Author Topic: Variation of ABOK #1410 - Offset knot for rappelling (shemlock knot).  (Read 829 times)

shemseger

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A few years ago I started experimenting with tying offset knots for rappelling in an effort to discover a new knot that would inspire more confidence than the dubious "Euro Death Knot" (EDK) which is a flat overhand (ABOK #1410) used to join two ropes at the end for rappelling/abseiling.

After rediscovering several knots already established in Ashley's book, I eventually came up with a variation of #1410 that is a pairing of a single overhand, and a double overhand. It's not that much of an upgrade from a flat overhand, but it feels much more secure than the EDK. I shared it on another outdoor site about two and a half years ago (https://outdoors.stackexchange.com/questions/9356/whats-this-knot-called), and was just recently introduced to the IGKT. I've searched this forum a bit and found feeds for pairings of other knots, but was unable to find one for this particular pairing.

I've been using this knot for a couple years now, joining ropes for rappelling and tying abalakovs. I've shared it with members of my chapter of the Alpine Club of Canada (ACC), and they've dubbed it the "Shem-lock". I was thinking of submitting it to the ACC's newsletter, the Gazette, but would like to determine whether or not this is already an established knot before I do.









« Last Edit: March 26, 2018, 07:27:37 PM by shemseger »

knotsaver

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Re: Variation of ABOK #1410 - Offset knot for rappelling (shemlock knot).
« Reply #1 on: March 26, 2018, 08:04:55 PM »
Hi shemseger and welcome,
have you already read Mark Gommers' (aka agent_smith) document at
http://www.paci.com.au/knots.php
(at #3) ?
(you can find the discussion here
http://igkt.net/sm/index.php?topic=5896.msg40669#msg40669)
In particular look at page 23: the variation by Mark is the "same" knot dressed with a different geometry. I don't know which "geometry" performs better.
[edit]
You can find the knot shown here
http://igkt.net/sm/index.php?topic=5508.msg37378#msg37378


there you can find an OHBend choked lower too

[/edit]
Hope this helps and  Mark replies soon.
Ciao,
s.
« Last Edit: March 26, 2018, 11:02:40 PM by knotsaver »

shemseger

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Re: Variation of ABOK #1410 - Offset knot for rappelling (shemlock knot).
« Reply #2 on: March 26, 2018, 11:47:10 PM »
Hey Knotsaver, that's a cool document, and that knot is significantly similar, though there are enough differences I think they could be considered two different knots. Mark's knot has the double-overhand dressed differently, my knot has the double-overhand dressed as you would in a double fisherman's, and it chokes the two strands of rope before passing through the single-overhand, which appears to me at least to choke the ropes a lot better, preventing the knot from spreading as much. I'd be interested to see if there are advantages to one variation over the other. I'd also be interested to know when Mark developed his variation, I imagine it was some time prior to publishing his study. I hope he weighs into the discussion, and I'm going to spend some time reading that other feed, thanks for sharing.

« Last Edit: March 27, 2018, 03:43:14 AM by shemseger »

Dan_Lehman

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Re: Variation of ABOK #1410 - Offset knot for rappelling (shemlock knot).
« Reply #3 on: March 28, 2018, 01:16:59 AM »
Mark's knot has the double-overhand dressed differently,
my knot has the double-overhand dressed as you would in a double fisherman's,
and it chokes the two strands of rope before passing through the single-overhand,
which appears to me at least to choke the ropes a lot better,
preventing the knot from spreading as much.
And this was my thinking, too, having developed solutions
the this rope problem like yours.  BUT, I've slowly come to
see that Mark's later added tuck of the tail works well as a
*lock* on that tail pulling out --drawn out by the forces
against it choking (just as it would were it tied off in an
overhand knot around the other tail.

The full turn of the choking strand does as you say, makes
a stronger choke.  The simplest way to implement this is
in what I've named the "offset 9-Oh", where the first
term is an adjective indicating the general nature of what
one desires in an abseil-ropes-joining knot --being offset
from the axis of tension.  (No, it is NOT "flat" --lousy term,
though popular (but then so is "half a dbl.fish." where "strangle
knot" should be)).

I think that this gets you to an image :
https://igkt.net/sm/index.php?action=dlattach;topic=5555.0;attach=20150;image
and this to the related thread:
https://igkt.net/sm/index.php?topic=5555.0

Franz Baochmann & I think also Heinz Prohaska have suggested
using an offset grapevine bend; this also gets that strangle
knot
choking, but need not top it with another full strangle
when a mere overhand works.

I've come around to recognizing that the --to coin a name--
"EDK-backed EDK" which Needlesports promoted (about
a decade & half? ago), though clumsy looking, is a simple
and effective way to guard against mistakes, as I think
it can suffer various imperfections of dressing/tying and
still hold.  --in contrast to the more clever knots that
require making the right tying decisions at various points.

--dl*
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Dan_Lehman

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Re: Variation of ABOK #1410 - Offset knot for rappelling (shemlock knot).
« Reply #4 on: March 28, 2018, 01:22:40 AM »
I've been using this knot for a couple years now,
joining ropes for rappelling and tying abalakovs.
Ha, I had to Google that term!
From the image in Wikipedia about the structure shown here:
https://en.wikipedia.org/wiki/Abalakov_thread#/media/File:Abalakov_thread.jpg
I'd expect THIS offset water knot to just walk right out
... to oblivion ! ! !  (But, where there a back-up EDK, even so
poorly dressed, it would arrest the rolling, and then that
would be seen as clever force mitigation vs. lousy tying!

 ;)

shemseger

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Re: Variation of ABOK #1410 - Offset knot for rappelling (shemlock knot).
« Reply #5 on: March 28, 2018, 03:38:56 AM »
I'd expect THIS offset water knot to just walk right out
... to oblivion ! ! ! 

The knot's not the only thing going wrong in that picture. The biggest concern is his choice of ice, you want to drill in recesses in the ice, not on bulges. The next concern is you don't want to place your abalokovs near other drill holes. If you don't succeed drilling your holes on your first try you need to pick a new patch of ice. Lastly, but this is just being picky, abalokovs are stronger when the holes are one over top of the other vertically (A-thread) as opposed side by side horizontally (V-thread).   

So you're calling a 1410 choked below the knot with an extra wrap an offset 9-0h? I'm curious; when did you develop this knot? The feeds shared so far were started coincidentally only a couple weeks after I first shared this knot online: https://outdoors.stackexchange.com/questions/9356/whats-this-knot-called. No doubt we both independently developed this knot, but for vanity purposes I'd be interested to know who came up with it first  ;) mostly so I can continue sharing it as the Shemlock ;D.

As an aside, you may be interested to know that the Alpine Club of Canada has promoted the use of an appropriately sized link of steel chain below the 1410, to act as a choke and prevent the knot from spreading.
« Last Edit: March 28, 2018, 03:40:11 AM by shemseger »

agent_smith

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Re: Variation of ABOK #1410 - Offset knot for rappelling (shemlock knot).
« Reply #6 on: March 30, 2018, 03:45:16 AM »
Quote
As an aside, you may be interested to know that the Alpine Club of Canada has promoted the use of an appropriately sized link of steel chain below the 1410, to act as a choke and prevent the knot from spreading.

I would advise the Canadian Alpine club to run some load tests of the offset overhand bend (#1410) and observe that under nominal loads of 1 person - the knot remains stable.
People seem to forget this small but crucial question...how much load is actually being applied to #1410?
In a worst case scenario, such as in a rescue, you could reach loads up to around 2.5kN (approx 250kg).
Even at this load, the knot remains stable.

I have asked Alan Lee to investigate the load threshold which triggers instability - but something has happened and the testing has stopped? I hope that Alan can regroup and get this important testing done asap.
What we are also wanting to investigate is the effect a simple 'rotation' has on the stability of #1410. This is something that Dan Lehman had been an advocate of for quite some time (several years ago?). Nobody has bothered to investigate this! The question is; Why? If Alan Lee can test the effects of rotation - this could be a world first...

My suspicion is that instability is triggered in the vicinity of 5kN (but this is only a hunch - I need to see the evidence).

Quote
A few years ago I started experimenting with tying offset knots for rappelling in an effort to discover a new knot that would inspire more confidence than the dubious "Euro Death Knot" (EDK) which is a flat overhand (ABOK #1410) used to join two ropes at the end for rappelling/abseiling.
I wish you would refrain from the totally incorrect use of the term 'flat overhand'. It is not flat.

Quote
I've been using this knot for a couple years now, joining ropes for rappelling and tying abalakovs. I've shared it with members of my chapter of the Alpine Club of Canada (ACC), and they've dubbed it the "Shem-lock". I was thinking of submitting it to the ACC's newsletter, the Gazette, but would like to determine whether or not this is already an established knot before I do.

The concept isn't new. As knotsaver has already pointed out - I had tied and experimented with multiple variations of this structure. I dismissed it as a dead-end street because ultimately, it is defeating the very heart and sole (or purpose) of #1410.
And that purpose is (in a word) 'simplicity'.

This is why I devised my simple solution of adding one extra turn of a rope (refer to my offset knots paper and also attached image).
I also experimented with a 'wrapped' #1410 where I had the idea of a prusik hitch and wanted to somehow translate that into an offset rope joining knot (see attached image).

So I have come to the inescapable conclusion that if the rope joining knot isn't elegantly simple, it will never develop legs and gain mainstream popularity. So future efforts and work should concentrate on simplicity.

Mark G

EDIT: images altered to fit within 100 KB limit
« Last Edit: March 30, 2018, 03:57:16 AM by agent_smith »

Dan_Lehman

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Re: Variation of ABOK #1410 - Offset knot for rappelling (shemlock knot).
« Reply #7 on: March 30, 2018, 09:21:18 PM »
So you're calling a 1410 choked below the knot with an extra wrap an offset 9-0h?
I'm calling the fusion of a Fig.9 + OverHand knots loaded
in the offset manner (such that the 9 is loaded on the usual
end, not the other --THIS version is asymmetric (there are
symmetric versions)), that, with the choking knot getting
first mention.

Quote
I'm curious; when did you develop this knot?
... No doubt we both independently developed this knot,
but for vanity purposes I'd be interested to know who came up with it first  ;)
mostly so I can continue sharing it as the Shemlock ;D.
I think I has such knots prior to the 2004 publishing of
Clyde SOLES's Outdoor Knots book (on which I had a hand),
but Google will find the RC.com posts at 2009, at least,
so it was prior that.

Quote
As an aside, you may be interested to know that the Alpine Club of Canada has promoted the use of an appropriately sized link of steel chain below the 1410, to act as a choke and prevent the knot from spreading.
I think that this is a bad idea.  They should teach the
proper tying, and if in doubt, the back-up overhand
which suffers all sorts of indignities --while the more
material-efficient and maybe simpler ways do require
making the right choices,
but merit teaching too.  NOT taking extra (and fiddly!)
hardware along!

BTW, not sure that the link would assuredly prevent
>>> cyclical loading's ratcheting out material <<<
--which is NOT something break testing will show,
and which is much a YMMV per materials & forces thing.


--dl*
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