Author Topic: the Sheet bend bowline-like loop, as a locked sliding noose-hitch.  (Read 7021 times)

X1

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   The best collection and review of sliding lockable knots I am aware of, by :
   
   Joris Hage and Lydia P. E. van der Steen 
   Locking, Jamming, and Ratchet Mechanisms of Sliding Surgical Knots Topologically Revisited
   http://link.springer.com/article/10.1007/s00268-008-9904-2/fulltext.html

   In this article, the interested knot tyer can find references of the original papers where those knots were presented for the first time. Reading one of those articles, I suddenly realized that the Weston knot is identical to the ABoK#1991 "Jam Hitch" - just as the Dundee knot is identical to the ABoK#1987, and the capsized Tennessee slider is identical to ABoK#1060.
   This made me think that it would be very interesting to start by already known bowline-like (PET) loops, and, by reverse engineering  :), investigate the possibility that they will be generated by the capsizing of some sliding lockable knot. This may sound a little complicated, but, in fact, it is quite simple :
   Take a bowline-like (PET) end-of-line loop.
   Pull its bights, and feed the knot s nub with as much rope length as needed, to get a very loose form of the original loop. You will probably have to consume much more than the original rope length, so you should better start from a loop with a very long tail and a very large eye.
   Pull the tail and the eye-leg-of-the-bight of this loop, to the point the segment of the rope between them is completely straightened - it is turned into an unknotted straight line. The original knot would now be transformed into a "reversed" knot.
   ( Of course, this is possible only in those cases where the collar structure of the original bowline-like loop is also topologically equivalent to the unknot, just as its nipping loop structure. Otherwise, in loops where the collar structure is topologically equivalent to the overhand knot, the fig.8 knot, etc, you will not be able to straighten the segment by which it is formed completely... By pulling the tail and the eye-leg-of-the-bight, you will only tighten an overhand knot, a fig.8 knot, etc, but you will not be able to arrive at a straight unknotted line ).
   Now, pull the standing end and the eye-leg-of-the-standing-part of this "reversed" knot.
   If you are lucky, you may arrive back at the original loop. 

   We can not know in advance if a bowline-like loop would be "reversible" - or not : i.e., we can not know if its "reversed" knot would be such that, when we will pull the original standing end and the original eye-leg-of-the-standing-end, we will get the original knot - or we will get another knot, topologically equivalent, but geometrically distinct from the original. Topology does not determine geometry ! (*) Every knot has a "reversed" form, but very few are "reversible"- because, most of the time, the "reversed" loose form, when tightened and compactified, will settle to a knot very different from the original.   
    One would probably think that the complexity of the knots would be the decisive factor : It would be more likely that the most simple knots would be reversible, and the more complex ones would not. Nooope ! Very simple knots, when loosened, will not return to their original form, while more complex ones will. The interested knot tyer should try this "reverse engineering" on the four variations of the "Eskimo bowline" (2), and see what happens...
   So, I tried my hand on one of the simpler - if not the simplest - bowline-like loops, the Sheet bend "bowline" - which. although it "looks" like a bowline, and it is PET, is not a "proper" bowline  : because it has neither the bowline s "proper" nipping loop, nor the bowline s "proper" collar. ( In fact, it is a loop knot made by interlocked half hitches (1)(2)(3).

   Beginner s luck:) See , at the attached pictures, the loose form of the sliding noose-hitch which, when capsized, locks in the form of the Sheet bend bowline-like loop.

1.  http://igkt.net/sm/index.php?topic=3233.msg23702#msg23702
2.  http://igkt.net/sm/index.php?topic=3233.msg23797#msg23797
3   http://igkt.net/sm/index.php?topic=3233.msg23712#msg23712

P.S. 2012-12-10

   As it was pointed out to me by Charles Hamel ( Nautile ), this is not an accurate statement. Perhaps I should had written "Topology doen not uniquely determines geometry ", or something like that. He kindly offered to me the following correct sentence :
  Topology does determine zero to several allowable *knotted* geometrical conformations, in other words it determines a *set* of materially *possible*  geometrical configurations.
 
« Last Edit: December 11, 2012, 02:07:24 AM by X1 »

kd8eeh

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Re: the Sheet bend bowline-like loop, as a locked sliding noose-hitch.
« Reply #1 on: December 16, 2012, 02:32:09 AM »
I look at this knot as all sheet bend, no bowline, because it is this knot, with one topological manipulation that makes it look like a bowline like loop.  When I applied any load to this knot, it transformed into this form.

X1

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Re: the Sheet bend bowline-like loop, as a locked sliding noose-hitch.
« Reply #2 on: December 16, 2012, 03:06:52 AM »
  When I applied any load to this knot, it transformed into this form.

   Not any load, this load. Many loop knots are transformed into the "corresponding" bends, if loaded this way.That does not make them bends, they are still loop knots, capsized into a different form that looks like the form of the parent bend. Bends are loaded from two ends, loop knots are loaded from three - the angle of the three loaded limbs of the loop knot does change its final form, but does not turn it into a bend...

kd8eeh

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Re: the Sheet bend bowline-like loop, as a locked sliding noose-hitch.
« Reply #3 on: December 16, 2012, 05:01:27 AM »
You have a point.

Still, the nipping loop you have in this not is a loop purely by chance arrangement of the strands.  There is nothing here that makes it a bowline; the tail end forms a nipping loop, and the standing part does not (there is a loop, but it can be protrayed identially as a simple bend in the rope).  What do you say constitutes it as a bowline like loop?

X1

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Re: the Sheet bend bowline-like loop, as a locked sliding noose-hitch.
« Reply #4 on: December 16, 2012, 01:26:57 PM »
the tail end forms a nipping loop, and the standing part does not

   The tail and the standing part in this knot have the same form. The loop of the tail is loaded only from one end - so it is a half hitch - while that of the nipping loop is loaded from both ends - so it is a nipping loop. A long discussion of what is a nipping loop and what is a half hitch, and why there is no Sheet bend component in the standard bowline ( while there is in this bowline-like loop ) , at (1). Anyway, we are discussing about definitions only because they help us tie new and better knots, and understand what is a knot and how it works, not for their own sake.

1.  http://igkt.net/sm/index.php?topic=3233.0