Author Topic: Offset joining knots (abseil / rappel)  (Read 53253 times)

knot rigger

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Re: Offset joining knots (abseil / rappel)
« Reply #90 on: December 28, 2015, 05:14:04 PM »
Hi alpineer

I agree that the "flat" version of ABoK #776 (aka MWDK) doesn't inspire much confidence in security, but I would offer the same criticism of the EDK. 

I didn't find if (or where) Ashley describes #776 as a flat bend... with standing legs splayed, rather than parallel.  Now that I've played a bit more with this loading of this knot, I see that it capsizes into a form very similar to the Ashley bend (ABoK #1452).  This nearly, but not quite Ashley bend (capsized MWDK) does seem to pass a 90 deg edge fairly easily (at least on my desk).. but not as easily as the EDK (ABoK #1410)

As far as security goes... we'll I haven't done any shake tests, or cyclical loading, or anything like that.... but pulling it to 5kN without jamming does indicate some merit, perhaps more strength than security, but the two qualities, while separate, often correlate.  I'm certainly not inspired with confidence in security of the EDK, with it's rolling down the tails behavior at high loads or if set poorly, but I understand why so many climbers use it, there doesn't seem to be a better alternative when it comes to rope retrieval.

Granted, when I rappel, I generally do not have to retrieve my ropes over 90 degree edges and rough terrain... so for me, the risks of the EDK outweigh the merits.

Do you (Alpineer) use the EDK to join your absail ropes?

I'll leave off with quoting ashley's description of #1410 (my italics):

"It is used in joining the ends of rope ... by which hams ... and bananas are hung."  ;)

alpineer

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Re: Offset joining knots (abseil / rappel)
« Reply #91 on: December 28, 2015, 11:11:23 PM »
I didn't find if (or where) Ashley describes #776 as a flat bend... with standing legs splayed, rather than parallel.  Now that I've played a bit more with this loading of this knot, I see that it capsizes into a form very similar to the Ashley bend (ABoK #1452).
 

I don't think you'll find Ashley describing #776 as a flat bend. As you noted, and show the result in your photo, when loaded in an offset (off-axis) manner #776's form is transient. The resultant knot is none other than ABoK #1409.     


Do you (Alpineer) use the EDK to join your absail ropes?

Yes, I do, backed up - using the appropriate strand - with a single Fisherman's tight up against the twinned OH's.

 

 
« Last Edit: December 29, 2015, 12:25:03 AM by alpineer »

knot rigger

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Re: Offset joining knots (abseil / rappel)
« Reply #92 on: December 29, 2015, 01:44:06 AM »

The resultant knot is none other than ABoK #1409.     


Indeed! I sure missed that one! The education is appreciated.


Do you (Alpineer) use the EDK to join your absail ropes?

Yes, I do, backed up - using the appropriate strand - with a single Fisherman's tight up against the twinned OH's.


In the interest of my continued education, could you elaborate on your backing up of the EDK.  Which is the appropriate strand? By "single fisherman" you mean an overhand tied with one tail, around the other tail?  This back-up mitigates the risk of the EDK rolling down the tails?  Do you then tie it with shorter tails? Or still on the order of 18 to 24 inches?

Thanks for humoring my EDK ignorance :)

alpineer

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Re: Offset joining knots (abseil / rappel)
« Reply #93 on: December 29, 2015, 04:36:13 AM »
https://www.mountainproject.com/v/joining-unequal-diameter-ropes-for-rappel/108214858

Rgold's third "Secured" photo shows what I do (applies to same diameter ropes), noting that the tails were tied short to keep them in the picture frame. I like my tails at least 18" (45cm) long before tying the single Fisherman's backup, which I tie in the same direction as the twinned OH's (not opposite as shown in the photo).

 
   
« Last Edit: December 29, 2015, 09:36:43 AM by alpineer »

Dan_Lehman

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Re: Offset joining knots (abseil / rappel)
« Reply #94 on: December 29, 2015, 05:31:53 AM »
a flat overhand
Please do knot nomenclature a big favor and
REJECT "flat" as an acceptable modifier in this
knot moniker.  (Oh, yes, I know that it's already
out in common parlance; but such things can be
drowned out, especially with an apt modifier, "offset"!)

--dl*
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Dan_Lehman

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Re: Offset joining knots (abseil / rappel)
« Reply #95 on: December 29, 2015, 06:50:28 AM »
I don't think you'll find Ashley describing #776 as a flat bend.
That is, per my remark above, perfectly acceptable;
to so describe it would be flat out objectionable!   ;D

Quote
As you noted, and show the result in your photo, when loaded in
an offset (off-axis) manner #776's form is transient.
The resultant knot is none other than ABoK #1409.     
1) That's not a happy resulting (from flype) knot,
and more importantly,
2) recall (w/vigor!) my note some years back (which you
rightly applauded --and, ack, to learn such things by chance!)
that I had similarly adopted one of Ashley's "lanyard knots"
(#781) qua offset end-2-end knot and found that en route
to flyping into sure-&-sound #1452 it actually spilled ! ! !
  whooOOOPS!   :o
(I.e., it could --and did-- spill, in those particular ropes;
although it could work and flype into Ashley's bend #1452.
The "failure mode" of (complete) flyping was expected/known;
the "partial flyping" that led to spilling was a surprise, and one
I'd not know how to test for!)

(Now, the frightening thing to consider here is how
we learned of this --my simple stressing in some ropes
fortuitously amenable to the vulnerability--,
and not by some considered, reasoned, deliberate
testing!  --an unknown unknown becoming known.
Can other flypings yield such potentially lethal behavior?)

Quote
Do you (Alpineer) use the EDK to join your absail ropes?

Yes, I do, backed up --using the appropriate strand--
with a single Fisherman's tight up against the twinned OH's.
Egadz, arborists utter such a misnomer, but for a rockclimber
to do so amazes me!!  (For we should all know by now
from Knots 101 that the named knot is an end-2-end
knot composed of (single) overhands --the component
knot that you use to tie off the offset water knot !)

Quote
I like my tails at least 18" (45cm) long.
Goodness, Grandmother, what long tails you have!!!
Kinda blows the claim of confidence in the chosen knot,
doesn't it --just as it did for the original (unadorned "EDK") :
"Oh, perfectly dandy,
 just have a furlong of tail and good life insurance!"


--dl*
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alpineer

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Re: Offset joining knots (abseil / rappel)
« Reply #96 on: December 30, 2015, 07:46:04 AM »
Egadz, arborists utter such a misnomer, but for a rockclimber
to do so amazes me!!  (For we should all know by now
from Knots 101 that the named knot is an end-2-end
knot composed of (single) overhands --the component
knot that you use to tie off the offset water knot !)

Ouch! Yes. You are correct to point out my error. I have always referred to the knot as an OH. Though, in that moment my thinking was Fisherman's. And... adding my own insult to injury, even stating my error incorrectly (should've been Half of a Single Fisherman's ;D).
« Last Edit: December 30, 2015, 07:53:46 PM by alpineer »

alpineer

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Re: Offset joining knots (abseil / rappel)
« Reply #97 on: December 30, 2015, 08:41:35 AM »
(Now, the frightening thing to consider here is how
we learned of this --my simple stressing in some ropes
fortuitously amenable to the vulnerability--,
and not by some considered, reasoned, deliberate
testing!  --an unknown unknown becoming known.
Can other flypings yield such potentially lethal behavior?)

Hence, my comment re not inspiring confidence.

alpineer

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Re: Offset joining knots (abseil / rappel)
« Reply #98 on: December 31, 2015, 02:14:02 AM »
Goodness, Grandmother, what long tails you have!!!
Kinda blows the claim of confidence in the chosen knot,
doesn't it --just as it did for the original (unadorned "EDK") :
"Oh, perfectly dandy,
 just have a furlong of tail and good life insurance!"

This is the 2nd most stupid thing you've said on this forum. You know the 1st.
« Last Edit: December 31, 2015, 07:14:52 AM by alpineer »

DerekSmith

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Re: Offset joining knots (abseil / rappel)
« Reply #99 on: January 04, 2016, 09:25:30 PM »
Mark,

I have only quickly scanned these seven pages of posts, and so have to ask - have you considered the Carrick Bend?  It meets your four 'knot requirements' and translates well over an edge.

Any thoughts?

Derek

knot rigger

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Re: Offset joining knots (abseil / rappel)
« Reply #100 on: January 05, 2016, 07:08:03 AM »
Goodness, Grandmother, what long tails you have!!!
Kinda blows the claim of confidence in the chosen knot,
doesn't it --just as it did for the original (unadorned "EDK") :
"Oh, perfectly dandy,
 just have a furlong of tail and good life insurance!"

This is the 2nd most stupid thing you've said on this forum. You know the 1st.

Makes me wonder what the 1st most stupid thing DL has said on this forum is ;)

I can see DL's point, both long tails and a locking overhand seem a bit of a "belt and suspenders" approach to improving security of the EDK.  Isn't the point of the added overhead to prevent the body of the knot rolling down the tails in overload or shock loading?  If it's doing it's designed job, why do you still need the long tails?

On the other hand, one uses the EDK because there is no other knot that rides over an edge as well.   So when using it, you're accepting the drawbacks of lower strength and security in favor of the positive (and necessary) feature of easy rope retrieval.  Under those circumstances, it seems entirely reasonable to employ redundant added safety measures to the basic EDK.

belts and suspenders be damned ;)

cheers
andy
« Last Edit: January 05, 2016, 07:09:26 AM by knot rigger »

Dan_Lehman

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Re: Offset joining knots (abseil / rappel)
« Reply #101 on: January 05, 2016, 10:13:12 PM »
Goodness, Grandmother, what long tails you have!!!
Kinda blows the claim of confidence in the chosen knot,
doesn't it --just as it did for the original (unadorned "EDK") :
"Oh, perfectly dandy,
 just have a furlong of tail and good life insurance!"

This is the 2nd most stupid thing you've said on this forum. You know the 1st.

Makes me wonder what the 1st most stupid thing DL has said on this forum is ;)
Indeed, you're not alone (but if it's as "stupid" as this,
there must be lots!  ;)  ).

Quote
I can see DL's point, both long tails and a locking overhand seem a bit of a "belt and suspenders" approach to improving security of the EDK.  Isn't the point of the added overhead to prevent the body of the knot rolling down the tails in overload or shock loading?  If it's doing it's designed job, why do you still need the long tails?
Exactly!  In a sense, one does have long tails,
it's just that they are engaged into the knot --well,
the material is, and thus is no longer "tail".
.:.  Rather than having lots of (mere) material, I say,
DO something with it!  And we can do things that
obviate the need for such dubious safety (i.e., if they
are to take up "rolling"/"flyping", whose to say that
such action doesn't just repeat-until-tails-run-out?!
(Tom Moyer's testing has some cases where one could
wonder, with the offset fig.8, IIRC --the 8 distinguishing
itself by consuming much material per flype vs. overhand.)

Quote
On the other hand, one uses the EDK because there is no other knot that rides over an edge as well.   So when using it, you're accepting the drawbacks of lower strength and security in favor of the positive (and necessary) feature of easy rope retrieval.
Here we should reject "lower strength" : it is equally
strong --won't break-- under the target circumstances.
Now, stability & security, well, that's our focus for improvements,
and I think we have various solutions (of which the offset
fig.9-Oh
is perhaps the most effective-efficient and the
EDK-backed-up-EDK the most error-proof (resisting
three errors : wrong orientation of mis-matched ropes per
thick/thin; poor dressing-&-setting; and spacing between
the main & back-up/"safety" knots.  (I.e., I think that even
badly oriented, loosely/carelessly set, and spaced-apart knots
might still come to hold (the first roll might do much for the
main knot's initial looseness!) --but I've never tested this
conjecture.)
Btw, I was not a fan of the latter knot at first
--as it lacked the cleverness of more efficient ones--,
but I come to realize that error-proofness of it
and simplicity to learn & tie are significant pluses
(where the knot tyers are not experts and might be
under duress of poor & worsening conditions).

Mobius, perhaps you could run that EDK again with
both a snugged-close-to-it back-up and a spaced-apart
one, and see how they fare in such hard-to-hold cord
that has so far defeated the knot quickly!?
(We should be prepared to view w/some doubt results
that seem okay --rolling onto back-up and then ...
holding-- as possibly lucky ones, with rolling ... being
something maybe of such potential variety that one
success might not indicate any surety of success!)




--dl*
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agent_smith

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Re: Offset joining knots (abseil / rappel)
« Reply #102 on: January 06, 2016, 02:05:10 AM »
Quote
have you considered the Carrick Bend?
Yes

Quote
It meets your four 'knot requirements'
  Perhaps in other applications... but I am not convinced in the case of using it to join 2 ropes together in preparation for an abseil descent. On the requirement of 'ease of tying', 'footprint', 'verifiable' and 'security' (slack shaking security).... the problem I have with #1439 is that it 'capsizes' into its final form - and you first have to get the over-under-over sequence started correctly. Its footprint is larger than #1410. As for verifiability - if you know what you're looking for fine - but, most climbers aren't like IGKT members - they use knots simply as tools and dont care for the details/science (sort of like some people dont care whats inside a PC and how all the components plug in, function and perform... they just want to press the 'on' button' and use social media). There is a lot to be said for the simplicity of #1410!

Quote
and translates well over an edge.
No, it does not.

#1439 (Carrick bend) is not 'offset' and therefore it does not present a uniform 'flat underside' surface when translating around a 90 degree edge. Note that I am careful with the the term 'flat'. For example, #1410 Offset overhand bend aka 'EDK' is not 'flat' or 'one sided'. There are numerous posters on the internet referring to #1410 as being 'flat' or 'one-sided' knot... and they are all using laymans terms to try to describe what they see.

...

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.

Dan will probably bark at my 'loose' use of the 'choking' descriptor.

PS... I just had a vision of creeping past a large guard dog called Dan    he growls as I sneak past - but the growling gets deeper and louder  :o
« Last Edit: January 06, 2016, 02:09:15 AM by agent_smith »

Dan_Lehman

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Re: Offset joining knots (abseil / rappel)
« Reply #103 on: January 06, 2016, 06:09:43 AM »
WOOF!!

.... the problem I have with #1439 is that it 'capsizes' into its final form
 - and you first have to get the over-under-over sequence started correctly.
Not so, and with very stiff ropes, it's not tied
in this way by the Alaska crabbers (reportedly)
--which by one glimpse of "Most Dangerous Catch"
t.v. show, I saw using a method I'd read of in KM
by Pieter van de Griend :: one man formed a sort of
crossing-hitch in one line while another reeved
the other end through this structure.  (I don't know
whether they tape the tails for added security.)
BUT, tying this way allows more variation than the
two that can arise --which look so alike-- by the
lattice-capsizing method you refer to.

One climber opines that the wrong-way version of
the two can all too easily spill (where tails/SParts
of the joined ends lie on the same side, not at
diagonal positions).

Quote
Quote
and translates well over an edge.

No, it does not.
I concur in this.  (And, if it did, then why note
choose the more solid #1452 which is similar!?)

Quote
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.

Dan will probably bark at my 'loose' use of the 'choking' descriptor.
Well, I believe that you have a couple variations,
and in the first/older one this "choking" turn wasn't
--it came later along--; then you got one in which
the turn lies fully, properly at the point of actual choking;
and this variation is much akin to the offset 9-Oh.

Dan has presented the nice images of the offset 9-Oh
ARJ knot and Mobius had put to the tough test in his
uncooperative cord (in which the offset water knot fares
so poorly, despite it's good job in climbing rope),
and there --yes-- it is a full "choking" turn that
gives surety to the knot's resisting being pried open.


--dl*
====

Mobius

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Re: Offset joining knots (abseil / rappel)
« Reply #104 on: January 08, 2016, 05:58:43 AM »
I am conducting research into knots for joining 2 abseil ropes together (eg for retrievable abseil system) - with the eventual aim of authoring a paper.

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.

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.

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).

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.

And Dan said:

Quote from: agent_smith
Dan will probably bark at my 'loose' use of the 'choking' descriptor.

Quote from: Dan
Well, I believe that you have a couple variations,
and in the first/older one this "choking" turn wasn't
--it came later along--; then you got one in which
the turn lies fully, properly at the point of actual choking;
and this variation is much akin to the offset 9-Oh.

Dan has presented the nice images of the offset 9-Oh
ARJ knot and Mobius had put to the tough test in his
uncooperative cord (in which the offset water knot fares
so poorly, despite it's good job in climbing rope),
and there --yes-- it is a full "choking" turn that
gives surety to the knot's resisting being pried open.


--dl*
====

I will probably trial out Dan's 9-oh (and my own knot) in the best climbing materials available in a few weeks. I am on holiday for 2 more weeks, then 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 ;)

Cheers,

mobius
« Last Edit: January 08, 2016, 06:01:49 AM by mobius »