Author Topic: Offset knot for climbing  (Read 24229 times)

Mobius

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Re: Offset knot for climbing
« Reply #75 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.



« Last Edit: July 04, 2016, 05:18:45 AM by mobius »

Dan_Lehman

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Re: Offset knot for climbing
« Reply #76 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*
====

Mobius

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Re: Offset knot for climbing
« Reply #77 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.


« Last Edit: July 17, 2016, 10:06:18 AM by mobius »

agent_smith

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Re: Offset knot for climbing
« Reply #78 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
« Last Edit: July 18, 2016, 04:03:54 AM by agent_smith »

SS369

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Re: Offset knot for climbing
« Reply #79 on: July 18, 2016, 01:48:18 AM »
Off topic contribution:
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/

SS

Dan_Lehman

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Re: Offset knot for climbing
« Reply #80 on: July 20, 2016, 11:40:06 PM »
Off topic contribution:
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*
====

knotsaver

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Re: Offset knot for climbing
« Reply #81 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.

Dan_Lehman

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Re: Offset knot for climbing
« Reply #82 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*
====

knotsaver

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Re: Offset knot for climbing
« Reply #83 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.
« Last Edit: July 25, 2016, 07:08:07 PM by knotsaver »

Dan_Lehman

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Re: Offset knot for climbing
« Reply #84 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*
====