Author Topic: Offset knot for climbing  (Read 24231 times)

Mobius

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Re: Offset knot for climbing
« Reply #60 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.


agent_smith

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Re: Offset knot for climbing
« Reply #61 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

Dan_Lehman

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Re: Offset knot for climbing
« Reply #62 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*
====

Mobius

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Re: Offset knot for climbing
« Reply #63 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.
« Last Edit: June 22, 2016, 06:53:43 AM by mobius »

agent_smith

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Re: Offset knot for climbing
« Reply #64 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
« Last Edit: June 23, 2016, 02:56:34 AM by agent_smith »

Dan_Lehman

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Re: Offset knot for climbing
« Reply #65 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*
====
« Last Edit: June 24, 2016, 08:52:46 PM by Dan_Lehman »

Mobius

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Re: Offset knot for climbing
« Reply #66 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.



agent_smith

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Re: Offset knot for climbing
« Reply #67 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

Dan_Lehman

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Re: Offset knot for climbing
« Reply #68 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*
====
« Last Edit: June 29, 2016, 11:22:06 PM by Dan_Lehman »

Mobius

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Re: Offset knot for climbing
« Reply #69 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.





Mobius

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Re: Offset knot for climbing
« Reply #70 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.

agent_smith

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Re: Offset knot for climbing
« Reply #71 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

Mobius

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Re: Offset knot for climbing
« Reply #72 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.


agent_smith

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Re: Offset knot for climbing
« Reply #73 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
« Last Edit: June 29, 2016, 10:50:44 PM by agent_smith »

Dan_Lehman

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Re: Offset knot for climbing
« Reply #74 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*
====
« Last Edit: June 30, 2016, 01:10:39 AM by Dan_Lehman »