Author Topic: Joining Ropes for a Rappel  (Read 10448 times)

IPAtch

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Joining Ropes for a Rappel
« on: June 07, 2013, 05:59:07 AM »
First some history:

The Euro-Death Knot (EDK), ABOK 1410 is commonly used to join 2 ropes for rappelling (abseiling). It may be weak, but the forces generated while rappelling are typically very low, so it isn't a problem and its shape makes it unlikely to snag when retrieving the rope, making this knot one of the safest options (there are few common problems more difficult and potentially dangerous to deal with than a stuck climbing rope). It does have the disadvantage that it could capsize, and if it repeatedly capsizes, come undone. This is very unlikely, but some recommend tying a second as a backup and to prevent repeat capsizing. This works but increases the likelihood of the rope getting caught, by adding bulk to the knot and making it top heavy, so many climbers prefer to just leave long tails, which also increase the likelihood of it catching, though less so.

One solution proposed was to add an extra turn (I wish I had thought of this first, though I did come to it independently, and then found it at in the following document online, see clippings 1 and 2 if you dont want to read the whole thing, though its interesting and worth reading, and notice in clipping 2 how the shape of the knot helps it deal with corners/ledges)

http://www.paci.com.au/downloads_public/knots/01_Knots.pdf password thankyou if it asks for one

I have yet to use this new knot in the field, and until now have used the EDK, leaving long tails without a back up, because I have gotten into some sketchy situations trying to retrieve stuck ropes and now do everything feasible to prevent getting into these messes.

This knot looks like a great solution, but I can't help myself, so when I was reading:

http://www.paci.com.au/downloads_public/knots/21_Book_Ropeanditsuses.pdf

and looking at the strange method for tying the alpine butterfly (lineman's rider in the document, clipping 4), I tied it a few times, and thought, who would ever use this method, why not modify this to use it as a bend? It produced an abnormally loaded butterfly; what would normally be the loop strands were both standing ends, what would normally be the standing parts were the bitter ends. I took a picture of it tied in different colors of paracord, not the best picture I know but notice the shape looks like it would have the advantages of the EDK for negotiating ledges, but is an alpine butterfly.

Any thoughts or opinions? I am going to start trying it out in different climbing ropes to see how it behaves, obviously well before hanging my life on it. Any one see any problems? Keep in mind that the EDK is right now one of the best options available, if you want to explore that, start a new thread or go find one of the many out there, it is a hot topic for debate, but I don't want to focus on that here.

My hypothesis about the abnormal butterfly (AB) vs the EDK breaks down as follows:

Downsides:
-Tying the AB is more difficult and time consuming, even though this is a knot that many climbers are familiar with, most would have to learn this new method of tying and would need to be able to check it too
-Possible to end up with the less secure false butterfly, though I am not sure the knots would perform all that differently, as the knot is loaded in a way that prevents the false butterfly from its typical pattern of failure

Same:
-both have same profile for sliding over ledges... or at least it it looks like they do
-Typically untying the EDK isn't an issue, though the AB may have a mostly theoretical advantage here

Upsides:
- AB is less likely to Capsize... I think (is it possible for it to capsize? and does the EDK ever capsize in real world use?)
- AB is stronger....? This could be important in emergency rescues, or might make this of interest to the SAR community
- No need for a back up knot or very long tails...? if so, the AB might be less likely to get stuck, which is the main advantage of the EDK

Unknown:
-Security. Could the AB work itself undone?

I will probably throw this up on climbing/guide/SAR forums but thought I would start here.  Thanks!


roo

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Re: Joining Ropes for a Rappel
« Reply #1 on: June 07, 2013, 06:40:28 AM »
The Euro-Death Knot (EDK), ABOK 1410 is commonly used to join 2 ropes for rappelling (abseiling). It may be weak, but the forces generated while rappelling are typically very low, so it isn't a problem and its shape makes it unlikely to snag when retrieving the rope,
Not so fast.  Knots like these tend to be absolutely huge, making them more likely to act like a stopper knot on crevices, branch forks, etc.

Anyway, with regard to ring loading a Butterfly Loop, I think others have found that the knot form can suddenly capsize into a standard Butterfly Bend form.  I just confirmed this response with various types of smaller line.  You may want to search this forum for a discussion of it, assuming it wasn't lost, as some older posts have evaporated.
« Last Edit: June 07, 2013, 06:58:01 AM by roo »
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Dan_Lehman

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Re: Joining Ropes for a Rappel
« Reply #2 on: June 09, 2013, 05:44:15 PM »
To my mind, the simplest solution to the long-standing
use of the "EDK" is to redress the need/advice "to use
long tails" --which is hardly a reassuring bit of advice,
and the condition shouldn't be needed.  To this end,
I recommend either making the extra turn with the tail
shown in the PACI image (blue rope, i.e.) (though my
revision is to do this prior to tucking it out through
the loop), or tying off this tail around the other with an
overhand knot --it's this tail that needs stopping,
so to prevent the knot from being pried open and flyping
(rolling); so, tying an entire 2nd "EDK" as a back-up is
material inefficient.

You can read much more analysis of the "EDK" issues here
(images of Offset 9-Oh, 8-Oh, & orientations of stoppered OWK/EDK):
www.rockclimbing.com/cgi-bin/forum/gforum.cgi?post=2091962;search_string=offset%20fig.9;#2091962

I strongly advise against using your reversed buttefly bend,
as it too might be vulnerable to a biased capsizing in which
one rope's part distorts ahead of the other's (consider that
one is often joining dissimilar ropes : thinner/thicker,
flexible/stiffer), and the knot spills, not taking on the
secure, if no longer offset, form of the butterfly --this is
a result I accidentally discovered (thankfully!) when using
the similar reversal of Ashley's bend #1452, which is like
the butterfly (but symmetric).


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James Petersen

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Re: Joining Ropes for a Rappel
« Reply #3 on: July 21, 2013, 12:45:54 PM »
I have never climbed, but several years ago I became interested in this problem. One option I came up with was to start with the overhand knot and then bring the working ends back through the knot, over themselves, but under the standing end where it has just entered the knot. The pictures are clearer.

In my limited experimentation with this knot in small lines, it doesn't seem to exhibit the less-than-desirable behavior of the EDK, which does spill rather often before it jams. (I generally test the lines to failure, which may not be relevant to mountain/rock climbing.) I would be interested to hear the findings of other forum members with this knot.

SS369

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Re: Joining Ropes for a Rappel
« Reply #4 on: July 21, 2013, 04:24:20 PM »
Hello James, nice tying.

I have just tried this configuration out using static BW ProTac in 10.5mm. It works well, draws up nicely, addresses the requirement of an easy-to-go-over an edge (tails arrange themselves to 90 degrees perpendicular to pull) and after loading to my hard bounced weight, it was easy to untie.

Not a bad bend at all. Thank you.

Rock climbers don't test their ropes to failure generally (it has happened though), but we hope that someone has! In a facility.

SS

James Petersen

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Re: Joining Ropes for a Rappel
« Reply #5 on: July 21, 2013, 04:45:55 PM »
I neglected to mention in the original post that the topology of this knot is the same as the bowstring knot (ABOK #151). The loading and use are obviously different -- I have taken to calling it the "life knot."

Dan_Lehman

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Re: Joining Ropes for a Rappel
« Reply #6 on: July 21, 2013, 04:49:53 PM »
Hello James, nice tying.

I have just tried this configuration out using static BW ProTac in 10.5mm.
Though we need keep in mind that often the joined
ends will be of a different nature --by diameter, stiffness,
flexibility, or elasticity.

Quote
(tails arrange themselves to 90 degrees perpendicular to pull)
The knot can be set to orient the tails over the
range of approximately 180degrees; this can be
done after (even during, and manually) modest loading.

Of James's image, the ends can be pulled up/down,
fore/aft, or aft/fore, resp. of upper,lower strands.


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knot4u

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Re: Joining Ropes for a Rappel
« Reply #7 on: July 21, 2013, 11:18:21 PM »
-both [butterfly and EDK] have same profile for sliding over ledges... or at least it it looks like they do

Really?

Dan_Lehman

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Re: Joining Ropes for a Rappel
« Reply #8 on: July 22, 2013, 07:57:48 PM »
-both [butterfly and EDK] have same profile for sliding over ledges... or at least it it looks like they do

Really?

NOT really; maybe surperficially.
The former's eye (or tails for end-2-end knot) stands
perpendicular to the axis of tension, yes; but the
knot isn't offset from this axis as is the latter,
where the two ends confront each other and there
go off into the knot/nub.  The former, in contrast,
has collars around these parts which can abut
surface elements and impede rope flow.


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knot4u

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Re: Joining Ropes for a Rappel
« Reply #9 on: July 29, 2013, 09:34:46 PM »
In IPatch's pic, does the lower working end (blue rope here) always do the loop around?  Or can the upper working end (yellow rope) do the loop around instead?
http://igkt.net/sm/index.php?action=dlattach;topic=4411.0;attach=10841;image


In James Peterson's pic, is that just a Double Overhand?
http://igkt.net/sm/index.php?action=dlattach;topic=4411.0;attach=11501;image

Never mind.  No it's not a Double Overhand.  This exploration makes me think there has got to be a widely accepted improvement to the EDK.  However, are rappellers willing to try something new?  Are there any rappellers who have used these improvements?
« Last Edit: July 30, 2013, 06:13:08 AM by knot4u »

Dan_Lehman

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Re: Joining Ropes for a Rappel
« Reply #10 on: July 30, 2013, 06:36:52 PM »
In IPatch's pic, does the lower working end (blue rope here) always do the loop around?
Or can the upper working end (yellow rope) do the loop around instead?
//
This exploration makes me think there has got to be a widely accepted
improvement to the EDK.  ... Are there any rappellers who have used these improvements?

It's pretty simple, except in requiring understanding
of the knot & its dynamics --understanding being not
so simply depended upon.  Since we're concerned here
with abseiling, let's try a contrived case involving this,
sort of.

Consider a flag-pole painter who is painting it from the
top, downwards, slowly rappelling (i.e., short lower then
lock-off to paint; repeat); and we see some prankish kids
or maybe it's a playful dog ... take hold of the end of his
line and start to run away with it.  You go quickly to
the pole and hug it & line, to keep the line straight
along the pole; I "second your opinion" and likewise
wrap my arms around line & pole, right above you.
Now, when that line is pulled, YOU --but not I--
will feel its tug hard against your hugging arms.
Only as you yield a bit will such forces bear upon me.

This is the aspect of the twin turns of the "EDK"
where the SParts enter : only the "outer" one will
be resisting the pull to pry open the knot, until it
yields and then ... .  So, the key to this knot's
security/stability is resisting this prying-open
effect by securing this outermost turn.

The solution best comes in two *steps* with actual
abseiling, recognizing that the joined lines are often
of different natures --a thin and more flexible "haul
line" joined to a climbing rope, or two of the latter
where flexibility & diameters differ.  So, a first step
is to orient the knot so that the thinner & more
flexible --let's hope we don't need to choose between
these characteristics(! :: if so, "flexible enough" will
be fine to let the thinner one do the work)--
should be the one that does the "choking"/binding/
securing of the knot.  For it should be harder to
pry a thin line out & around a thick one than
vice versa(!); and a more flexible line should be
able to be more tightly set.

The 2nd "step" to orienting different ropes is the
actual knot.  The simplest solution IMO is to tie
the offset water knot / EDK AND THEN tie off
the choking line's (should be thinner...) tail around
the other tail with an overhand knot set snug against
the main knot --which stopper will prevent material
from being pried out and opening the binding turn.

What Agent_Smith shows with his extra turn in the
outer (blue) line is an additional turn within the nub,
which should also help resist the prying effects.  I've
argued with him, though, that this extra turn is best
made at the throat/choke-point (*all-at-once*), and
then the tail traces the twin (yellow) tail in the final
tuck.  I think this full/"round" turn makes a sure nip,
and with a closed helix vs. the slightly opened one of
his knot ("open" by having the thicker yellow rope
come between the overlapping parts of the blue).


As for testing : consider the forces that are expected
to be handled --not just anything, in all sorts of sizes
and types of cordage, but specifically YOUR OWN body
weight on YOUR OWN cordage (and with some reasonable
estimate of effects of like weight & cordage).  People can
make effective tests, IMO, by simply hanging and bouncing
upon a typical abseil set up, or by exaggerating forces
by doing so on just the single, knotted lines, or even
by making a crude 2:1 pulley with a 'biner and roughly
doubling those already doubled (via single line) forces.
I.e., one expects the knot to see half of the rappeler's
weight, and with simple means, one can impart up
to four times this force.
.:.  We do NOT need BREAK TESTS for this knot!!!
.:.'  And climbers should see how THEIR PARTICULAR ROPES
behave, not relying solely upon someonElse's testing.

Much of this is laid out already in the posts cited by the
URLink in my reply (#2) above.  These include showing
how the knot can assume orientation across about a
180deg range of rotating the knot as though a dial.


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NotSure

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Re: Joining Ropes for a Rappel
« Reply #11 on: August 13, 2013, 07:05:27 PM »
I'm new here and love you guys for all the great info you've shared (I've been lurking for quite a while).

This is an interesting topic that I haven't really considered until now (specifically, having a smooth side on the knot for gliding over a ledge).

James' idea of the doubled up bowstring/honda knot for this application is fantastic, and got me thinking that a simple slip knot loop would do the same thing. Just tuck the working ends back through the doubled slip loop before cinching it up for added security (and form the slip loop opposite that of the Ashley stopper so that the working end does the cinching instead of the standing end. That way it will be virtually free from jamming). 

It's faster and easier to tie (I use the marline spike hitch method to form the loop). It is also easier to untie (similar to "breaking the back" on a bowline, to get the working ends out of the cinched up loop). The only drawback I see is that it is a little bulkier than the Honda on the non-smooth side of the knot....

Actually more and more, I'm finding the slip knot to be my go-to knot for many things and practice it a lot. Whether it's for a trucker hitch, ashley stopper, marline spike hitch, falconer's knot, or even just to form a very quick end-of-line adjustable loop and half-hitching the working end on the standing end to lock it in place.

This is the first time I've considered it for a bend though. Good thread!

James Petersen

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Re: Joining Ropes for a Rappel
« Reply #12 on: August 13, 2013, 07:34:58 PM »
... got me thinking that a simple slip knot loop would do the same thing. Just tuck the working ends back through the doubled slip loop before cinching it up for added security (and form the slip loop opposite that of the Ashley stopper so that the working end does the cinching instead of the standing end. That way it will be virtually free from jamming). 

It's faster and easier to tie (I use the marline spike hitch method to form the loop). It is also easier to untie (similar to "breaking the back" on a bowline, to get the working ends out of the cinched up loop). The only drawback I see is that it is a little bulkier than the Honda on the non-smooth side of the knot....
Welcome to the forum.

I have to say that this knot looks like it would be immune from spilling, but I have not played with it at any length. Nor have I ever climbed, but I suspect the bulk added by the loop and the working end passing through it may be a little bit more than climbers want or would accept. Perhaps some of the climbers among us can address that.

And I have the feeling that when you tell people/climbers that you use a slip knot as a bend in climbing ropes, they may call it the "certain death knot," -- after (and if) they stop laughing. :);)

Seriously, though, once again, welcome.

« Last Edit: August 13, 2013, 07:41:41 PM by James Petersen »

knot4u

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Re: Joining Ropes for a Rappel
« Reply #13 on: August 14, 2013, 12:11:03 AM »
I have yet to try out James' knot.  However, I did try out the knot in the original post.  It seems to work OK, and it logically makes sense.

Regarding the idea of a slip, there is no way I'm going to use a slip in a bend for rappelling.  I'd prefer to spend an hour loosening up a tight knot, but that probably wouldn't be necessary anyway.
« Last Edit: August 14, 2013, 12:13:53 AM by knot4u »