Offset joining knots (abseil / rappel)

[Dan_Lehman]

Not true regarding "research".

Among research approaches can be:
1) survey of what *knots* are in use, with regard to
 1.a what knot per named *species* (e.g., grapevie, "EDK")
  but also
  1.b how the knot is oriented (as I keep emphasizing but
  so far w/o the slightest hint that this point is understood
  --and one shocking response indicating quite the contrary!),
  and
  1.c user comments about such ARG knotting.
(Some of this research can be carried on immediately, i.e., in
extant rockclimbing-site-forum chatter and other texts; some
can be raised by a new query.)

 2. stressing of various knots (and orientations!) in pertinent
 materials, looking for insight to knot behavior, such as
   2.a vulnerability to any sort of snagging of part of the knot
    when pulling down joined ropes,
   2.b potential to jam, or
   2.c loosen (maybe not to come untied but to aggravate (2.a) risk.
 ... ?
Among materials should be those most naturally used,
which are dynamic ropes by rockclimbers, the same for
one end but a "haul line" of smaller-diameter, low-elongation
rope (5?..8mm), and then also all low-elongation ropes
(all of relatively smooth-sheath, kernmantle construction, here),
as well as some others which might help look "over the horizon"
to see what risks might lurking, though likely at safe remove
to the application's materials (thinking both the quite stiff
and quite elastic materials --shock cord, in latter case).

I have reached my own conclusions as to the best offset rope joining knot. Its #1410 with an extra 'choking' turn - a very simple maneuver and does not increase the footprint significantly.

And without seeming to understand the "orientation" aspect!?
But, one must acknowledge that in a way there has been SOOO
much practical *testing* of this by the decades of usage
--that is a higher frequency and perhaps broader (perhaps!)
range of materials than any tester is likely to have.  (I hesitate
re "materials" because not only is the usage I think parochial
to rockclimbing and hence those kernmantles, but also there
is general doubt of employing the offset water knot with ropes
of different natures  --though it might, if the smaller or more
flexible rope makes the choke, be more sure!

I am not a climber and perhaps I take a different perspective about knot security/stability, however I do not now feel completely alone in my earlier criticism of the #1410 after reading recent posts by several posters.

I'm not sure to what posts you refer --I know that I have
both remarked about its seeming dubiety (my initial impression,
e.g.) and its history of usage.  I'm much inclined to accept the
judgement from those working "at the sharp end" versus those
sitting in the arm chair!  And you too should be tempering your
assessment of it, irrespective of one material's behavior; but
you are setting a standard of acceptance beyond practical needs,
and you must admit this.

(Consider the importance of easy tying, vis-a-vis cold gloved fingers
--perhaps of frozen-stiff ropes(!)-- :
the "EDK backed-up EDK" is something that an alpine climber
can manage, in gloves & fading light; more intricate reeving of ends
just so brings along an accident waiting to happen.  Which is
not to put off seeking some "better" Knot in terms of efficiency of
material, for situations where careful tying is reasonable; but there
should be in the knots toolbox something that works in hard times
--and I think that the aforementioned ARJ knot is IT!

I will probably trial out ...

I slipped in a suggestion for you to see how your challenging
cord worked with the just-cited knot : your testing puts quite
some challenge, and gets the capsizing --yes, or was it not
this but really some purer "slipping"?!--, so can this knot
safeguard this situation?

I need to find a 'local' Australian supplier who will provide 10m-20m of this expensive material at a reasonable price. The new 6mm climbing material looks interesting too. And do not forget, there are seemingly a lot of readers who will not believe any test anyway

Or you might do as well in finding (also, perhaps) some
climbers willing to part with some old, used rope pieces
(e.g., I have some that were retired to be top-rope anchors).
Sometimes, a climbing gym might have some small bits
to give away or sell (sometimes this rope though is a sort
of hybrid rope --not the purely dynamic rope taken outside
but one with tougher/thicker sheath ...).

As for that "6mm climbing material", I call "B.S." :: I saw no
real indication that this was at all suitable for lead climbing
--i.e., that it has any dynamic capability (and, in fact, usually
such rope is made of hi-mod fibres that are STATIC and which
deliver severe shock forces!!).


--dl*
====

[alpineer]

  1.b how the knot is oriented (as I keep emphasizing but
  so far w/o the slightest hint that this point is understood
  --and one shocking response indicating quite the contrary!),
 

Speaking for myself, I do understand your point about the orientation of the S.Parts, and agree that it needs addressing. Research will not be complete without doing so.
While your images are good quality they don't show the correct perspective. It's much easier to appreciate the S.Parts' discrete orientations when the nub's base is viewed directly along its central axis. Post images of all three orientations from this perspective and you might get a resonant response.   

[agent_smith]

      1.b how the knot is oriented (as I keep emphasizing but
      so far w/o the slightest hint that this point is understood
      --and one shocking response indicating quite the contrary!),
     

Speaking for myself, I do understand your point about orientation of the S.Parts as they enter the nub, and agree that it needs addressing. Research will not be complete without doing so.
It's easy to see these orientations when viewing the nub's base along its central axis. Post images of all three orientations from this perspective and you might get a resonant response. 

...

Its not a question of not understanding; its a question of time and energy.

I had chosen to confine my examinations according to the symmetric 'orientation' as shown in my previous posts. I am also making an assumption about how the masses will tie #1410 - and adopting that as the baseline.

Also, the business of taking photos of a reasonable quality is slow and tedious work. I like to be systematic and methodical in my approach to this subject.

Also, I am directing my energies towards sorting out the next revision to my Bowlines paper. There are many issues to work through just in that subject alone.

EDIT: Dan, I will photograph #1410 with the SParts in what you refer to as "different orientations' tomorrow. I have never categorically denied your assertions re 'orientations'. For the record, I understand and concur with your views that this should be properly photographed, documented and tested. I think you have been trying to point out that by a simple manipulation of the SParts in #1410, you can arrive at what appears to be a more stable and secure version. If this is what you are postulating - then I concur.
This is because in the symmetric orientation I had previously shown, the SParts are acting in opposition which has the effect of contributing to the tendency of #1410 to capsize. However, a simple adjustment of one of the SParts - by exchanging its position with its adjacent SPart- one can induce a kind of 'choking' effect around both tails which also appears to reduce the 'shearing apart' effect which the 'offset' structure has by its very nature a tendency to do.
Anyhow, I'll do my best to photograph and document in side-by-side images.
I also agree that nobody has properly photographed and done a direct side-by-side comparison - and compared the test results. Note that I dont care about the MBS break load - I only care whether the threshold load at which instability is likely to manifest is raised (if it also boosts the jamming threshold - then that would also be a bonus).

Mark

[agent_smith]

Not true regarding "research". I believe the thread was originally nothing more for Mark than 'get someone else to trial the knots he wanted tested'. Later we get the following "conclusions" quote, after NOBODY has tested/trialled any knot properly.

You're right; this was a conspiracy all along. Damn, I didn't hide my tracks well enough.

Quote from: Mark

    I have reached my own conclusions as to the best offset rope joining knot. Its #1410 with an extra 'choking' turn - a very simple maneuver and does not increase the footprint significantly.

Yep, guilty as charged. My thought processes led me to believe that simplicity is a major design goal. Using #1410 as the baseline, any attempts to 'improve' its security and stability must not significantly do the following:
[ ] (not) significantly increase the footprint of the knot structure
[ ] (not) significantly increase the number of rope maneuvers to arrive at the finished structure (avoidance of complexity)
[ ] (not) alter the 'offset' structure where both SParts converge and enter the nub/core in parallel - so as to maintain the design goal of ease of translation around a 90 degree edge.

Merely because I make a comment in passing that I had reached certain conclusions does not by itself mean a lockdown of this topic - it simply means that I am directing my thoughts in new directions in response to observations and discussions. No conspiracies here either.

And this emphasises my disgruntlement earlier in this thread: I believe the outcome of this whole discussion was predetermined in Mark's mind from the very first post. Those of us who wasted our time with Mark's hidden agenda: Show the #1410 slips, but you can still feel good about it and doesn't deserve it's EDK moniker (blah); followed by Mark's 'choked' #1410 lookalike that he has already approved from 2012 (see PACI document mentioned earlier by me). It still slips, according to Mark's own tests (blah).

The knot study guide has been out in the public domain for several years - nothing hidden here. I wanted to re-open this subject to see where it would lead... and to inject new thought processes into an old subject.

I find it both sad and ludicrous that you needed to make the comment... "those of us who wasted our time with Mark's hidden agenda".

Its amazing how someone can twist good will into something of a sinister character. One wonders what kind of emotional roller-coaster you are riding?

Honestly, how hard is to work together in this forum to find a better knot? If we can't do that then we truly are wasting our time.

The whole concept of finding a good knot to do this important job has largely been ignored by Mark in my opinion. There is some really good feedback (for Mark) to be had in this thread. I am not a climber and perhaps I take a different perspective about knot security/stability, however I do not now feel completely alone in my earlier criticism of the #1410 after reading recent posts by several posters.

Hmmm......... more accusations of a personal nature.

It isn't hard to work together. You seem to have formed a view of my sinister and conspiratorial character - and did this without ever actually having met me face-to-face - you arrived at your view through written words on social media alone.

And I have ignored nothing. I carefully consider and respect everyones opinion. After considering information received - I then accept or reject based on my own cognitive processes.

In the case of #1410, it has withstood considerable real-world use and field testing. I have used it myself on many occasions in 'bailing out' from big mountain routes or difficult rock routes. I am writing this post today so clearly I am still alive. I did not die while using #1410 (and I never back up #1410 with another #1410 as that would - in my personal view - defeat one of the primary reasons why I chose it in the first instance - small footprint and less likely to jam up somewhere).
NOTE: Maybe I died in another 'multiverse' - per quantum theory?

Mobius - you seem to have difficulty in confining your feedback/posts to a professional level (and instead resort to personal attacks).

I consider this topic still open for business as usual.

[Dan_Lehman]

      1.b how the knot is oriented (as I keep emphasizing but
      so far w/o the slightest hint that this point is understood
      --and one shocking response indicating quite the contrary!),

...

Its not a question of not understanding; its a question of time and energy.

I had chosen to confine my examinations according to the symmetric 'orientation' as shown in my previous posts. You must understand that this is how 90% (or more) of users will tie #1410.

THIS is just such indication that you in fact DO NOT
UNDERSTAND the point at all --your prior remark about
"chirality" was the other : my "orientation" focus has
nothing to do with either chirality or symmetry (by which
you must mean "dressing-without-crossing : pure tracing",
for the knot is asymmetric).

As for best perspective, hmmm, a *side* one might be
best but for the natural obscuring of much of one S.Part
by its twin on the entry point : but, --maybe w/some graphic
to indicate parts-obscured (e.g., dotted lines)--, by such
perspective it certainly would be perspicuous to show in
one extreme (of the range of variation) the left S.Part
making the backwards loop vs. the right's forward arc
and then vice-versa, and the mid-range "side-arcs" of
the two.  And the position of the tails --running roughly
perpendicular to the axis of tension (at extremes) or
parallel (mid-range)-- could be noted verbally or shown
w/cross-section of tails in the perpendicular cases --which
would have them going to or away from the viewer,
in this left-to-right presentation.

Just as a glance at tied shoes can gather a strong hint of
granny / reef by wether bows run perpendicular (reef),
one might deduce likely offset water knot orientaitons
--esp. the mid-range one.

One more try ... :
In post/reply #56, owk images are presented
--blue + white ropes.

And here is the series of photos of #1410 (Offset overhand bend) showing different rope diameters.

Photos show orientations/positions of the smaller rope relative to the larger rope.
...
Mark G

I'd describe the orientation shown in image #2 as being
roughly mid-way between the perpendicular- & parallel-tails
positioning, which is thus nearer the extreme of the range
where the blue rope makes the backwards loop and the
white the forwards arc --which would be reached if one
were to reach to the shown knot and rotate its nub --just
a little-- viewed-side rightwards, bringing the tails to point
AT the viewer (& perpendicular...).
Rotate the nub just a little the opposite way,
and the tails swing to lie parallel above the left/blue rope,
and both S.Parts make a "side arc" : jointly upwards,
and THEN curving ... .
Rotating it further in this direction will swing the tails
away from the viewer and thus put a forwards
arc in the blue, backwards loop in the white.

All of the above done w/o re-tying or re-dressing the knot
--just having it oriented some way when setting it (or after
a lesser setting qua stopper knot, loading it qua end-2-ender).

These are not things obtainable from one position
using a mirror reflection to make another.
Reflect #56's image and the blue rope STILL makes
nearly a backwards loop, etc. --that doesn't change.
But the re-orientation I describe does change things;
to what degree it affects behavior is an open question.

This is like a dancer doing the splits fore/aft, facing the
audience --right leg fore, say--;
and then while still also facing the audience, another
(or same, with movement to effect ...) dancer has
the left leg forward.
More to the knot case, let both dancers be bending leftwards
supported by left arm, right raised in graceful harmony.
.:.  Their split legs stand in different orientations to this.
(We could add a third, legs split left & right, and she too
leaning leftwards.)  The commonality in all these dancers
is orientation of waist & above --torso & arms--; their
differences lie in the position of their legs.
One might expect different torsions & muscular strains
& uses among them.
And in an analogous view, I think that those "ARJ kinots"
(offset end-2-end knots) should be examined for possible
effects/influences of such variation.  (Even just to learn ...
and without real chance of finding significance, given that,
again, the infamous offset water knot ("EDK") has endured
so much successful usage[*1].)


--dl*
====

[*1]  I believe I voiced this conjecture previously somewhere
among our deliberations on this forum ("this" = "IGKT", not
so surely/narrowly "Practical"),
but when Agent_Smith presented/discussed/tested the offset
fisherman's knot --which had been tested in a backed-up variation
by Jost Gudelius (which he initially misnamed "triple fisherman's")--,
it occurred to me that perhaps the partial untying and then
reconsidered re-tying of the supposed EDK (by the fellow in
the trio where "Karen", 2nd to abseil, had the knot spill and she
suffered a fall) resulted in not the EDK but this offset fish.
--it's just possible to go wrong and get this similar-looking,
inferior-performing knot!?
And this is the lone? case I can think of where the behavior has
been cited as dubious.  (But perhaps there are others, at least
where the users are fairly sure that the knot's tails at the end
of rappelling were shorter than at the start --indicating some
rolling!?)

[agent_smith]

Where are you getting your cut and pasted quotes from? It is incorrect and not my words...

Its not a question of not understanding; its a question of time and energy.

    I had chosen to confine my examinations according to the symmetric 'orientation' as shown in my previous posts. You must understand that this is how 90% (or more) of users will tie #1410.

THIS is just such indication that you in fact DO NOT
UNDERSTAND the point at all --

Furthermore, I indicated that I will do my best to photograph #1410 with the SParts re-oriented - and present it in a side-by-side comparison image.

Do you not want me to do this?

[agent_smith]

Some photos of #1410

Note the different orientations - look at the blue SPart...

[Dan_Lehman]

Some photos of #1410

Note the different orientations - look at the blue SPart...

BINGO!   
(1 of 2 orientation-range "extremes" & the "mid-range")
So, a 3rd one fits nicely, and it would be where
the white S.Part now in loop is on viewer's side.
(BTW, are you right-handed and these images show your
natural orientation (re handed-ness) of the knot?
I'm R-H and will produce the mirror image, holding lines
in left hand and turning the working ends around sort of
clockwise.)

IMO, the extreme that you show (blue loop & white arc)
--which I'll call "choking loop" to denote strand & shape--
is the more difficult one to reach --i.e., naturally, it might
be that this orientation doesn't go as *far*, put the tails
as perpendicular, as the other extreme?!  --that set to
the extreme will see increased forces rotating it a bit
back from that, whereas "choking-arc" holds?!  --IMO.

Run through these orientations w/mis-matched ropes,
and ... --what?!

In hand, now, I've some thin (1/8"4mm) cheap, wimpy
solid-braid-like sheathed poly-fibre-core fabric cord tied
to rockclimbing nylon?-sheather Spectra 5.5mm, stiff cord,
and tied so that the thin ("wimpy") cord makes the choke
(above-post's blue's position).  At first, I had the opinion
that the extreme with the choking line making the arc
seemed most stable; but after stressing and then some
rotating-through-orientations some times, now the knot
seems pretty stable no matter which orientation.  (At first,
by manual (in-hand) stressing, which w/thin cord biting into
skin will only see, hmmm, 25# force(?); then, quickly going
to a 35# dumbbell and that holds the same.) Suffice it to
say that there's no elasticity in these play cords.

I'd guess that for strength of the knot tied with thinner & weaker
to thicker & stronger ropes, the choking-loop orientation (which
is show above) is strongest : it puts the weaker rope in what
IMO looks a decent initial curvature --the loop).  --not that
strength is usually regarded as an issue with such knots.

One might wonder how hay-bale ropes are typically oriented
--assuming that machine-tying will be regular/predictable!?
And --yet further motivated to try imitating scientific study--
out I go and quickly fetch a batch of salvaged loops of baling
twine, fibrillated PP(PE?) in blue (w/one orange loop/round sling).
All of the blue cords show the "choking-loop" orientation.
The orange cord --which seems slightly thinner than the blue--,
appears to have the same though with --judged by tails angle--
less of the extreme orientation,
but then I see that its arc strand crosses beneath the loop
one and ultimately is the choking strand --but the overall
knot looks to be in same orientation (i.p., re handedness)
as the blues :: has a "roll" happened in this, to pull an
initial choke-loop around the arc, substantially?
In any case, it is different (but also seems pretty well
locked into its state).

Okay, all this scientific study ... has elevated my hunger :
time for brunch!


Thanks for the further nice images,
--dl*
====

[agent_smith]

An interesting link from Petzl.

https://www.petzl.com/INT/en/Sport/RAD-LINE-joining-knots?ProductName=RAD-SYSTEM&Familly=Ropes#.Vpgt5cu2VaR

In my personal view, the testing and the reported results are invalid on account of ignoring the effect of dressing and orientation. Precise details of knot geometry used for the testing is absent.

I guess it shouldn't surprise me - the focus is on MBS break test results rather than stability and security (and simply 'assume' how users will tie the offset knots).

Although in a somewhat saving grace...Petzl do mention that all of the offset knots are 'strong enough' anyway.

i wonder who was the lead tester (ie his name)? One day, large companies such as Petzl will check in with the IGKT - even if only informally - before posting results in the public domain (to allow for some critique prior to going to print).

I would say that the real root cause of my issue with Petzl is that they are perceived to be an 'authority' and that any technical information posted on their website will be interpreted as 100% factual and entirely accurate.

I think that large high-profile companies such as Petzl have a higher onus (or duty) than individual freelance testers to get it 'right'.

Anyhow, I have posted some images of #1411 in its offset form...I am of the view that dressing and orientation of SParts would have significant impact on any tests results probing for instability/security. Petzl did not appear to examine this effect? There are some dressings of Offset F8 that are inherently unstable...

Legal notice: I am not defaming Petzl nor are my remarks intended to be of a defamatory character. Petzl is a respected roping hardware manufacturer. My comments are directed at the (lack of) rigor of their knot testing. Petzl's core business is metal hardware manufacturing - and not knot testing!

Mark

[Dan_Lehman]

An interesting link from Petzl.

https://www.petzl.com/INT/en/Sport/RAD-LINE-joining-knots?ProductName=RAD-SYSTEM&Familly=Ropes#.Vpgt5cu2VaR

... to say the least !   
Good find!!

FYI, I see that in on-page info Pretzl show the strangle noose
to tie off a carabiner --this is not easy to discern in their
video of crevasse rescue.  But what I DID see there was
the use of a fig.9 eye knot with loading done on the
*exterior* strand.  (I think that it might be stronger on
the interior one, and IIRC this is Lyon Equip's conclusion
for the kernmantle ropes that they tested --IIRCorrectly.)
(I also remarked at how fortunate for that scene that
the fallen skier could help herself so much; real life is
not always so kind.)

As for the use in the video of the end-2-end knot (an
offset water knot), that seemed like rather short
span between tied-in skiers, and what were those two
mid-line eye knots for?  (and what knots?)

Although in a somewhat saving grace...Petzl do mention
that all of the offset knots are 'strong enough' anyway.

"All of the..."?  Am I missing something.  In fact, they
show the offset fig.8 as stronger (10kn > 9kn) than the grapevine!?
(AND, nb, give at least nominal testimony that the latter knot
break in contrast to things we've heard previously
from other sources (and maybe also Petzl --anyone care
to research this?) that the mere g. / dbl.fisherman's SLIPS
without breaking; and from this came the well-promulgated
recommendation to use the treble fisherman's knot when tying
"Dyneema/Spectra" (cored) cord!

Now, I've see abysmal test reporting, from Practical Sailor
(a magazine supposed to be of high quality, not taking ad.
money and so supported by enthusiastic readers who value
good information), in which the implied or even nominally
stated behavior was shown by other statements or information
to be otherwise.  (Say, not breaking but spilling --admittedly,
a distinction w/o merit to the practical user in such a situation.)

I would say that the real root cause of my issue with Petzl is that they are perceived to be an 'authority' and that any technical information posted on their website will be interpreted as 100% factual and entirely accurate.

Let's see what Petzl's exact words giving the two sets
of test behaviors/results?!  --of the two offset knots
above and then those two again with the grapevine bend.

[tied as for abseil/rappel-ropes joining,
presumably ropes around a pin at one end
and both ends tied off to the other end,
and so a dual-line tension member
of which ONE side has the knot!]

Figure 8 knot: strength greater than 12 kN.

Simple knot: knot slips at 7 kN,
 then the rope is released and the knot fails.


[end-2-end tested, single strand loaded]

Figure 8 knot: cord breaks at 10 kN.

(Knot begins to capsize at 7 kN, then the knot tightens).

Simple knot: cord breaks at 8 kN.
 (Knot begins to slip at 4 kN, then the knot tightens).

Double fisherman's knot: cord breaks at 9 kN.

These results are inconsistent, at best.  Let's take them
knot by knot. (By their graphic, I assume they mean 2 strands
are loaded, as I annotated within the quotation --loaded as
though by an abseiler (which saves them dividing by 2?  )

For the offset fig.8 the two-strands (hence, half-force)
testing has that configuration exceeding 12kn and so the
knot must be >6 is the simple-minded deduction; but even
with some *slippage*, it must be taking on 5kn and showing
no problems.  And for single-strand testing, they have it
reaching 7kn and then it "begins to capsize", and breaks at
an impressive 10kn.  Now, I have trouble conceiving of just
beginning to capsize for this of all knots --one that others
have remarked seems especially bad in capsizing in that it
"flips" and releases a LOT of material in so doing; I don't
see a happy mid-capsize arrangement that could "then tighten"
--bit late for that.

For the infamous "EDK" / offset water knot, it "slips at 7kn"
(half of which = 3.5kn --maybe a bit high...), then spills (though
"rope is released and knot fails" is a curious expression!?).
And in single-strand testing "begins to slip at 4kn, then the
knot tightens" (!! no release of rope & failure) to break at 8kn,
not too shabby (this time).  --which implies "greater than 12kn"
for an overall score in the double-strand loading, but ... no!?

And finally, only showing for the single-strand testing,
and not offset (Franz Bachmann & Heinz Prohaska have suggested
offset loading, btw; Jost Gudelius tested this, 12yrs back?),
the grapevine bend breaks (?) at 9kn, "close, but no cigars"
vs. the offset fig.8!

Well, the results aren't as contradictory as my initial impression,
thinking that all testing was the same (but why repeated?);
but they still smack of quite limited variety/repetition, and
are at least inconsistent to the point of making such
conclusions --i.e., the results might be within a range
of expected variance, but the conclusions imply that
this is what happens for this knot, generally.

--dl*
====

[Dan_Lehman]

Here's important remarks from Tom Jones, who has been
a rockclimber and then perhaps more active in shaping
things as a canyoneer!?  As his remarks indicate, he got
to see the ropes of a tragedy well known of two British
climbers in Zion National Park (USA) rappelling : one of
them fell to his death from an apparently failing offset
fig.8 --Tom notes how stiff the ropes were.  (I had
called out TomJ's promoting this knot on his site; he
replied, but later changed it, nevertheless, as seeing
the offset water knot as a simpler safer alternative.

I'm intrigued and puzzled by the bold maroon assertion
--"either version of the EDK" : he has carefully written
'EDK8' & ...9 which by number also go beyond "either"
so that implies that it is not them!?

source site : http://canyoncollective.com/threads/tech-tying-two-ropes-together.4590/

--- In Yahoo Canyons Group, hmoon@p... wrote:
The knot you refer to (EDK8) was shown by Tom Moyers' 1999 testing to be a potentially dangerous knot and TO BE AVOIDED. What is the title of the book you saw this knot in?
It's clear we'll never know what *exactly* what happened in the Zion > accident. Most likely given what we know is that Ross (the deceased) tied an EDK8 too loose or with insufficient tail. The report prompted a lot of people (myself included) take another look at Moyers' EDK8 test data to confirm that the EDK8 is pure junk. That be good. Partner checking is also good when possible.
I use an EDK for fat, thin, and any combination thereof. Testing supports it. If I were feelin' paranoid for some reason, I would use the Double EDK. See below for some references on this subject.
http://www.xmission.com/~tmoyer/testing/EDK.html
http://www.needlesports.com/gearreviews/abseilknots.htm  [EDK-backed EDK]
http://jost.gudelius.bei.t-online.de/spst.htm           [offset fisherman's +overhand ; offset grapevine]
[Jost's location currently is : www.gudelius.de/spst.htm ]
> hank

Tom Moyer's test data is the best available, but...

I have also pulled a few EDKs and EDK8s on a test machine, and reached somewhat different conclusions than some have reached from Mr. Moyers.

Critique of TM's report. A. Loading was done across the knot, single strand. Actual field loading is half as much, therefore, TM's numbers should all be doubled. B. ANY analysis of knots in ropes is inherently limited by the inability to test all the combinations.

What I noticed is that both the EDK and the EDK8 do tend to capsize. On a 10.5mm used climbing rope, dry, the load to capsize on either was quite large ~ 1000 lbs, difficult to achieve in a rappel.

Capsizing on a test machine relieves the stress, unlike in the real world, where it would just drop the rappeller a bit, and the force would stay much the same. On a test machine, each capsize requires slightly larger force. Each capsize crawls 3" to 6" along the rope.

Even a very loosely tied backup knot prevented the capsize from getting past the backup knot.

Mostly, what I am concerned about is not equal ropes, dry; IS ropes that are quite different in size and stiffness, possibly wet.

My conclusions are: A. Almost always back up the EDK or EDK8 or EDK9 with an overhand knot. Even more important if the ropes are "different". B. Either version of the EDK works fine. C. Dress the knots well and tighten firmly.

If really worried about the knot getting stuck - re-rig rappel or do other tricks (pre-pulling knot, etc). At worst, use single EDK for the LAST person (me), rappelling carefully to minimize force.

I got to see the ropes from the accident in Zion. They were super- stiff, big fat climber cords, the kind you would retire and perhaps only use for fixing ropes on big walls. The knotability of those ropes was very, very bad. If people are using ropes like that for canyoning, I would suggest that they not do so. If people are using ropes like that for climbing, rigging or fixing ropes, you would obviously want to take great care in tying them, because they obviously tie very poorly.

You might reach other conclusions. It's your (and your friends's) life (lives), so be smart.

Tom

And that's "Tom JONES", not to be confused with
"Tom Moyer" --who's more oriented towards SAR.

TJ now recommends the EDK-backed EDK --which he shows
with opposite handedness, curiously.
www.canyoneeringusa.com/techtips/tying-two-ropes-together


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[Dan_Lehman]

Contributing to the previously suggested research into
what-happens-in-the-RealWorld(tm)/Wild re ARJ knots,
here's a snapshot posted of the offset water knot (EDK) plus
an overhand stopper knot where two aspects regarding
this knot combination are done *wrong* :

www.mountainproject.com/v/using-a-tagline-which-rope-do-you-pull-on/110269243
  [EDK +stopper w/diff.dia.ropes backwards !]

1) the joining of thick & thin ropes has the thick one choking,
and
2) the tying off of one tail is (a) done in the wrong (non-choking)
rope and (b) not tied around the other tail (maybe a minor
offense, but it should be easier to snug this stopper to the
base knot if tying around the other tail).
!!

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[knot rigger]

I'm not an Alpineer, these are just my impressions based on what I can find on Petzl's website and my general knowledge of ropes access and rope rescue.

Pretzl show the strangle noose
to tie off a carabiner

This may be for three reasons
1) it's compact
2) the noose traps the carabiner in the correct orientation (a favorite feature of arborists, I understand)
3) this knot will contract somewhat under shock loading and provide some limited shock absorption.  This would be of advantage with the low stretch rope, but I feel a better choice for dyneema would be a triple overhand noose

and what were those two
mid-line eye knots for?  (and what knots?)

Take a look at this link for your answer:
https://www.petzl.com/US/en/Sport/Approaching-a-glacier-as-a-roped-team-of-two?ActivityName=Mountaineering#.VpoMpa6rQUE

The mid line knots purpose is the help slow the falling skier as the knots pass over and break through the snow and ice at the edge of the crevasse.   The show an offset fig 8 loop (same loading as a EDK8  ie Tom Moyer's "instant death knot") but they mention an "overhand" loop will do (same loading as EDK)  It would seem that a butterfly loop might be a better choice, but perhaps the offset profile of the EDK is desirable.

from agent_smith

I would say that the real root cause of my issue with Petzl is that they are perceived to be an 'authority' and that any technical information posted on their website will be interpreted as 100% factual and entirely accurate.

I completely agree.  I think it would be wise to attempt to bring this to Petzl's attention.  I wonder if a letter from Antoine Leroy, the Guild President, citing relevant available testing would be well received by petzl? 

We could, of course do our own testing on EDK etc in the RAD cord, the system only costs USD $400 LOL

It is possible (but seemingly incredibly unlikely) that the EDK performs well in Dyneema cord.

cheers
andy

[agent_smith]

I concur with knot rigger - well crafted words.

I also am unclear as to the effect of the material composition of the cord on various 'offset' joining knot structures.

Eg: Technora based cords and the like

My personal view is that we shouldn't see any great variances in resistance to instability - eg the point at which instability manifests. Although the only way to conclusively address this is to test - so that means purchasing such cordage and test and compare accordingly.

[Dan_Lehman]

I also am unclear as to the effect of the material composition of the cord on various 'offset' joining knot structures.

Eg: Technora based cords and the like

My personal view is that we shouldn't see any great variances in resistance to instability - eg the point at which instability manifests. Although the only way to conclusively address this is to test - so that means purchasing such cordage and test and compare accordingly.

I've pointed to likely differences previously:

1) elasticity will enable greater deformation, which increases instability

2) frictiveness can aggravate (1) by giving the S.Parts more *grip*
to pull apart the choking strand;
2.b) ... whereas slickness I suppose can see greater force delivered
*into* the nub, maybe increasing pull-out force on whatever is
toggling that (nipped tails, e.g.).

It seemed to me that some old 11mm climbing rope --stuff that
had been retired to anchor-line duty for some cliff-side top-roping--
was more prone to open up than thinner, weaker, new stuff;
I inferred that this resulted from the ropes greater elasticity
(?! even vs. weaker rope which thus worked at higher % ?!)
and a frictive surface to make the draw of the S.Parts more
effective at pulling the choking strand along.  !?

Whereas a no-stretch rope should see its choking strand
holding tight depending upon the grip on its continuation
(e.g., on the tail, in the EDK) --why that tail should
be what is tied off!).

Otherwise, the magic of just changing tensile strength of
rope in the knot --touch w/magic wand and ...(!)-- should
have no effect : what matters is the deformability and the
compressibility of the strands and structure of knot.

A fair question : what's the practical difference in elasticity
between common dynamic ropes and canyoneering/SAR/caving
ropes, at expected, in-use forces?  (One might expect that
in the case of thicker and stiffer low-elasticity ropes there could
be some *modeling* of elasticity/stretch in their being more
prone to not drawing up tightly --i.e., what would have come
from stretch is here got by non-tight setting!?


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