Author Topic: Call for assistance with #1410 Offset overhand knot testing  (Read 371 times)

agent_smith

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Call for assistance with #1410 Offset overhand knot testing
« on: April 29, 2019, 01:22:58 AM »
I am in the process of updating my paper on Offset rope joining knots - with a particular focus on #1410.

In particular, the objective is to investigate what effect rotation has on #1410 stability.
It is hypothesized that:
1. The mid-rotation state of #1410 is more vulnerable to instability
2. The anti-clockwise rotation state (with choking turn displaced one rope diameter from axis-of-tension) - raises the threshold of instability (ie the load threshold where instability is triggered).
Note: Clockwise and Anti-clockwise are arbitrarily chosen relative to the mid-rotation state (refer attached image).

Testing is required to either prove or disprove this hypothesis.
In other words, it is currently an unanswered question - and as far as I am aware, no one on planet Earth has made a concerted effort to investigate this matter.

There are three (3) rotation states of #1410 as follows:
1. Mid-rotation state (this is the 'control' for any testing - and appears to be the 'default' orientation (either as a deliberate conscious intent or as an 'unconscious' action).
2. Anti-Clockwise rotation state (relative to mid-rotation perspective) - choking turn is is displaced one rope diameter from axis-of-tension.
3. Clockwise rotation (relative to mid-rotation perspective) - choking turn is aligned with axis-of-tension.
NOTE: Clockwise and Anti-clockwise are arbitrarily chosen to signify opposite states relative to the mid-rotation perspective (refer to attached image).

Any testing should be carried out using human-rated ropes of equal diameter.
The reason for this is four-fold:
1. The class of users of this type of rope joining knot are predominantly climbers and canyoners - and they only use human rated ropes (NOT rope purchased from their local home hardware store) - any knots used in their rigging is life critical - and any error or failure could have catastrophic consequences
2. Consistency and repeatability of testing - if testers are using ropes purchased from ACME Dodgy ropes Pty Ltd or from a home hardware, there will be no consistency and little possibility for other serious testers to try to repeat results.
3. Ropes manufactured to be human rated obviously meet stringent quality and performance criteria - they are built to provide consistency and reliability.
4. Equal diameter ropes will ensure consistency - otherwise we have no control over how a tester positions one rope relative to the other - including the myriad arrays of rope diameters currently available which would result in zero consistency from one tester to the next.

The principle human rated rope standards are:
1. EN 892 (dynamic climbing ropes); and
2. EN1891 (low elongation / abseiling ropes).

Typical rope diameters used by climbers/canyoners:
1. Climbers will use EN892 ropes in the range 8.5mm - 10.2mm
2. Canyoners will use EN1891 ropes typically around 9.0mm diameter.

Rope age:
For consistency of testing, the ropes used to form the #1410 join should both be of the same age (ie it is invalid to unite a new rope to an old rope).
It is not necessary to use brand new ropes.
This author is of the view that age is not a valid discard criteria (I refer any doubter to Walter Siebert research  Link: https://www.facebook.com/SiebertResearch/ )


Control
It is proposed that the 'control' for the test would be #1410 in its mid-rotation state (using same diameter ropes)
It is preferred that both EN892 and EN1891 human rated ropes be tested (that is, test EN892 and then test EN1891 as a comparison).
Testing of #1410 should NOT be with a mixture of EN892 + EN1891 (that is, don't join a dynamic climbing rope to a low elongation 'static' abseil rope).

...

Summary:

The results of this testing could have a profound impact on the climbing/canyoning community.
It may also contribute to safety - which is a noble aim.
It never ceases to amaze me that climbers/canyoners still often refer to the Tom Moyer tests of #1410 - which are now some 20 years old - and which completely failed to investigated the effect of rotation (and the effect of positioning of different rope diameters).

PS: As it happens many times in a technical forum such as the IGKT - people will bog down in detail and not get any actual testing done. Obviously, some parameters need to be established for testing otherwise results will be in a scatter-gun effect. All testing must follow some basic principles - otherwise the test results will be invalid.

Mark Gommers
« Last Edit: April 30, 2019, 12:55:35 AM by agent_smith »

SS369

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Re: Call for assistance with #1010 Offset overhand knot testing
« Reply #1 on: April 29, 2019, 03:19:18 PM »
Good day Mark.

Correct me if I am having a senior moment please.
Should we be considering the #1410 in place of the #1010 ?

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agent_smith

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Re: Call for assistance with #1410 Offset overhand knot testing
« Reply #2 on: April 29, 2019, 03:34:48 PM »
Yes... #1410 it is.
My keyboard has died - another laptop bites the dust.
Lasted 6 years - not a bad run of life for a second hand laptop!

SS369

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Re: Call for assistance with #1410 Offset overhand knot testing
« Reply #3 on: April 29, 2019, 03:42:21 PM »
Can't stand laptops!
Seems I am way too heavy-handed. Power cord connections always seems to go first for me. And then there are the scroll pad challenges...

Glad you were able to edit.

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Dan_Lehman

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Re: Call for assistance with #1410 Offset overhand knot testing
« Reply #4 on: April 29, 2019, 11:04:39 PM »
In particular, the objective is to investigate what effect rotation has on #1410 stability.
It is hypothesized that:
1. The mid-rotation state of #1410 is more vulnerable to instability
2. The anti-clockwise rotation state (with choking turn displaced one rope diameter from axis-of-tension) - raises the threshold of instability (ie the load threshold where instability is triggered).
I don't follow "anti-clockwise", which isn't a full description
of a knot, given mirror images et cetera.  --you must have
some reference image/state in mind, to which then this makes sense.

NB: In the given middles state, the tails generally will run along
the axis of tension
(and they are roughly perpendicular to it,
one side or the other, respectively, of the two extreme states).
Quote
choking turn is is displaced one rope diameter from axis-of-tension.
???  I really don't follow this, and won't go into details,
but urge that a perspicuous description is as follows:
"choking strand makes a forward arc"
& "choking strand makes a backward loop"
& leaving " ... & other strand make lateral arcs".

(Another way to look at this is whether the loop around
the tails is away-most (nearer ends ; in which case the
choking strand is a forward arc) or the other way.)

Quote
Any testing should be carried out using human-rated ropes of equal diameter.
The reason for this is four-fold:
1. The class of users of this type of rope joining knot are predominantly climbers and canyoners - and they only use human rated ropes (NOT rope purchased from their local home hardware store) - any knots used in their rigging is life critical - and any error or failure could have catastrophic consequences
2. Consistency and repeatability of testing - if testers are using ropes purchased from ACME Dodgy ropes Pty Ltd or from a home hardware, there will be no consistency and little possibility for other serious testers to try to repeat results.
Although if there are not many testers, having consistency
amounts to having tested very little of possible cordage combos!

Quote
4. Equal diameter ropes will ensure consistency - otherwise we have no control over how a tester positions one rope relative to the other - including the myriad arrays of rope diameters currently available which would result in zero consistency from one tester to the next.
As above, and as measuring of diameter sometimes smells
like marketing more than science, and so on.  Again, given
the variety of ropes and paucity of testers, consistency like
you are describing amounts to an arguably too parochial
examination of conditions.
While a diversity of test conditions leaves one wondering
... (absent repeated results to verify...), it might be more
helpful in *suggesting* that there *can* be conditions
where things might go amiss.  THEN one can try to forus
on that, possibly with some unlikely cordage that can be
seen to aggravate a suspected characteristic (e.g. strechiness,
frictiveness).

Quote
Typical rope diameters used by climbers/canyoners:
1. Climbers will use EN892 ropes in the range 8.5mm - 10.2mm
2. Canyoners will use EN1891 ropes typically around 9.0mm diameter.
IMO, it is common enough for "accessory" cord --aka "haul line"--
to be joined to a climbing rope to extend an abseil; and for
the joined ropes to be different in other ways (size, age).

If testers are expected to understand the rotational states,
surely they can understand --per them!-- the significance
of which rope is in which position.  ("choking" vs. not is
the choice ; generally, one thinks "thinner & more flexible
should choke --for strength isn't the issue, but rolling!")

Quote
This author is of the view that age is not a valid discard criteria (I refer any doubter to Walter Siebert research  Link: https://www.facebook.com/SiebertResearch/ )
His is a most dubious assertion; elsewhere, I've read
that (a) age reduces strength by more than he suggests,
and (b) it more significantly reduces ability to absorb force!
(That he makes no reference to dynamic aspects of aged rope
is a warning sign, IMO.)
((For some of us, the old ropes are not only that --aged--,
but they come from a time when ONE FALL was the acceptance
threshold.  (But I think that my Goldmantle was a 5-fall time?)

And the loading?
You have a previously posted-in-this-forum test report of
some knots showing various loads, presumably got by
steady increasing of force.
Abseiling can involve more cyclical yet low-level loading.
And most of us won't have calibrated test set-ups; but we
could bounce on various configurations to try to discover
potential vulerabilities.

Btw, I'm reminded that I never really much realized the
supposed vulnerability of an offset fig.8 e2e joint capsizing
--though I HAVE warned about that.  .:.  It might be good for
us to try that knot, too, seeing if we are getting bad
results from a supposed known bad knot (!).


Thanks,

(-;

ps: I see I noted my possible cordage, in prior thread.
>>>
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(!!).
(Frankly, these might be unlikely to form an offset knot
that any sane person would actually use!), and other
7mm kernmantle low-elongation ropes, & 6mm.

agent_smith

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Re: Call for assistance with #1410 Offset overhand knot testing
« Reply #5 on: May 03, 2019, 05:37:07 AM »
Dan,
I believe that I have addressed the rotational perspective issues you had identified.

I have had multiple computer failures in the past week - the tally so far:
[ ] Faulty keyboard - mechanical type - some keys failing
[ ] one HP laptop blew up with puff of smoke from A/C power lead connector to motherboard socket
[ ] second (replacement 2nd hand) HP laptop - operating system unrecoverable crash - needs total OS installation + software
[ ] my daughters PC went 'pop' - sudden loss of power - suspect Power Supply unit blew up.

This has really slowed me down...

...

Anyhow, I am wondering if you can run some tests of #1410 to determine effects of rotation?
I need some data sets other than my own - as you would be aware - a singular source of data is not sufficient to draw conclusions - need multiple data sets from different testers to confirm/deny theories.

I have made contact with Mr Walter Siebert (Germany) - and he has also agreed to run some tests on #1410.

I regard this as important because this data could improve safety and awareness in various roped sports (eg climbing / canyoning, etc).

If you could test and publish your results - it would be appreciated :)

Mark
« Last Edit: May 03, 2019, 05:37:40 AM by agent_smith »

Dan_Lehman

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Re: Call for assistance with #1410 Offset overhand knot testing
« Reply #6 on: May 20, 2019, 08:40:05 PM »
I think that I didn't note that
CYCLICAL LOADING with incremental tail creep
might be an issue.

I recall using some small cordage with the offset
water knot and seeing the tail of the choking strand
get pulled ever more into/through the knot.
So, it's not only some force working to capsize or
"roll" the knot, but even the retained form just giving
out material, maybe then so loosened & tail-shortened
that when rolling DOES occur, it does so with big effect.

 - - - - - - -

I mentioned the offset fig.8 as a sort of *calibration measure*:
thinking, that that knot is reported to be easily failing (in some
sort of orientation & drawing up), so if individual testers cannot
get IT to fail, we might question how much faith to put in their
results of the OWKnot not failing!?

(I did some light testing w/o results of any note --body weight
or less (actual forces, after all), and old dynamic rope(s).)

--dl*
====