Shock absorption in cowstail/QAS?

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Shock absorption in cowstail/QAS?

Postby chrismc » Mar 30, 2008 1:16 pm

I have been a loyal Ropewalker user for over a decade, but have decided to switch over to the dark side and get a Frog system. My system will be largely customized (since I already have many of the parts), but I'm using On-Rope 1's Frog system as a reference point. I had everything figured out until I got to the cowstail/QAS part.

With my Ropewalker system, in which the QAS is not an integral part of the climbing system, but instead a "safety" item, I have always just used a piece of 8mm accessory cord (static) with figure-8 knots on both ends to link the handled ascender to the harness. The newer, better way of doing this is with a "prusik enabled" cord like the QAS lanyard that On-Rope sells (and could easily be made). This adjustable-length QAS is pretty spiffy.

Now that I'm looking at On-Rope1's Frog system, I see that this is not necessarily the standard way of doing things since they spec the "shock absorbing" Spelegyca two-ended cowstail instead. This has some obvious drawbacks. There is a complete lack of adjustability- not only on a daily basis, but even to make it the optimal length for you body, or arm's reach. Since it is sewn at the factory, you're stuck with adjusting to the arm length of the Petzl designer. Additionally, the working-end loops are sewn to a very small diameter, only allowing enough space for a single carabiner. My current 8mm-cord QAS has a large enough loop tied in it to allow for both a Mallion to connect to my ascender, and a second locking carabiner to allow conveniently clipping into an anchor or safety line when an ascender may not be appropriate (ascenders are only safe to use in a specific orientation- if you have a dual-end-anchored horizontal safety line, you should clip a carabiner on it instead of an ascender). I've been given the suggestion to just use a single carabiner in the Spelegyca, and then clip an additional biner into it for the same functionality, but I'm not a fan of the carabiner chain. I've always been taught to only attach "hard things to soft things", ie. no carabiner to carabiner (or mallion), and no rope to rope (or webbing). Given those drawbacks of the Spelegyca, how important are the shock-absorption properties of the cowstail? My view at this point is that the benefits of the Spelegyca don't outweigh the drawbacks and I should stick to what I'm used to.
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Re: Shock absorption in cowstail/QAS?

Postby NZcaver » Mar 30, 2008 2:01 pm

chrismc wrote:Now that I'm looking at On-Rope1's Frog system, I see that this is not necessarily the standard way of doing things since they spec the "shock absorbing" Spelegyca two-ended cowstail instead. This has some obvious drawbacks.

Personally, I recommend using at least 9mm diameter dynamic rope to cut and tie your own double cowstail to your personal specifications. To my knowledge, this is the most common "standard" (dare I use that word) for a Frog system. Or course other variations are rampant, as are the range of different knots which people choose to use. My grotto has a couple of loaner Frog systems for training purposes, and they were purchased with Spelegyca assemblies. This would not have been my choice, but they seem to work OK and they do have a slight advantage for novices in that it's easy to tell your cowstail apart from the rope. This shouldn't really be an issue for the experienced caver, though.

Most authoritative texts do not recommend static/low-stretch rope or accessory cord (8mm or otherwise) be used to construct a cowstail or other safety lanyard which could potentially take a fall. That's why devices made from otherwise-static webbing like the Spelegyca incorporate a "screamer" function, which allows portions of the stitching to rip when shock loaded. This of course is designed to help reduce the peak impact force on your body, anchor points, and other system components. Dynamic rope stretches a little (and the knots may snug up a bit) which should help reduce any shock load. But just like webbing screamers, dynamic cowstails should definitely be replaced after a hard fall.

More discussion on cowstails can be found in several topics including this one and this one.
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Re: Shock absorption in cowstail/QAS?

Postby ek » Mar 30, 2008 2:51 pm

I have to admit, Chris, ever since our discussion of the slowness of frog systems on long drops at NCRC last year, I didn't see this coming. Congratulations...but I am curious what has possessed you to switch over to (or begin limited use of) a frog system?

I agree with NZcaver--given your needs, it sounds to me like you should make your own cowstail out of dynamic (climbing) rope. This will give you substantially greater shock absorption than the Petzl Spelegyca, will be perfectly adjusted to you, and if you use thin rope it won't weigh much more. The only major advantage of the Petzl Spelegyca that I am familiar with is that, assuming mild enough conditions of use, you don't have to retire it as quickly. Common wisdom is that a cowstail tied from dynamic rope should be replaced every 2 years regardless of use history, and more often if it shows substantial wear. A friend of mine replaces his cowstail every couple months...but he lives in TAG, caves a lot, and goes in a lot of caves with calcite crystals in the mud.

Last year, I decided to stop using the Spelegyca and make my own cowstail. But I didn't want extra rope bulk (and weight). Thick rope gets in the way, and its huge knots rub against everything and abrade quickly. I'm not a big fan of using twin or half rope for cowstails, because those types of rope (especially twin) may not withstand factor-2 falls. Accessory cord--even dynamic accessory cord--is designed for prusik loops, the threading of stoppers, and the construction of sport anchor systems (as well as other, non-load-bearing, uses.) Dynamic accessory cord adds an additional shock-absorbing component to a system but is not designed to constitute the primary shock-absorbing component of any fall-arrest system. I wasn't about to buy a whole climbing rope and then cut a piece off the end, and the thinnest dynamic single rope that I was able to find for sale by the foot was PMI's 9.7mm rope on Inner Mountain Outfitters. So I contacted a whole bunch of manufacturers and asked them if they sell short sections of their rope.

The first manufacturer to reply was Sterling. (This doesn't necessarily reflect negatively on other manufacturers though--I didn't write all the emails on the same day.) Sterling makes a 9.2mm dynamic single rope that masses (weighs) 52 grams per meter, which is quite thin and light. John Branagan (Sterling's Outdoor Product Manager) told me that Sterling does sell short sections of rope, but offered me some free samples, asking me how much rope I'd need to make a cowstail. I told him, but he sent me 16 meters of rope anyway! I got 8 meters of blue and 8 meters of yellow. Not only did he sent me this rope for free, and not only did Sterling pay for the shipping, but the reason I got the yellow was that I had thought at the time that it would be more visible in a cave, and upon mentioning this, John drove to the factory to get me the yellow sample. It turns out that the blue is also quite bright, and I ended up using that. I've been offering this rope to other members of my grotto, but so far nobody's taken me up on it.

I used this cowstail in a few northeastern caves, and then I went to Alabama for a week and used it there, including for the 437' Surprise Pit (in Fern Cave). Then I can back to the northeast and did a bit of caving, and then the caves were closed due to WNS. My experience with this cowstail is entirely positive.

I decided to use a figure eight for the attachment to my maillon, since that knot absorbs more energy by tightening down in a fall than the overhand. I used barrel knots for the terminations. These tighten down on the carabiners and hold them in place. If you want to clip multiple carabiners into the end of your cowstail, you'll want to use some kind of fixed loop knot (a figure-eight or an overhand). If you're going to put heavy loads on two carabiners in that loop, capsizing the loop knot from the inside might be an issue. (To reduce bulk, I do not recommend tying a backup stopper knot on a cowstail. I have never seen this done, and I am happy that I haven't.)

Tying a cowstail myself enabled me to get it just right for my body. The long arm is just short enough that I an still reach an ascender when hanging off the end. I measured the length ratio of long cowstail to short cowstail (from the attachment to the maillon to the attachment to the cowstail carabiner) of the Petzl Spelegyca and I used that ratio to determine the length for the short arm. I don't know if there is some better way to decide on that length.

If you make your own cowstail, you could make both arms long, and use a prusik on the short arm to adjust its length. Of course, the thinner the rope of your cowstail, the thinner accessory cord you will need for your Prusik loop, and thinner tends to be weaker. (But then, if it breaks, the short cowstail will absorb the shock of the short fall that results, anyway.) Assuming the Prusik loop doesn't break in a fall, hopefully it would slip some to absorb some of the shock...but maybe it just wouldn't. Due to that concern, and the extra complexity associated with having an adjustable short arm, I decided to go for fixed lengths.

Anyway, I have an 8 meter piece of yellow 9.2mm dynamic single rope up for adoption. Dynamic rope is considered to have a shelf life (I don't remember what it is), so I can't just hold onto it forever. If you want it, and you think you and your buddies can actually use most of it, I'll mail it to you. I'll still have the rest of my blue piece to outfit fellow SUOC cavers (whenever we get to go caving again...).

chrismc wrote:I've always been taught to only attach "hard things to soft things", ie. no carabiner to carabiner (or mallion), and no rope to rope (or webbing).

No metal-to-metal contact? Do you attach your ascender directly to a lanyard? Do you not worry about the thin sheet metal of your ascender cutting through the lanyard in a shockload? And how do you rig off bolts? When you climb trad, if you climb trad, do you avoid wired stoppers?

I think that in some cases where you have a carabiner chain, twist is an issue. If you twist an interface between two pieces of hardware, you could break something. But I don't think that's a major issue here, because your cowstail will itself twist rather than force the twist into the carabiner-carabiner interface. Alpine Caving Techniques actually recommends using non-locking carabiners on your cowstails but attaching your upper ascender to your long cowstail via a second, locking carabiner. (I don't do this--I just use non-locking carabiners on my cowstails and attach ascenders directly to the non-locking carabiners. But Marbach and Tourte make a good argument for this practice. I did it for a while but got sick of it.)

You might also consider the three cowstail system, where you have your upper ascender attached to a third, single lanyard, leaving your short and long cowstails free to clip into anchors and traverse lines. This system is too bulky for me and I dislike what I perceive to be the added complexity, but many people, far more experienced than I, swear by it.
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Re: Shock absorption in cowstail/QAS?

Postby Dwight Livingston » Mar 31, 2008 7:40 am

ek wrote:I wasn't about to buy a whole climbing rope and then cut a piece off the end, and the thinnest dynamic single rope that I was able to find for sale by the foot was PMI's 9.7mm rope on Inner Mountain Outfitters.


IMO sells dynamic rope by the foot in a range of sizes: 8.1, 8.6, 9.7, 10.2, and 10.6 mm.
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Re: Shock absorption in cowstail/QAS?

Postby Scott McCrea » Mar 31, 2008 7:59 am

The dangers of short, static falls: LINK

Blue Water makes 7 & 8mm dynamic Prusik cord. I use it on my cows tails. The sheath is thinker than the average 8mm dynamic climbing rope. :kewl:
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Re: Shock absorption in cowstail/QAS?

Postby chrismc » Mar 31, 2008 9:26 am

ek wrote:I have to admit, Chris, ever since our discussion of the slowness of frog systems on long drops at NCRC last year, I didn't see this coming. Congratulations...but I am curious what has possessed you to switch over to (or begin limited use of) a frog system?


It was actually that experience at NCRC that made me realize how "clunky" the RopeWalker is for everyday caving, and especially rescue situations. I'll still keep it around for Mystery/Surprise/Ellison's, and hopefully Mexico someday, but for the vast majority of caves, a Frog system is lighter, way less bulky, and far simpler. The various pieces used also offer far more flexibility than the "only works as a system" Ropewalker.

It sounds like you already did an immense about of work for finding a decent rope stock for a cowstail. I started down that road, and stalled when I got IMO's answering machine. I've had mixed feelings about Sterling's rope in the past (due to a scary moment involving a climbing fall and some serious sheath damage), but seeing how out-of-their-way they went for you, I'll be happy to give them a clean slate.

ek wrote:Anyway, I have an 8 meter piece of yellow 9.2mm dynamic single rope up for adoption. Dynamic rope is considered to have a shelf life (I don't remember what it is), so I can't just hold onto it forever. If you want it, and you think you and your buddies can actually use most of it, I'll mail it to you. I'll still have the rest of my blue piece to outfit fellow SUOC cavers (whenever we get to go caving again...).


I'd be overjoyed to take that off your hands. I think it would actually all be put to use within 24 hours, as I know a couple other people that are waiting for me to straighten this out before making a decision about their QAS setup. Is your contact info in the NCRC contact list still good? Let me know how to get in touch with you and I'll at least get you some money for shipping.

ek wrote:
chrismc wrote:I've always been taught to only attach "hard things to soft things", ie. no carabiner to carabiner (or mallion), and no rope to rope (or webbing).

No metal-to-metal contact? Do you attach your ascender directly to a lanyard? Do you not worry about the thin sheet metal of your ascender cutting through the lanyard in a shockload? And how do you rig off bolts? When you climb trad, if you climb trad, do you avoid wired stoppers?

Of course there are exceptions, those being that a carabiner is needed for any hardware that is designed to have a carabiner (and not nylon) attached. You'd always want to have nylon attaching to a radiused edge, not a sharp one. I have noticed that On-Rope1 does sell their pre-made QAS's in just the arragement you mentioned- with the rope going directly through the hole in the ascender (with an open piece of tubular webbing around the rope for protection). That's not an arrangement I'd be comfortable with, and I'd use a mallion in the ascender instead. In general, though, I try to avoid connecting carabiners to carabiners if at all possible, especially if they are dissimilar metals with different hardnesses (metal/steel) as that is a recipe for premature wear. In designing my new climbing system, I'm working through that last issue at the moment. How do I connect cowstail to half-round? It needs to be a carabiner, as I want to be able to remove the cowstail without opening the half-round (I don't consider mallions to be "removable", but instead use them as semi-permanant). It should be steel, since the half-round is steel, but I have not found any small steel carabiners. I want it to be as compact as possible, as that is a "cluttered" area, and I don't want any more parts there than necessary. I'm leaning towards breaking my rule and using some compact locking Al carabiners and just carefully monitoring their wear,and replacing as necessary. Of course, everytime I clip gear while climbing I guess I'm breaking that rule. I guess the important factor here is "contact time while loaded", as that is what will wear the metal. Anywho, things to think about.

ek wrote:You might also consider the three cowstail system, where you have your upper ascender attached to a third, single lanyard, leaving your short and long cowstails free to clip into anchors and traverse lines. This system is too bulky for me and I dislike what I perceive to be the added complexity, but many people, far more experienced than I, swear by it.

I agree, too much complexity. I'm switching to a Frog system to clean things up and reduce unnecessary bulk. If you were using Euro-style rigging with rebelays, I could see the need, however. Not likely with the US IRT (indestructable rope technique).
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Re: Shock absorption in cowstail/QAS?

Postby NZcaver » Mar 31, 2008 10:27 am

chrismc wrote:In designing my new climbing system, I'm working through that last issue at the moment. How do I connect cowstail to half-round? It needs to be a carabiner, as I want to be able to remove the cowstail without opening the half-round (I don't consider mallions to be "removable", but instead use them as semi-permanant). It should be steel, since the half-round is steel, but I have not found any small steel carabiners. I want it to be as compact as possible, as that is a "cluttered" area, and I don't want any more parts there than necessary. I'm leaning towards breaking my rule and using some compact locking Al carabiners and just carefully monitoring their wear,and replacing as necessary.

Why do you need your cowstail to be easily removable from the half-round harness maillon? It's far more common among Froggers to have the mid-point knot in the double cowstail be directly attached to the harness maillon. It's generally safer, more compact, and more efficient - especially if one side of the cowstail will normally be used as a safety for your upper ascender. That's the way I've always done it.

If you really insist on departing from conventional wisdom by having a cowstail which is removable independent of the harness maillon, I suggest not using a carabiner. A steel oval maillon might be a good choice here for several reasons, including not having to worry about orientation in the event of a shock load (there being no weak gate or minor axis loading concerns). And finally, I wouldn't worry quite so much about dissimilar metals. I know plenty of folks who use steel harness maillons, and they clip aluminum alloy carabiners to them all the time. I also see the opposite, where (for example) a rack is connected to an alloy harness maillon via an oval steel maillon. Either way, there seems to be negligible wear-and-tear on the alloy in these situations - at least when put in context with all the other wear that caving hardware normally receives.

Take a look at these two examples of Frog systems here and here. Both are slightly different from the way my own system is set up, but the basic concepts are the same.
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Re: Shock absorption in cowstail/QAS?

Postby ek » Mar 31, 2008 11:52 am

chrismc wrote:It was actually that experience at NCRC that made me realize how "clunky" the RopeWalker is for everyday caving, and especially rescue situations. I'll still keep it around for Mystery/Surprise/Ellison's, and hopefully Mexico someday, but for the vast majority of caves, a Frog system is lighter, way less bulky, and far simpler. The various pieces used also offer far more flexibility than the "only works as a system" Ropewalker.

You should try tandem climbing out of Surprise Pit with a frog system. I did this twice in one day. If you have good form on rope and your system is properly adjusted and you are synchronized with your partner, it's actually not too bad. If you're the top climber, I strongly recommend using a foot ascender, as it holds the taught rope away from your crotch.

Actually, I almost always use my foot ascender, and I'd recommend you try one, at least if you can borrow it from a friend when trying it instead of having to pay for it. I find that using a foot ascender improves my form slightly, decreases the physical effort necessary to maintain good form significantly, and helps me to exert about equal force with both of my legs (one through the foot ascender, and one through the foot loop attached to the upper ascender). The foot ascender also makes weight transfers easier in cases where something goes wrong, and backs up the foot loop in the sense that if the foot loop fails, you can still progress. If you're downclimbing, though, then you'd really wish you still had that footloop...

chrismc wrote:It sounds like you already did an immense about of work for finding a decent rope stock for a cowstail. I started down that road, and stalled when I got IMO's answering machine.

I emailed a whole bunch of companies, yes. Most did not reply. There are many more I didn't contact. Other dynamic single ropes, besides the Sterling Nano 9.2mm, that might be worth considering for light rope cowstails, are:

(1) The Mammut Serenity 8.9mm. As far as I know, this is the thinnest dynamic single rope in the world. However, it weighs the same as the Sterling Nano, and is probably less abrasion-resistant due to its smaller circumference.

(2) The Beal Joker 9.1mm. This actually masses 53 grams per meter, one gram per meter more than the Nano. For a cowstail, that produces an inconsequential weight difference.

(3) The WildCountry Sprint 9.2mm. This has the same thickness and weight as the Sterling Nano, but appears only to be available in the UK.

There were a whole bunch more that I looked into, but those were the thinnest. It is also worth mentioning that the folks at PMI do provide short sections of their 9.4mm rope on request, and were getting ready to send me a free sample...but that was after I had already received the 16 meters of Sterling Nano 9.2mm.

chrismc wrote:I've had mixed feelings about Sterling's rope in the past (due to a scary moment involving a climbing fall and some serious sheath damage), but seeing how out-of-their-way they went for you, I'll be happy to give them a clean slate.

What...happened? Which rope were you using, and what were you doing, and what kind of damage ensued?

I'd be overjoyed to take that off your hands. I think it would actually all be put to use within 24 hours, as I know a couple other people that are waiting for me to straighten this out before making a decision about their QAS setup. Is your contact info in the NCRC contact list still good? Let me know how to get in touch with you and I'll at least get you some money for shipping.

PMs sent.

chrismc wrote:Of course there are exceptions, those being that a carabiner is needed for any hardware that is designed to have a carabiner (and not nylon) attached.

But what is the actual justification for the idea that metal-to-metal contact is bad?

chrismc wrote:You'd always want to have nylon attaching to a radiused edge, not a sharp one. I have noticed that On-Rope1 does sell their pre-made QAS's in just the arragement you mentioned- with the rope going directly through the hole in the ascender (with an open piece of tubular webbing around the rope for protection).

I know. The thought of that fills me with great fear. Perhaps the justification is that the ascender cuts the pit rope before it cuts the cowstail. I would have a hard time being convinced that this is true, though. Especially for applications where you are using a Petzl ascender on its maximum rope diameter (12.5mm).

That's not an arrangement I'd be comfortable with, and I'd use a mallion in the ascender instead. In general, though, I try to avoid connecting carabiners to carabiners if at all possible, especially if they are dissimilar metals with different hardnesses (metal/steel) as that is a recipe for premature wear. In designing my new climbing system, I'm working through that last issue at the moment. How do I connect cowstail to half-round? It needs to be a carabiner, as I want to be able to remove the cowstail without opening the half-round (I don't consider mallions to be "removable", but instead use them as semi-permanant).

Do you actually use a steel carabiner to attach your rack to your maillon?

The vast majority of froggers, as NZcaver has said, keep the cowstail permanently attached to the harness maillon (at least always attached when on rope), attaching it directly to the maillon with the loop knot at the bottom of the cowstail that joins the short and long legs.

I would be concerned that, in a swing against a wall, a carabiner might shatter. I also dislike the idea of having to worry about which axis I am loading and where the gate is pointing (it should point toward you so it doesn't get knocked off by something from the outside). All these are issues when rappelling, too, but just because something presents a danger in one situation doesn't mean that it's good to accept that same increased risk again in another situation when you can easily avoid it. The other thing is, the most likely situation where you will slam into a wall is if an anchor component blows out. Good rigging will prevent even that, but sometimes the rigging is not as good as it appeared to be. While occasionally anchor components blow out on rappel, typically they fail during ascension, since ascending is what puts the most peak tension on the rope (unless you have really terrible rappelling form...I actually saw nylon webbing visibly stretching under the weight of one of my friends rappelling --he would get going really fast, and then slam to a stop, over and over again).

Another problem with using hardware to attach your cowstail to your harness maillon is that you have extra bulk and complexity. That's what you're trying to avoid, right? I would recommend that you instead make your upper ascender and footloop easily removable from the long cowstail. It's really very convenient to have the cowstail available all the time, and you can clip each end to a gear loop when you want it out of the way. I use a Petzl Basic as my upper ascender, and I use a Spectra cord footloop that is tied through the small hole on the Basic. If you use the Petzl Ascension, or any of the several other handled ascenders like it, the small hole is big enough to put a quicklink through the small hole.

I do have a friend who attaches his cowstail to his maillon with a locking carabiner. His system works fine. I still think it's unnecessarily complex. This doesn't address a situation where you are stuck due to one of the arms of the cowstail being stuck in tension, because you can't unclip the carabiner when your weight is on the cowstail through it. Why do you want your cowstail to be removable?

If you insist that it be removable, and dislike the notion of contact between aluminum and steel, perhaps you should use an aluminum harness maillon! This would be lighter, too. If you do go this route and have the cash, you might consider the Petzl Omni Screw-Lock. One issue with aluminum maillons is that they really are liable to break on you if you forget to screw them shut. Since the Omni is actually a special, three-way-loadable carabiner, it has a convenient swinging gate that shuts by itself, and it is just as strong with the gate unlocked as locked (unless, of course, the gate gets pushed open). It is also so easy to lock and unlock that you can just lock it every time you close it, and still be efficient.

You might also compromise, make your cowstail with a large bottom loop, and girth hitch it to your maillon. You will need to take your ascenders off to remove the cowstail, and it will not be as quick and easy to remove as if you attached it with a carabiner, but you won't have that carabiner in the way of things. Of course, girth hitching tends to decrease the strength of a material...but perhaps not much more than an overhand knot. And unlike if you were to choose the overhand knot for your cowstail, if you girth hitch it you can still have the loop be formed by a figure-eight on a bight, retaining the shock-absorbing function of that knot tightening down in a shockload.

Climbers tend to girth hitch lanyards to their harnesses, and the Beal Dynadoubleclip, which is also perfectly usable as a caving cowstail (though it is not as shock-absorbing as one you build yourself, since it has sewn terminations instead of tied knots), is designed to be girth hitched.

Another disadvantage of girth-hitching, though, is that then the cowstail will take up even more real estate on your maillon than if you had clipped it with a carabiner.

chrismc wrote:
ek wrote:You might also consider the three cowstail system, where you have your upper ascender attached to a third, single lanyard, leaving your short and long cowstails free to clip into anchors and traverse lines. This system is too bulky for me and I dislike what I perceive to be the added complexity, but many people, far more experienced than I, swear by it.

I agree, too much complexity. I'm switching to a Frog system to clean things up and reduce unnecessary bulk. If you were using Euro-style rigging with rebelays, I could see the need, however. Not likely with the US IRT (indestructable rope technique).

Plenty of European cavers use the two-cowstail system and negotiate complex European-style rigging. Plenty of American cavers use the three-cowstail system. And vice versa.

You may not want to assume that all the American vertical caving you'll be doing will be IRT. A wide range of techniques has proliferated in the US, as well as in Europe, to deal with different conditions and situations. Some European cavers are using IRT occasionally to explore new leads, and a friend of mine who lives in TAG has told me that he has actually caved, in TAG, on 8mm rope.
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Re: Shock absorption in cowstail/QAS?

Postby chrismc » Mar 31, 2008 2:45 pm

ek wrote:... a friend of mine who lives in TAG has told me that he has actually caved, in TAG, on 8mm rope.


What is this world coming to?!! Dogs and cats sleeping together..?!

I think I'll keep it simple for now. Double cowstail made from a single length of 9mm dynamic rope and figure-8 in the middle, and on both ends. I may throw some prusik magic in there for adjustability, but will have to test 6mm and 7mm cord for that. I'll forego the attachment hardware for now, and attach the cowstail directly to the half-round. Worst-case scenario is that I don't like it and add a 'biner later. "Working ends" get a 6mm mallion to the ascender's small hole, and a locking biner. Foot loop gets 'biner'ed to the ascender's large hole. I'll work with this and make changes as I see fit. Now to reverse-engineer On-Rope1's magic cowstail, and read some 6mm cord specs... (what kind of knot is that? where is the prusik loop's double fisherman? is there one?)
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Re: Shock absorption in cowstail/QAS?

Postby Scott McCrea » Mar 31, 2008 3:16 pm

chrismc wrote:Double cowstail made from a single length of 9mm dynamic rope and figure-8 in the middle, and on both ends.

You could try the Double Overhand Noose on the biner ends. It uses less rope, is more compact and makes a nice handle. Here's a Nylon Highway article about it with testing info. LINK
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Re: Shock absorption in cowstail/QAS?

Postby ek » Mar 31, 2008 4:04 pm

Dwight Livingston wrote:
ek wrote:I wasn't about to buy a whole climbing rope and then cut a piece off the end, and the thinnest dynamic single rope that I was able to find for sale by the foot was PMI's 9.7mm rope on Inner Mountain Outfitters.

IMO sells dynamic rope by the foot in a range of sizes: 8.1, 8.6, 9.7, 10.2, and 10.6 mm.

Sorry I didn't reply to this earlier. The 8.1mm and 8.6mm ropes are not single ropes, and they are not designed to catch high-factor falls when used in single strands. PMI's 8.6mm Fusion rope is a half rope, and PMI's 8.1mm Verglas is a twin rope. The half rope would probably hold, as other factors, like the knots and the deformation of the climber, are significant in reducing the effective fall factor when the fall is short. The twin rope might well not hold--twin rope is always used in pairs run in tandem, so that the load is evenly split between two ropes. (The exception is that twin rope is considered suitable for use in single strand for glacier travel, but in glacier travel the maximum fall factor is 1, and practically speaking is always considerably less than that. You could probably also get away with belaying a second on a single strand of twin rope, but again, the possible fall factors here are low. In a cowstail, there's no dynamic belay, and there are knots in the rope that reduce its strength.)

Scott McCrea wrote:Blue Water makes 7 & 8mm dynamic Prusik cord. I use it on my cows tails. The sheath is thinker than the average 8mm dynamic climbing rope.

I think this is a bad idea, for two reasons. The first reason is that, assuming the Prusik cord is as strong as 8mm climbing rope (which is quite possible), it's still not necessarily strong enough to hold a factor-2 fall (see above).

The second reason is that accessory cord, even dynamic accessory cord, is not designed to be the primary shock-absorbing component in a fall arrest system. Does this dynamic accessory cord lack any of the characteristics of a dynamic rope? If not, why isn't it called "rope" and sold for a higher cost? If so, those are all characteristics that are important for cowstails.

If you wouldn't take a 40-foot lead fall onto a longer length of the stuff, I can't see a valid reason to use a short length of it to make a shock-absorbing lanyard, especially given the availability of short sections of thin, single dynamic rope.

chrismc wrote:Now to reverse-engineer On-Rope1's magic cowstail, and read some 6mm cord specs... (what kind of knot is that? where is the prusik loop's double fisherman? is there one?)

I may be mistaken, and it is hard to tell from just that one angle, but the main rope appears to be tied with a double fisherman's eye and then threaded with accessory cord to pinch down the loop and fix the carabiner in place, while enabling the user to easily remove the 'biner and replace it in the field. That's kind of cool. On the other hand, using a barrel noose, a.k.a. double overhand noose, as Scott McCrea suggests, is simpler and less bulky, and way easier to do yourself. This is what I do, and I've been very happy with it, though you do have to wiggle the carabiner around quite a bit to get it out of the eye of the knot, and this knot does not safely accommodate more than one piece of hardware in the eye (because it would jam them together).

Chapter 1 of Al Warild's book vertical includes a brief discussion of cowstails, including a picture of a cowstail with barrel nooses on the ends (see page 11). Chapter 3 contains a description of how to tie that knot (see page 50 of the book, which is the 12th page of the 3rd chapter).
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Re: Shock absorption in cowstail/QAS?

Postby Scott McCrea » Mar 31, 2008 5:00 pm

chrismc wrote:Now to reverse-engineer On-Rope1's magic cowstail, and read some 6mm cord specs... (what kind of knot is that? where is the prusik loop's double fisherman? is there one?)

Previously discussed here.
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Re: Shock absorption in cowstail/QAS?

Postby hunter » Mar 31, 2008 5:07 pm

But just like webbing screamers, dynamic cowstails should definitely be replaced after a hard fall.

I'm curious about the justification for requiring replacement of a cowstail made of dynamic rope after a hard fall? Many climbers take hundreds of lead falls on a rope before retiring it. These tend to be much less than factor 1. Are you considering a hard fall a factor 2?

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Re: Shock absorption in cowstail/QAS?

Postby ek » Mar 31, 2008 5:10 pm

I think the reason is that it tightens down the knots enough that they no longer absorb significant shock afterwards. I wonder if you could just loosen and re-set them...

I would personally consider a hard fall onto a cowstail to be a fall of near factor 1, or higher. But perhaps there is a more scientific definition of "hard fall."
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Re: Shock absorption in cowstail/QAS?

Postby fuzzy-hair-man » Mar 31, 2008 6:44 pm

hunter wrote:
But just like webbing screamers, dynamic cowstails should definitely be replaced after a hard fall.

I'm curious about the justification for requiring replacement of a cowstail made of dynamic rope after a hard fall? Many climbers take hundreds of lead falls on a rope before retiring it. These tend to be much less than factor 1. Are you considering a hard fall a factor 2?

James

I'd argue that the dynamic rope on our cowstails sees a lot more abuse than most climbers ropes, it's also a lot cheaper to replace so why not replace it? falls in caving should be a rarity so it should not be a big deal.

I'm not really a climber but as you said I'd guess that a large portion of the falls taken aren't near a ff1 and are probably a smaller ff than those falls taken on cowstails (it would be relatively easy to get a ff1 fall on cowstails, then think about what your falling on, in most cases a caver would be falling on to a anchor that is very static, climbers by comparison fall onto a belayer and belay device which will often soften the fall the rope also runs through thier runners each of which as I understand takes out a little force. Lastly cavers generally accept that they can't put thier harness maillon above the anchor point but if you take into account the central maillon and the crabs at the end of your cowstail then you fall factor is actually more than ff1. Incidentally there's another reason not to attach your cowstails to your central maillon with a crab or maillon :wink: ).
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