7mm cordelette for making cows tail?

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Re: 7mm cordelette for making cows tail?

Postby SDcaver » May 7, 2013 4:45 pm

Derek- perhaps when you have the time and actually read the article, you will notice that they did test static rope (see page 14) and elude to their conclusions many times. Plus they tested the Petzl tails which are static as well. I guess that means dynamic is no longer "standard practice". I guess I do not know what your definition of "standard practice" is since many cavers I know do not use dynamic, and a certain cave rescue organization that I am involved with does not require a dynamic tail.

I trust 40' of dynamic rope to catch a 20' leader fall just the same as I trust a 2' dynamic cowstail to catch a 1' fall in a cave.


Of course you would trust 40' of dynamic rope- that is because at that length the rope is able to do its job and stretch the needed amount, but at 2 feet it cannot! I guess that we disagree as to how you are using your tail. You call it fall protection and I call it misunderstanding fall prevention.
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Re: 7mm cordelette for making cows tail?

Postby chh » May 7, 2013 6:13 pm

I'd use a 7mm cordelette cow's tail. I'd keep an eye on the wear, but I'd use it. But I have 10mm dynamic on my harness. Mostly for the hand, the abrasion resistance and the fact that it was free. One good thing about a smaller diameter cow's tail is that in really muddy situations it's an easy way to tell things apart in a fustercluck at a rebelay or more complicated thing, when everything is the same color and sticking together.
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Re: 7mm cordelette for making cows tail?

Postby Extremeophile » May 7, 2013 6:40 pm

SDcaver wrote:Derek- perhaps when you have the time and actually read the article, you will notice that they did test static rope (see page 14) and elude to their conclusions many times. Plus they tested the Petzl tails which are static as well. I guess that means dynamic is no longer "standard practice". I guess I do not know what your definition of "standard practice" is since many cavers I know do not use dynamic, and a certain cave rescue organization that I am involved with does not require a dynamic tail.

I trust 40' of dynamic rope to catch a 20' leader fall just the same as I trust a 2' dynamic cowstail to catch a 1' fall in a cave.


Of course you would trust 40' of dynamic rope- that is because at that length the rope is able to do its job and stretch the needed amount, but at 2 feet it cannot! I guess that we disagree as to how you are using your tail. You call it fall protection and I call it misunderstanding fall prevention.

Looking back through some old threads, this doesn't seem to be a new argument, and there are some long standing differences of opinion on whether a cowstail is fall protection. I'm not SPRAT certified or an NCRC instructor, so I must be in the wrong, but the entire point of the referenced article seemed to be about testing the performance of cowstails in catching falls. I mistakenly interpreted this as fall protection.

I'll also need to do a little research on dynamic ropes because I wasn't aware that they don't stretch below a certain length. I had learned at some point that shock load (impact force) was a function of rope stretch and fall factor (i.e. length of fall / length of rope). If that's not correct then I've made some bad assumptions in how I'm using cowstails.
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Re: 7mm cordelette for making cows tail?

Postby Carl Amundson » May 7, 2013 7:38 pm

My experience is that short dynamic ropes do stretch that is why I switched to simi-static rope.
Dynamic rope with knots stretch even more.
Take a look at the following ITRS doc from 2001 - "Fall Factors & Life Safety Ropes: a closer look"
http://web.mit.edu/sp255/www/reference_vault/ITRS_01_FF_report.pdf

Most of the testing was done with 11mm & 12mm static. The dynamic rope used in the testing was 10.6mm
Excerpts from the summery:
• For all static and low-stretch ropes tested, the results indicate that impact forces do increase as the length of rope & fall increase for any given Fall Factor.
• Dynamic rope in comparison only showed minimal increased impact forces when rope lengths and FF were increased.
• Knots are significant energy absorbers compared to rope itself.


While this does not specifically test cowtails, it does show (as does the Lanyard testing) that knots are significant shock absorbers.
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Re: 7mm cordelette for making cows tail?

Postby SDcaver » May 7, 2013 7:58 pm

I did not mean to imply that short chunks of dynamic rope do not stretch, obviously they will. My point is that at short lengths the stretch will be insignificant, and be a small factor in the overall function of what is happening. Several tests do show that the cinching of the knots play a larger role than the type of rope- thus my point.

And yes Derek, this is an old debate. I think dating back to the time of the Romans and Persians.
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Re: 7mm cordelette for making cows tail?

Postby snoboy » May 7, 2013 9:25 pm

Fall prevention - preventing a fall. AKA Fall restraint
Fall protection - nebulous term... Usually refers to the whole work at height regime - including railings, restraint and arrest.
FALL ARREST - catching a fall after it happens...

That's how it is in my world, maybe using those terms would help.

I see no harm in using dynamic cowstails. I see potential harm in using low stretch cowstails. 'Industry standard' (IRATA/SPRAT) is dynamic.
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Re: 7mm cordelette for making cows tail?

Postby paul » May 8, 2013 6:31 am

FWIW, our national caving organisation, the British Caving Association, recommend the use of dynamic rope in cows tails.

See: http://british-caving.org.uk/equipment/Cows%20Tails%20article%20v2.pdf.
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Re: 7mm cordelette for making cows tail?

Postby hank moon » May 8, 2013 12:39 pm

snoboy wrote:Fall prevention - preventing a fall. AKA Fall restraint


Notes:
- AKA "travel restraint"
- Normally means that the user is supported by a (relatively) broad, horizontal surface, and is using a tether to prevent a fall to a lower level. The user can't fall off, because the tether prevents him getting close enough to the edge. If the system is configured so that the user CAN fall off, it's not a fall prevention system. The system only comes under tension when the user gets too close to the edge, so it's normally not loaded. No harness is required; the tether can be attached to an appropriate belt, often at the rear. The entire system can be relatively weak and ergonomically unsound (compared to a fall protection system) as it should never see a significant load.

Travel restraint is rare in recreational caving, though it can come into play during rescue, where rescuers need the freedom to move around at pitch heads.

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Re: 7mm cordelette for making cows tail?

Postby Extremeophile » May 8, 2013 1:46 pm

hank moon wrote:
snoboy wrote:Fall prevention - preventing a fall. AKA Fall restraint


Notes:
- AKA "travel restraint"
- Normally means that the user is supported by a (relatively) broad, horizontal surface, and is using a tether to prevent a fall to a lower level. The user can't fall off, because the tether prevents him getting close enough to the edge. If the system is configured so that the user CAN fall off, it's not a fall prevention system. The system only comes under tension when the user gets too close to the edge, so it's normally not loaded. No harness is required; the tether can be attached to an appropriate belt, often at the rear. The entire system can be relatively weak and ergonomically unsound (compared to a fall protection system) as it should never see a significant load.

Travel restraint is rare in recreational caving, though it can come into play during rescue, where rescuers need the freedom to move around at pitch heads.

Based on Marc's posts it sounds like NCRC likely has different definitions. These discussions around defining the use of cow's tails as prevention vs. protection seem irrelevant if we're all referring to the exact same use. There are obviously different styles of vertical caving in different caving regions, but I believe a good percentage of cavers are at times using their cow's tails clipped to something (anchor, traverse line, rebelay loop) with a little slack with the expectation that it can catch a small fall. If not, and the cow's tail is only used to hold body weight statically during rebelay crossings or when resting on an upper ascender, then it doesn't seem to matter much whether you use dynamic or static material, use knots or sewn terminations, or that you use anything more than 7mm cord. If there is some expectation that the cow's tail will catch a small fall without causing anchor failure, cow's tail failure, or bodily injury from the impact force, then it seems wise to reduce the potential fall factor, use knots instead of sewn terminations, and use dynamic rather than static tethers (perhaps in that priority order). It seems like some are arguing that if you do the first two then using dynamic rope is unnecessary, or provides an insignificant benefit. I'm not sure I agree, but without clear objective data or the proverbial trail of dead bodies I guess this is likely to remain a personal choice.
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Re: 7mm cordelette for making cows tail?

Postby Scott McCrea » May 8, 2013 2:33 pm

Maybe it would be more accurate to call it a "slip" instead of a "fall."

Slip on a cowstail = you live to clean skid mark out of your shorts.

Fall on a cowstail = your worst day of caving.
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Re: 7mm cordelette for making cows tail?

Postby SDcaver » May 8, 2013 3:57 pm

Based on Marc's posts it sounds like NCRC likely has different definitions. These discussions around defining the use of cow's tails as prevention vs. protection seem irrelevant if we're all referring to the exact same use. There are obviously different styles of vertical caving in different caving regions, but I believe a good percentage of cavers are at times using their cow's tails clipped to something (anchor, traverse line, rebelay loop) with a little slack with the expectation that it can catch a small fall. If not, and the cow's tail is only used to hold body weight statically during rebelay crossings or when resting on an upper ascender, then it doesn't seem to matter much whether you use dynamic or static material, use knots or sewn terminations, or that you use anything more than 7mm cord. If there is some expectation that the cow's tail will catch a small fall without causing anchor failure, cow's tail failure, or bodily injury from the impact force, then it seems wise to reduce the potential fall factor, use knots instead of sewn terminations, and use dynamic rather than static tethers (perhaps in that priority order). It seems like some are arguing that if you do the first two then using dynamic rope is unnecessary, or provides an insignificant benefit. I'm not sure I agree, but without clear objective data or the proverbial trail of dead bodies I guess this is likely to remain a personal choice.


Not so much NCRC's view, but mine. If we got all the NCRC instructors in a room to discuss this I am sure that we would run out of oxygen long before opinions. Regarding the rest of your thread- I agree!

I think Scott is right on track with the slip vs fall. Cavers truly are never (in general SRT) in the position to take a true fall like rock/ice climbers are. This is why we do not use a dynamic component in our vertical systems. If you clip into a rebelay, edge line, or traverse line, you are preventing a fall- thus creating fall prevention. Losing your footing a foot or two is a "slip" not a true fall. Yikes, this can get verbally icky! This gets all real blurry when different rope user groups share data, reports, etc... since we tend to use some of the same equipment and terms but with different uses, meanings, or context. Cavers, climbers (rock and ice), mountaineers, arborists, industrial workers at height, sailors, mine rescue, S&M enthusiasts, etc... all use rope but can vary drastically beyond that.

To drag this out further I will throw out a question-

If I have a traditionally tied cowstail, or a Petzl prefab for that matter, and connect both long and short into an anchor- how many points of contact am I hanging on?
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Re: 7mm cordelette for making cows tail?

Postby snoboy » May 8, 2013 6:17 pm

One.
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Re: 7mm cordelette for making cows tail?

Postby Carl Amundson » May 8, 2013 6:26 pm

It depends.
If both biners are connected to the same anchor, then one.
If each biner is connected to separate anchors, then two.
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Re: 7mm cordelette for making cows tail?

Postby Scott McCrea » May 8, 2013 6:34 pm

If you connect the short and long to the same hanger, both in the hanger, it's two. It's just like if you attach two ascenders to the same rope.

If you connect your short to the hanger and the long to the short's biner, then that is one.
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Re: 7mm cordelette for making cows tail?

Postby hank moon » May 8, 2013 7:51 pm

SDcaver wrote:If I have a traditionally tied cowstail, or a Petzl prefab for that matter, and connect both long and short into an anchor- how many points of contact am I hanging on?


ha! fun one. a "traditionally" tied cowstail has a single loop at the harness end, so it's one point, regardless of how many arms are clipped to whatever...unless that "anchor" is an ascender on rope, in which case it's only half a point... :big grin:

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