Author Topic: Figure 8 Loop  (Read 14744 times)

alpineer

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Re: Figure 8 Loop
« Reply #15 on: May 15, 2015, 06:04:10 PM »
Suspect water acting as a lubricant in those capsizing cases?

Dan_Lehman

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Re: Figure 8 Loop
« Reply #16 on: May 15, 2015, 06:27:58 PM »
Suspect water acting as a lubricant in those capsizing cases?
That helps, how?  And the yachting lines ... ?
(And all the other marine testimony of "sailors" ?!)

I'm thinking it might have something to do with surface
friction ("frictive" --my contribution to language-- vs. slick)
and thus a draw of opening the turNip rather than
sliding against ... and tightening w/less opening pull?!
AND --purely my surmise--, seeing one trawler (or was
it an apparent owner's pair?) with tail-outside bowlines
(aka "Cowboy", "Left-handed") and thinking that they
had deliberately so tied as a defence against capsizing
(so, work into the thinking the position of tensioned
side of the collar bight).   !?

I will anticipate others' having my suspicion that the lines
were particularly stiff, and that the stiffness essentially
made for looseness, which gave vulnerability to capsize:
no, these thick lines are rather flexible, in many cases.

Another idea : friction around a piling which resulted
in biased tension on the eye legs !?  Eh, that seems
a bit of a desperate grasp for a reason ... .


--dl*
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xarax

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Re: Figure 8 Loop
« Reply #17 on: May 15, 2015, 06:41:47 PM »
I expect that X. et al. can all express having no such experience w/"bowlines"!

  Are you living up to the mountains ?  :) Have you seen marine ropes, immersed into salt:)
  Capsized bowline ? Never ! I mean, real bowlines, real mooring lines, real boats, real sailors - and real sea !  :)
This is not a knot.

xarax

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Re: Figure 8 Loop
« Reply #18 on: May 15, 2015, 06:48:07 PM »
   Suspect water acting as a lubricant in those capsizing cases ?

   On the contrary, water, acting as lubricant, may prevent capsize - because, perhaps, the segments of the rope are offered the chance to rearrange themselves into the nub, fill the gaps, and absorb the more evenly distributed forces more efficiently ? ?
   That would be an interesting experiment : See if a bowline tied on a wet line ( or, a wet line tied as a bowline... :) ) capsizes earlier or not.
« Last Edit: May 15, 2015, 07:13:09 PM by xarax »
This is not a knot.

xarax

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Re: Figure 8 Loop
« Reply #19 on: May 15, 2015, 07:00:34 PM »
  <material> <so-knotted>

  You are a material-fundamentalist !  :)
  <Knot> formed on <this-material>, is the correct description.
This is not a knot.

xarax

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Re: Figure 8 Loop
« Reply #20 on: May 15, 2015, 07:08:42 PM »
   I would like to repeat something that I believe may be interesting : What about modifying the fig. 8 loop or bend, to make it easier to untie ?

... modify this thing, adding or subtracting a tuck of the last part /Tail End, for example, through this or that opening, in order to facilitate its untying easiness after heavy and repeated loading
« Last Edit: May 15, 2015, 07:10:07 PM by xarax »
This is not a knot.

Dan_Lehman

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Re: Figure 8 Loop
« Reply #21 on: May 15, 2015, 07:55:57 PM »
I cannot find the quote quickly, but somewhere Knot_Rigger
remarked --and posted URL to image of...-- that the S.Part
of the fig.8 eyeknot in the "strong form" would pull under
its twin and so achieve a tight turn ... .  Well, this might be
behavior dependent upon both dressing & setting and material.

I, too, can see this.  But is it inevitable, and is it --although
*apparent* in a highly loaded knot-- achieved without some
benefit --i.e., might there be some offloading of force in
the process of the S.Part pushing (against a well-set twin
part)?!  --that the S.Part had to press hard against its twin
in order to run fairly straight, and so ends up stronger in
this than where it runs straight more "unopposed" ?!

It does suggest that in material that is resistant to being
set as I muse could be beneficial for the "strong form"
the benefit of this form cannot be achieved readily (i.e.,
it might take devices to set the knot well enough, as
manual strength vis-a-vis expected forces is just too low).
(There is another factor : elastic, compressible material
should do things that static or firm material won't!)

I attach two views of a newspaper photo of a fellow doing
training rescue work in which one can see two fig.8 eyeknots
--in red & gold ropes.  Note how UNloaded one of the twin
strands is in the red rope; I believe that this is the twin
of the "strong form", and so we see how the S.Part gets
"into" making a tight turn, missing bearing against this
twin for offloading, the twin too loose in the setting.
And note the gold/yellow knot : it, too, is amply loose
--one can see through gaps in its parts--, maybe because
it's a stout, stiff rope, and not given special effort in its
setting (but even so, it might be one that, with higher
loads --those that only can show a strength difference--,
see the S.Part bypassing the "bear-against" aspect of my
conjecture.

I, too, like Knot_Rigger remarks, had viewed the knot as
showing a milder (if any difference) curvature with the
"weak" (inner twin) strand (which bears into parts that
turn around it, and pulls away from its twin (which will
show its lack of tension by sort of standing aloof in a loaded
knot)), and so wondered at Chisnall's assertion.  Looking
with Chisnall's result as an assumption, I arrived at my
conjuecture of this "bearing against" curvature leading
to the tight, around-eye-legs U-turn.  (But, also, one can
see a *brief* harder curve in the "weak form" S.Part
where it first is deflected around parts; but this might
quickly straighten w/o much consequence.)
AND . . . this conjecture led directly to my "building"
the "Lehman8" (vanity made me choose this moniker
over "bowlinEight" of my word-fusion formation).  I used
the 8 as a base, and then deliberately looked at how the
returning eyeleg could go into this and give the "padding"
("bearing against") benefit conjectured to benefit the
fig.8, and worked that around with a finish that has
some of the easy-to-loosen collar of the bowlilne.
A side benefit is that it seems to be a pretty slack-secure
knot, to boot.

X., I have anticipated your --sent whilst I'm keystroking--
thought:
Quote
I would like to repeat something that I believe may be interesting :
What about modifying the fig. 8 loop or bend, to make it easier to untie ?
Exactly my design goal (I was "designing" actually, rather
than just "fiddling" "what if..." variations (often productive
on its own)!) for the Lehman8 (not an end-2-ender).

Per X.'s & my discussion of the Lehman8, I attach two
(previously posted somewhere) images of this, with the smaller
2nd one showing the "easy untying" collar aspect's reverse
side, i.p.; YMMV on how very tight this might become, though
(needing a marlinespike for the "easy untying" aspect?
--but, nb, that IS easier than knots in which the spike is only
a hope, with no obvious point of insertion and use : here,
it would be at the colloar, to pry it around/off binding S.Part
to "padding" part, which I think would not require so much
stretching of material but just getting tightly pressed parts
to move against each other.  I recall one knot-forum person
admitting to having used this as a climbing tie-in, generally
liking it.

The knot in orange & B&W (an interesting seen-in-marine
setting hollow braid of PP (B) & polyester (W)) is merely a
"quick8" were it stopped before collaring the S.Part
--yes, just the pinch of the 8 on the tail's leg will hold(!)--;
that I doubted such brevity led me to put in a bowlinesque
collar (and stuff a 3rd diameter out through the S.Part's
U-turn.  Looking at it now, I muse about turning it around
the collar clockwise, and then taking it not as shown
but to run "twin" qua "padding" against the orange S.Part's
turn, and so back out twinning the S.Part.
Well, with setting just so, and ... , maybe ....
All of which suggests the practical silliness of such contrivances,
if they require Advanced Knot Setting courses and guesstimations
of ultimate forces effects on particular_material_M !!
BUT, it is not w/o merit, I submit, that in pursuit of learning
what affects knot "efficiency" and so on, that we are able
to build such nearly-alike (small differences to isolate things
that might affect ...) knots for testing, and see what matters
(and in what material_M it matters or not).


--dl*
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xarax

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Re: Figure 8 Loop
« Reply #22 on: May 15, 2015, 08:39:27 PM »
   I believe that the only answer to our problems, is this :
   http://www.alibaba.com/product-detail/20T-Pull-Back-Ram_984242477.html

   ( Nice, clear pictures ! )
« Last Edit: May 15, 2015, 08:43:01 PM by xarax »
This is not a knot.

xarax

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Re: Figure 8 Loop
« Reply #23 on: May 15, 2015, 08:50:54 PM »
    Perhaps if one "plants"/"nails" the Tail End another time into some opening of the knot... and the sheer compressible bulk / volume of this segment prevents the nub from being too tightly clinched around itself ?
   I believe that climbers and rescue workers would be more easily persuaded to use a more easily untied knot which has something more than their beloved fig.8 bend or loop, than something less !
« Last Edit: May 15, 2015, 09:22:13 PM by xarax »
This is not a knot.

Dan_Lehman

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Re: Figure 8 Loop
« Reply #24 on: May 15, 2015, 08:55:59 PM »
This is how I see the world:
Upside-down, from DownUnder!   :D

Quote
The notional concept a right Vs wrong (or strong Vs weak) method of tying
a Figure 8 connective eye knot (#1047) is more likely than not,
only for the realm of discussion and debate among knotting theoreticians.

There is no real-world practical application of the 'strong form' over the 'weak form'
of #1047 within climbing or rescue contexts.

As I have pointed out many times before, strength is irrelevant in climbing/rescue applications.
It might be relevant for the purpose of setting "high lines"
which will require high tension for staying closer to straight,
and if not needing *strength* of the knot for this, might need
preferable/easier untying of one vs. other versions.
Perhaps the "ease of untying" difference (is there...?) will
have (some) significance in other uses, too.

Quote
The 'ideal' knot is one that is secure and stable and doesn't jam.
Also (preferably) it can withstand loading from multiple directions (eg refer to 'wrap 3 pull 2' anchoring knot).
There might be some seen difference in offset loading (aka "EDK")
between the forms, although there is now some advice to
avoid the offset fig.8 in favor of the simpler and more
widely used offset waterknot (overhand) already.

((
BTW/FYI : Clyde Soles introduced the name "offset overhand"
which I liked --esp. the "offset" adjective, which is spot on
(such knots are NOT "flat"!)--, but I opted to go for "water knot"
as the least confusing name (not liking "ring bend" as this
knot doesn't *bend* to a ring; I no longer support Ashley's
desire to hijack "bend" for "end-2-end", as history used it
otherwise --a point that C.L. Day made).

Similarly, as an essential aspect of webbing/tape IS its
"flat"ness, I do not like "flat" vs. "tubular" for tape types
but "solid" vice "flat" --again, to the point!)
))

Quote
A person can tie #1047 deliberately 'messy' - and it will still hold a falling climber.
NB : "messy" is a non-particular description!  One messy
orientation and another one might be quite different in effect?!
NB-2 : "properly dressed" is sometimes advised, but is there
EVER any given specification to what this is, actually?!
(All I've seen is the further verbal guidance to avoid parts
"crossing over" each other, which is subject to interpretation.)
This goes to X.'s point about authors not having real knowledge
(in the No Author is Wrong challenge), but just parroting what
they've heard elsewhere!

TO THE POINTS WE DEBATE ("strong"/inner vs. "weak"/outer versions):
NB-3 : TWO sources --viz., CMC (3rd; & 4th?) & Dave Richards-- have
thought to test "tied in the bight & "follow through" *versions* of the
fig.8 eyeknot !!!  I believe that Agent_Smith has remarked at this,
as have I --that the knots (presumed to have been "dressed & set"
to whatever believed ideal the particular knot tester had, AND that
it was specific enough...-- that the knots cannot care about their
tying method : they are the same entanglement receiving force.
THIS IS A FAR LESS DIFFERENT CIRCUMSTANCE THAN "STRONG/WEAK"!!
And yet it was tested !!

It just would NOT occur to me to do this,
UNLESS
I had done some in-the-field, practical, actual-factual empirical
research
that revealed that there was a difference in
orientation (or a statistically significant bias) of result obtained
from the different tying methods.  THEN, well, yes, test these
different *knots* !!  But neither CMC nor D.R. give such thinking;
they just indicate tying method, for which there is no evidence
of differing results (and general guidance that results should be =) !!
(I find this amazing, appalling.  Mostly, also, w/o remark or critique.)

Quote
... a 'dressed' form of #1047 ... behaves more predictably under load
 and holds its form
... is in a vague way at least better specified
than the open-ended, who-knows-what, "messy" result.

Quote
Knotting theorists have long tried to pinpoint with precision the locality of knot rupture but to date it has eluded them. This in my view might be a prime driver for the subject matter of this thread.
Whoa, this K.T. has made some small effort to learn this,
and --speaking of "thread"-- has introduced the technique
of sewing into test specimens colored threads to mark the
locations at pertinent points of interest.  (See attached!)
I think that I've seen clearly enough that it is the INNER
yarns/strand(s) of a part in a bend that by compression
break, and not the outer, presumed-more-stretched parts,
which was a commonly voiced theory (i.e., outer breakage).
One might see this in following the twist of laid rope where
one of three strands breaks, others stretch out intact, and
see that it leads to concave side of curve at rupture,
not the convex/outer side.

I'll attach two (elsewhere here previously posted?) pics
of such thread-marked tested knots --the ruptured one,
and the survivor eyeknot showing where the marked
spots were (likely) at point of rupture.  (I'm thinking
that these qualify me for a Nobel Prize in Knotting.)   8)


Quote
From a purely theoretical standpoint, narrowing down the precise nature of rope rupture in tensile pull-to-failure tests is interesting and helps us to learn more about the science of knotting. Altering the path of a curve/turn of rope within a knot might yield a few % points difference in strength - and this is exciting for theoreticians as it moves the science a notch forward.
But only if the testing comes with specifics of geometry
and so on, not merely --and as is common-- knot names
and test data, a not showing the pre-loaded geometry,
and the near-rupture geometry, and so on.
(I feel a lock on the Nobel!)

Quote
If someone posted news of a discovery of a new knot climbing tie-in knot that is:
[ ] easy to tie - ('easy' is based on an inexperienced climber attempting to tie the knot)
[ ] is secure
[ ] is stable
[ ] is easy to untie after high loading event (eg a 100 kg+ falling climber - who generates significant impact force)
... would be more interesting than pure theory about 'strong' Vs 'weak' form of #1047 (more interesting to me personally)
That is spelled 'L e h m a n 8' (and spells "Nobel") !   ::)

In the attached photos of tested knots (in Dyneema, 5/16" 12-strand),
a pink thread marked a point I thought likely for rupture, and a gold
thread led or trailed this, anticipating movement in tightening
--i.e., that the gold might move for rupture where the pink had been.
Some white threads are at entry points, to show how much
material is drawn out during tightening/compression (this is
quite INelastic cordage).
The reverse fig.9 eyeknot was chosen over the common
one with this thinking : common one might benefit, in usual
material/fibre
, from some gripping effect, but in HMPE
the material is too slick for this,
so go instead for a form that seems to give a broader curve.
Note that the break point looks to be rather well around
this curve, maybe beyond the U-turn point, where the S.Part
bears against entering eye legs!?

In these cases, it will take more scrutiny to conjecture about
concave/convex side of curve vis-a-vis break point.


--dl*
====

SS369

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Re: Figure 8 Loop
« Reply #25 on: May 15, 2015, 10:01:58 PM »
I agree with agent_smith for practical purposes and that is how I would use the figure 8 loop - without unnecessary worry. I personally tie in with a simple-locked bowline, but that's diverting.

I think that there are tests out there that have been done, measured and video captured that show the parts orientations well enough and the motion of the knot during destructive testing. Thermal imagery included that indicates where the destructive heat is generated and most likely the cause of the rupture. I think so at least.

Watch the video. https://www.youtube.com/watch?v=s3fHYGY3YTo

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roo

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Re: Figure 8 Loop
« Reply #26 on: May 15, 2015, 10:28:37 PM »
Thermal imagery included that indicates where the destructive heat is generated and most likely the cause of the rupture. I think so at least.
I think some strain energy gets converted to heat and since strain is proportional to stress, this can be used to give an approximate indication of where high stress areas are, and thus where rupture is most likely.

But other effects can mask this.  There may be friction-generated heat, and some parts of the knot may lose heat faster just due to geometry.

edit to add related link:  http://www.researchgate.net/publication/252707600_Correlation_of_infrared_thermographic_patterns_and_acoustic_emission_signals_with_tensile_deformation_and_fracture_processes

It's interesting to see the high stress areas from the rope surface become more uniformly distributed as the rope travels away from the knot. 
« Last Edit: May 15, 2015, 10:44:31 PM by roo »
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xarax

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Re: Figure 8 Loop
« Reply #27 on: May 15, 2015, 10:46:34 PM »
From DownUnder :
Right and wrong Figure-of-8 knot
http://www.ropelab.com.au/right-and-wrong-figure-of-8-knot/
This is not a knot.

SS369

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Re: Figure 8 Loop
« Reply #28 on: May 15, 2015, 10:49:31 PM »
Thermal imagery included that indicates where the destructive heat is generated and most likely the cause of the rupture. I think so at least.
I think strain energy gets converted to heat and since strain is proportional to stress, this can be used to give an approximate indication of where high stress areas are, and thus where rupture is most likely.

But other effects can mask this.  There may be friction-generated heat, and some parts of the knot may lose heat faster just due to geometry.

Yeah, I know friction can be included along with pressure, both contributing to the demise of this and other knots. But, I think in this case, this Fig. 8 loop test video, it shows clearly enough with enough data, with this particular dressing, what and where the demise is going to take place. If you were to zoom in close enough...

Of course the rest of the surrounding knot parts (geometry) will carry away/absorb the heat, though I don't really see what that statement proves here. Maybe it slows the flow too much?
This was a slow pull test, but I am of the opinion that a fast pull test or drop test would have very similar results, just faster.

I am of the opinion that if you were to stop the pull test just short of the projected rupture point, it would take a Herculean effort to untie this. As well, the rope would be ruined there.

Regardless, the video shows a well enough completed test.

SS
« Last Edit: May 15, 2015, 10:53:44 PM by SS369 »

roo

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Re: Figure 8 Loop
« Reply #29 on: May 15, 2015, 10:51:29 PM »
I think some strain energy gets converted to heat and since strain is proportional to stress, this can be used to give an approximate indication of where high stress areas are, and thus where rupture is most likely.

But other effects can mask this.  There may be friction-generated heat, and some parts of the knot may lose heat faster just due to geometry.

edit to add related link:  http://www.researchgate.net/publication/252707600_Correlation_of_infrared_thermographic_patterns_and_acoustic_emission_signals_with_tensile_deformation_and_fracture_processes

Slightly off topic, but this is an interesting related experiment:

http://demo.physics.uiuc.edu/LectDemo/scripts/demo_descript.idc?DemoID=1193

However, they left off the really fun part.  Once the rubber band is stretched and the heat dissipates, let it shrink back again and it really feels cold against your skin.
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