International Guild of Knot Tyers Forum

General => New Knot Investigations => Topic started by: Mobius on October 31, 2015, 08:05:20 AM

Title: Offset knot for climbing
Post by: Mobius on October 31, 2015, 08:05:20 AM
I do not want to clutter this thread: http://igkt.net/sm/index.php?topic=5508.60#lastPost so what follows is probably a new knot though still relevant to the above thread.

A little background:

#1410 (Ashley), trialled and the tail slips and the nub rolls over itself, almost from initial load
#1414 (Single Fisherman's), collapsed at around 30% MBS
9-oh (Dan Lehman), appears to work well in the form Dan prefers

The knot I propose here not only 'works' in terms of preliminary trials, it has a small footprint. An offset knot has a particular geometry and a small footprint is an important safety feature (both these aspects described in the aforementioned thread).

I have considered the knot footprint objectively by measuring how may diameters are swallowed by the nub after tying a snug knot. A #1410 uses ~37 diam. The 9-oh uses ~49.5 (48 when measured more carefully a second time) diam. The knot I show below uses ~41 diam.

I originally thought that offset style knots would pretty much all have trouble handling big loads (in mbs terms). I was wrong, a properly designed knot (some sort of 'choke' appears to be needed) will do the job. At this stage of my trialling, Dan's 9-oh and 8-oh work and so does Mark's 'offset choked upper' and Jame's knot. So does the knot I show you next.

I spent a couple of weeks trialing various 'linked overhand' offsets and nearly getting them to work to my satisfaction.... but alas, not quite. One might work, I just could not find it. When I moved over to trying an overhand linked with a figure 8 then I found something that I was much more happy with. I use the tag lohf8 'linked overhand figure 8' for the knot I show. There will no doubt be other lohf8's that will work too.

More images from trials to follow in future posts.

Cheers,

mobius

[EDIT: the Ashley #1410 I initially trialed when writing this post was his 'twist' version, it performed very badly. The #1410 tied flat as an EDK performs better. All this is discussed later in the thread]
Title: Re: Offset knot for climbing
Post by: Mobius on October 31, 2015, 08:42:47 AM
The knot images are hopefully self explanatory in terms of mbs.

I am not interested in breaking these offset knots, just in being able to untie them after a high load. That my trial material does not collapse and that I can get it undone gives me confidence I will be able to do the same in larger diameter and better ropes.

Cheers,

mobius
Title: Re: Offset knot for climbing
Post by: Mobius on October 31, 2015, 08:48:51 AM
200kg is not a particularly high load. I will go to 500kg next time.
Title: Re: Offset knot for climbing
Post by: Mobius on November 01, 2015, 04:27:33 AM
This thread might better belong in "Knotting Concepts & Explorations".

There are presumably a lot more overhand and figure 8 offset combinations that could be explored, not just the one I came up with. This assumes that a small footprint for an offset knot really is important to the application.

Cheers,

mobius
Title: Re: Offset knot for climbing
Post by: Dan_Lehman on November 02, 2015, 08:28:56 PM
This is an interesting interlocking of components,
and in my quick play-test it looks good.  But I'm afraid
that the very "interlocking" tying aspect will keep
it from becoming a winner in the wild.

200kg is not a particularly high load. I will go to 500kg next time.
!?
200kg is more than double the weight of most
abseilers,
and hence will be over four times the forces that
an abseil-ropes-joining knot is expected to endure.
4:1 of expected forces is not nothing!
(It might be worth noting that one of the peculiar
results of the water knot (in tape) slipping under
cyclical loading was evident only in low loading of
the knot, so that it never took a hard set, and thus
could gradually ratchet out material of the *exterior*
tail.  I don't know what sort of similar-loading behavior
might occur only there, for ARJ knots.)

Nice contrasting & bright ropes used for the presentation,
thanks!  (Why not also in the loaded sampling?)

Btw, your observation about nearly immediate rolling
of the offset water knot (EDK) quite surprises me :
I've not seen that (though in some shopping-bag braid
I did just get some movement, though on a firm load),
and the knot does exist broadly in the wild.

And re "footprint", cordage consumption is somewhat
beside the point, in that knot shape will more likely be
any influence.  E.g., think of two horseshoes placed one
atop the other vs. facing opposite such that each straddles
one leg of the other --stacked height vs. width.  (I've found
an offset knot that resembles that latter case, and the
offset 9-Oh is more like the former.)

My measurement of the offset 9-Oh is approx. 31dia,
and (by subtraction, basicly) the OWK 22dia --quite
a bit less than yours, but with slightly greater evident
difference, proportionately --yours a third greater, mine
a half greater (with me measuring a 3/16" dia kernmantle
cord, using tea-bag strings to mark points).  !?



--dl*
====
Title: Re: Offset knot for climbing
Post by: Mobius on November 07, 2015, 11:35:02 AM
This is an interesting interlocking of components,
and in my quick play-test it looks good.  But I'm afraid
that the very "interlocking" tying aspect will keep
it from becoming a winner in the wild.

Thank you for the feedback Dan. I will make some other responses to issues you raised, however here is a tying method to start with. I don't think it is too hard, though admittedly it is not as easy as a 9-oh.

Cheers,

mobius
Title: Re: Offset knot for climbing
Post by: Mobius on November 08, 2015, 07:14:36 AM
My measurement of the offset 9-Oh is approx. 31dia,
and (by subtraction, basicly) the OWK 22dia --quite
a bit less than yours, but with slightly greater evident
difference, proportionately --yours a third greater, mine
a half greater (with me measuring a 3/16" dia kernmantle
cord, using tea-bag strings to mark points).  !?

I am not sure what is going on here. The material I use for such measurement is 11mm kernmantle. Last time I used my more worn (slightly) black rope, this time I did it with the blue and orange lengths i save for pictures.

Image one is the actual knot measured, snugged, however not loaded.. The black marking is where I taped the Sparts together. The tails were measured at 195mm each prior to untying.

Image two is just measuring and calculation (515+400-390)/11= ~48 diam.

Cheers,

mobius

Title: Re: Offset knot for climbing
Post by: SS369 on November 08, 2015, 05:24:14 PM
Quote
I am not sure what is going on here.

Hi mobius.

Please explain a bit more.

SS
Title: Re: Offset knot for climbing
Post by: Mobius on November 08, 2015, 10:13:55 PM
Quote
I am not sure what is going on here.

Hi mobius.

Please explain a bit more.

SS
 
Dan gets a 9-oh to consume 31 Dia,  I first get 49.5 (see op) then 48. Quite a difference between 31 and 48.

Cheers,

mobius
Title: Re: Offset knot for climbing
Post by: Dan_Lehman on November 09, 2015, 08:20:46 PM
Dan gets a 9-oh to consume 31 Dia,
I first get 49.5 (see op) then 48. Quite a difference.

Cheers,

mobius
Which moves Dan to re-measure.  This time, I used
a commercial-fishing kermantle, which I measured
to be about 9/32" (2 strands adjacent measured :
9/16), and ... I, now, also get 48.)
(And, frankly, I think that if I'd referred to some paper
on which I have made some similar notes about knot
sizes, I'd have doubted my lower figure based on that
for a fig.8 eyeknot among others!)
.:.  science, moves by replicated testing, verification, ...

Sorry for the false lead (which I'm not going to try to figure
out, right away, though I did employ the tea strings and ... ;
I might try that yet again, though, out of curiosity!).

Hmmm, measuring with small diameters is likely prone
to making large errors --tough to make the diameter
measure!  Maybe I'll try measuring some relatively thick
rope (1" or so).  As rope size increases, it might become
problematic to determine how to set the knot for
measuring --how much force ... .


--dl*
====
Title: Re: Offset knot for climbing
Post by: Mobius on December 20, 2015, 07:43:50 AM

Hmmm, measuring with small diameters is likely prone
to making large errors --tough to make the diameter
measure!  Maybe I'll try measuring some relatively thick
rope (1" or so).  As rope size increases, it might become
problematic to determine how to set the knot for
measuring --how much force ... .


--dl*
====

Knot efficiency in terms of diam.'s consumed is one of the many things we need an (unofficial) standard for. i.e. Comparing 11mm kernmantle vs 11mm kernmantle means  a lot more than 11mm kernmantle vs some small diam. soft rope.

The knot I show here is efficient as far as I am concerned.
Title: Re: Offset knot for climbing
Post by: Mobius on December 25, 2015, 09:39:40 AM
I redid my trial of this bend, taking more note of slippage. Image 1 shows tails of around 50mm at zero load, Image 2 shows the same knot at 200kg. The 'slippage' is around 3-4 mm, perhaps better described as settling.

The rope material is stiff, well-worn 11.2mm Dynamic rope

Cheers,

mobius

Edit: the rope material is dynamic
Title: Re: Offset knot for climbing
Post by: Mobius on January 26, 2016, 04:57:48 AM
I found out that the well worn climbing rope I was given is dynamic, not static (the pale green rope with gold/blue flecks I show in the thread).

In theory this knowledge should make the knot I show more interesting to the climbing community, considering the trials already conducted and shown in previous posts: ie This lohf8 style knot is a simple to tie, verifiable, small footprint offset knot that did not slip in dynamic rope at 200kg, and was easy to untie. This knot might be interesting to someone who has not already made their mind up about what offset knot to use.

As it turns out, I am going to trial this knot again shortly in both 10.2mm static and 10.2mm dynamic rope when my new rope purchases arrive. I am getting a new crane scale as well and will probably trial up to 500-600 Kg max and see what happens. I won't be doing sudden pull tests, that will be for someone with a tractor/truck and bit of space to do them.

I have also purchased some 6mm dynamic accessory cord which should prove useful in tying this knot combined in different diameters.

Cheers,

mobius



Title: Re: Offset knot for climbing
Post by: Dan_Lehman on January 27, 2016, 07:02:31 AM
... dynamic, not static ...
In the cordage world, there are a trio of definitions
with the above two having "low-elongation" between
them --and most of what is casually called "static"
falls into this middle class, with the "hi-mod" ropes
being true "static"s.

Quote
I have also purchased some 6mm dynamic accessory cord
which is unlikely that but "low-elongation".

Maybe I'm rusty re current definitions; I recall something
about the stretch at 10% of tensile strength being what
slotted ropes into one or another category?!

Rather than the great forces you envision,
what could be enlightening is seeing a configuration
in which you make a round sling of both of any two
or your ropes --e.g., the 10mm of low-elong & dynamie--,
by joining them with non-concern knots (#1408, say)
and then loading the knots simultaneously.
(I'm having trouble envisioning the actual set-up.
But a simple solution is to have a 3rd rope, or two
such pieces, tie off each of the specimens in the
subject-knotted rope.)
((How long are your samples?))

What I'd like to see is how the like-knotted different
ropes behave, side-by-side.  (Thinking we might see
how in the dynamic case that at 100kg already the
knot has taken much more deformity, while the
low-elongation rope holds its set shape still.)

Ideally, one would want a pulley so that differences
in elasticity would not bias the loads on each (which
if joined around a pin lacking such efficiency as a
pulley could see the lesser-stretching rope actually
be taking a higher load into the knot while the
dynamic rope just elongated!).


--dl*
====
Title: Re: Offset knot for climbing
Post by: Mobius on February 06, 2016, 12:09:35 PM

What I'd like to see is how the like-knotted different
ropes behave, side-by-side.  (Thinking we might see
how in the dynamic case that at 100kg already the
knot has taken much more deformity, while the
low-elongation rope holds its set shape still.)


I took a lot of photos today to try and show how this knot behaves in 10.2mm low-elongation and high-elongation ropes. My photography efforts were very poor today, The few I show are the best of a bad lot.

Image 1: the rope specs of the 10.2 dynamic rope I purchased.

Image 2: the 10.2 mm static rope at 300kg. The knot has not distorted much from zero load. I marked the tails at 100mm and could detect negligible tail movement at 100kg, 200kg or 300kg (i.e. the tail markings looked to still be at 100mm to my eye). The knot was very easy to undo after load.

Image 3: this time I have 10.2mm dynamic rope with the tails  marked at 50mm. The image is at 200kg and looks a lot like Image 2 (though 100kg less loading). I measured around 3mm of tail movement at 100kg, though the knot did not appear to have experienced any more tail movement at 200kg when I measured again.

Image 4: Now the knot is showing some distortion. The knot has not collapsed in my opinion, though there was another 3mm of tail movement (6mm in total). Perhaps interesting is that I repeated this test in the same rope to 300kg, though I used the winch to get quickly to 300kg directly. Second time around the knot did not look so deformed, though it too showed overall tail movement of around 5-6mm after 300kg. Both the trial knots were easily untied after the test. The second one a little more so than the first.

I am a bit disappointed to see even the relatively small amount of tail movement i saw in the dynamic rope trials.

Cheers,

mobius
Title: Re: Offset knot for climbing
Post by: Mobius on February 21, 2016, 07:25:32 AM
I am still interested in finding what I consider to be a good offset knot for climbing.

The EDK simply does not meet certain fundamental requirements: It slips way too easily. That this controlled slippage is known about and accepted as normal by some is not a good reason to place undeserved virtue on the EDK. The argument goes that the EDK has been used for quite some time and has not been attributed to deaths (or a bunch of accidents), hence it is good. This is a subjective argument that is fallacious from my viewpoint. Good knots do not slip. So objectively, there are better knots to find: A knot that does not slip easily is a good criteria for any knot, let alone one you are climbing a mountain with.

The lohf8 version I first proposed here does an 'ok' job from my perspective: It does not slip in low elongation rope up to 300kg and up to 200kg in dynamic high elongation rope. This result is already way better than any of the trials I have read about (or conducted) on the EDK. Still, I do not think it is good enough and I am working on new knots.

One new knot I trialled recently is in the attached image. In 11.2mm dynamic rope it too worked 'ok'. However, about 250kg load it changed shape and slipped a bit, then becoming hard to untie. There are numerous knots to try and several ways to orientate either their tails or the loaded sides of the knot. Subtle dressing changes might dramatically effect different results.

At some stage I will find time to look at Dan Lehman's 9-oh and Rodger Callahan's 'snowdrop' knot (IGKT publication) in more detail. Other knots I have looked at seem too big to be strongly considered.

The image below is rubbishy... new camera on its way  :)

Cheers,

Ian






Title: Re: Offset knot for climbing
Post by: Dan_Lehman on February 22, 2016, 05:40:44 PM
The EDK simply does not meet certain fundamental requirements: It slips way too easily.
That this controlled slippage is known about and accepted as normal by some is not a good
reason to place undeserved virtue on the EDK. The argument goes that the EDK has been
used for quite some time and has not been attributed to deaths (or a bunch of accidents),
hence it is good. This is a subjective argument that is fallacious from my viewpoint.
Spitting into the wind is one thing,
mischaracterizing arguments is worse.
There is nothing "subjective" about pointing to the
quite objective point that the offset water knot has been
used for ages --in the very materials of issue-- without
failure.  And it's certainly worth pointing that out.

Yes, if one greatly overloads the knot, then it might
"roll"/capsize.  But I don't think that this behavior
is seen in abseiling.  And the simple remedy of tying
a back-up "EDK" snug to the first is one that even
I who found it so *ugly*/crude must admit has strong
factors in its favor --namely : it uses *known knot tying*
(just a repetition), it survives pretty much all ways
of "improper / not-so-well-dressed-&-set tying (vis-a-vis
thick+thin, soft+stiff joined ropes, and it's easy to tie
(esp. in severe conditions)).

Since you have some material in which you found
the popular knot to fail --"to slip easily"--, how about
trying the backed-up structure in that, as a severe
(& unrealistic) test of the knot.  We can maybe at
least advance to having this test case done.

For some, there might be yet the desire to tie knots
of greater material efficiency --of adding just another
full turn (for the offset 9-Oh) or tying off just the
appropriate (from choking turn) tail of the offset water knot--,
but these knots do require that one get certain things
right in orientation & loading whereas the "ugly" one
does not.   It's an old struggle between wanting folks
to know how ...., but wanting to anticipate errors --to
"dummy proof" things.

Quote
Good knots do not slip. So objectively, there are better knots to find:
The first is an assertion wanting support,
that latter is a non sequitur.
In fact, the tarbuck knot --which was a variation of the
rolling hitch was devised and advocated for rockclimbing
especially because it could slip : this slippage was supposed
to consume force and reduce peak impact force.  (That
was a theory more than fact.)  And the absence of something
doesn't imply that it must exist.  Ih HMPE cordage, the
venerable bowline slips, but it continues to be widely
used without issue.

Quote
At some stage I will find time to look at Dan Lehman's 9-oh and Rodger Callahan's 'snowdrop' knot (IGKT publication) in more detail. Other knots I have looked at seem too big to be strongly considered.

Roger's knot isn't offset, and fails simple evaluation.
Now, the reverse is one that might be interesting
to see perform.


--dl*
====


Title: Re: Offset knot for climbing
Post by: Mobius on February 23, 2016, 07:34:30 AM
The EDK simply does not meet certain fundamental requirements: It slips way too easily.
That this controlled slippage is known about and accepted as normal by some is not a good
reason to place undeserved virtue on the EDK. The argument goes that the EDK has been
used for quite some time and has not been attributed to deaths (or a bunch of accidents),
hence it is good. This is a subjective argument that is fallacious from my viewpoint.
Spitting into the wind is one thing,
mischaracterizing arguments is worse.
There is nothing "subjective" about pointing to the
quite objective point that the offset water knot has been
used for ages --in the very materials of issute-- without
failure.  And it's certainly worth pointing that out.

--dl*
====

I am not mis-characterizing anything.

An objective measure of a knot is 'does it slip' at a certain load or % of mbs or other well defined criteria. Trying to convince anyone that the EDK is objectively good because it has been "used for ages" is plainly wrong. The "without failure" part is without qualification. How is the knot tied? Is it being embellished by a back-up knot? The EDK slips in the materials that it is used in at working loads, that is "a failure" to me. We have seen trials showing us exactly this.

To me, the EDK is a poor knot objectively, no matter how much I hear this "used for ages" argument. If you want to believe the "used for ages" argument I suppose a "granny knot" would be an even better knot to try mountaineering with, since that does not fail in everyday life (we would hear about all the accidents) and has been used by millions a lot longer than the EDK. Very few climbing accidents/deaths from it, so it must be good, right? I make a deliberately stupid argument, however not much more so than the EDK one I keep hearing in my opinion.

I have said this a number of times: Find a better knot. Anyone who wants to help, great. If not, I will find one on my own.

I am working towards a set of criteria I can practically trial offset knots to. Something along the lines of tolerable knot settling/slippage up to 300kg in 10mm high and low elongation ropes. Anyone is welcome to input into this, or suggest a knot to test.

Cheers,

Ian.



Title: Re: Offset knot for climbing
Post by: Dan_Lehman on February 24, 2016, 12:11:22 AM
The EDK simply does not meet certain fundamental requirements: It slips way too easily.
That this controlled slippage is known about and accepted as normal by some is not a good
reason to place undeserved virtue on the EDK. The argument goes that the EDK has been
used for quite some time and has not been attributed to deaths (or a bunch of accidents),
hence it is good. This is a subjective argument that is fallacious from my viewpoint.
Spitting into the wind is one thing,
mischaracterizing arguments is worse.
There is nothing "subjective" about pointing to the
quite objective point that the offset water knot has been
used for ages --in the very materials of issue-- without
failure.  And it's certainly worth pointing that out.

--dl*
====

I am not mis-characterizing anything.
Okay, you don't deny the facts of non-failure in
long-standing practice, but challenge that that
ipso facto is a good basis.
IMO, it certainly IS.  Consider it "trialling" and then
ask if anything else has been so thoroughly tested?!

Quote
An objective measure of a knot is 'does it slip' at a certain load or % of mbs or other well defined criteria.
Except that we've seen that even defining "slip"
is a matter of debate --is it really in any way doing
some dangerous "slipping" if it's just adjusting to
forces from a low-force setting?!  When a knot is
taken to break point, one might conclude that
slippage wasn't a problem (YMMV).

Quote
Trying to convince anyone that the EDK is objectively good because it has been "used for ages" is plainly wrong. The "without failure" part is without qualification. How is the knot tied? Is it being embellished by a back-up knot? The EDK slips in the materials that it is used in at working loads, that is "a failure" to me. We have seen trials showing us exactly this.
?!  On the contrary, while we might not know in
given detail even on most uses, we can know by
testimony and example how folks tie and use the
knot, and have otherwise to think how thousands
& repeated thousands of application-specific uses
have not brought anyone --even!-- to grief.  Again,
that is a vast amount of "practical testing" to deny!

Quote
If you want to believe the "used for ages" argument I suppose a "granny knot" would be an even better knot to try mountaineering with, since that does not fail in everyday life (we would hear about all the accidents) and has been used by millions a lot longer than the EDK. Very few climbing accidents/deaths from it, so it must be good, right? I make a deliberately stupid argument, however not much more so than the EDK one I keep hearing in my opinion.
This defies reason : the granny knot has NOT been used
AT ALL in the materials or application of rockclimbing, point
blank obvious, and in stark contrast to the offset water knot
which has long-standing usage.

(Now, as an aside, the "longstanding usage ..." reasoning must
be chary of all assumptions/contexts :: bring a new material
such as HMPE into the situation, and you might have other
than the longstanding happy behavior!  One had a sort of this
realization in seeing the ca. 2001 HSE (UK) study of using
the clove hitch for termination, where of their several tested
ropes, only the dynamic one held (IIRC), all of the tested
low-elongation ropes slipping at widely different loads ::
one could see a rockclimber who had confidence from
longstanding use of the knot in climbing ropes finding
unpleasant behavior in more inelastic stuff.
But you don't have any experience of granny knots climbing.)

Quote
I have said this a number of times: Find a better knot. Anyone who wants to help, great. If not, I will find one on my own.
And so you have --and have already done some testing of just
such a Found-Better Knot--, viz., the offset 9-Oh, which takes
the design goal of being offset (for smooth traverse of rough
services including edges), efficient tying and consumption
of material ("small footprint" to cite a term), and suitability
or joining dissimilar (within application bounds (6mm + 11mm?))
ropes, and began with the offsetting of the S.Parts and then the
sure nipping of the choke point with a full turn by one
of the two ropes --spec'd the thinner / more flexible one,
and thus the accommodation of dissimilar ropes.

And it works, as you've shown.

Even *hastening* the tying above, to yield the offset 8-Oh,
one gets a half-turn less choking but now has the new
(vs. EDK) aspect of tails going out of the nipping area
in opposite directions, so that there is an end on either side,
not both on one and connected parts on the opposite side.
That looks promising, but somehow it has seemed to me
that its resistance to capsizing looks less good, and with
the 9-Oh looking good and just a half-turn away,
I would favor that.

BUT, unlike the "EDK-backed EDK", both require that one
orient the thick-2-thin tying in just such a way, for ideal
and most sure results, at least --perhaps in reasonable
counter orientations per the application (e.g., 6mm tied
with 10mm), they still work, albeit with less of a margin
of surety!?

Ditto for simply tying off the offset water knot's choking-part
tail (which again should be the thinner/flexible rope if uneven) :
it works well in the specified orientation, but does require
that one note and achieve such orientation,
and should offer less security if botched in this regard.
IMO, that clumsy EDK-backed EDK might suffer not only
botched & varied per-knot orientation (e.g., thickier rope
choking) but also spaced back-up (which could enable
a "roll" of the primary knot before hitting the stopper)!?


--dl*
====
Title: Re: Offset knot for climbing
Post by: Mobius on May 10, 2016, 07:47:20 AM
I have not forgotten this thread, indeed the last 3 months have been full of trials involving knots tied in 10-11mm dynamic rope taken to at least 3 kN if they do not jam prior to that. I have found two knots I like, and one in particular. I believe 3 kN is significant in this application and is perhaps close to twice the tension needed after looking at force fall factor (FF) considerations I have read about. Others might confirm this.

My trial requirements were simple. Take a knot in 10-11mm dynamic climbing rope to 3 kN and see whether it slips and/or jams. I simply do not believe ''all knots slip" as I was told by an 'expert'. I do not (and never will) believe that #1410 is a good knot for this application. The EDK is a knot that has a donkey beside it in Ashley's book for a good reason in my opinion.

For the moment, I would kindly ask Dan Lehman to check the image below to see whether I tied the 9-oh to his satisfaction.

Cheers,

Ian.
Title: Re: Offset knot for climbing
Post by: Mobius on May 11, 2016, 06:17:50 AM
I have done a lot of  trials in various rope materials with the #1410. In particular here are some images of the knot tied in worn 11.2mm dynamic climbing rope. I have trialed the knot in both new 10.2mm dynamic rope and 10.2mm kernmantle climbing rope as well.

The first image is simply the trialed knot. The tails were carefully set to 110mm each in length. I believe the knot was snugged appropriately. The legs were orientated as shown.

Image two has the knot at a modest 0.5 kN and the tails are now at 95mm.

Image three is at 1.5 kN and we now see the tails are at 85mm.

The last image is at 2 kN and the tails are now at 80mm.

This knot stopped slipping somewhere around the 2 kN mark and was jammed at 3 kN having first slipped a total of 30mm.

Other trials in newer dynamic rope materials suggested to me that if you were climbing with new rope you could probably expect less slippage, however when the knot stops slipping it starts jamming, hardly a bargain either way the way I see it.

Cheers,

Ian.
Title: Re: Offset knot for climbing
Post by: Mobius on May 11, 2016, 08:05:54 AM
Despite my misgivings about the #1410 from very early on, I have trialed it in different ways. The images that follow actually proved very useful to me in that it showed me that orientation changes to a knot (perhaps, particularly to an offset one) can make a quite a difference.

Image one is a #1410 with legs reversed, set carefully with tails at 100mm.

Image two shows how the knot slipped 10mm at 0.5 kN, and turned itself around to leave the legs in a position like the trial above. Will that always happen (rhetorical)?

There is not much difference in terms of mm slipped than the results in the previous post at 0.5 kN or later levels of tension, however it became clear to me that offset knots need to be trialed in both ways in terms of leg orientation. More on this later.

Cheers,

Ian.

Title: Re: Offset knot for climbing
Post by: Mobius on May 12, 2016, 09:04:59 AM
One knot I said I would trial earlier in this thread was "The Double Snowdrop Bend" as given in the September 2015 edition of KNOTTING MATTERS. Mr Roger Callan's misgivings about the EDK are perhaps even stronger than mine, that you could see for yourself if you get a chance to read his article and viewpoint.

Mr Callan's Snowdrop bend was immediately interesting to me, since he too had combined a simple overhand and figure 8 into a form that showed promise in being one that would not "unravel" (his term).

I have trialed his knot in 11.2mm dynamic climbing rope. I have not done much with this knot to date, here is what I found so far.

Image 1: the tying diagram (borrowed)

Image 2: the actual knot I trialed

Image 3: the knot at 2.1 kN. At this point I could see the tails being 'swallowed' and suspected jamming was not too far away. The actual knot jammed around 2.6 kN.

I can come back to trialing this knot if there is particular interest.

Cheers,

Ian.

PS. Roger is spelled with a d in the main article heading (Rodger), I think that is wrong judging from the signed diagrams
Title: Re: Offset knot for climbing
Post by: Dan_Lehman on May 13, 2016, 08:32:50 PM
One knot I said I would trial earlier in this thread was "The Double Snowdrop Bend" as given in the September 2015 edition of KNOTTING MATTERS. Mr Roger Callan's misgivings about the EDK are perhaps even stronger than mine, that you could see for yourself if you get a chance to read his article and viewpoint.
And sadly he shows little of comprehension and fair
consideration to the widespread usage of the knot
he faults, which greatly weakens his position.  (But
I cannot so easily dismiss his remarks about seeing
the knot in "climbing gyms," and yet cannot figure
out why this would be : climbers use single ropes
run floor-to-ceiling-area anchor sheave down to
climber (to my on-site awareness in USA), and no
end-2-end knots are required.  Climbers tie in,
belayers might clip in to floor-anchors if at all.
So that part of his statement puzzles me greatly!

His proposed solution only further exhibits his lack
of understanding --and you, who better understand,
thus took it backwards, where it makes more sense!

Quote
I have trialed his knot in 11.2mm dynamic climbing rope.
No, and I think I remarked about this point above:
you have tested the reverse of his knot.
HE shows SParts as the arrowed ends,
and his ends-adjacent side is thus the tails
(though you are right to see this as being
 like-other-*offset*-knots paired SParts;
 and *I* see it so because in my long-ago use
 of arrows/non I did the opposite to Roger,
  *pointing* the flow into & out of a knot body thus!)

Quote
PS. Roger is spelled with a d in the main article heading (Rodger), I think that is wrong judging from the signed diagrams
Yes, "spare the 'Rod' !" was my joke at this.
Roger took issue with it in the follow-up issue of KM.
But "D" is the highest grade we can give for his knot
as a solution.

--dl*
====
Title: Re: Offset knot for climbing
Post by: Dan_Lehman on May 13, 2016, 08:53:32 PM
Despite my misgivings about the #1410 from very early on, I have trialed it in different ways. The images that follow actually proved very useful to me in that it showed me that orientation changes to a knot (perhaps, particularly to an offset one) can make a quite a difference.

Image one is a #1410 with legs reversed, set carefully with tails at 100mm.
I don't see this as well set for sustaining this reversed
(reverse extreme : arc & loop <=> loop & arc)
orientation; one really needs to set it tight pulling
SParts together opposing knot qua stopper,
AND THEN
pulling SParts apart as desired and getting it to hold
the orientation.
That said, I think that one extreme --likely this one,
I'm not going to check now-- is less sure than the
other; I think your dual-orientation testing has that.

But I see more that you've turned --in this latter and
less stable case of arc-&-loop-- not to the other extreme
(which takes quite a swing!) but to the approximate
mid-range state (half-arc & half-arc),
WHICH
I think might be the LEAST secure/stable state.

In the extremes (arc-&-loop),
the tails exit roughly perpendicular to the axis of tension;
in the mid-range state,
 tails lie parallel.  NB!
(In the Autralian BushWalkers testing, they recommended
orienting the tails in a parallel way (they, thinking of which
way up or down they should point, missing these determining
distinctions of orientation being described & explored here.)

Quote
Will that always happen (rhetorical)?
To the non-rhetorical question, as noted above, I do believe
that the case of arc-&-loop where the loop is more *inner*
will tend to rotate some measure away from the extreme,
whereas the other extreme orientation is better sustained.

To the rhetorical question, GOOD POINT TO HOLD ::
that in any given testing that might be presented,
there is good reason do question how applicable the
supposed demonstrated behavior is to different combinations
of materials & forces & ... so on !!
I.p., in the mountain-project thread about the recent (May)
rappelling fatality, one poster gives a URLink to testing of
a WET offset water knot / EDK in which one sees the knot
roll & roll & continue until I think pulling out, with quite
an explosion of losing grip --and HUGE forces, vis-a-vis abseil
(maybe 3_000 pounds force at START of rolling, in old
climbing rope(s)).  Coming up after viewing this (Youtube?)
on a small page of other-videos-like-what-you-saw is one
that shows "EDK & EDK-8" testing.  Contrary the popular
viewpoint of those-in-the-know (i.e., that the latter knot
is LESS stable, more vulnerable to catastrophic flyping),
the EDK-8 sustains a well higher force; both knots hold
until rupture, IIRC --just viewed it once, so we need to
double-check this.  In any case, THIS particular presentation
would move one if anything to use what I think is better
understood as a more dangerous knot.  (E.g., those Bush-
walkers claim to have made if fail with just manual loading.)
To this all, we should note that what might be
common across inconsistent presentations
is NAME ONLY, less so the exact knot geometry!

Quote
however it became clear to me that offset knots need to be trialed in both ways in terms of leg orientation. More on this later.
Spot on.
AND in combination of materials,
thick & thin joined; new slick & old rough.
Preferably ELASTIC, to emphasize potential
deformation (but, no, not so much shock/bungee cord
--that's WAY elastic).

Quote
Cheers, Ian.
Close,
but first letter is better "D", gotten from 'RoDger',
which makes 'Dan'  ;D

--dl*
====
Title: Re: Offset knot for climbing
Post by: Dan_Lehman on May 13, 2016, 09:12:12 PM
I have found two knots I like, and one in particular. I believe 3 kN is significant in this application and is perhaps close to twice the tension needed after looking at force factor (FF) considerations I have read about. Others might confirm thi
Or challenge it.
Expected abseil forces are WAY less than this:
your 1kn is already around double what ONE ROPE
(& hence, the knot) would get in the joined-ropes abseil!

Going beyond this is reasonable to try to find
any lurking issues, which might be tickled upon
some slip and more-dynamic loading.

Your "FF" ("fall factor") is something conceived of
to explain falls while climbing, and the UIAA drop
test uses one a little under 2, which could occur
if a climber falls before putting in any protection,
and hence falls the length of rope out to pass
the belay point and then of course that length
of now-slack rope until it takes hold --TWO times
length.  A rappeller would need to have some bit
of rope slack out at the start and then just fall
on that, to get a say 2m fall on 2m (doubled!)
rope and FF-1/2 on the knot.  And that's bizarre.

Quote
I do not (and never will) believe that #1410 is a good knot for this application.
I'm sort of okay with your not favoring it,
but I continue to view with dismay your
lack of appreciation that ACTUAL ON-SITE USAGE
has effectively *trialed* this dubious knot FAR
more times, in DECADES/thousands of uses
beyond what you have done.
AND NB :: your own testing show here could well be used
by advocates of the offset water knot / EDK as proof of its
suitability !!

So, it's fine that you seek something surer;
it's worrying that you dismiss the extensive
practice so fully.

BTW, I really do wish that you'd test the knot tied
with itself as back-up, pretty snug together
in that small cord in which it failed SO quickly !!
I want to see to what extent in that challenging
medium the backed-up structure can endure.


Quote
The EDK is a knot that has a donkey beside it in Ashley's book for a good reason in my opinion.
Ashley's reason, we should note, is re strength,
which is irrelevant to the abseiling application;
re security, he only remarks that it's better than
the (commonly used) sheet bend --though we might
question his basis for both judgements (I think that
the latter was based on his testing rig's check for
mohair(-like) fibre cord).

Quote
For the moment, I would kindly ask Dan Lehman to check the image below to see whether I tied the 9-oh to his satisfaction.
... instead of making all his other comments ... !   :P
Yes, that looks fine.
It is the full wrap made by the choking strand
that is believed to give the knot good resistance
to being pried open and then flyping.

Cheers,
I/Dan
Title: Re: Offset knot for climbing
Post by: Mobius on May 14, 2016, 07:35:26 AM
Quote from: me
I have trialed his knot in 11.2mm dynamic climbing rope.
No, and I think I remarked about this point above:
you have tested the reverse of his knot.
HE shows SParts as the arrowed ends,
and his ends-adjacent side is thus the tails
(though you are right to see this as being
 like-other-*offset*-knots paired SParts;
 and *I* see it so because in my long-ago use
 of arrows/non I did the opposite to Roger,
  *pointing* the flow into & out of a knot body thus!)

--dl*
====
I have to laugh at myself for this one. I saw the arrows and fleetingly thought it a little strange to use arrows for the tails, however, reversed, the paired SParts were exactly the offset bend I was expecting.

Mr Callan's knot as intended is not offset so I won't be testing it in it's proper form. It did not do too bad a job in the reversed way I tried it, however I believe I know of better knot alternatives that I will share with you.

I'm debating whether to show you what I have now or get more material for testing. I have exhausted the supply of used indoor climbing rope I was given and my 'new' purchased rope has now seen a few tests. It doesn't look too bad, however one wonders how long new stays 'new' when I am trialling the same 2m sections of rope to 3 kN repeatedly.

I chose the 3 kN mark knowing (at least for this application) that it was quite a high mark to aim for. As Dan says here:
Quote
Going beyond this is reasonable to try to find any lurking issues, which might be tickled upon some slip and more-dynamic loading

This is part of the reason I choose higher than normal testing limits. Honestly, who is going to listen to a mathematician with a rig and a bent for knots telling you the knot he came up with slips 10% less at 1 kN than some other knot... whoop-de-doo-dah. On the other hand, I find a knot that does not slip at all up to 6 kN and maybe someone looks at that and says "this maths geek who has never climbed a mountain" might actually be on to something.

On top of that, doing trials for this site is no bargain, so I do them as well as I can.

Eg. Someone will agree with you in one breath and tell you something close to 'you are tying in noodle, or grandma's thread' when the trial result does not suit them. This last was just vitriloic nonsense, however it is the comments that follow from someone I respect that nearly made me give up trialing altogether. One was this: 'the slow pull tests have been done and done and I have a strong foundation of what works', followed later by 'I know these selected knots already pass because I have and continue to use them'.

So the first tells me that it doesn't matter what I come up with at least some members are unlikely to take much notice, they have made up their mind already. The second tells me that whatever knot someone uses is a 'pass' as long as it does not fail for them. Threre is no point in me finding any new, objectively better performing knot(s) if the mind of one's audience is closed. There are plenty of agenda's to overcome on this site. The last agenda I questioned here earned me a bunch of red writing and a tag of 'unprofessional'. Thank goodness my profession is not tying knots for a living :P

I do not believe slow pull tests have been done to death. There is so much to learn from watching knots unravel, twist, collapse, stretch, bulge, jam or hold firm on a rig. Here is a conjecture for you: I get to see what happens to a knot that might experience a sudden jolt, except in slow motion. Some who do not like slow pulls do uncontrolled fast pulls. Before my rig, I nearly pulled my front garden palm tree out with my 4 wheel drive doing a fast pull. What did I learn about the knot?... almost nothing. That is not to say fast pull tests are unimportant, there just has to be a controlled way of doing them to make them worthwhile.

I believe knot testing is in it's infancy and the backbone of it for present has to be slow pull tests. Later on working on a consistent way to do fast pull tests (without a laboratory) would be great. Do we expect a high correlation between slow and fast pull testing(?), well I do, however let us see.

So, although my attitude to the EDK may seem overly harsh, I am not immune to the statistical argument that Dan says I am not paying enough attention too. It is just that I cannot test the statistics, however I can look at the knot in terms of objective rig testing qualities, and try to do a better knot. That is what I have done.

Cheers,

Ian.

[edit: small changes so it reads better]
Title: Re: Offset knot for climbing
Post by: Dan_Lehman on May 15, 2016, 06:48:23 AM
You got a picture's worth of words there, and I read every
one of them --that alone separates you from the variable
X (or was that a constant  8) ) !

And not one word was about using that super-challenging
core in which your favorite villain of a knot fails strikingly
quickly (where in some other materials it yields only grudingly
or holds to break) with the backed-up variation.  This would
be --i.e., testing the EDK-backed EDK in that material--
going beyond expected conditions to find lurking issues!
We will be most grateful for this trialling --if the knot holds,
rising to such challenge!  As there is a LOT of reason to have
this compound knot in the toolbox : climbers can be in situations
entirely unwelcoming for doing math or much of any thinking
and matching careful ropes-threading, and have a recourse
that is doing something most simple times two (or more!)
is a significant asset (and noting as I did previously that the
compound knot I think allows a lot of the recommended
tying/orienting (dressing & setting) choices to go wrong
and STILL work.

Quote
doing trials for this site is no bargain, so I do them as well as I can
And we're grateful for them,
but your notion of "well" is also what makes
them --in terms of material expense, at least--
no bargain.  Tested to much lesser forces, which
STILL leaves them going well greater than expected
abseil forces (which let us stipulate would be about
0.5kN (on the single knotted half of twin lines abseil,
1kN the total load per anchor measurement)),
would let the ropes work longer for you.
--a material savings, but not time & effort ... .

You could regard this as some sort of "basic safety level"
and have in mind more severe cases beyond, to do at
some point ... .  The 1kN loading could sort out knots
to go further with, for your purposes; while qualifying
them for others'.  YMMV.  And, as you noted, there is
that aspect of how-SParts-depart-from-knot which isn't
on anyonElse's radar, even (but ours) !!  Which adds
one more factor to consider (and one more reason
to hope that the compound knot aforementioned
can endure any orientation!).

Here's some info from www.geir.com/mythbuster.html (http://www.geir.com/mythbuster.html)
regarding abseil forces --with humans, not elephants
(who take the long way down  ;) )
Quote
It is difficult to produce loads of even 600 pounds on a rappel.
Jeff Fassett and I measured the force produced on an anchor
during a double-rope rappel using a dynamometer. Not surprisingly,
during normal rappelling the force on the anchor was simply body weight
(in our measurements, 150 pounds).  In this case, the load on the
[offset water knot is 75 pounds.  Even with rigorous 5-foot deadfalls
close to the anchor, we were unable to produce a load greater than 600
pounds on the anchor. In this case, the load on the [knot] is only 300 pounds.
(These tests were conducted with a heavily-used 10.2 mm Beal dynamic line
and a 150 pound person.)

Now, something else :
Quote
what happens to a knot that might experience a sudden jolt, except in slow motion.
You might be misleading yourself, here :
i.e., what happens in slow(-pull) motion does NOT
model dynamic loading, which doesn't let up on the
knot's rolling (say) but sustains its force --there is
no lag time of a slow-pull device catching up to
re-tension the line!  --there might be even a little
shock load?!  (I've often wondered at this.)  A suspended
mass could be accelerated a little by a capsizing then its
resultant load would not only come more quickly but be
greater for this acceleration, unlike a test machine's slow
take-up of capsized slack/reduced tension!?

Quote
On the other hand, I find a knot that does not slip at all up to 6 kN and maybe someone looks at that and says "this maths geek who has never climbed a mountain" might actually be on to something.
Except that you first have to convince this person
that the used-by-everbody-to-do-what-is-needed knot
"slips" and that this slipping is somehow of concern,
even though the knot has been used for 50 years
or more w/o problem!  (And that doing some clever
reaving just so in order to get a non-slipping knot
is a winning proposition --the learning curve, the
remembering-when-in-duress odds ... (though for
half a century the rumored slippage hasn't troubled us).)

I have made that pursuit,
and the offset 9-Oh and some other knots resulted
from the exploration,
along with the tie-the-choking-tail-of-EDK securing,
and orienting mis-matched lines to choke with thinner,
and ...
I must admit that each such *instruction*/requirement
amounts to a chance to go wrong!  But I'd likely use one
of these more-secure knots.

Still, having that super-safe/-resistant compound knot
in the toolbox adds assurance.

Cheers,
--dl*
====
Title: Re: Offset knot for climbing
Post by: Mobius on May 15, 2016, 11:26:38 AM
Thank you for your feedback as always Dan.

Quote from: Dan
And not one word was about using that super-challenging
core in which your favorite villain of a knot fails strikingly
quickly...

I am going to retrial the #1410 and a back-up to it tomorrow in my 'challenging' material. I think I know the answer to what worries Dan already and it is to do with Ashley's diagram (reproduced below). The way it is shown is the way I tied it and trialed the #1410 initially. Later all my trials were in climbing rope and tied without the funny twist Ashley shows.

When I first trialed the #1410, tying it the way Ashley shows it, did not seem like a bad idea. I have to look again at my original post(s) on the #1410 results, however the amount of knot movement I saw then I think is out of keeping with what I have seen in low-elongation kernmantle later on. Huge movement is not typical from my experience with the EDK. Dynamic rope is a different story, you see more movement.

Quote from: mobius
what happens to a knot that might experience a sudden jolt, except in slow motion.
Quote from: Dan
You might be misleading yourself, here :

Possibly, it was a conjecture. However some behaviour elements might be in common. It sure would be nice to see some slow motion photography of a knot I have studied under sudden load. For example, is it even clear that a knot behaves worse (the usual assumption) under a sudden load? Some might behave better!

Cheers,

Ian.



Title: Re: Offset knot for climbing
Post by: Mobius on May 17, 2016, 01:16:45 PM
First image: The top knot is Ashley's. If the #1410 is tied like this when climbing... good luck ;) At 30 Kg in this material (mbs ~ 2 kN) the knot had rolled and collapsed with a slippage of 15mm. 15mm when we have a 3mm diameter is hard to ignore, it is a lot. The words 'rolled' and 'collapsed' are deliberate, that is what I saw.

The bottom knot is the flat version. I tied all my climbing rope trials like this (see other images for yourself). This time the #1410 has slipped about 2-3mm at 30kg. Scale things up and think kernmantle 10-11mm and 3mm movement turns into ~10mm with larger diameter rope and equivalent load in mbs terms. That is not far from the results I actually saw.

How close my trial material (3mm polyester braid, ~10% elongation at 50% mbs) replicates (10-11mm kernmantle, ~7% elongation) is not the point here.

The issue was tying the #1410 in the wrong way initially. Rest assured, any climbing rope trials I have done have been the flat version, not with Ashley's twist.

Cheers,

Ian.
Title: Re: Offset knot for climbing
Post by: Mobius on May 21, 2016, 03:43:21 AM
I trialed Dan's offset 9-oh knot again in 10.2mm dynamic kernmantle and it works as far as I am concerned.

The approach I took to search for a better offset than the EDK was simple:
Choose 3kN trials of each proposed knot with the expectation that a knot could be found that would not slip or jam at that force. The knot should be no bigger than 50 diameters in the knub.

(48 diameters swallowed in the knub for a 9-oh).

The knots I trialed were not too big. An offset knot that is flat on one side and looks like a 'tower' on the other side makes little sense to me in terms of not getting caught up on a mountainside somewhere. The tower would defeat the flat side to my mind. Smaller is better the way I see it, as long as it doesn't slip or jam.

Dan has argued that 3kN is probably too high a benchmark for this application, however, that as it may be, I have found 3 knots that can do it. One of them is the 9-oh.

The images below:

1) 9-oh set at 70mm tails

2) At 0.5 kN the knot has settled to 65mm

3) At 1.5 kN the knot has settled to 60mm

4) At 3kN none, or very little further movement observable

10mm movement is not what I am going to be picky with and call slipping, the knot has just settled. One could argue that if I had taken the knot to 6kN and it kept moving then some of that first movement was slippage. The knot did not jam at 3kN and was reasonably easy to undo. I took the 9-oh to 3.5 kN on one other occasion and found it was tighter to undo, however not jammed.

It should be acknowledged that dynamic rope trials are generally a much harder task master than static rope trials. One could expect no problems with the 9-oh used in static kernmantle to 3kN (I have trialed it once in 10.2mm static climbing rope and saw the knot perform well).

Cheers,

Ian.
Title: Re: Offset knot for climbing
Post by: Mobius on May 21, 2016, 03:58:08 AM
Possibly of interest only to me is how the top overhand looks when it is getting tight in some of these offset knots.

The first image is borrowed as a reminder of the knot in question.

The second image shows some compression of the 9-oh after the choke has been easily slid away after a 3kN load. That top overhand looks easy to undo, however I can attest that once that knot gets a bit more on it a hacksaw has been the only remedy I found to undoing it.

Cheers,

Ian.
Title: Re: Offset knot for climbing
Post by: Mobius on May 21, 2016, 07:23:30 AM
Here is a knot I spent months finding. It is extremely easy to come up with a knot that looks promising until you stick it on a rig and trial it. A knot will slip, jam, twist, collapse and do all sort of unexpected things.

I know the lohf8 style knot I show below looks simple. I was not happy with the knot I first showed here in this thread because it jammed at 2kN in 11.2mm dynamic kermantle rope (see very first post and following discussion). That first post knot was still way better than an EDK in my opinion.

The knot shown in this post is also a 'linked overhand figure 8', however it does not slip or jam at 3kN in 10-11 dynamic climbing rope. It is small and does not even hint at jamming at 3kN. It settled no more than 5mm, no slippage.

Despite the effort that went into this knot I show here, I have one I like better. The work I did trialing the EDK was beneficial in finding that.

The knot in this post is one I will come back to if needed.

Cheers,

Ian
Title: Re: Offset knot for climbing
Post by: Mobius on May 22, 2016, 06:35:54 AM
Here is the knot I like most for the offset application. I have tested it the most and I like its compact form. It is small knot, not much bigger than an EDK.

I make no excuses/apologies for my often criticized view of the EDK knot that does get used for this application, in many cases with little problem. My preferred knot doesn't slip or jam in dynamic/static climbing materials up to 3kN, the EDK does (and lower levels), simple as that. If you want to entertain using a small profile knot that does not slip, jam and is easy to tie, then this may be it:

http://bit.ly/1VmOZXy

This knot, rather ironically, is the same knot I started this thread with, except the legs are not twisted. Personally, that finding is rather miffing considering the work I put into finding a better knot than the one I first came up with in this thread ::) Playing with the EDK one day made me try the legs the other way. For the EDK that did not help (see a previous post), however it made a big difference to my originally posted lohf8 knot.

Reversing the legs (parallel instead of the twist I thought was a good idea originally) turned my first knot into one that meets the requirements I set, and quite a lot more. The knot I show below does not slip or jam at 3kN in dynamic and does not jam when I took it to 6kN. I did not see any slippage at 6kN either, though I did not measure for it apart from an eyeball.

I have images showing the knot perform at 3kN in static materials, to show later perhaps. There were no observable performance issues in the 10.2mm static material I tried, a material I believe is generally way easier to test successfully compared to similar size dynamic material.

First image: My knot

Second image: Step one in tying the knot. Step two is not hard to work out and that is it, however look at my first post if in doubt. Keep the legs parallel. I really do not think anyone would have too much trouble tying this knot in the wild.

Third image: Knot at 2kN after being set with 100mm tail markings at nil load. There is no movement/slip as far as I am concerned.

Fourth image: Knot at 3kN; we see a nice flat surface still and there was no movement yet

From here:
1) I am going do a presentation doc that will show this knot in a better to see fashion
2) I will test the knot with different size ropes and post results
3) Hopefully, quick pull tests, properly done by someone with lab facilities, however not by me

Cheers,

Ian.
Title: Re: Offset knot for climbing
Post by: Mobius on May 22, 2016, 12:34:31 PM
Here are two more tying diagrams, the last one is deliberately loose and needs snugging

Cheers,

Ian
Title: Re: Offset knot for climbing
Post by: Mobius on May 28, 2016, 02:29:16 PM
Work in progress as a presentation, however some better images to look at here http://bit.ly/1VmOZXy

See the knot at 3kN in both kernmantle static and kernmantle dynamic climbing materials.

Cheers,

Ian
Title: Re: Offset knot for climbing
Post by: Dan_Lehman on May 31, 2016, 09:04:21 PM
Here are two more tying diagrams, the last one is deliberately loose and needs snugging

Cheers,

Ian
Your knot is a sort of "opposed-directions, offset 8-Oh"
in that you have an overhand & fig.8 resp. in the two
ends but instead of their turning in the same direction
and the latter just making its extra half turn --which
would result in the tails exiting in opposite direcitons,
nb!--, you turn them from the start in opposite
directions and thus that extra half turn of the fig.8
brings its tail to join the overhand's in the exit.

The offset 9-Oh makes a surer *choke* of the
SParts's offset entry into the nub.


--dl*
====
Title: Re: Offset knot for climbing
Post by: Dan_Lehman on May 31, 2016, 09:12:25 PM
First image: The top knot is Ashley's. If the #1410 is tied like this when climbing... good luck ;) At 30 Kg in this material (mbs ~ 2 kN) the knot had rolled and collapsed with a slippage of 15mm. 15mm when we have a 3mm diameter is hard to ignore, it is a lot.  ...
//
The issue was tying the #1410 in the wrong way initially.
Rest assured, ...

We will rest assured if you would please trial the
"EDK-backed EDK" in this material WITH THE ASHELY TWIST
--a sort of worst case scenario (worse yet would be with
dynamic material, maybe wet to boot! ).

I'm not sure why this requested (several times) knot
(knot-combo) continues to be avoided --are you
worried that it will look (too) good?   ::)   ;)
And only load it to a moderately high load,
not a materials-damaging, like-abseiling-bulldozers
among!

It is MUCH more relevant to the particular task of
abseil-ropes joining than loading things to several
times any reasonable force (i.e., > 200 pounds force,
really, an acceptably exaggerated, 2-B-Sure force).


--dl*
===
Title: Re: Offset knot for climbing
Post by: Tom_Zal on June 01, 2016, 01:24:59 AM
Mobius, just wanted to let you know I did a few informal tests of your knot against other knots with paracord and light cord in a homemade "apparatus" and your knot performed great. Of course the tails did not get pulled in, but also, even after loading to near breaking point, it was easy to untie and and barely damaged the rope. (Jammed one time out of 4, probably I did something tied or dressed it wrong, because it didn't come close to jamming the other times.)

I only tested the plain overhand bend once, and you may be happy to know that ultimately the 12-diameter tails were sucked completely through. I'm sure I tied this knot correctly and set it well. It's just one trial though. And before extreme load, only about 3 diameters were sucked in.

You might want to make some tying pictures/instructions following what Dan said about how it's tied - I think that makes clear that it's similar to tying the basic overhand bend, but one rope turns in the opposite direction, and therefore has gone an extra half turn when it emerges along with the other. I don't know about others but I can learn a new knot easier if it's presented as "it's like this other knot you know, with this difference".

Seems clear that EDK backed by EDK would be secure, since the backup knot is just functioning as an overhand stopper? (Edit: I'm not saying it shouldn't be tested - and I'm aware there are materials in which it would fail.) I would think that's the most realistic option for someone concerned about EDK safety - I mean, that's what they're most likely to use, rather than learning a new knot.

Hey if you're testing the 9-oh I hope you're clear on how it's tied - I just wondered because you asked in a previous post if you tied it right and I didn't see a response. I'm sorry if I'm butting in but wouldn't it be a shame if you tested it and it turned out it wasn't tied to Dan's specs?
Title: Re: Offset knot for climbing
Post by: Mobius on June 01, 2016, 07:45:23 AM
First image: The top knot is Ashley's. If the #1410 is tied like this when climbing... good luck ;) At 30 Kg in this material (mbs ~ 2 kN) the knot had rolled and collapsed with a slippage of 15mm. 15mm when we have a 3mm diameter is hard to ignore, it is a lot.  ...
//
The issue was tying the #1410 in the wrong way initially.
Rest assured, ...

We will rest assured if you would please trial the
"EDK-backed EDK" in this material WITH THE ASHELY TWIST
--a sort of worst case scenario (worse yet would be with
dynamic material, maybe wet to boot! ).

I'm not sure why this requested (several times) knot
(knot-combo) continues to be avoided --are you
worried that it will look (too) good?   ::)   ;)
And only load it to a moderately high load,
not a materials-damaging, like-abseiling-bulldozers
among!

It is MUCH more relevant to the particular task of
abseil-ropes joining than loading things to several
times any reasonable force (i.e., > 200 pounds force,
really, an acceptably exaggerated, 2-B-Sure force).


--dl*
===

Hi Dan,

I honestly thought the poorly tied #1410 was the answer to your concern, though not your request(s).

Two poorly tied (Ashley's twist version) back to back will effectively be a knub size of over 70 diameters and therefore, so what if it works? If you cannot tie a knot tie a lot! A knot that size defeats one of the premises of this knot application, that a small footprint is better. I don't think it will 'work' anyway, however let us see.

So, you win, I'll tie it back to back in dynamic climbing material and take some photos at different loads. I have ordered some new rope, so be a little patient please :D

The #1410 is MUCH more relevant for abseiling? I disagree, people are looking at (already using) alternatives as evidenced right here in this forum. The #1410 is simply a benchmark, and not a very good one. If it was so much more relevant then most would be happy with it and this thread (and others on this topic) would not exist; some here and elsewhere are far from happy with it.

An 'offset style knot' has already had several bad press cases , deserved or (perhaps) not, depending on what offset knot it was exactly. However, the EDK moniker did not come from nowhere.

I suspect that the issue for some climbers is not about using the best offset knot, it is about using an offset knot at all!  So I can see the case of where someone reading this could easily say to themselves that an offset knot is not for them, regardless of what trial results show. I knew that view before I even started looking at a new offset knot.

It would be interesting to me to hear from climbers about their current choices in this application.

I am quite happy to trial alternatives to an offset, if there is some agreement about what to test and why.

Cheers,
 
Ian.
Title: Re: Offset knot for climbing
Post by: Mobius on June 01, 2016, 08:47:11 AM
Mobius, just wanted to let you know I did a few informal tests of your knot against other knots with paracord and light cord in a homemade "apparatus" and your knot performed great. Of course the tails did not get pulled in, but also, even after loading to near breaking point, it was easy to untie and and barely damaged the rope. (Jammed one time out of 4, probably I did something tied or dressed it wrong, because it didn't come close to jamming the other times.)

Thank you very much for taking the time to do some trials. Regardless of the results you reported I would have been very happy to read about them.

Quote from: Tom
I only tested the plain overhand bend once, and you may be happy to know that ultimately the 12-diameter tails were sucked completely through. I'm sure I tied this knot correctly and set it well. It's just one trial though. And before extreme load, only about 3 diameters were sucked in.

I have never seen the tails sucked through, I normally get a jam somewhere. Really interesting, thanks.

Quote from: Tom
You might want to make some tying pictures/instructions following what Dan said about how it's tied - I think that makes clear that it's similar to tying the basic overhand bend, but one rope turns in the opposite direction, and therefore has gone an extra half turn when it emerges along with the other. I don't know about others but I can learn a new knot easier if it's presented as "it's like this other knot you know, with this difference".

I know one reason Dan's 9-oh is easy to tie is that you can tie an EDK first and undo it a bit before re-wrapping one tail. Unfortunately there are other knots that look like a 9-oh and are tied similarly. Those other alternatives might be ok, or not, however I believe I have a better knot regardless. At the end of the day, an overhand knot linked with a figure 8 knot should not be too hard to learn!? Easier than some of the new bowlines, methinks ;)

I can look at another tying method for my knot, however please feel free to suggest something.

Quote from: Tom
Seems clear that EDK backed by EDK would be secure, since the backup knot is just functioning as an overhand stopper? (Edit: I'm not saying it shouldn't be tested - and I'm aware there are materials in which it would fail.) I would think that's the most realistic option for someone concerned about EDK safety - I mean, that's what they're most likely to use, rather than learning a new knot.

Hey if you're testing the 9-oh I hope you're clear on how it's tied - I just wondered because you asked in a previous post if you tied it right and I didn't see a response. I'm sorry if I'm butting in but wouldn't it be a shame if you tested it and it turned out it wasn't tied to Dan's specs?

I am clear how the 9-oh is tied.... just wanted Dan to be clear on that too :)

Cheers,

Ian
Title: Re: Offset knot for climbing
Post by: Mobius on June 02, 2016, 10:52:54 AM
Here are two more tying diagrams, the last one is deliberately loose and needs snugging

Cheers,

Ian
Your knot is a sort of "opposed-directions, offset 8-Oh"
in that you have an overhand & fig.8 resp. in the two
ends but instead of their turning in the same direction
and the latter just making its extra half turn --which
would result in the tails exiting in opposite direcitons,
nb!--, you turn them from the start in opposite
directions and thus that extra half turn of the fig.8
brings its tail to join the overhand's in the exit.

The offset 9-Oh makes a surer *choke* of the
SParts's offset entry into the nub.


--dl*
====

Hi Dan,

I agree with you from a theoretical perspective, the 9-Oh does appear to make a surer *choke* than my knot (let's call it lohf8m "linked overhand figure 8 mobius" for the moment). I was surprised to see the 9-Oh move (settle) as much as it did in trials whereas the lohf8m does not apparently move at all at similar loads. Why?

One thing that comes to mind for me is that when I look at the lohf8m it reminds me of a Zeppelin style bend. This is especially true for me after I changed the SParts to a parallel orientation and showed everyone the current knot form. All of a sudden the knot worked really well for me in trials, is that just a coincidence?

I do not think so, however theory should meet practice as much as practice should meet theory. I am quite a fan of the Zeppelin style bends and how well I see them working, I suspect that is less true for many. I am interested in your comments please Dan.

Cheers,

Ian.



Title: Re: Offset knot for climbing
Post by: agent_smith on June 04, 2016, 01:37:44 AM
I think the concept of interlinking #570 'figure  8' with #46 'overhand knot' has merit and is worthy of further investigation.

The overall 'footprint' is not significantly greater than #1410 - and keeping the volume/size as small as possible is an important design goal.

The important goals of stability and security are (at first instance) being achieved... further followup testing by other interested individuals will confirm.

The are a number of possible variations in how the overhand knot (#46) can be woven into the structure of the figure 8 (#570). I will look into which combination is most effective/efficient.

A desirable goal is to find an easy tying method - that consistently produces the correct structure.

Overall - Mobius has discovered a promising line of thinking.
Title: Re: Offset knot for climbing
Post by: Mobius on June 04, 2016, 04:22:36 AM
I think the concept of interlinking #570 'figure  8' with #46 'overhand knot' has merit and is worthy of further investigation.

The overall 'footprint' is not significantly greater than #1410 - and keeping the volume/size as small as possible is an important design goal.

The important goals of stability and security are (at first instance) being achieved... further followup testing by other interested individuals will confirm.

The are a number of possible variations in how the overhand knot (#46) can be woven into the structure of the figure 8 (#570). I will look into which combination is most effective/efficient.

A desirable goal is to find an easy tying method - that consistently produces the correct structure.

Overall - Mobius has discovered a promising line of thinking.

Thank you Mark, I appreciate the acknowledgement.

A little background. Several months back I spent a number of weeks playing around with and trialing 'linked overhands' in an offset application. I found nothing I liked enough to show here. I generally found knots that would either collapse or jam at too lower load for my tastes. That is not say there is not a good one, I just could not find it.

The linking of an overhand and a figure 8 showed much more promise right from the start for me. I am quite happy to keep trialing these style of knots, if someone has something they think is good. I made this offer to all earlier in this thread, however it is here again. Just because I found one I like, does not mean I am stopping here.

While I am waiting for some new rope to arrive, I think I will do some pictures of the other lohf8 I found (Reply#32). Some might like the way that lohf8 is tied in preference to what I currently like the best.

Cheers,

Ian.
Title: Re: Offset knot for climbing
Post by: Mobius on June 05, 2016, 04:29:57 AM
Here is the knot I first showed in Reply#32 (let's call it lohf8m2 for now)

Some quick things to note:

1) It has the figure 8 above the overhand, the lohf8m is the opposite case (better or worse?)

2) The lohf8m2 has not been trialed a lot by me, though I am confident it does meet the standards I set at present

3) It looks slightly bigger than a lohf8m (41 diams), I have not measured it yet

4) Look at the last 6 slides of http://bit.ly/1VmOZXy for a way to tie

5) One possible advantage of this knot is that you could start with an EDK and devolve it a bit before re-wrapping the top into a figure 8 (see 4)

(A bit of a hurried effort overall ... work in progress)

Cheers,

Ian.

Title: Re: Offset knot for climbing
Post by: agent_smith on June 13, 2016, 09:25:56 AM
Hi Mobius,

I would like to include your creations in my 'Analysis of abseil rope joining knots' paper.

What I need most is the following data:

[ ] load threshold at which instability is triggered
[ ] load threshold where jamming occurs
[ ] force required to initiate translation of offset knot around 90 degree edge
[ ] tail draw-in at various load milestones (Note avoidance of the term 'slippage'. What we are observing is changes in the tail length as the knot compresses under load).

NOTES:
1. instability is defined as: A dynamic event where there is a sudden change in the knot structure (eg capsizing) - compression is not instability and neither is tail draw-in.
2. rope diameters tested must fall within the 8.5mm - 11.0mm range.
3. data obtained for both low stretch and dynamic ropes - must be identical diameters so comparisons can be drawn.
4. unequal rope diameters should also be tested - eg 9.0mm joined to 10.2mm - the variance should be more than 1.0mm.
5. wet rope test (it is assumed that all testing is with dry ropes) - it will be useful to look at data obtained from wet ropes (soak rope specimens in water for 1 hour to condition the ropes).
6. a sample set of 5 tests should be conducted for each test objective - this will enable some statistical analysis of results.

If you can obtain these data points, it will be greatly appreciated.

I would suggest that #1410 be used as a control.


Mark Gommers
Title: Re: Offset knot for climbing
Post by: Dan_Lehman on June 13, 2016, 08:47:09 PM
What I need most is the following data:

[ ] load threshold at which instability is triggered
[ ] load threshold where jamming occurs
[ ] force required to initiate translation of offset knot around 90 degree edge
[ ] tail draw-in at various load milestones (Note avoidance of the term 'slippage'.
 What we are observing is changes in the tail length as the knot compresses under load).
We'd be making far better progress were at least
an initial battery of tests done purely to see how
the various knots in various materials behaved at
forces that correspond to expected abseil forces
(either in direct materials expected to see such use,
or in scaled forces for other materials, based on some
kind of reasonable scaling estimation).

Notably, such testing would not be sacrificing test cordage
because of excessive loading!!!  It is much more helpful
to see some several tests of material & knot (put into
various orientations) at expected loading (or some small
excess of this) than to have break/jamming tests coming
from loading that would never be matched in application!

(I need to think up some easy way of applying and
removing such reasonable loading --done perhaps with
decent 2:1 pulley and approx. 100# load (which load
could be simply bumped by application of manual force
or attachment of a 2nd harnessed weight; or something
I stand in for initial load, and then can pre-load w/weight
before standing in it again).
)

Re the reddened assertion,]
no, I think that what Mobius has observed isn't compression
but in fact slippage as the prying-open forces rise (WAY past
expected forces!) and so pull out more tail(s) --at least in
some cases.  Compression doesn't suck tail in, just feeds
material out to loaded parts.
But it's worth noting that the slippage comes only with an
increase of load, not just given a loaded state and then
holding the load (suspended weight, say) and having some
creeping slippage.


--dl*
====
Title: Re: Offset knot for climbing
Post by: agent_smith on June 13, 2016, 11:08:47 PM
Quote
We'd be making far better progress were at least
an initial battery of tests done purely to see how
the various knots in various materials behaved at
forces that correspond to expected abseil forces

Yes - and one might also comment that we need meaningful data points - that can be replicated/reproduced by other testers. To me, this has been one of the biggest issues with historical testing. It is difficult if not impossible for anyone to try to reproduce others results (and we may well ask why...?). Part of the underlying reason (I think) is the fixation on pure 'MBS yield' break tests instead of looking at the salient features I have advanced.

The data points I am requesting are easy to understand milestones.
[ ] like what is the load threshold where instability is triggered?

Quote
Notably, such testing would not be sacrificing test cordage
because of excessive loading!!
We are talking about small quantities of cordage - not whole lengths of rope.
It is possible to work with 1.0m test articles - by simply uniting both ends with an offset knot - thus forming a circle/loop (a side-effect of testing a loop is that the forces must by definition be doubled - and so the test bed must be capable of achieving higher loads).

Quote
Compression doesn't suck tail in, just feeds
material out to loaded parts.
And yet, testing has demonstrated that tails do shrink in length as load is increased. I have documented this before - and I haven't seen a reversal of this - that is, I have never seen tails grow in length as load is applied. The reduction in tail length that I have observed has not been 'slippage' - it certainly was not a case of any sudden movements. The tail draw-in was always in a progressive manner in response to compression caused by increasing load.

As for jamming - this is a useful data point - and one could argue that it is useful to know for all knots.
I have thus far found that in the 9.0mm class of ropes, jamming appears to occur once the load reaches 3kN (approx 300 kg).
Once jamming occurs - there is no need to continue applying load - testing can cease at that point.
I define 'jamming' as a state where it is not possible to untie the knot by hand (without the use of any tools).
If a knot can be untied by hand - it is not 'jammed'.

Another point that I might make is that I have not been talking about loads to probe the MBS yield point. This is what virtually all other testers have focused their efforts on (which is pointless and proves nothing).
What I am requesting is more useful and meaningful.
[ ] for example - what is the force required to initiate translation around a 90 degree edge?
[ ] at what load is instability triggered?
[ ] at what load does the knot become jammed?

These are data points that others could stand a reasonable chance of reproducing in future tests.

Mark G

PS I can foresee a situation brewing where we get caught up in an endless debate about what to test - and the wheels just keep spinning and spinning in the dust...
Title: Re: Offset knot for climbing
Post by: Dan_Lehman on June 14, 2016, 10:15:34 PM
Yes - and one might also comment that we need meaningful data points - that can be replicated/reproduced by other testers. To me, this has been one of the biggest issues with historical testing. It is difficult if not impossible for anyone to try to reproduce others' results (and we may well ask why...?). Part of the underlying reason (I think) is the fixation on pure 'MBS yield' break tests instead of looking at the salient features I have advanced.
Given the many variables in such testing --of materials,
their orientation in the knot, the knot's orientation
(as has been previously discussed), the application
of force (which at its easiest might not be the best
for modeling actual behavior)--
it's not surprising that replication is difficult.
But before concluding that outright,
yes, it would be good were the many factors at least
recognized and reported.

Quote
Quote
Notably, such testing would not be sacrificing test cordage
because of excessive loading!!
We are talking about small quantities of cordage - not whole lengths of rope.
And yet some are talking about multiple test
repeats for the sake of Sacred Statistics, and
THAT even for a fixed-set-of-variable-factors!!
.:. Given all that, one is talking about hundreds
of these "small quantities" --not small at all,
and not small of required test effort!

Quote
Quote
Compression doesn't suck tail in, just feeds
material out to loaded parts.
And yet, testing has demonstrated that tails do shrink in length as load is increased. I have documented this before --and I haven't seen a reversal of this-- that is, I have never seen tails grow in length as load is applied. The reduction in tail length that I have observed has not been 'slippage' --it certainly was not a case of any sudden movements. The tail draw-in was always in a progressive manner in response to compression caused by increasing load.
"Not been slippage" :: however do you come to this
assertion?  How could compression possibly bring
material INTO the compressed object?!  It is necessary
in fact that material goes OUT of the knot, as compression
stretches & shrinks-in-diameter material (exp. such as is
used for abseiling; less so for hi-mod, static stuff).

Quote
As for jamming - this is a useful data point
FIRST, let's clear knots for expected loads PLUS
some bump for "just-in-case" excess; in short,
for actual USE,
not academic aspects to fill some table.

JUST to do this --for a variety of materials combinations
and knot orientations and loading variance-- will take a
LOT of effort; it need not take so much of materials.

--dl*
====
Title: Re: Offset knot for climbing
Post by: agent_smith on June 15, 2016, 04:18:44 AM
Quote
"Not been slippage" :: however do you come to this
assertion?  How could compression possibly bring
material INTO the compressed object?!

By observation Dan.

Here is data from a test:

Test date:    July 2011
Knot: #1410 with 1 additional binding turn (refer PACI knot study guide)
Tails initially set at 100.0 mm length.
Measured by digital load cell (dynafor 5 ton)
[ ] EN 892 dynamic ropes (9.1mm Beal Joker joined to 9.0mm diameter Edelrid rope)

Static load test:
[ ] at 0.0kN = 100.0mm tails
[ ] at 0.5kN = 90.0mm tails
[ ] at 1.0kN = 85.0mm tails
[ ] at 1.5kN = 85.0mm tails
[ ] at 2.0kN = 80.0mm tails
Test stopped at 2.0kN load.
Dynamic test drop also performed with 80kg mass + 1.0m free-fall.

The tails started at 100.0mm and ended at 80.0mm length.
That's a 20% reduction in length.
The tails did not 'slip' - as in, there were no sudden movements that one could discern as being slippage. Rather, it was a gradual and progressive response to increasing load.

How do you account for this result Dan?

Mark G
Title: Re: Offset knot for climbing
Post by: Mobius on June 15, 2016, 07:40:17 AM

 What we are observing is changes in the tail length as the knot compresses under load).

Re the reddened assertion,]
no, I think that what Mobius has observed isn't compression
but in fact slippage as the prying-open forces rise (WAY past
expected forces!) and so pull out more tail(s) --at least in
some cases.  Compression doesn't suck tail in, just feeds
material out to loaded parts.
But it's worth noting that the slippage comes only with an
increase of load, not just given a loaded state and then
holding the load (suspended weight, say) and having some
creeping slippage.


--dl*
====

I agree with Dan here. What movement I see happening in my trials I largely attribute to slippage. If you increase the load the knot can slip some more, or jam. That later movement observed from increased load has little to do with compression in my opinion.

If compression is the culprit why does a knot like I propose in this application show little to no movement of the tails even at 3kN and beyond? I have images showing my knots under load and compressed, yet the tails have not apparently moved, this is what I strove to achieve in all the testing I did of this knot style.

This is also a point I tried to make a long time ago: I look at some test results and see slippage. When I look at a knot that does not slip I see results where the tails have hardly moved at all under increasing load.

Cheers,

Ian.
Title: Re: Offset knot for climbing
Post by: agent_smith on June 15, 2016, 08:35:56 AM
In puzzlement over test results and ones observations... I am thinking that the English word 'slip' or 'slippage' is being used in a way that belies what is actually taking place.

Oxford dictionary online:  Examples...
[with adverbial of direction] (Of an object) accidentally slide or move out of position or from someone's grasp
* The envelope slipped through Luke's fingers
* A wisp of hair had slipped down over her face
More example sentences Synonyms
* Fail to grip or make proper contact with a surface: the front wheels began to slip
* (as adjective slipping) a badly slipping clutch
* [with object] Escape or get loose from
* (a means of restraint): The giant balloon slipped its moorings.
* An act of sliding unintentionally for a short distance: a single slip could send them plummeting down the mountainside.
*[mass noun] Relative movement of an object or surface and a solid surface in contact with it.

I am unclear whether Mobius and Dan have actually taken notice of the test results I had posted?
I measured a 20% reduction in the overall tail length at a load milestone of 2.0kN. At each load milestone - the load was held for a short interval. During these holds, there was no observed 'slippage' of any tail segments.
It is important to note that this 20% reduction did not occur suddenly or within a very short time interval.
The shrinkage of the tails occurred progressively (ie gradually) in direct proportion to increasing load.

The English word 'slip' or 'slippage' is not an appropriate descriptor in my opinion.

I would also comment that in all the testing I have done, I have never seen tails increase in length as load is applied.
I have however, always seen tails decrease in length as load is increased.
I have also observed that as load increases, the knot core compresses.

I would also comment that if one was attempting to cast #1410 in a negative light - then such a person might be persuaded to use the term 'slip' to promote such a purpose. The average reader (layperson) might also be drawn to, and fixated on the word 'slip' - and therefore also form a negative view. Furthermore, the word 'slip' conveys feelings of danger - and since climbers/canyoners would be placing absolute trust in #1410 (or some other joining knot) - the word 'slip' further exacerbates any negative feelings.

Deleting the word 'slip' (or 'slippage') from the test observations and inserting "progressive tail draw-in", might cast offset knots such as #1410 in a different light.

The paradox here is that offset #1410 (aka 'Euro death knot' - a poor descriptor that some almost manically adhere to) is actually safe to use in competent hands. I personally have used #1410 on or about 200-300 occasions in my lifetime and I have never observed 'slippage' while trusting my life to it. I still exist - that is, I am still alive (I must be since I am typing this post). If on any of those occasions I would have observed 'slippage' - I would have ceased and desisted in using #1410. Note that the vast majority of my personal use is with EN892 dynamic climbing ropes in the 9.0mm range of diameters ('half' ropes - and more recently, triple certified ropes such as the Beal Joker).

Mark Gommers

EDITS: To correct grammar and typos...
Title: Re: Offset knot for climbing
Post by: Dan_Lehman on June 15, 2016, 11:56:35 PM




I am thinking that the English word 'slip' or 'slippage' is being used in a way that belies what is actually taking place.
...
I am unclear whether Mobius and Dan have actually taken notice of the test results I had posted?
I measured a 20% reduction in the overall tail length at a load milestone of 2.0kN.
It is important to note that this 20% reduction did not occur suddenly or within a very short time interval.
The shrinkage of the tails occurred progressively (ie gradually) in direct proportion to increasing load.

The English word 'slip' or 'slippage' is not an appropriate descriptor in my opinion.

I would also comment that in all the testing I have done, I have never seen tails increase in length as load is applied.
I have however, always seen tails decrease in length as load is increased.
I have also observed that as load increases, the knot core compresses.

But this is going silly : we know what "slippage" means,
but there can be the discrimination between you & Mobius
of slippage forced by transformation of the knot to some
more stretched or compressed form
and what might come at certain forces continuously,
the knot failing to hold, then --as is shown impressively
in the French, Beal video of "pure Dyneema" braided rope
just pulling through even a double grapevine/trip.fish.
(until it did break)!!

IMO, what Mobius sees is, yes, some "silppage", but it's
what comes in the knot opening wider (the particular one
pulling in some tail from choking strand to accommodate)
on increased load --upon which it holds, but then the load
is raised and ... <repeat>.
There is also the sort of "ratcheting" slippage that was
reported by both Tom Moyer and some other testers of
solid nylon & solid HMPE webbing in the water knot
which came at light, cyclical loading, where on the
relaxing of load there was this peculiar absorption of some
SPart but not the "exterior" [my term] tail, and so by
cyclic increments, it got pulled through --and slowly (to the
puzzlement of those who recall needing tools to untie such
knots after usage!).

"I have never seen tails get longer" :: well DUH!!  But you
have seen --or sh/could have done-- SParts lengthen.

.:. So I take A_S's point in resisting "slippage" as not seeing
the sort of it-just-keeps-flowing-out sort of thing one would
worry much about, but technically it is some bit of slippage
at a point (nipping the tail) in the knot in accommodating
forces that does happen.  (And one might wonder if it could
happen in the going-one-direction-only way that was seen
for webbing in that "ratcheting" --something to be worried
about for repeated loadings, e.g. !)

AND we can note that Mobius is seeing things at relative
forces WAY WAY beyond expected usage --costing him
materials, and me gasps of exasperation (air pollution!).

AND TO THIS POINT --of EDK tail slipping, and choking tail i.p.--,
I tried amending this knot by tucking the choking tail around
back under its SPart's initial turn into the knot.  This tucking
works okay with thin+thick, but is problematic (in being
rightly oriented and not botching dressing) in like-diameter
ends (meaning "do NOT do it"!).  Done rightly, the lock
looks good --that tail can't **slip** but only stretch a bit,
the nip coming w/high load and all.
SOOOO, that particular detail might be something to see
about incorporating into a *new knot*, avoiding the issues
of dubious dressing/positioning/stability.
(A stopper knot in the choking tail works similarly,
 at the cost of this added knot-bulk.)

And please stop grousing about "EDK" :: we have enough
confusion in this world --growing in leaps & Trumps, now,
courtesy of shoot quickly and broadly Net communications--
w/o furthering that :: best info is that the name arose from
dubious Yankee observers of Euro practice (a practice that
yes we hope was safe); with the knot's broad acceptance,
though still not wholly bereft of doubters, it becomes kind
of an inside joke.  --less funny when avoiding the safer
variety (overhand) a worse one (fig.8 ) is employed;
though that one, too, has been used safely much,
just sadly not as much.   "EDK-8" is something generally
understood when uttered; "offset fig.8" is the prettier term,
which we'll hope finds traction, as "offset" then gains legs
to go where needed.

Positive tests in this setting are less helpful than ones
that reveal problems.  And my urging Mobius's testing
of the material AND dressing that got such amazingly
quick failure w/the commonly used & working EDK
is wanted to see if the backed-up version can stand up
to that --yeah, a mere single positive, but one that
should impress us (if it works) into seeing how badly
tied things can be and yet be saved.
We won't so much do this all 'round,
and can recommend something *cleaner* and so on,
but for an ace-up-the-sleeve (or wildcard!), knowing
a clumsy but stupid-tired-proof solution is a lot.
(And SAR team might be working in deliberate ways
amenable to doing some careful things; climbers in
threat of weather after overreaching their abilities
can make mistakes.)


--dl*
====
Title: Re: Offset knot for climbing
Post by: agent_smith on June 16, 2016, 04:53:58 AM
Quote
as is shown impressively
in the French, Beal video of "pure Dyneema" braided rope
just pulling through even a double grapevine/trip.fish.
(until it did break)!!

I haven't seen EN892 dynamic climbing ropes constructed from 100% 'dyneema' - have you? If you have, where? And by whom I wonder?
You can purchase this material in accessory cord form and in slings - but I don't think manufacturing has extended to EN892 certified dynamic ropes?

This then raises the question: Why test offset rope joining knots with dyneema? What will this prove?
Would it not be more relevant (and realistic) to test with commonly available EN892 climbing ropes?

One could use the term 'slip' or 'slippage' in dyneema cordage - as indeed this is what the ordinary person might witness in dyneema load testing. This ordinary understanding of the language is not applicable to EN892 certified dynamic climbing ropes - where the word 'slip' or 'slipping' is not what occurs within the operation loads of abseiling on offset joining knots.

Again, language such as 'slip' conveys the wrong impression to the layperson (as I have stated before) applying an ordinary interpretation. If ones objective was to attempt to convey mixed feelings or doubt about a particular joining knot (eg #1410) - then use of the word 'slip' would promote that purpose.

Quote
But this is going silly : we know what "slippage" means
Indeed! Ordinary understanding of this word by the layperson (in relation to life support knots) would convey feelings of doubt and apprehension.
I am careful in avoiding use of such a word - where its use is misplaced under a normal operational loading profile for an abseil descent.

Quote
And please stop grousing about "EDK" :: we have enough
confusion in this world
Indeed.
And imagine the use of this phrase to new learners. What feelings/emotions would it convey if an instructor chose to use this phrase in front of new learners?
This is casting #1410 offset joining knot in a controversial light right from the outset.

It is a sad and tired old joke - yes - and I concur with your historical musings - but under careful and close scrutiny, is #1410 worthy of such controversy? If you answer this in the affirmative, then yes the 'EDK' term should continue.

If you answer in the negative, then perhaps no, the 'EDK' term should be quietly dropped.
But who is driving this phrase? Is it the instructors who pass this on to their new climbing students? Is it forums like this on the internet?
Most climbers are not knotting theoreticians and simply latch on to popular topics they hear about and run with it. Perceived notions are obtained from those who choose to propagate them. Perception then becomes reality.

To advance my own theory:

New climbers/abseilers/canyoners have no pre-conceived notions about offset #1410. Their opinions must be derived from exposure to public forums, contact with other climbers/abseilers/canyoners, editorial/articles from books and magazines, and of course during instruction from professional climbing instructors and Guides.
If #1410 was presented in a positive manner with avoidance of the phrase 'EDK' and demonstrated effectively to new learners - the 'joke name' might quietly disappear (albeit slowly over time).
If on the other hand, those who are in positions of influence (eg Instructors/Guides/Editors and content creators of magazines and online forums) make a conscious decision to continue the use of the phrase 'EDK' - they are therefore deliberately choosing to propagate the use of the phrase. Laypeople and new learners will simply adopt and then repeat what others are telling them. If enough people are using the phrase - it reaches a 'critical mass' and it becomes self-perpetuating.

Quote
commonly used & working EDK
is wanted to see if the backed-up version

I do not support nor promote backing up #1410 with another #1410 (if that's what you had in mind). Although one can of course do this...but why would you if there is good data coupled with empirical evidence that #1410 is stable and secure within all expected operational loads (based on 1 person mass).

This is why we need some robust testing to establish reliable data points that can be reproduced by other testers.
For example: Probing for the load threshold where instability is triggered.

Mark G
Title: Re: Offset knot for climbing
Post by: Mobius on June 16, 2016, 10:49:31 AM
Hi Dan (for you  ;D),

Here are some images of a poorly tied back-to-back #1410 duo trialed in 11.2mm dynamic kernmantle (old climbing gym pieces I salvaged).

I kept the test loads 'low' so Dan doesn't have to remind me how I am testing WAY too high  :)

A missing image is at 1.5kN and if you want to see that, you can later.

Observations: I think the knot is so big it has not settled yet (even at 2kN). The top #1410 did quite a bit of moving (though no observable tail slip); hopefully you can see that from the images I provide. I thought the knot would collapse and perhaps it would eventually. However taking this knot double up to 5 or 6 kN does not prove anything much anyway.

Cheers,

Ian.
Title: Re: Offset knot for climbing
Post by: Mobius on June 16, 2016, 11:54:06 AM
What follows is off topic, though still relevant to recent discussions here I think.

The nomenclature of knots is very difficult. I have loved knots and read about knots since I was a boy. I have never studied them in earnest, until relatively recently. Despite that, I really thought I knew what words like 'stable', 'slippage' and 'secure' (for example) meant when it came to a knot.

Later I learned to qualify such words and think more in terms of statements like "xknot does not slip at 50% mbs", or, "xknot does not slip at the working load of the rope". That be may fine, however I think that hides the real problem: The problem seems to me that words like 'slip' mean different things to different people. The lexicon is in doubt.

Additionally, I have tried searching words like 'stable', or, 'instability' (for example) in Ashley (and the internet wrto knots) and got nowhere.

I suspect at least some of the reason that progress is very slow with regard to knot technology is knot nomenclature. We have not got the lexicon right yet. In some cases we do not speak the same knot language, so it seems.

If this is something others are willing to discuss, our moderators might fresh start this topic (post) for us.

Cheers,

Ian.




Title: Re: Offset knot for climbing
Post by: Mobius on June 17, 2016, 09:35:50 AM
Here are some images of back-to-back #1410's that are tied properly. Dan might be interested in these too.

This knot duo behaved better than two poorly tied #1410's, as one would hope. There was far less movement of the top #1410 with increasing load and there was no discernible tail movement.

Cheers,

Ian.
Title: Re: Offset knot for climbing
Post by: Mobius on June 18, 2016, 02:52:35 AM
Hi Mobius,

I would like to include your creations in my 'Analysis of abseil rope joining knots' paper.

What I need most is the following data:

[ ] load threshold at which instability is triggered
[ ] load threshold where jamming occurs
[ ] force required to initiate translation of offset knot around 90 degree edge
[ ] tail draw-in at various load milestones (Note avoidance of the term 'slippage'. What we are observing is changes in the tail length as the knot compresses under load).

NOTES:
1. instability is defined as: A dynamic event where there is a sudden change in the knot structure (eg capsizing) - compression is not instability and neither is tail draw-in.
2. rope diameters tested must fall within the 8.5mm - 11.0mm range.
3. data obtained for both low stretch and dynamic ropes - must be identical diameters so comparisons can be drawn.
4. unequal rope diameters should also be tested - eg 9.0mm joined to 10.2mm - the variance should be more than 1.0mm.
5. wet rope test (it is assumed that all testing is with dry ropes) - it will be useful to look at data obtained from wet ropes (soak rope specimens in water for 1 hour to condition the ropes).
6. a sample set of 5 tests should be conducted for each test objective - this will enable some statistical analysis of results.

If you can obtain these data points, it will be greatly appreciated.

I would suggest that #1410 be used as a control.


Mark Gommers
Hi Mark,

Firstly, you are welcome to use any knots I come up with that may be useful to your paper.

With regard to the one other point raised above:

The triggering of instability (as Mark defines it) is a tricky one for me to determine. My personal approach would be to first take a proposed knot up to a level of 50% mbs (~1 kN) in the 3mm polyester braid I often still use for preliminary trials. If the knot could go to that level without seeing a collapse (looking for no jamming, acceptable tail movement as well of course) than I would then feel pretty confident that the same knot would perform well in (say) 10.2 mm static kernmantle to very high load levels.

I would be much less confident about the performance of (say) 10.2mm dynamic kernmantle. Dynamic rope in climbing is a tough material to trial in, especially in terms of finding a knot that meets the standards I set. I have sometimes been tempted to trial knots in bungee cord; if the knot worked for me in that, dynamic climbing rope would be no problem ;)  ::)

The real issue here is I suspect I will not see any instability (or jamming, tail movement) in the knots I have proposed at the load level I can take 10.2 mm climbing rope to. The rig I have worries me if I take it above 6kN. I have seen my work bench start bowing at around 7kN and my winch (though rated above 10kN) starts makes some disconcerting noises.

I could do a battery of trials with 10.2mm static and dynamic ropes to 6kN and report what I see. Is that useful?

Cheers,

Ian

[Edit: normal typos and grammar fixes]

Title: Re: Offset knot for climbing
Post by: agent_smith on June 19, 2016, 09:36:23 AM
I'll be thankful for any quality data on tests involving offset rope joining knots.

Quote
The triggering of instability (as Mark defines it) is a tricky one for me one for me to determine.

If you look at historical test results floating around on the internet - the bulk of it is fixated on MBS yield break tests.

You will have trouble finding data on 'instability threshold' and 'jamming threshold'. The other data that is lacking is on the force required to initiate translation around a 90 degree edge. As far as I can see, Dave Drohan looks like the only person to have seriously investigated this aspect.

I strongly recommend that you read Mr Drohan's report here: http://www.bwrs.org.au/sites/default/inline-files/1%20main%20paper.pdf

[ ] page 7: illustrations of knot specimens (note his naming conventions)
[ ] page 12: test rig for measuring force required to initiate translation of knot over 90 degree edge (see also pages 22-26)
[ ] page 13: reference to tail 'slippage' (see also page 8 )
[ ] page 18 (table 2): knot strength comparisons.... (Note that I prefer to use the term "Knot MBS yield point")
[ ] page 19 (last para): another reference to 'slippage'
[ ] page 27: conclusions

A note on Mr Drohan's use of the term 'slippage'.
My personal view is that what Mr Drohan was observing was not 'slippage' or 'slipping' per se. What he observed was what I refer to as "compression induced tail draw-in".
I again make reference to the fact that when #1410 (offset overhand knot / offset water knot / offset overhand bend) is used in the field in real situations - we do not see any 'slip' or 'slippage' of the tail under nominal loads. The tails do not 'slip' - if climbers/canyoners ever observed any 'slippage', you can be assured that they would immediately stop and abandon using #1410 due to fear of death. In artificial test situations in the lab - where we deliberately load offset knots to study their behaviour - we also don't see tails slip, we see a gradual tail draw-in which is induced by compression of the knot core. I have observed this myself when applying load to offset knots - at various load milestones I paused and held the load constant for several minutes. During these temporary 'pauses / 'holds' - I never observed any evidence of 'creep' of 'slipping' of tails.
The opposing SParts are pulled and stretched away from the core while the core is also being compressed. In response to the stretching of the SParts and the compression of the core, the tails have a corresponding 'draw-in'. I would not characterize this 'compression induced tail draw-in' as slippage. Mr Drohan was not looking at knots in the way some theoreticians do in the IGKT. He certainly was not aware of technical terms such as 'offset' and what the term 'offset' actually means (the core of the knot is displaced from the axis of tension and the SParts converge along a parallel pathway).

What I like about Mr Drohan's research is that he is one of the first to look at this issue in a different way than his predecessors. His examination of the force required to initiate translation of the knot over a 90 degree edge is excellent and provides us with an opportunity to replicate his results. And this is one of my biggest gripes with much of the knot testing done around the world - it is difficult if not impossible to reproduce the test results of others.

He had a chance to examine 'instability' - but did not. I think he was still caught up in an era where the focus was mostly on knot MBS yield points.
he also did not examine the jamming threshold of offset knots.

I define 'instability' as: A dynamic event, where a sudden change occurs in the knot geometry in response to load. The sudden change can be 'capsizing' or some other tipping point where structural change is triggered.
I would urge future testers of 'offset' knots to probe the load threshold where instability is triggered.
...

Quote
The nomenclature of knots is very difficult.
With regard to nomenclature, others have tried but in virtually all cases - it seems to bog down and evaporate. Derek Smith realised early on that terminology, definitions and knot components needed to be clarified...link: http://igkt.net/sm/index.php?topic=5594.0

Mark Gommers
Title: Re: Offset knot for climbing
Post by: Dan_Lehman on June 20, 2016, 08:56:26 PM
Hi Dan (for you  ;D),

Here are some images of a poorly tied back-to-back #1410
duo trialed in 11.2mm dynamic kernmantle (old climbing gym pieces I salvaged).

I kept the test loads 'low' so Dan doesn't have to remind me how I am testing WAY too high  :)
Thank you.  And so as to satisfy your thirst for high
load values, you could do multiple low-loadings and
add them (1kn + 1kn + 1kn...), having fun just throwing
together intentionally careless tyings of this EDK-backed EDK.

It won't do well in general practice to have quite loose
knots, as those might disappear prior push coming to shove!
But somewhat so, and with some space between knots,
I think gives a fair idea of how robust this knotted structure
is, if it can handle a case that might arise in fatigued hurry
and stiff ropes (looseness somewhat modeling knotted
stiff cordage which by stiffness hasn't set well).


 :)
Title: Re: Offset knot for climbing
Post by: Mobius on June 21, 2016, 10:28:34 AM
Here is my preferred knot and one that I currently call lohf8m, tied in 6mm accessory and 11.2mm dynamic climbing ropes. The larger rope is well used, the smaller one is new.

The loading's were deliberately low. I took the knot to 1kN without seeing any sign of knot collapse or noticeable tail movement. The knot was easy to untie after this load.

I could do a battery of tests on this configuration if deemed useful.

Cheers,

Ian.

Title: Re: Offset knot for climbing
Post by: agent_smith on June 21, 2016, 04:13:50 PM
Quote
tied in 6mm accessory and 11.2mm dynamic climbing ropes
If you intend to test this offset structure, I would comment that the use of 6.0mm accessory cord is not realistic.
Nobody abseils with two ropes of such a wide variance of diameters fed through a tubular belay device. There would be a significant risk of 'differential' rope movement through each slot of the belay device.

Those climbers who carry ultra thin accessory cords - use them as 'pull cords' to retrieve the larger diameter rope.
They typically jam/trap the knot structure up against the anchorage - hoping that the volume/mass of the knot is sufficient so that it will not pull through the anchorage. Abseil descent is performed on a single rope. Therefore, the offset knot is not being loaded in the normal way.

Mark Gommers
Title: Re: Offset knot for climbing
Post by: Dan_Lehman on June 21, 2016, 09:08:56 PM
Quote
tied in 6mm accessory and 11.2mm dynamic climbing ropes
If you intend to test this offset structure, I would comment that the use of 6.0mm accessory cord is not realistic.
Nobody abseils with two ropes of such a wide variance of diameters fed through a tubular belay device. There would be a significant risk of 'differential' rope movement through each slot of the belay device.

Those climbers who carry ultra thin accessory cords - use them as 'pull cords' to retrieve the larger diameter rope.
They typically jam/trap the knot structure up against the anchorage - hoping that the volume/mass of the knot is sufficient so that it will not pull through the anchorage. Abseil descent is performed on a single rope. Therefore, the offset knot is not being loaded in the normal way.
Although as a recent accident report you cited indicates,
maybe they SHOULD do so --and if the stopper fails to
stop, then there's at leas be the hope of catching safety
via rap. device.  (One might engage a special one for
the smaller rope ("special" ="separate" ?) !)
(Likely anyone w/6mm might have the modern,
equiv. of old "11mm" --something beginning with "9"!)

As for loading, at lighter forces of rope-pulling the
offset end-2-end knot will see effect.


--dl*
====
Title: Re: Offset knot for climbing
Post by: Mobius on June 22, 2016, 06:50:13 AM
Quote
tied in 6mm accessory and 11.2mm dynamic climbing ropes
If you intend to test this offset structure, I would comment that the use of 6.0mm accessory cord is not realistic.
Nobody abseils with two ropes of such a wide variance of diameters fed through a tubular belay device. There would be a significant risk of 'differential' rope movement through each slot of the belay device.

Those climbers who carry ultra thin accessory cords - use them as 'pull cords' to retrieve the larger diameter rope.
They typically jam/trap the knot structure up against the anchorage - hoping that the volume/mass of the knot is sufficient so that it will not pull through the anchorage. Abseil descent is performed on a single rope. Therefore, the offset knot is not being loaded in the normal way.

Mark Gommers

Thank you, MarK.

I have some 8.5mm dynamic rope on order which I will put with some 10.2mm dynamic I have and test that. That should be more realistic I hope.

Static rope wise, I could try 11.2mm with 10.2mm which should be ok I suppose as well.

Any point me trying to jam the 6/11.2 knot I show up against an anchorage as a test? Does climbing have a need for a bend for end-2-end use that will handle two quite differently sized ropes (not necessarily an offset one)?

Cheers,

Ian.
Title: Re: Offset knot for climbing
Post by: agent_smith on June 22, 2016, 09:08:37 AM
Mobius,

I would urge you to first concentrate on a battery of tests on #1410.
If you do this, it could serve as a valuable reference for all future researchers to cite...at the moment, most people keep citing the Tom Moyer tests - which is limited in scope and concept and dates back to Nov 1999. I think it is alarming (and sad) that we have no solid new ground-breaking test data to refer to some 17 years later!
Tom Moyer tests: https://user.xmission.com/~tmoyer/testing/EDK.html

Testing #1410 will serve as a useful 'control' against which, all other offset end-to-end joining knots can be compared.

Start with equal rope diameters and then progress to unequal rope diameters.
Document everything.

Some ground rules for all testing:
1. Always begin with identical length tails in each test - this provides an opportunity to also look for differential tail movement at various load milestones. For example, you might be able to report that one tail moved more relative to the other - or, you might observe no difference - ie no differential movement. Measure the tails so you have a baseline reference point (eg 100.0mm tails).
2. Always use equal lengths of rope when creating your test specimen - eg 2 x 1.0m lengths of rope (and not a 900mm length joined to a 1000mm length).
3. Be consistent in the starting knot dressing state for each test. Cinch the knot tightly by pulling on each individual rope segment - there are 4 segments...work each one to cinch and dress the knot. Be consistent with your applied hand force. What we are trying to achieve is consistency rather than randomness. This provides other future testers with an opportunity to try to replicate your results.
4. Be consistent with the rate at which you increase load - and report this rate. For example, you might take 20 seconds to reach each load milestone (or you might increase load at a faster rate or a slower rate... they key is to be consistent and to report this rate of increase).
5. Provide an overview photo showing the test rig setup. There are 2 fundamental methods of approaching this test:
      i) use 2 separate lengths of rope
      ii) use one piece of rope and form it into a loop - but this means you must use high efficiency pulleys at each end of the loop and forces must be doubled.


Test #1410 without any rotation.
Then test #1410 again - this time with a rotation to see what effect it has (refer to attached images).

Establish load milestones - as each milestone is reached, perform a 3 minute hold and make observations.
For example:
[ ] 1.0 kN - 1st milestone
[ ] 1.5 kN - 2nd milestone
[ ] 2.0 kN - 3rd milestone
[ ] 2.5 kN - 4th milestone
[ ] 3.0 kN - 5th milestone (jamming is probable at this milestone)
[ ] continue until instability is triggered (record the load threshold where instability is triggered).
......cease test when instability has been triggered.

I have thus far found that 3.0kN is the jamming threshold of #1410.
I have not observed evidence of instability up to 3.0kN.

You should record the speed at which load is increased (ie the rate at which load is increased - need timing device).

At least 5 tests should be performed - so statistical results can be calculated (you're the mathematician, so you should be able to get a bell curve and work out the mean and SD!).

It would be nice to try to get some repeatability in these test results.

SAFETY WARNING
The offset knots depicted in the images below are shown loosely dressed with short tails. This was necessary so that the image would fit within the macro field-of-view of the camera lens. The loose dressing is necessary so that both the external and internal structure is clearly visible and so easy to understand.

Mark Gommers
Title: Re: Offset knot for climbing
Post by: Dan_Lehman on June 22, 2016, 09:42:03 PM
SAFETY WARNING
The offset knots depicted in the images below are ...
... per my (working) terminology, respectively
"mid-range" & "choking-loop" (and "rotated"
in the the opposite direction would give the other
endpoint to the range of rotation, "choking-arc").
(I think that one of the endpoints' orientations is
a harder thing to sustain --think it's the missed one--
than the other.)

nb: my terminology doesn't presume some basis
to which "rotated" might apply, but is absolute
(non-relational) in reference to the choking strand's
curvature being like a loop or forward arc or to an
in-between-range state).


--dl*
====
Title: Re: Offset knot for climbing
Post by: Mobius on June 27, 2016, 11:33:19 AM
I have decided to trial the #1410 again after having already done so in a number of materials and at various loads.

Mr Mark Gommers may be able to use the results I am able to achieve in the near future. I am hoping to find some time in a week or so to do such trials. I am not trying to dot every 'i' and cross every 't' at present. I have only had a quick look at what I think needs to be done, here is what might suffice, or nearly so.

The images that follow are there for comment:

1) the dynamic rope (specifications) I want to use for trials

2) two 750mm sections of dynamic rope tied with close to identical eye knots at one end

3) a 1410# (one version of it) tied and showing 100mm tails

4) the tails marked A & B to allow for a later differential of tail movement (by measurement) to be determined.

The image at 4) can be replicated 5 or 6 times and then each tied duo of rope section can be tested in turn, carefully recording tail movement at various milestones.

Cheers.

Ian.


Title: Re: Offset knot for climbing
Post by: agent_smith on June 27, 2016, 04:06:28 PM
Quote
I have decided to trial the #1410 again after having already done so in a number of materials and at various loads.

Many thanks.

Considering that the most people tend to cite the Tom Moyer tests from some 16 years ago...I think it is about time we cast this subject into a whole new light!

When you say that you "have already done so in a number of materials and at various loads"... I presume that you hadn't specifically used EN892 compliant dynamic climbing rope before?

With close attention to detail - this will serve as a useful baseline for other testers to try to repeat the results (or at least start to build a useful database).

If you can achieve each of the load milestones...with a 3 minute hold at each milestone - and make observations - this will be a great start :)

What really interests me is the load threshold where instability is triggered. With say 5 tests, you should be able to generate a bell curve and produce some statistical results.

Some predictions:
(educated guesses)... for #1410:
[ ] jamming will occur at around 3.0 kN.
[ ] instability will be triggered at a load threshold somewhere above 3.0 kN

As for a duplicate set of tests with #1410 'rotated' so as to create a choking effect with one of the SParts... I don't know, but, I am very keen to see your results.

This also assumes equal rope diameters.
Will be very interesting to compare results with unequal rope diameters.

With your permission, I would like to publish these results in my upcoming paper - and hopefully it will become a new body of work that will be cited in the modern era :)


Mark G
Title: Re: Offset knot for climbing
Post by: Dan_Lehman on June 27, 2016, 09:45:58 PM
I have decided to trial the #1410 again after having already done so in a number of materials and at various loads.

...
4) the tails marked A & B to allow for a later differential of tail movement (by measurement) to be determined.
It occurs to me to suggest that prior your more
forceful test-bed loading, you would do well to anchor
one end of a tied test specimen to something for
vertical loading and make yourself a step-into harness
to tie onto the bottom end,
and try some series of repeatedly & variously
stepping onto the specimen and off --cyclical loading
AND RELAXING--, which can give some sense of
anything untoward & surprising going on in such
conditions!?  (There was a discovery of some effects
on the water knot (tape) by both Tom Moyer and
a pair of other testers --they got a slippage, a sort of
ratcheting per load cycle, under low loading and
relaxing!)

Perhaps it's even best to start with a round sling tied,
as that shows expected forces in loading (i.e., the knot
taking about half body weight); then the sling can be
opened to test it single-strand, and approx. doubling
of force.  (And to take a tails-measurement after the
first couple of loadings, to account for any initial setting,
beyond which we might find further shortening attributable
to a repeated "slippage" (or however one cares to name it).
(I can try this in some ancient Goldline, 11mm dynamic
rope, and maybe some other ollld stuff.)


--dl*
====
Title: Re: Offset knot for climbing
Post by: Mobius on June 28, 2016, 05:17:30 AM
When you say that you "have already done so in a number of materials and at various loads"... I presume that you hadn't specifically used EN892 compliant dynamic climbing rope before?
Mark G

Have a look at my posts #20 and #21 on page 2 of this thread. I did a few trials of #1410 (tied flat) in 11.2mm, well used dynamic rope, and took photos. Even these earlier posts were not my first trials in climbing rope. The rope had no EN number, however it would have to have met certain standards to have been used in an indoor climbing gym application, one would hope.

I saw the tails move at various milestones (see images), and even mentioned jamming might occur at around the 3kN mark.

Cheers,

Ian.




Title: Re: Offset knot for climbing
Post by: Mobius on June 28, 2016, 05:40:23 AM
It occurs to me to suggest that prior your more
forceful test-bed loading, you would do well to anchor
one end of a tied test specimen to something for
vertical loading and make yourself a step-into harness
to tie onto the bottom end,
and try some series of repeatedly & variously
stepping onto the specimen and off --cyclical loading
AND RELAXING--, which can give some sense of
anything untoward & surprising going on in such
conditions!?  (There was a discovery of some effects
on the water knot (tape) by both Tom Moyer and
a pair of other testers --they got a slippage, a sort of
ratcheting per load cycle, under low loading and
relaxing!

--dl*
====

I could also try cyclical loading of the #1410 to (say) repeated loads of 0.5kN at regular intervals. What I have come to call my 'little rig knot' does not move significantly under rig loads, yet it does get tighter after repeated loadings. A #1410 might do something quite different.

Cheers,

Ian.
Title: Re: Offset knot for climbing
Post by: agent_smith on June 28, 2016, 08:27:37 AM
Quote
Image two has the knot at a modest 0.5 kN and the tails are now at 95mm.

Image three is at 1.5 kN and we now see the tails are at 85mm.

The last image is at 2 kN and the tails are now at 80mm.

This knot stopped slipping somewhere around the 2 kN mark and was jammed at 3 kN having first slipped a total of 30mm.

Hopefully on your next round of testing with #1410, you will also be able make observations at each 3 minute hold at the various load milestones. During the 3 minute hold, I am predicting that you will not see any compression-induced tail draw-in (or induced because of SPart stretching). I am predicting no net tail movement at each hold - and so perhaps the word 'slip' (or 'slipping') might disappear?

Also, need to observe and report any 'differential' tail movement (ie one tail moving more relative to the other...or, both tails have identical movement).



Mark G
Title: Re: Offset knot for climbing
Post by: Mobius on June 29, 2016, 07:06:45 AM
.... I am predicting no net tail movement at each hold - and so perhaps the word 'slip' (or 'slipping') might disappear?

Mark G

I have never observed the tails move after the load reaches a milestone and steadies, in previous trials. The tail movement that I observed and previously called 'slippage' happened as you went from one milestone to another.

So, if we do not want to call that movement slippage then what do we call it? Perhaps just the word 'creep' or word duo 'tail creep'. Maybe we use the expression 'increased load creep' i.e. as in 'if the load is increased we see some creep of the tails'. That does not sound too sinister I think, nor does it understate or dismiss the observation.

Cheers,

Ian.

Title: Re: Offset knot for climbing
Post by: agent_smith on June 29, 2016, 08:20:16 AM
Quote
So, if we do not want to call that movement slippage then what do we call it?

Right now, I really just want to see some test results so we can finally have something to refer to other than Tom Moyer's results from last century!

It is now 2016.. and i think it is time to redefine the state-of-play with testing of offset end-to-end rope joining knots.

In terms of your specific question re "slippage"; clearly, tail movement is a phenomena that we only see when there is increasing load. If there is no load or the load is in equilibrium/unchanging, then we should see no net tail movement. And this is a key point in my view. If we have good reliable data that tells us the tails are not moving when the load is held at a fixed level, then this tells us something important about the particular knot we are testing.

On the other hand, if we have reliable data that tells us that the tails are moving - even when the load is held steady - then this would indicate something to be concerned about.

The fact that we tend to see tail movement only when the load is increasing - strongly suggests that tension and compression are playing an important role. As the knot core compresses - the SParts are also being stretched outwards by the tension force. So material is being drawn out from the core and, at the same time, it compresses. The side-effect is a shortening of the tails.

To call this phenomena 'slippage' - is, in my view - incorrect.

Perhaps a more useful descriptor is 'compression induced tail draw-in', or 'tension induced tail draw-in'.

Careful observations during load testing will shed further light on this phenomena - particularly at each hold point after reaching a milestone load.

Mark Gommers
Title: Re: Offset knot for climbing
Post by: Dan_Lehman on June 29, 2016, 11:40:58 PM
Quote
So, if we do not want to call that movement slippage then what do we call it?

To call this phenomena 'slippage' - is, in my view - incorrect.

Perhaps a more useful descriptor is 'compression induced tail draw-in', or 'tension induced tail draw-in'.
I'm not thrilled with "slippage" but prefer it to the not
only awkward-sounding but more misleading offered
terms.  Let's see it for what it is, slippage during setting
--slippage from the tied form into a more loaded form.
That it so far has stopped in most observations (notably
not with the HMPE / Dyneema, slippery cordage), is nice,
but doesn't change the fact that it exists such that
it needs to (be) stop(ped)!  --that it takes some time for
the nip to strengthen and prevent the, yeah, slippage.

And we can muse about "fact that we tend to see tail movement
only when the load is increasing" suggesting a close examination
of repeated increases (following repeated diminutions, relaxing)
--hence my note about the more-less-more_again-less...,
"cyclic" loading observations.

Also, it's probably the case that any rearrangement of
the positions of parts of some of these knots --notably
the offset water knot / EDK-- will NOT resume the
pre-loading state, even if otherwise stretched-out parts
more or less return; might this be a factor that lessens
the surety of the knot?

(E.g., when I dress-set the OWK, I haul on the choking
tail to set it in anticipation of the draw of the SParts'
nipping turn --and this particular setting, I realize, is
just one-more-thing that can be ignored/missed
and which potentially weakens the effect of the knot ...!?
Well, after loading, the tail will be moved a bit;
now, does that pose a problem if the line's relaxed
and re-loaded, repeatedly?  .:. Something to look at.)

Ahhh, I'd been thinking of changes in forces during
an abseil
and now realize that in many cases the
knot will be used for multiple abseils --so complete
"relaxing" will occur.  YMMV on how much (re-)attention
is given the knot prior to resumed use.

Also,while a certain rope type might be the norm,
we should be chary about the knotting being used
at least in some closely associated ropes --climbers
using the clove hitch to anchor belayers and there
being a good history of sucess, confronting testing
by Lyon Equip. showing this knot to slip (and at
various loads in various brands of rope) in low-elongation
(often called "static") kernmantle ropes.  (While we might
ignore cases in laid marine cordage, for the moment.)


--dl*
====
Title: Re: Offset knot for climbing
Post by: Mobius on July 04, 2016, 04:48:58 AM
Quote
So, if we do not want to call that movement slippage then what do we call it?

To call this phenomena 'slippage' - is, in my view - incorrect.

Perhaps a more useful descriptor is 'compression induced tail draw-in', or 'tension induced tail draw-in'.
I'm not thrilled with "slippage" but prefer it to the not
only awkward-sounding but more misleading offered
terms.  Let's see it for what it is, slippage during setting
--slippage from the tied form into a more loaded form.
That it so far has stopped in most observations (notably
not with the HMPE / Dyneema, slippery cordage), is nice,
but doesn't change the fact that it exists such that
it needs to (be) stop(ped)!  --that it takes some time for
the nip to strengthen and prevent the, yeah, slippage.

I am quite happy to move away from the word 'slippage' for this phenomena and I suggested something else. When studying a knot in climbing materials, a few mm tail movement does not worry me much, a few cm does. Sometimes I think I am overly fussy about climbing knots.

If I can talk to others here about what I do not like about a knot, while avoiding the word 'slippage' for this phenomena, then so much the better in this case.

Quote from: Dan
And we can muse about "fact that we tend to see tail movement
only when the load is increasing" suggesting a close examination
of repeated increases (following repeated diminutions, relaxing)
--hence my note about the more-less-more_again-less...,
"cyclic" loading observations.

I was thinking of taking 5 near identical knot samples and doing a 0-0.5kN x 5 cyclical loading of each and seeing what happens. This might be my first set of trials. I do not think any of those 5 samples would jam, so using the rope for later trials would be ok for me.

Quote from: Dan
Also, it's probably the case that any rearrangement of
the positions of parts of some of these knots --notably
the offset water knot / EDK-- will NOT resume the
pre-loading state, even if otherwise stretched-out parts
more or less return; might this be a factor that lessens
the surety of the knot?

(E.g., when I dress-set the OWK, I haul on the choking
tail to set it in anticipation of the draw of the SParts'
nipping turn --and this particular setting, I realize, is
just one-more-thing that can be ignored/missed
and which potentially weakens the effect of the knot ...!?
Well, after loading, the tail will be moved a bit;
now, does that pose a problem if the line's relaxed
and re-loaded, repeatedly?  .:. Something to look at.)

I will try and observe/photograph everything.

Quote from: Dan
Ahhh, I'd been thinking of changes in forces during
an abseil
and now realize that in many cases the
knot will be used for multiple abseils --so complete
"relaxing" will occur.  YMMV on how much (re-)attention
is given the knot prior to resumed use.

Also,while a certain rope type might be the norm,
we should be chary about the knotting being used
at least in some closely associated ropes --climbers
using the clove hitch to anchor belayers and there
being a good history of sucess, confronting testing
by Lyon Equip. showing this knot to slip (and at
various loads in various brands of rope) in low-elongation
(often called "static") kernmantle ropes.  (While we might
ignore cases in laid marine cordage, for the moment.)


--dl*
====

I am quite happy to trial in both static and dynamic kernmantle ropes. I have over 150m of now mostly new climbing rope. I have close to 180m marine grade 6mm 3-ply that may be useful when I get around to testing where knots are supposed to break.

Cheers,

Ian.



Title: Re: Offset knot for climbing
Post by: Dan_Lehman on July 05, 2016, 07:26:13 PM
I have close to 180m marine grade 6mm 3-ply that may be useful when I get around to testing where knots are supposed to break.
Oh, yes, that reminds me that although the
knot is ages old, we've no idea of which of the
asymmetric *halves* of a sheet bend is which
side breaks (presuming there to be a bias to
one or the other --the hitch vs. the bight)!?
AND
what happens strength-wise when the bight's
rope becomes ever larger --the knot so often
being promoted for mixed-size joints.  E.g.,
perhaps in equal cordage the break occurs
in the bight at say 55%; then increasing the
size of cordage there, knot strength rises
--as a % of (smaller) hitching rope strength--
with the increase of bight-rope size,
the hitching turn being around broader
material!?

--dl*
====
Title: Re: Offset knot for climbing
Post by: Mobius on July 17, 2016, 10:03:32 AM

Oh, yes, that reminds me that although the
knot is ages old, we've no idea of which of the
asymmetric *halves* of a sheet bend is which
side breaks (presuming there to be a bias to
one or the other --the hitch vs. the bight)!?
AND
what happens strength-wise when the bight's
rope becomes ever larger --the knot so often
being promoted for mixed-size joints.  E.g.,
perhaps in equal cordage the break occurs
in the bight at say 55%; then increasing the
size of cordage there, knot strength rises
--as a % of (smaller) hitching rope strength--
with the increase of bight-rope size,
the hitching turn being around broader
material!?

--dl*
====

The sheet bend is yet another knot I would like to find some time to trial properly. I.e..... (just some quick thoughts)

In same size rope
1) which is best for the tails to sit (same side or opposite side)?
2) how much does a second turn add to knot security?

In different diameter rope
3) What sort of differential in rope size 'works' and what does not? What defines 'works' and what does not is application dependent.

What is the application? Is this just a general usage knot?

Cheers,

Ian.


Title: Re: Offset knot for climbing
Post by: agent_smith on July 18, 2016, 01:27:44 AM
Although this is off-topic and nothing to do with offset rope joining knots:
Photos of Sheet bends #1431 and #1432 are below...

Ashley reported that #1432 was inferior compared to #1431.
However, need to keep in mind that they did not use synthetic fibre (Kernmantel) ropes in those days...so Ashley's remarks are in relation to vegetable fibre (hawser lay) ropes.

I don't know if anyone has seriously looked at testing these 2 bends with modern kernmantel ropes - with stability and security being the focus of testing and not MBS yields (ie break testing). And this is where you might see tail 'slippage' (and maybe even Xarax's capstan effect might play a role?).
NOTE: In accordance with the theory I had advanced in my Bowlines paper, there is no functioning nipping loop in a Sheet bend because it is not loaded at both ends. Instead, what is happening is that the SPart of the blue rope is trapping and crushing its own tail.


MG
Title: Re: Offset knot for climbing
Post by: SS369 on July 18, 2016, 01:48:18 AM
Off topic contribution:
http://rope-work-101.wikidot.com/sheet-bend-testing (http://rope-work-101.wikidot.com/sheet-bend-testing) Video
Modern 8mm rope and modern rope to webbing.

Other on topic subjects at http://rope-work-101.wikidot.com/ (http://rope-work-101.wikidot.com/)

SS
Title: Re: Offset knot for climbing
Post by: Dan_Lehman on July 20, 2016, 11:40:06 PM
Off topic contribution:
http://rope-work-101.wikidot.com/sheet-bend-testing (http://rope-work-101.wikidot.com/sheet-bend-testing) Video
Modern 8mm rope and modern rope to webbing.
...
SS
Oh, this is nice.
I see it as:

1) lower rope hitched to upper bight in rope,
same-side sheet bend :: bight part breaks,
after about 2 stripes-worth have slipped through
the "hitch"/turNip part (which itself might have had
some slippage, but less.

2) lower rope hitched to upper bight in tape,
opposite-side sheet bend :: hitch/rope breaks,
after considerable rope tail has slipped through
--'tis but a short bit that's broken off!!  (I count
4-nearly-5 red stripes at start, and barely 2 at end.)

3) upper tape hitched to lower bight in rope,
same-side sheet bend :: rope/bight-part
slips and pulls out (tape I think doesn't slip).
(It seems to my eye that the turn of the tape SPart
presses mostly against tape tail, not directly biting
against the rope/bight tail, which might be part of
what enables the rope to slip.)


--dl*
====
Title: Re: Offset knot for climbing
Post by: knotsaver on July 23, 2016, 07:32:46 PM
Hi all,
I'd like to know if the knot in the picture is used or it could be used as an offset joining knot. It is based on ABoK #523 with only 2 turns.

Ciao,
s.
Title: Re: Offset knot for climbing
Post by: Dan_Lehman on July 24, 2016, 07:31:50 PM
Hi all,
I'd like to know if the knot in the picture is used or it could be used as an offset joining knot. It is based on ABoK #523 with only 2 turns.

Ciao,
s.
My short answer is "hmmm, maybe so, but I have some doubts,"
as there is only mininal turn for the choke with the extra *knotting*
(over simpler knots) coming elsewhere.
(It will take more examination, with appropriate cordage,
to get a feel for amount of deformation et cetera with this.)

More involved answers will point to using the *knot*
by loading what your image shows as tails, and then
for that there is even some test data confirming its
viability (by Chris Harmstrom [?], then of Black Diamound
Equipment, IIRC).  What I have presented as the
"offset 9-oh" is essentially this knot but with one
line making only an overhand vice the fig.9 (which
is put in the choking line).


--dl*
====
Title: Re: Offset knot for climbing
Post by: knotsaver on July 25, 2016, 01:31:33 PM
Thank you, Dan, for your comments!
with reference to "offset 9-oh"
(if I've tied it correctly, as shown here http://igkt.net/sm/index.php?topic=3199.msg19197#msg19197 ) 
the turns (of the choking line) are two equal turns, whilst in the knot I've presented the turns are inverted (one is a right turn and the other is a left turn).
EDIT: you are referring to the reversed knot (tails loaded) and you're right, ABoK #523 with only 2 turns is the reversed of a figure 9 knot
ciao,
s.
Title: Re: Offset knot for climbing
Post by: Dan_Lehman on July 25, 2016, 10:34:29 PM
...
the turns (of the choking line) are two equal turns,
whilst in the knot I've presented the turns are inverted
(one is a right turn and the other is a left turn).
No, your knot is one formed by doubled lines,
and turns are the same in the adjacent parts.

There is an issue in how to dress & set what you've
shown, and what I've done with that is to have it loose
enough so that I can haul the tails straight, putting
the curvature in the parts they were twisting with,
giving more curving in the SParts' path.  Having the
tails pull into the knot straight enables one to set
the choke tight --my reason for seeking to do this.
But the result looks overly bulky/wide.

(I will reiterate that I increasingly see the value of the
"EDK-backed EDK" (offset overhand & overhand stopper)
vis-a-vis the lack of careful tying that is necessary!)


--dl*
====