Author Topic: An IGKT glossary? Nipping loop example  (Read 481 times)

RGB

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An IGKT glossary? Nipping loop example
« on: September 23, 2018, 06:37:22 AM »
Perhaps IGKT should compile and make public (on the IGKT website?) a current glossary of knotting terms? If contributors to IGKT publications, including this forum, then used terms as defined in the glossary, it would allow contributors to use concise writing without creating ambiguity for readers. Of course, language evolves. So some of the definitions in any glossary may need be changed over time to reflect current meanings (think of the historical uses of 'bend', 'bight' or 'loop'). But a glossary can also indicate important historical meanings, and when they were widely used (including precise dates of change in formal IGKT usage, if that becomes advisable).

In technical writing it is common to define important terms to be used with a particular meaning throughout a particular treatise, particularly if the definitions are non-intuitive or different from na?ve usage. Sometimes this is done for clarity; and sometimes (as commonly seen in the patent literature) it appears to be done for obfuscation. Either way, the provision of a definition to be used within a particular treatise is perfectly legitimate. But it is not automatic, and for non-intuitive usages it is with good reason very rare, for such idiomatic definitions to be adopted for wider use.

In his excellent technical treatise An Analysis of the Structure of 'Bowlines' (www.paci.com.au/Downloads/Bowlines_Analysis.pdf), until ver 2.7a at least, Mark Gommers has defined a usage of the term nipping loop as a:
"component that encircles and compresses all material within its helical structure. This author posits that the nipping loop must be loaded at both ends (ie both the SPart and the ongoing eye leg must be loaded). The nipping loop must be free to increase compression in direct proportion to the load applied. If the nipping loop is not freely acting (ie it is seized or occluded in some way) ? it is non-functional ? which in turn casts doubt on its claim to the title of 'nipping loop'."
Elsewhere in the same treatise, this is condensed to a:
"closed helical structure (that is) loaded at both ends and can freely operate to produce a compression force in direct proportion to the applied load."
And elsewhere again in the same treatise:
"The nipping loop clamps and compresses all material inside the helical structure ? and this compressive force is generated by tension in both the SPart and the ongoing eye leg. .... The Sheet bend (#1431) does not have a functioning nipping loop because it is only loaded at one end. Force is only provided by the SPart."

All of this is fine to inform the reader of a usage in that particular technical treatise, and Mark warns readers, following the first definition of the usage in that treatise, that "Not all knotting experts entirely agree on this salient point." But later (e.g. http://igkt.net/sm/index.php?topic=6207.0) Mark seems to argue for, or assume, wider use of this definition.

I present here the view that this definition of the term nipping loop should not be adopted for wider use, because:
(i) It is a non-intuitive definition, which has therefore the potential to cause more obfuscation than clarity in wider use.
(ii) Some of the restrictions in this definition are not necessary to accomplish an unambiguous definition of a bowline.
(iii) The common bowline may be (and commonly is) made without bi-loading the nipping loop: to tighten, just pull one way on the standing part and the opposite way on the two arms of the collar where they emerge from the nipping loop. Day (1947) provides photographs and instructions for many ways to tie the common bowline, none of which requires bi-loading of the nipping loop (which Day calls the hitch or cuckold's neck). The knot is unquestionably a bowline, before the eye is loaded. It is possible that Mark tightens some bowlines by pulling on the standing part and the proximal part (ongoing leg) of the eye, leaving the collar loose around the standing part (but without capsizing the nipping loop, which would convert the knot into a noose). This would explain why Mark can manipulate the collar under heavy load (whereas I have to remove the load in order to manipulate the collar). Either method of tying yields a bowline.
(iv) The restrictive definition creates the problem that a knot may drift in and out of the bowline category with the tide. With the eye around a high-friction pole like a rough-barked tree, or formed into a round turn as described by Brion Toss (2009), there are times when a moving load on the standing part may bring a load onto only the distal part (returning leg) of the eye, thus loading only one end of the nipping loop, yet the knot by common opinion would remain a bowline.
(v) The underlying posit does not always apply. The fact that a common sheet bend under high load in some ropes requires a lock such as an overhand knot in the tail of the loop to prevent it from slipping (http://caves.org/section/vertical/nh/50/knotrope-hold.html), tells us that under these conditions at least tension is transmitted through the entire loop. Under such conditions the loop must exert some force on both arms of the bight / collar (all material within its helical structure).
(vi) Use of this non-intuitive definition of a nipping loop is apparently claimed to exclude a long-accepted bowline:
"This structure was published in 'Knotting Matters' issue #19 (1987) at page 2 by John Smith. ... The geometry of the core (nub) is structurally the same as #1017 (Anglers loop) but the loading profile is completely different ? there is no functioning nipping loop."
I think that John Smith's tucked bowline (which Mark calls the Lehman lock, though I understand that Dan Lehman has made clear he was not the first to tie or document it) has a nipping loop even by the restrictive definition in Mark?s treatise. The enclosed arms of the bight / collar are crossed, but so they are in the "Yosemite bowline" which is not similarly excluded in the treatise. Despite best efforts, I must be misunderstanding something. John Smith's tucked bowline is an easily tied and very secure bowline for most purposes, but that is another story (http://igkt.net/sm/index.php?topic=6291.0).

So I suggest more intuitive definitions:

A nipping loop is a loop that nips (exerts pressure, and thus creates friction that is relevant to the security of the knot).

This usage existed before the treatise cited above. It follows the broad concept of nip used by Warner (1972) who thought more than his predecessors about nip. However, readers should also be aware of Ashley's (1940) definition of the nip as "the spot within a knot where the end is gripped and is thereby made secure" as it helps to explain some subsequent discussion of knots with "good nip" vs "poor nip".

Nipping loops may be uni-loaded or bi-loaded (with equal or different tensions on the arms when bi-loaded).

Security of a knot is the resistance of the knot to slippage under load, to changing shape (capsizing) into a form more prone to slippage, and to loosening (or eventually coming apart) under adverse conditions that may be encountered in the intended use of the knot, including (for example) cyclic loading, tail loading, or ring loading of eye knots. Security of any knot depends on the material in which the knot is tied as well as the conditions in which the knot is used.

Following Mark's lead, I suggest definition of a bowline as a fixed-eye knot, in which the nub comprises (i) a bight/collar that wraps around the standing part and (ii) a nipping loop that encloses both arms of the bight/collar, and that can be bi-loaded by tension on the standing part and the proximal part (ongoing leg) of the eye.

I see that much of this has been argued in the IGKT forum before, with different perspectives presented (perhaps for the sake of clarification through argument) by two respected Smiths, among others. Is IGKT up to the challenge of consensus about definitions of knotting terms, in an IGKT glossary?

agent_smith

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Re: An IGKT glossary? Nipping loop example
« Reply #1 on: September 24, 2018, 05:29:16 PM »
In seeing my name quoted several times - and with some inaccuracies in both intent and theoretical proposition, it is important that I reply in kind...
Full disclosure clause: I want to make it 100% clear that what I type herein as a reply is not intended to be offensive, derogatory or demeaning in any way. It is simply a statement of fact as I understand it.

Per RGB
Quote
Perhaps IGKT should compile and make public (on the IGKT website?) a current glossary of knotting terms?
This has been tried several times on this IGKT forum - and all have crashed and burned.
In fact, I had tried to gather some momentum recently - and it too crashed and burned.
The reasons for this are both obvious and - at the same time - complex.
I have come to form the view that consensus will likely never be reached - whilst this is unfortunate, it should not come as any surprise.

per RGB:
Quote
until ver 2.7a at least, Mark Gommers has defined a usage of the term nipping loop as
VER 2.7a has long ago been superseded....
In fact, I am currently working on a new revision which will both clarify concepts and make new advances...

per RGB:
Quote
I present here the view that this definition of the term nipping loop should not be adopted for wider use, because:
(i) It is a non-intuitive definition, which has therefore the potential to cause more obfuscation than clarity in wider use.
You might be interested to join forces with Derek Smith?
It is obvious that you have some difficulty both with terminology and theoretical concepts underpinning the very 'essence' of all 'Bowlines'.
You of course have a right to object to anything you desire - and are free to advance your own structural analyses and supporting theories.
I of course completely disagree with your conceptualization of what a 'nipping structure/loop' is.

Per RGB:
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The common bowline may be (and commonly is) made without bi-loading the nipping loop:
This is factually incorrect (in terms of your implied meaning of 'bi-loading').

per RGB:
Quote
Nipping loops may be uni-loaded or bi-loaded (with equal or different tensions on the arms when bi-loaded).
And it is here that you reveal your dislike of the concept of loop that is loaded at both ends...when in fact it is 100% obvious that in all 'Bowlines' - the nipping loop (or nipping structure) is always loaded at both ends. The defining element of all 'Bowlines' is the nipping structure which is always loaded at both ends.

per RGB:
Quote
Use of this non-intuitive definition of a nipping loop is apparently claimed to exclude a long-accepted bowline:
"This structure was published in 'Knotting Matters' issue #19 (1987) at page 2 by John Smith. ... The geometry of the core (nub) is structurally the same as #1017 (Anglers loop) but the loading profile is completely different ? there is no functioning nipping loop."
I think that John Smith's tucked bowline (which Mark calls the Lehman lock, though I understand that Dan Lehman has made clear he was not the first to tie or document it) has a nipping loop even by the restrictive definition in Mark?s treatise.
Refer to the attached image showing correspondence between the Bowline presented by John Smith in 'Knotting Matters' and #1017 Anglers loop.
I have asserted elsewhere that #1017 'Anglers loop' is not [a] 'Bowline'. In the same way, I have asserted elsewhere that #1431 Sheet bend has no 'nipping structure' (in accordance with the definition I had tendered elsewhere).
In the current VER 2.8b paper, there is grammatical errors regarding the alleged 'Lehman lock' and #1017 Anglers loop. This will be corrected in the upcoming revision.
Dan Lehman has never raised objections to associating his name with the alleged 'Lehman lock'. This would be a matter for Dan to revisit and comment...

per RGB:
Quote
This usage existed before the treatise cited above. It follows the broad concept of nip used by Warner (1972) who thought more than his predecessors about nip. However, readers should also be aware of Ashley's (1940) definition of the nip as "the spot within a knot where the end is gripped and is thereby made secure" as it helps to explain some subsequent discussion of knots with "good nip" vs "poor nip".
This passage from your post suggests/implies that certain concepts in relation to the term 'nip' and how it relates to the function of a Bowline has already been accurately and succinctly advanced. Your post is related to 'Bowlines' and 'nipping loops' - so this passage is somewhat ambiguous in terms of your implied intent.
In making a best guess as to what you are implying...To the best of my knowledge, no knotting enthusiast or knot book author has published any coherent work that clearly defines and characterizes the structure and function of a Bowline - including the key components (or elements) that comprise all 'Bowlines'. If such a coherent work had previously existed, I wouldn't have been compelled to open debate on this forum and publish my work. In any case, the term 'nip' and 'nipping loop' are different elements and have different meanings.
And this relates to what a 'loop' is. In the first instance, it is necessary to define what a 'loop' is. In my opinion, having researched several notable knot book authors - there is ambiguity as to what a 'loop' actually is.

per RGB:
Quote
Following Mark's lead, I suggest definition of a bowline as a fixed-eye knot, in which the nub comprises (i) a bight/collar that wraps around the standing part and (ii) a nipping loop that encloses both arms of the bight/collar, and that can be bi-loaded by tension on the standing part and the proximal part (ongoing leg) of the eye.
You are seemingly heading in the right direction but, your proposition overlooks key salient features.
Bowlines can be classified by the geometry of their nipping structure.
In the primary Bowlines, the nipping structure take the form of a helix.
However, other types of nipping structures exist...such as those based on #206 Crossing hitch and #559 Marlinspike hitch. And, we also have #1012 which could be interpreted to mean that a nipping structure can take the form of #1245 Clove hitch.
In the attached image (below; at top) - all of the key elements that underpin a nipping structure are identified.

RGB

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Re: An IGKT glossary? Nipping loop example
« Reply #2 on: September 25, 2018, 01:40:03 AM »
Thanks Mark for thinking about some of the points in the OP. I guess time will tell about wider usage of proposed terminology. I have enjoyed and learned a lot from your analysis of bowlines, and I hope that you will continue to refine it in the future.

Dan_Lehman

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Re: An IGKT glossary? Nipping loop example
« Reply #3 on: September 26, 2018, 09:07:17 PM »
Perhaps IGKT should compile and make public (on the IGKT website?) a current glossary of knotting terms? If contributors to IGKT publications, including this forum, then used terms as defined in the glossary, it would allow contributors to use concise writing without creating ambiguity for readers. Of course, language evolves. So some of the definitions in any glossary may need be changed over time to reflect current meanings (think of the historical uses of 'bend', 'bight' or 'loop'). But a glossary can also indicate important historical meanings, and when they were widely used (including precise dates of change in formal IGKT usage, if that becomes advisable).
Indeed it could be helpful to build such a listing,
at least to show what terms are used,
AND how their uses might conflict/confuse/confound
rather than clarify/harmonize.
(E.g., "bight" ranges in sense from something just
rather ungeometrically specified between end points
to a sharply folded span!  --not merely in cordage,
but in geography : from a not-nearly-a-cove ("sail
out of on a single tack") to a river's bend.)

And my contribution, which is seeing currency here,
at least, is "SPart", which was a sort of lexical shortening
of "standing part" but also a push away from the traditional
term which IMO applied to something during tying
to something relating to the completed knot.

Quote
In technical writing it is common to define important terms
 to be used with a particular meaning throughout a particular treatise,
...
Yes, and often for matters of precision.  But in doing so,
one can make some common parlance awkward when
taking the terms as strictly defined.  It's important IMO
that in shaping knotting nomenclature --possibly establishing
one that serves technical discussion and another that can do
for common presentations-- one keep in mind the purpose.
E.g., as you point out, one can end up having things change
definition by some loading or what-have-you, and this puts
a challenge to "same knot" as a term.
.:.  It is a challenging task!

Quote
"component that encircles and compresses all material within its helical structure.
And I've pushed back at what I feel is too much
--in even the mention-- of "helical", though I can
see that Mark by that wants to excluded e.g. an
overhand which also nips but ... .  Rather, though,
I'd move for establishing "loop", and noting that
there is no more than a fuzzy boundary from where
the loop's (necessarily) minimal-angle helix goes
to larger-angled helixes and looses it *loop*iness!

Quote
This author posits that the nipping loop must be loaded at both ends
Which reliance on behavior/force becomes a challenge
of some material dependence vs. pure structural analysis.
I feel their (Mark's & Xarax's) pain; but some things I think
that they'd include as *bowlines* --i.p., the mirrored bwl.
can be seen to have little if no such both-sides loading.
But for the most part, the distinction works (well enough?).


Quote
(iii) The common bowline may be (and commonly is) made without bi-loading the nipping loop:
So what?  It's not about making the knot but about
what it is in use.  --to which you offer a challenge (one that's
occurred to me as well, and for practical, will-it-hold concerns) :

Quote
(iv) The restrictive definition creates the problem that a knot may drift in and out of the bowline category with the tide. With the eye around a high-friction pole like a rough-barked tree, or formed into a round turn as described by Brion Toss (2009), there are times when a moving load on the standing part may bring a load onto only the distal part (returning leg) of the eye, thus loading only one end of the nipping loop, yet the knot by common opinion would remain a bowline.

Whether such a *knot* would remain ... is exactly what
I referred to above in having strictly defined nomenclature;
one would need to choose whether in fact such discrimination
was wanted, for the particular audience.  (And such knots
as "mid-line eye knots" pose just such problems, as they
are defined to have multiple loadings, but what transpires
in loading order & severity can affect knot geometry and
other behavioral aspects!  It is certainly easier to talk about
a butterfly knot than to have a trio of knots sharing one
*body* (being asymmetric, there would be two eye knots),
but the reality of loading and ... exist regardless of language.

Quote
(v) The underlying posit does not always apply. The fact that a common sheet bend under high load in some ropes requires a lock such as an overhand knot in the tail of the loop to prevent it from slipping (http://caves.org/section/vertical/nh/50/knotrope-hold.html), tells us that under these conditions at least tension is transmitted through the entire loop. Under such conditions the loop must exert some force on both arms of the bight / collar (all material within its helical structure).
Actually, even with #1010, the common bowline, on the test
bed, tied in HMPE the slippage of the nipping turn through
the knot puts force going in the pulled-by-SPart direction
only, though it certainly has a tightening effect, even as
it shrinks the eye.  (This was seen in a video by Brion Toss
with a double bowline!)  It's why I'm leery of putting
performance specifications into knot definitions; it's why
... this issue is so difficult.


--dl*
====