Rigging question

[NZcaver]

Knots declared as "non recommended" by Warild were and are regularly used by cavers and rescuers, and there's no trails of dead bodies in their wake. Knots like the clove hitch, the bowline and the butterfly.

In defence of Al, the knots you listed are under the 'other knots' section and have the foot note " 'Other rigging knots' are knots that work, and are often used, but there are better knots for the same purpose". I suppose he would argue you don't *need* any of them when there are more foolproof alternatives. Then again I know he uses some of them on a regular basis!

Are you referencing the 1988 edition of Vertical? This was my initial caving/SRT "bible" as described in my previous post. I realize there has now been at least 2 revisions, and the knots section has been tidied up quite a bit. But as of the 1988 edition, page 41 shows the table of non-recommended knots and the only footnotes are credits to Marbach and Rocourt and comments relating to certain knots such as "knot unties when loaded" (that's the reef - aka square - knot). Page 38 in the same edition has the heading "other knots" but the text does not relate to his list of non-recommended knots.

Anyway, moving on... I finally had a chance to look over the NSW SES knot testing material in the link you posted. No offence to you or Mr Sheehan, but I wasn't overly impressed. Of course the more testing the better, but these seem to be single examples not averages of several tests on each knot. Some of the knot choices and test parameters seem a little odd. Everything seems to revolve around huge 13mm rope that few of us use for caving or cave rescue, and then they test 6mm Prusiks with it?? Duh! Some of the photos are a little too close up to see what's really going on, and the occasional typo and use of KG loads rather than kN force is slightly distracting. [End nitpicking]

That said, a number of the failure values do seem surprisingly low. Which means we need... you guessed it... more testing!


PS Good post, kN!

[knudeNoggin]

Now, for that ULRinked-to page of pretty photos (yea!) of loaded & sometimes
ruptured knots. There are some obvious errors in this reporting, which suggests
some inattention or knowledge about testin/reporting/knots (as the disclaimer
allows).
Let's see what can be found.
...
Whew, enough for now.
The Butterfly's broken bits make me wish for a pre-break
image; it's a rather small part of the initial turn that remains,
and original orientation is unclear to me, now.

Further to this analysis: I find the photos of the (1st) broken Butterfly (qua bend, NOT loading the eye -- nb!) to be hard to explain. The images are of one eye leg passing through the nip/binding of the unbroken mainline's Overhand component, looping to form a collar around the broken-away opposite end (so, around air, in photo), and returning up through the nip to a short broken stub !! Really ?! How does this nipped stub come to be at this point -- that, I cannot figure!? What should have occurred was the break coming where the loaded mainline turned around an (untensioned, here) eye leg, and then it would have pulled away and left a broken, longish bit for the collar.

I can only surmise that there was some rather poor dressing such that a crossing of the mainlines occurred and this led to compression aggravating weakness in a turn and ... the busted end got nipped and pulled into that surprising position. -- speculation, but what else is there? Scrutinize this; play around with the knot; realize the puzzle here. (The usual result is a quick glance and moving on ... .)

*knudeNoggin*

[AlanfromOz]

(And there are many dubious statements to be found in LoaL , to beg questions.)

Agree. Dave M specialises in overarching definitive statements and dismissive mocking of detractors (eg his treatment of counterbalance lifting)

Are you referencing the 1988 edition of Vertical? This was my initial caving/SRT "bible" as described in my previous post. I realize there has now been at least 2 revisions, and the knots section has been tidied up quite a bit.

I'm reading the latest (2007?) edition, available free at cavediggers.com

Anyway, moving on... I finally had a chance to look over the NSW SES knot testing material in the link you posted. No offence to you or Mr Sheehan, but I wasn't overly impressed. Of course the more testing the better, but these seem to be single examples not averages of several tests on each knot. Some of the knot choices and test parameters seem a little odd. Everything seems to revolve around huge 13mm rope that few of us use for caving or cave rescue, and then they test 6mm Prusiks with it?? Duh! Some of the photos are a little too close up to see what's really going on, and the occasional typo and use of KG loads rather than kN force is slightly distracting. [End nitpicking]

That said, a number of the failure values do seem surprisingly low. Which means we need... you guessed it... more testing

All fair points. 13mm rope is sometimes used in Australia for rope rescue. Several reasons - much stronger for stupidity safety factor, easier to grip to haul on, and the old, rather scary, practice of calling a 'rescue load' 375kg (825lb) and hanging 2 outriders off the stretcher!

No offence taken by me at least. I'll let Mr Sheehan speak for himself - I don't know him personally, but I doubt he lurks around here!

Several people have used YMMV - perhaps sarcastically, but I think it's true that every rope/knot/loading/dressing combination will have its own unique results. Now THERE'S a killer experiment to design!

For just one possible scenario - someone has tied the rebelay loop too long so you clip your cowstail into the loop rather than the krab or anchor... What happens if you take a fall and shock load the loop in expansion? Has that been tested for fig8, bowline, ABK, etc?

Interestingly, the French have apparently done testing that indicates that a poorly tied knot doesn't perform very much worse than a 'properly' tied knot. I'll have to find the reference, unless someone can beat me to it (highly likely, cause I'm off to bed now!)

Alan

[knudeNoggin]

(And there are many dubious statements to be found in LoaL , to beg questions.)

Agree. Dave M specialises in overarching definitive statements and dismissive mocking of detractors (eg his treatment of counterbalance lifting)

I should be specific here; w/o grabbing the document I can at least recall that (1) he speaks of a problem "expansion-loading" the Butterfly but leaves the circumstance unaddressed for other eye-knots; (2) he mentions that there is a re-threaded Fig.9 (well, of course!) but claims it to be no stronger than a Fig.8 and thus to be eschewed (how can this be? --and see my quandary at CMC & Richards testing of Fig.8 tied by diff.methods); and the Dirctional (aka "Inline") Fig.8 is presented w/o strength data, though said to be indifferent to two markedly different geometries (i.e., whether the loadable tail lies within the nipping loop of the knot!). But he's apparently done much testing with open eyes on points such as different loading rates, noting effects of rope movement & friction/heat, and that's to be applauded.

use of KG loads rather than kN force is slightly distracting. [End nitpicking]

Ha. I find that ignorance of this sort of distinction, and ignorance in general, serves to make things go much easier, w/less hassle. I can almost see Russia from here, and can hear Rush.

That said, a number of the failure values do seem surprisingly low. Which means we need... you guessed it... more testing

No, that's not my guess. It means that we need better-done/-presented testing. What good would more of the same be? After all, there is much of that -- data w/o details.

Several people have used "YMMV" - perhaps sarcastically, but I think it's true that every rope/knot/loading/dressing combination will have its own unique results. Now THERE'S a killer experiment to design!

My hope is that some vast test matrix can be articulated in which after some concentrated testing of factors (such as loading rates, rope diameter, pre-test load cycling), subsequent testing could be done w/fewer samples providing results were within an expected/projected range. Because otherwise the combinations are just overwhelming.

Interestingly, the French have apparently done testing that indicates that a poorly tied knot doesn't perform very much worse than a 'properly' tied knot. I'll have to find the reference, unless someone can beat me to it (highly likely, cause I'm off to bed now!)

One should be chary of such claims (AMGA did some Fig.8 eyeknot tests with similar results): there is enough trouble determining what a "properly tied, dressed & set" knot is --where is there such precise, full explanation?!!-- ; but "improperly tied" covers a vast range of geometries. Merchant's recommendation for the Fig.8 is probably something others would deem "improper" (and is apparently the target of OnRope1's Knot Myth#6). We need something repeatable for testing; or at least a detailed exposition of the variety that obtains in the usual course of practice.

*kN*

[NZcaver]

use of KG loads rather than kN force is slightly distracting. [End nitpicking]

Ha. I find that ignorance of this sort of distinction, and ignorance in general, serves to make things go much easier, w/less hassle. I can almost see Russia from here, and can hear Rush.

Brilliant!

That said, a number of the failure values do seem surprisingly low. Which means we need... you guessed it... more testing

No, that's not my guess. It means that we need better-done/-presented testing. What good would more of the same be? After all, there is much of that -- data w/o details.

Well said. Of course that's what I really meant to say, anyway. Consider my earlier comment modified.


PS Alan, I guess I should declare my own knot choices. I currently have an overhand bight tied in the middle of my double cowstail and a barrel noose at each end to capture the carabiners (à la Alpine Caving Techniques, if I recall correctly). For rigging a simple (single) drop, I tend to rig releasable with a locked off Munter hitch and keep the spare rope at the top. Multi-point anchor systems are usually constructed with webbing and come together at the focal point carabiner. If a single bombproof anchor point (usually a big tree) is available, I might use a releasable tensionless hitch - again with the excess rope kept at the top. When rigging rebelays, by default I'd normally use a figure 8 bight. YMMV.

[Dwight Livingston]

I currently have an overhand bight tied in the middle of my double cowstail and a barrel noose at each end to capture the carabiners (à la Alpine Caving Techniques, if I recall correctly).

I've been rereading Alpine Caving Techniques and was surprised to find their cowstail had figure eights at the ends. (Rubber collars recommended to hold the 'biners in place.) I've been surprised at a few things in there, but that's progress I suppose.

Dwight

[NZcaver]

I currently have an overhand bight tied in the middle of my double cowstail and a barrel noose at each end to capture the carabiners (à la Alpine Caving Techniques, if I recall correctly).

I've been rereading Alpine Caving Techniques and was surprised to find their cowstail had figure eights at the ends. (Rubber collars recommended to hold the 'biners in place.) I've been surprised at a few things in there, but that's progress I suppose.

I stand corrected. Mid-cowstail knot - overhand bight (French influence). End knots - barrel noose (American influence?) Nice and compact in 9mm-ish dynamic rope.

[AlanfromOz]

PS Alan, I guess I should declare my own knot choices. I currently have an overhand bight tied in the middle of my double cowstail and a barrel noose at each end to capture the carabiners (à la Alpine Caving Techniques, if I recall correctly). For rigging a simple (single) drop, I tend to rig releasable with a locked off Munter hitch and keep the spare rope at the top. Multi-point anchor systems are usually constructed with webbing and come together at the focal point carabiner. If a single bombproof anchor point (usually a big tree) is available, I might use a releasable tensionless hitch - again with the excess rope kept at the top. When rigging rebelays, by default I'd normally use a figure 8 bight. YMMV.

Agree wholeheartedly!

Love the barrell noose for cowstails. Agree with fig 8 for rebelays, and like the ideas for lowerable drops. Agree with the multipoint anchor, although for cave rescue we are moving towards rope for slings - tape is great for not damaging trees, but it was pointed out to me that the bit that wears is also the bit with all the strength!