows tail to see if it could break the rope, I certainly can't rule it out. Attached is some data we generated a while ago. We could really do with access to a drop rig to sort this point out.

 

[Babyhagrid]

You can certainly generate forces which will seriously hurt you by falling on a cows tail. Especially if you don't relax your knots and are in an above belay point situation (so the FF is larger than 1). I have yet to sort out if one might be able to generate enough energy from a fall onto a cows tail to see if it could break the rope, I certainly can't rule it out. Attached is some data we generated a while ago. We could really do with access to a drop rig to sort this point out.

Does this account for the shock absorbtion of a cavers legs and body?

 

[ChrisB]

Although you'd normally do a hitch on the wide end of the krab ... (Or did chrisB, not Chrispy, mean a single overhand, rather than a loop?)

Yes, I meant a single overhand. They go so tight you struggle to get a spike in to undo them.

 

[Pony]

Maybe request a pull/drop test from someone like HowNot2

 

[mikem]

I have asked previously.

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)...

 

[topcat]

You can certainly generate forces which will seriously hurt you by falling on a cows tail. Especially if you don't relax your knots and are in an above belay point situation (so the FF is larger than 1). I have yet to sort out if one might be able to generate enough energy from a fall onto a cows tail to see if it could break the rope, I certainly can't rule it out. Attached is some data we generated a while ago. We could really do with access to a drop rig to sort this point out.

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.