Author Topic: TEST REPORT: Offset overhand bend (#1410)  (Read 4788 times)

agent_smith

  • Sr. Member
  • *****
  • Posts: 1377
TEST REPORT: Offset overhand bend (#1410)
« on: December 07, 2018, 04:52:22 PM »
TEST REPORT

Test date: 07 Dec 2018

Knot specimen: #1410  Offset overhand bend (aka 'EDK')
Knot class: End-to-end joining knot

Test objective:
To determine the effect of rotation.

Rope material:
[ ] EN standard: EN892 dynamic rope
[ ] Diameter: 9.0mm ('half' rope) - only tested equal diameter ropes to rule out any variables - unequal ropes will follow later...)
[ ] Manufacturer: Edelrid (Germany)
[ ] Condition: 10+ years old (retired from lead climbing)

Tester: Mark Gommers

Test configuration and parameters:
As per attached images.
[ ] Equal rope diameters used to form the end-to-end rope join (9mm to 9mm).

Assumptions:
It has been theorized that a simple rotation can improve stability (per Dan Lehman).
#1410 is typically tested in its mid-rotation state. This mid-rotation state is the default mindset. I am of this opinion because firstly, it is never reported and secondly, you have to make a deliberate effort to perform the rotation - its not a random occurrence - and only one particular rotation state appears to be effective. Furthermore, its never been photographed in detail by other testers.
As far as this tester is aware, nobody has tested and published the effect of different rotation states - with specific attention given to identifying the rotation state which is most effective at improving stability.

Conclusions:
The rotation state where the choking rope segment is lying furthest from the axis of tension is most effective.
At a peak load of 6.0kN, no instability was observed.
The rotation state where the choking rope segment lies closest to the axis-of-tension induces a torque - which causes the knot to revert to its mid-rotation state as load is increased.

Due to limitations of the test rig and equipment, peak loads were well below the MBS yield point of the knot.
Follow up testing is required to determine the threshold of instability with this rotation state compared to a 'control'.
The mid-rotation state would be the 'control'.
At this stage, I would posit that this rotation state will boost the threshold of instability compared to the 'default' mid-rotation state.

I encourage others to try to replicate my results using EN892 'half' ropes (or a similar facsimile rope if EN892 rope cannot be sourced).
NOTE: In my test, I used ropes of equal diameter. This was to done to rule out any potential variables.
Unequal diameter ropes would be tested at a later date...
« Last Edit: December 16, 2018, 11:38:30 PM by agent_smith »

Dan_Lehman

  • Sr. Member
  • *****
  • Posts: 4054
Re: TEST REPORT: Offset overhand bend (#1410)
« Reply #1 on: December 13, 2018, 06:18:43 PM »

Assumptions:
#1410 is typically tested in its mid-rotation state.
This mid-rotation state is the default mindset.
These statements might --leaned on hard-- be wanting
for factual support.  By which I mean that although we
might  see the knot presented in this orientation,
and even if we find by empirical observation that it is
frequently tied so,
likely we cannot be sure of the tested knot.
(IMO, you're probably correct; but we just don't know
for sure, as this aspect hasn't been noted and reported
on by anyone --testers or otherwise, for that matter
(save me/us)!)

--as you remark:
Quote
As far as this tester is aware, nobody has tested and reported on the effect of rotation.

As for
Quote
It has been theorized that a simple rotation can improve stability (per Dan Lehman)
,
more to the point is that while I have opined that the mid-rotation
state might be worst, we simply need to examine behavior
while paying attention to such states.  So, the pure point
is that orientation might make a difference.


Quote
RANT ON
Quote
furthest
Why do folks forget "far/farther/farthest" --measures of
distance, of linear position & sense (even if said
metaphorically) ?!?  These are (were) common, long-used
words.   "Further" is a note of continuance or difference
in broad measure, unlinear-like.
(Similar and sharper rebuke comes for the now seemingly vogue
esp. newscaster abuse of "reticent" for the perfectly known
word "reluctant" --egadz, folks are going lame-brained.
RANT OFF

I, too, have found one of the extreme-of-rotation states
not so stable, wanting to turn into the mid-span state;
but I do believe that this extreme case CAN be SET
and hold, to rupture, if not perfectly extreme in the
formation of "arc" & "loop" of its SParts, at least
more biased thus than is the mid-rotation state.
(Given the at least sometimes need for special
setting & dressing, though, we might conclude that
it's a state unlikely to occur in common usage.
But it would be worth making the effort, at least,
to get a clear test of it.  Maybe also much of a
"YMMV" per material, likely stiffer cordage being
more prone to shift orientation than soft stuff
which in dressing & setting is more obedient.)

Quote
I encourage others to try to replicate my results using
EN892 'half' ropes (or a similar facsimile rope if EN892 rope cannot be sourced).

ALSO DISsimilar ropes, as doing so with e.g. something
pretty elastic vs. static might shed light on the mechanics
of the knot.  AND, the general in-practice state is of ropes   [<- edit "if"=>"is"]
dissimilar in both elasticity & size : i.e., of a 6-7mm "haul
line" joining the 9-10.5mm dynamic rope.  (Whereas the
doubly long "twin" 8mm ropes are used sans knot on their
full twin length (does anyone ever join two such ropes
and thereby skip alternate belay/rap stations?!!)

Of course, in the case of dissimilar ropes, there is the added
orientation of which one is the "choking" rope (with the ideal
being the thinner & more flexible one).

ALSO, I suppose one can do some at least quick'n'dirty
testing of the offset fig.8 e2e bend, which maybe allows
even greater variance in orientation.  Maybe here, though
not seeking to recommend this knot no matter ... ,
we'll find that there is an especially dangerous orientation!
(Recall that some French folks seem to PREFER this knot,
and to have test data in which it performs better --i.e.,
rolls at only higher forces-- than the offset water knot!?
--which surprised me, but it is a presentation that came
up to my awareness in the past two years.)


Ropes available to me for my crummy 5:1 pulley stressing
--lousy pulley, but bouncing on it surely imparts surges
of force up to what ought to come by good sheaves alone--
are :  ancient "Goldmantle' --the name says it all (~40yrs)--,
some old 11mm Mammut dynamic, some other old bit
(discarded top-roping anchor lines), newer 11mm gym
rope, some newer & pretty unused 8mm ropes,
Sta-set 11ish mm yacht rope, 3/8 BW II, and the
incredibly intractable PMI pit rope & some Canadian
stuff that makes the former seem, er, not-so-bad
(!!  fankly, these might be unlikely to form an offset knot
that any sane person would actually use!), and other
7mm kernmantle low-elongation ropes, & 6mm.


--dl*
====
« Last Edit: October 24, 2020, 08:20:31 PM by Dan_Lehman »

SS369

  • Global Moderator
  • Sr. Member
  • *****
  • Posts: 1964
Re: TEST REPORT: Offset overhand bend (#1410)
« Reply #2 on: December 13, 2018, 08:32:26 PM »
Hi Mark.

I was thinking about this test, and btw, thank you for the work.

What I am thinking about is this: How about making a sling using two ropes and tying a comparable knot in each pair of ends. They could be oriented oppositely for that kind of comparison, even using different diameter, etc., ropes. Sort of as a tug of war, side by side.
It might be useful to have the ropes go around some pulleys to aid separation and limit any influences at the anchor points.

I wish you resided closer because I would help with labor, materials and friendship.

Again, thank you for your contributions.

SS

agent_smith

  • Sr. Member
  • *****
  • Posts: 1377
Re: TEST REPORT: Offset overhand bend (#1410)
« Reply #3 on: December 14, 2018, 05:46:05 AM »
per Dan Lehman:
Quote

These statements might --leaned on hard-- be wanting
for factual support.

By which I mean that although we
might  see the knot presented in this orientation,
and even if we find by empirical observation that it is
frequently tied so,
likely we cannot be sure of the tested knot.
(IMO, you're probably correct; but we just don't know
for sure

My position is this:
Nobody has specifically reported it in their tests.
As in, not one single report on planet Earth specifically deals with rotation.
I am willing to go out-on-a-limb and state that the default orientation in all tests is the mid-rotation state.
Another important piece of evidence (for me) is that you have to make a definite conscious effort to align the knot in the proper manner to achieve a choke - its not a random task - its a deliberate action. You have to know what you're doing. As such, surely a knot tester would have reported it? But no one has... (until now with yours truly - me!).

There are two ways to find proof of this assumption:
1. Track down every person who published test reports on #1410 - and ask them directly.
2. The other way is to do a 'reversal of the onus of proof' - that is, find evidence to the contrary.

Analogy with space flight:  Prove that it is safe to fly or; prove that it will fail (ie prove that it is unsafe to fly).

Quote
but I do believe that this extreme case CAN be SET
and hold, to rupture, if not perfectly extreme in the
formation of "arc" & "loop" of its SParts, at least
more biased thus than is the mid-rotation state.
I only examined 3 rotation states for #1410.
I considered the mid-rotation state to be the default mindset - and the one most vulnerable to instability.
Of the 2 other rotation states - only 1 was found to be stable - and this was the orientation with the rope segment lying furthest from the axis-of-tension.
Of surprise to me, the orientation state with the rope segment lying closest to the axis-of-tension was transient - it reverts under load to the mid-rotation state.
And this is partly why i believe that the mid-rotation state is default mindset... any inadvertent rotation with the rope closest to the axis of tension would simply transition back to the mid-rotation state.


Quote
Recall that some French folks seem to PREFER this knot (offset F8),
and to have test data in which it performs better --i.e.,
rolls at only higher forces-- than the offset water knot!?
--which surprised me, but it is a presentation that came
up to my awareness in the past two years.
I would suggest that the testers are likely blissfully unaware of the effect of rotation and various dressing states for both #1410 and offset F8.
Dressing state of offset F8 also has what appears to be a default mindset orientation - and no one has reported anything different.
Its a topic that is devoid of any data.
The reason is that climbers/canyoners/rescue technicians etc aren't knotting experts!
For example, most climbers wouldn't have a clue about rotation of #1410 and/or particular dressing states.
They are great at the gymnastic aspects of climbing and finding ways to push a route but not so great at the technical detail about knots.
They just follow routines they have learned and trusted over the years - and largely dont question them.
Also, technical details about knots is considered to be the realm of academia and perhaps a little nerdy - and perceived to be 'nice to know' but not 'need to know' information.
Knot book authors are partly to blame - by publishing information that is either inaccurate or simply parroted.
I would suggest that it should be possible to achieve a dressing state with offset F8 that is resistant to instability (up to a point) - but for the average climber its probably not going to be practicable (ie not worth the effort or risk) when you can more easily fiddle with #1410 or simply add another binding turn (as per my variant).

Quote
ALSO DISsimilar ropes, as doing so with e.g. something
pretty elastic vs. static might shed light on the mechanics
of the knot.  AND, the general in-practice state if of ropes
dissimilar in both elasticity & size : i.e., of a 6-7mm "haul
line" joining the 9-10.5mm dynamic rope.

I chose to rule out any uncontrollable variables in my test.
Joining unequal diameter ropes introduces additional variables.
It also makes it harder for other testers to try to reproduce my results (because they would have to source the same rope diameters for their tests).
Be that as it may - further down the track, I would hope that other testers do follow up work to investigate this area.
But for me, at the moment, I am staying with equal diameter ropes to reduce the number of possible variables.

I also initially focused on EN892 dynamic ropes.
I think it is also important to test EN1891 type A (low stretch) ropes in the 9.0mm class
For example: https://www.edelrid.de/en/sports/static-ropes/safety-super-ii-9-5-mm.html
In other words, we need data sets for both dynamic and low stretch ('static') ropes.
« Last Edit: December 14, 2018, 08:32:11 AM by agent_smith »

agent_smith

  • Sr. Member
  • *****
  • Posts: 1377
Re: TEST REPORT: Offset overhand bend (#1410)
« Reply #4 on: December 14, 2018, 05:55:27 AM »
per Scott:
Quote
What I am thinking about is this: How about making a sling using two ropes and tying a comparable knot in each pair of ends. They could be oriented oppositely for that kind of comparison, even using different diameter, etc., ropes. Sort of as a tug of war, side by side.
It might be useful to have the ropes go around some pulleys to aid separation and limit any influences at the anchor points.

A good idea but my issue is the amount of force required to achieve the same result compared to a linear setup is doubled.
With a doubling of force - comes increased risk - and more effort on my behalf.
I have been trying to use ropes in the 9.0mm class because that is the most commonly used (although it could in reality be anywhere from 8.5mm to 9.1mm). Larger than 9.1mm is less common for climbers using a double rope system.

Alan Lee has a more powerful test rig...he could easily managed this type of 'round sling' configuration. Might have to see if he is willing to give it a shot...

Quote
I wish you resided closer because I would help with labor, materials and friendship.
Again, thank you for your contributions.
Thanks, much appreciated.
It would be nice to have another knot god living somewhere close!

SS369

  • Global Moderator
  • Sr. Member
  • *****
  • Posts: 1964
Re: TEST REPORT: Offset overhand bend (#1410)
« Reply #5 on: December 14, 2018, 02:56:40 PM »
per Scott:
Quote
What I am thinking about is this: How about making a sling using two ropes and tying a comparable knot in each pair of ends. They could be oriented oppositely for that kind of comparison, even using different diameter, etc., ropes. Sort of as a tug of war, side by side.
It might be useful to have the ropes go around some pulleys to aid separation and limit any influences at the anchor points.

A good idea but my issue is the amount of force required to achieve the same result compared to a linear setup is doubled.
With a doubling of force - comes increased risk - and more effort on my behalf.
I have been trying to use ropes in the 9.0mm class because that is the most commonly used (although it could in reality be anywhere from 8.5mm to 9.1mm). Larger than 9.1mm is less common for climbers using a double rope system.

Alan Lee has a more powerful test rig...he could easily managed this type of 'round sling' configuration. Might have to see if he is willing to give it a shot...

Quote
I wish you resided closer because I would help with labor, materials and friendship.
Again, thank you for your contributions.
Thanks, much appreciated.
It would be nice to have another knot god living somewhere close!

Hi Mark.

My bad, I thought that was your test set up initially because of the photo of Test configuration on Test page 2.
I definitely understand about the increased risk and efforts and only offered the idea, no critique at all.

Yes, I do hope that Alan or someone with a suitable rig might try and contribute. I'm not able to invest in a test cell at this time, so my contribution(s) may be considered anecdotal.
I have been considering a drop rig and doing cyclic tests to some knots, but that's not for here in your thread.

As for "knot god"... just knotting enthusiast please.

SS

DerekSmith

  • IGKT Member
  • Sr. Member
  • *****
  • Posts: 1555
  • Knot Botherer
    • ALbion Alliance
Re: TEST REPORT: Offset overhand bend (#1410)
« Reply #6 on: December 14, 2018, 09:17:33 PM »
Mark,  thank you for bringing us a most interesting problem.

I believe it is an example of rotational cogging that seems to be manifest when the primary nipping loop (choke ?) is adjacent to the entry side of the knot, yet is more stable when it is located adjacent to the WE side of the knot.

The question of course is Why?

A lovely challenge.

Derek
« Last Edit: December 14, 2018, 09:51:32 PM by DerekSmith »

DerekSmith

  • IGKT Member
  • Sr. Member
  • *****
  • Posts: 1555
  • Knot Botherer
    • ALbion Alliance
Re: TEST REPORT: Offset overhand bend (#1410)
« Reply #7 on: December 15, 2018, 03:17:51 PM »
I think I am starting to get a handle on understanding this effect.  Unless I am mistaken (quite possible), this effect is much like the Whatknot, where SP orientation one way locks the knot, whilst the opposite orientation allows positive rotational cogging to proceed.

With this knot, we have two parallel OH knots with the SP legs splayed 180 degrees from each other.  The consequence of this is that one OH retains its open shape, while the other one is deformed into a nipping helix.  The susceptibility to the rolling effect, then depends on which of the two OH knots is deformed into the nipping helix - the one sited nearest to the SP legs or the one sited furthest from the SP legs.

If the nipping helix is formed furthest from the SP legs, then under load, it bears on the OH between it and the loaded SP legs.  This tends to act as jamming packing and so resists the rotational moment induced into the helix by the load.

If on the other hand the helix is immediately adjacent to the two loaded SP legs, then there is no buffer and the helix rotational torsion bears only upon the two tail ends and starts to rotate them into the belly of the knot.

Using slick cordage, the effect is quite noticeable, caused simply by rotating the knot 180 degrees relative to the line of the loaded SPs.

Hats off to Marks for spotting this and highlighting it for investigation.

Derek

Dan_Lehman

  • Sr. Member
  • *****
  • Posts: 4054
Re: TEST REPORT: Offset overhand bend (#1410)
« Reply #8 on: December 15, 2018, 10:59:26 PM »
Unless I am mistaken (quite possible), this effect is much like the Whatknot, where SP orientation one way locks the knot, whilst the opposite orientation allows positive rotational cogging to proceed.
No, you're looking at something else, here.

The point that I raised --some years ago, but to few
paying much attention, unlike Mark-- is that the knot
can be set so that the orientation of the body to the
axis of tension can be at any of approximately 180degrees
of "rotation" --like saying when looking down upon such
a knot pulled across a table top such that the loaded
SParts run from 9:00 to 3:00 in a clockface orienter,
the tails could point to any point in this clockwise range
from about 7:00, 8-9-.. 1:00, say.  (or mirror this).

And the two SParts will take respective general shapes
/curves up into the knot atop this table of:
extreme-1) left-side "arc" & right-side "loop";
mid-range) both SParts semi-arc & turn;
extreme-2) left-side loop & right-side arc (opp. ext-1)

The "arc" structure more pries open the knot,
whereas the "loop" better surrounds & grips/nips
its enclosed parts (the tails).

(I've gotten pretty good at being able to simply
change torsion on the SParts of a tied knot in hand
such that I can show one extreme to one person,
then turn and --torquing appropriately-- show the
opposite extreme to another :: I envision having
two people believing that they each see the same
knot (--a philosophical issue!) argue that the other
is loony in saying it's opposite to what they saw!)

Of the twinned parts forming this knot,
the opposed pulling of the SParts will be into
ONE until that one opens/yields and then the
twin part will also feel the prying force, which
works to flype/"roll" the knot into another version
of itself.  (With the fig.8 structure, this flyping
comes in a more dramatic way, consuming more
tail material; whereas the overhands are said
to tend to just rrrroolllll around.)

And a way to preclude such capsizing is to tie off
the "choking" (initially pried into twin part) strand
with a stopper overhand --preventing the draw
of its tail to feed the widening of its choke--, or as
Mark's further-tucked version goes, with that
further tucking; or with my two-turns (making the
overhand into a fig.9) version making
the choking turn a full round turn, which is less
accommodating of the prying-opening.


--dl*
====

DerekSmith

  • IGKT Member
  • Sr. Member
  • *****
  • Posts: 1555
  • Knot Botherer
    • ALbion Alliance
Re: TEST REPORT: Offset overhand bend (#1410)
« Reply #9 on: December 16, 2018, 04:25:37 PM »
Dan,

I think (again, unless I am wrong) that we are essentially in agreement.  Where you have used the term "flype/"roll" ", I have used the term "positive rotational cogging".  I see your aspect of "one opens/yields" and need to look more closely at the part this is playing in allowing/ blocking the "flype/"roll" mechanism.

Such a simple knot, yet a complexity of responses to loading.

Derek

Dan_Lehman

  • Sr. Member
  • *****
  • Posts: 4054
Re: TEST REPORT: Offset overhand bend (#1410)
« Reply #10 on: December 18, 2018, 12:08:28 AM »
I think (again, unless I am wrong) that we are essentially in agreement.
Where you have used the term "flype/"roll" ",
I have used the term "positive rotational cogging".

I don't see "rotational" or "cogging" as apt, here.
The rotations at issue are relative to tying/dressing
(and needing the setting to sustain), not mechanics
of handling force.

Or not so much.  The choking strand gets tension,
and it can thus draw out some of its tail and then
open the choke ... and lead to capsizing.  (Whereas
with the whatnot there is more of a *flow* of
material.  And a flow, as asserted by Xarax, that
can lead to a shift of orientation into locking
--or not, depending upon cordage (firm & round
I think is likely to keep flowing; compressible &
flexible can shift & lock more nearly into #1408).

Yes, #1410 /Thumb, Openhand, ... / Offset Water knot
is much more than meets the eye!
But, so too, is #1452, which allows of various dressings
for various effects --one can induce locking/jamming
(this might be for light enough loading so as to be
loosenable, but just secure-when-slack until ...)-- or
other geometries.  And likely a good many others
have subtleties of dressing & setting.

And re these sorts of things, I have retreated from my
once dismissive position vs. the "EDK-backed EDK"
(tying two of the knot adjacent, the tail-closer one
serving qua stopper knot to the inner one); I now
advocate on its behalf as a foolproof & quite easy
(to do; to remember how to do) solution to the
rap-ropes-joint problem.  While I do know of many
others, such as the offset 9-Oh, offset water knot
w/stopper, & <Marc's favored solution>
.


--dl*
====