Author Topic: Analysis of Bowlines paper uploaded for review and comment (PACI website)  (Read 196752 times)

xarax

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When the S.Part pulls hard against the normal positioning of the tail in usual tying, it pulls the tail towards the collar a little, in tightening the turNip --and the tail in moving will *roll* with this *punch*, a little

   OK, I see what you mean. Yes, the Tail End can revolve freely around its axis, but the Standing End can not - the "model" of the bowline I had tried to paint explains the fact that there is a not negligible reduction of the amount of tension running through the line, between point A, at the start of the first leg of the collar, just after it exits from the nipping loop, and point B, at the end of the second leg of the collar, just before it enters into the nipping loop for a second time. In its path from A to B, the continuation of the returning eye leg turns around the rim of the nipping loop, then around the Standing End, and then around the rim of the nipping loop again, and in all those arcs  we have friction, and absorption of tension. If in all those points the line could slide freely, or if those point belonged to freely revolving, around their axes, elements, the bowline would had been a much less efficient eyeknot. That was my point about the capstan effect - but the crux of the matter is the presence of friction at the area around the collar, which facilitates  the job the nipping loop has to do regarding the second leg of the collar. ( And, of course, the reduction of the tension when the nipping loop nips the first leg of the collar also reduces the burden it has to carry when it nips the second leg of the collar, but this is obvious - what is not obvious, is that the friction AFTER the first nipping, and BEFORE the second nipping, does play an important role - and it is what makes the bowline s locking mechanism more efficient than the Gleipnir.
This is not a knot.

xarax

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  Let me say the same thing, in other words :
   2. The bowline can not work, if only the first leg of the collar is nipped once, and there is no friction on the line AFTER the first leg of the collar.
And yet it does, in the sheepshank and bellringer's loop

  No, it does NOT - and the proof of that is that, in the Sheepshank, we need TWO nipping loops, and in the Gleipnir, we need some deflection, and some twisting, so additional friction, between the two tails - and even with those tricks, those knots are  NOT as secure as the bowline ! Of course, under light loading, it does ( but then, as anything does, and anything goes...) - I am always speaking about heavy loading, where the locking mechanism of the bowline reveals its superiority over more simple, direct locking mechanisms, as in the cases you mention ( which can NOT withstand such loading ! )
   An eyeknot based on a locking mechanism with a nipping loop but without a collar is a bowline so badly amputated, that I find it difficult to call it "bowline" any more... And by a "collar", I do not mean a "collar-like" mid-air U turn, as the turns of the Sheepshank - AND I do not mean a "collar-like" turn around a freely revolving element ( which would behave like a freely rotating pulley or a bearing ). I mean a collar with friction - and such a collar behaves in a way which, IMHO, can be modelled, and somehow explained, by the reference to the capstan effect. Of course, the REAL situation is much more complex - but I thought that the capstan effect can explain, in a simplified yet satisfactory way, the simple fact that the second leg of the collar, when it comes out of the nipping loop, is less tensioned than the first, just before it goes into the nipping loop again.   

One might experiment by using some tubes of metal/plastic to give "no friction" at certain points.

   I did, but not under the completely controlled, "laboratory" conditions I would had wished... What I had also seen, was yet another very interesting thing, which I had mentioned some time ago, in the long thread about the bowline : that the reduction of friction between the nipping loop and the one or both legs of the collar, has an unexpected effect : the nipping loop can "walk" towards the tip of the eye ! Therefore, the collar, and the friction around it, is not only needed to stabilize the nipping loop, and prevent it from opening up and degenerating into an open helix, and to reduce the tensile forces which arrive at the second leg of the collar, but also to prevent the "walking" of the nipping loop towards the tip of the eye. So much for the "secondary" role of the bowline s collar !
« Last Edit: June 28, 2015, 12:05:47 PM by xarax »
This is not a knot.

Dan_Lehman

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  Let me say the same thing, in other words :
   2. The bowline can not work, if only the first leg of the collar is nipped once, and there is no friction on the line AFTER the first leg of the collar.
And yet it does, in the sheepshank and bellringer's loop

  No, it does NOT - and the proof of that is that, in the Sheepshank, we need TWO nipping loops, and in the Gleipnir, we need some deflection, and some ...
And it's all nigh impossible to test empirically,
for the imbalances pointed to and necessary
countering somehow.

But the assertion "2" is just plain wrong :
necessary friction is a matter of material (you cannot
idealize this!), and we've seen strange things
when it's greatly reduced via HMPE cord (and
its great strength, though IIRC the slippage comes
in sub-super force range), and can certainly know
that in the other direction (frictive) there will be
much less need of structure built upon structure.

But, yes, I've seen constrictor knots get loose(r)
over time, though they are well-nipped.


--dl*
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xarax

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  Let me say the same thing, in other words :
   2. The bowline can not work, if only the first leg of the collar is nipped once, and there is no friction on the line AFTER the first leg of the collar.

  "2" is just plain wrong

  "2" is just plain correct, and obviously true ( and equivalent to equivalently and plainly correct and obviously true point 3., stated afterwards ) - because, otherwise, we would nt use any collar at all !  :) :) However, I believe that you simply had not understood the sentences of points "2" and "3" - perhaps because you had not noticed the word "once", or perhaps because they are not written correctly - their meaning is unambiguous, and can not be argued...
   
   Now, I see that the rather simple "thought experiments" ( Gedanken-experiments ) I had suggested were not, for some people, such easy things to "perform" as I had thought they would had been... OK. Then, I will try to say the same things otherwise - and in a form one can verify or falsify, with the help of a "real" experiment !  :) :)

   Let us tie two bowline-like knots, like the knot shown in Reply#252, and at the attached picture. In those knots, we can either use freely rotating pulleys / "lashing blocks", to simulate the absence of friction along the line of the collar, or use not-rotating pulleys ( where the axes of the pulleys are "glued", so the lines "feel" friction, as they slide along the grooves of the pulleys ), to simulate the presence of friction at the area of the collar.
   Moreover, in each of the two cases ( the case without friction, and the case with friction ), let us do one more differentiation : let us "isolate", from friction, the first, only, leg of the first "bowline", and the second, only, leg of the second "bowline", at the points where they go through the nipping loops, by the device described here :
   
   One might experiment by using some tubes of metal/plastic to give "no friction" at certain points.
   ( This "isolation" from friction inside the nipping loop may be complete or partial - in the later case, we may just reduce the friction forces around the first leg or the second leg by, say, 50%, so we would have the 100% of the "normal" friction around the one leg and the 50% around the other leg - I describe only the 100% - 0% situation, for clarity ).

   So, we have FOUR different cases :
   1a. No friction along the collar line - friction at the first, only, nipping point, before the first leg - no friction at the second nipping point, after the second leg.
   1b. No friction along the collar line - no friction at the first nipping point, before the first leg - friction at the second, only, nipping point, after the second leg.
   2a. Friction along the collar line - friction at the first, only, nipping point, before the first leg - no friction at the second nipping point, after the second leg.
   2b. Friction along the collar line - no friction at the first nipping point, before the first leg - friction at the second, only, nipping point, after the second leg.
   
   WHICH bowline-like eyeknots will hold more, in each case, in an tug-of-war type experiment ?
   The evaluation I had claimed of the less efficient, secondary, "dumb" way the first leg is nipped, in comparison to the more efficient, "clever" nipping of the second leg, was based on the answer of those experiments.

   1a is as efficient as 1b.
   It does not matter WHERE a line is nipped, if it is nipped once, and there is no friction anywhere else !
   
   2a slips first=less secure than 2b.
   Nipping, once, only after the second leg of the collar, is more efficient / "clever" than the "dumb" nipping, once, only before the first leg of the collar.

   1a slips first=less secure than 2a.
   1b slips first=less secure than 2b.
 
Friction along the first leg of the collar, along the rim of the collar, and along the second leg of the collar, does matter !
   Clear as mud ?  :) :) :) I can do no more/better !  :( :( :(
« Last Edit: July 11, 2015, 10:52:08 AM by xarax »
This is not a knot.

Tex

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Hi a_s

I just scanned through to suggest adding the bowline on a bight with one loop pulled up, just to find someone beat me to it, so good.

I'll just point out the obvious, that you don't have to tie it that way, either TIB or in the end. You can start with the loop already short-circuited. IMO Compared to some of the creative abcdedbd bowlines it's not a complicated retuck tied in the end even. At least you have a map in front of you and when you're done it's easier to verify than some double reversed-reeved pretzel hitch bowline with a yosimite finish.

Speaking of which, I'm not sure if any pretzel-nip bowline has made the list yet, for what it's worth.

I also thought it could be nice to show the TIB method for at least the BotB and point out that basically the same method can be used to produce any number of single or double (or transformed) bowlines starting with any number of single or double nipping structures (and a simple retuck comes along for the ride).  Of course it's not a tying guide, so, maybe not...

agent_smith

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Another Eye Knot (Bowline based around the so-called 'Myrtle maneuver' - I hate that moniker) that I finally found time to photograph (in better quality than my previous attempt)...
Note: I used the term myrtle manoeuvre, and not 'collar'

Its just a modification of one of Alan Lee's brilliant existing work.

No other comments from me at this point in time.

Quote
I'll just point out the obvious, that you don't have to tie it that way, either TIB or in the end. You can start with the loop already short-circuited

Tex, have you got any photos or diagrams to lend assistance? I am struggling with work (in real life) and other issues at the moment. An uphill battle for every step forward..

Quote
Speaking of which, I'm not sure if any pretzel-nip bowline has made the list yet, for what it's worth.

Working on it... time is against me at the moment (sorry).

Mark Gommers
« Last Edit: July 16, 2015, 11:48:10 PM by agent_smith »

xarax

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   There is no Myrtle collar here ! The first leg of the collar exits from the nipping loop from the same side the second leg enters into - as it happens in the "proper" collar, of the classic bowline.
   The main disadvantage of this eyeknot is that the "Tail Part" ( = the last part of the Stranding Part, before it exits the nub and becomes the Tail End ) is not secured very tightly : First, it passes through the centre of those two interlocking loops (  the main nipping loop and the loop of the "link" ), where it is "protected" rather than squeezed by the surrounding segments, which act more like a cocoon ( an armour ) rather than constricting structure ( a corset  :) ). The stiffness of the climbing ropes make this central opening a "soft" spot, a segment which we need to secure tightly should rather avoid. (*) Second, it passes through through the bight of this very round and very wide collar almost freely...
   However, it does have a great advantage, which makes it interesting, and which should always be explicitly mentioned, and appreciated. It is TIB. (1)

(*)
  The central opening of this ... knot, contrary to what one might had expected, is not nipping the tail as hard as I would like to... I believe that, in this tight entanglement of the two rims and the four limbs of the two nipping loops < ( the main nipping loop, and the nipping loop of the "link" ) >, a great portion of the tensile forces that would otherwise tend to shrink the diameter of the central opening and grip the penetrating tail forcefully, is "wasted" - it is absorbed by the strong friction forces between the many tightly embracing rope segments that turn around the central opening, and around the penetrating tail that is supposed to be nipped.

1. http://igkt.net/sm/index.php?topic=4695.msg30329#msg30329
« Last Edit: July 16, 2015, 05:50:57 PM by xarax »
This is not a knot.

Tex

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agent_smith:
Quote

(quoting Me:)
Quote
    I'll just point out the obvious, that you don't have to tie it that way, either TIB or in the end. You can start with the loop already short-circuited

Tex, have you got any photos or diagrams to lend assistance? I am struggling with work (in real life) and other issues at the moment. An uphill battle for every step forward..

A_S it's not a big deal to me.  Tied in the end, I think it's obvious how to short circuit the second loop, when you start retracing the bowline, taking the end around the main loop(s) the second time, you just go around as little as possible (and not through your harness for example).

as for tying the BoB in the bight,
normally, as a baseline instruction set for your reference, so you understand me, you
1) fold rope in half
2) make nip with both lines together
3) pull tip of double-folded rope through nip a little and do the collar manoeuvre with it.

To short circuit one loop instead, step 3 becomes:
3) pull a bight from ONE SIDE of double folded rope through the nip and do the collar manoeuvre with it.

You should pull that bight from as close to the nip as possible.

I think you should prefer to pull the bight  from the side related to the tail, not to the standing end, but it probably doesn't matter much, just adds that much more security to the tail.

agent_smith

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Re: Analysis of Bowlines paper uploaded for review and comment (PACI website)
« Reply #263 on: September 23, 2015, 02:19:20 AM »
Still progressing this work...one step-at-a-time.

Part of the paper will include a discussion on knot terminology/anatomy.

I have attached a scoping document to obtain opinion on correct terminology for each structure/segment/part of a knot structure.

I would appreciate any replies.

Format for reply would be:

[ ] A  your answer
[ ] B  your answer
[ ] C  your answer
[ ] D  your answer
[ ] E  your answer
[ ] F  your answer

You may choose from the list of descriptors provided (or feel free to add your own) and so on...

Hopefully the image is readable (difficult to get reasonable image quality with 100KB size limit)

Thanks,

Mark
« Last Edit: September 23, 2015, 02:29:01 AM by agent_smith »

DerekSmith

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Re: Analysis of Bowlines paper uploaded for review and comment (PACI website)
« Reply #264 on: December 28, 2015, 07:18:57 PM »
Well, not wishing to contradict Xarax, but this



certainly looks like a Myrtle core to me, with the tail reworked into a collar around the load line and tucked through the double nipping loops of the Myrtle.

How can anyone not see the simple Myrtle core?

@Mark  do you find any significant advantage from the final tuck under the collar?

DerekSmith

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Re: Analysis of Bowlines paper uploaded for review and comment (PACI website)
« Reply #265 on: December 28, 2015, 07:36:45 PM »
Follow the shading

Mobius

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Re: Analysis of Bowlines paper uploaded for review and comment (PACI website)
« Reply #266 on: December 29, 2015, 03:50:34 AM »
Follow the shading
xarax notes earlier that the knot is TIB, this being the advantage of the final tuck. xarax also discusses that the final tucks are not tight. For this reason the knot does not load very well in my opinion, I trialled this knot a few months ago along with two other TIB loops of a slimilar a vain. Load sharing wise the last few tucks do very litlle and the knot, though secure, distorts (it kind of rolls) too much for my liking.

Cheers,

mobius

DerekSmith

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Re: Analysis of Bowlines paper uploaded for review and comment (PACI website)
« Reply #267 on: December 29, 2015, 12:04:45 PM »
Hi Mobius,

Unless TIB has changed its meaning since last I was on here, it means tied without access to the ends, which would totally preclude the ability to make 'the final tuck'.

The other alternative would be to tie the knot 'with' a bight which effectively forms a doubled knot, which this clearly is not.

If we ignore the diversion of the collar and final tucks of the end, this is simply a Myrtle Loop knot.  The Myrtle resolves to the basic knot form of 5,1 and it is impossible to make the 5,1 'in bight' resorting only to our rather restricted three dimensional space.

Dependent upon the cordage, the Myrtle can range from the most exquisite simple little knot, to a rather risky beast.  despite having two counter locking nipping loops, it has nothing else to keep the nipping loops working.  The slightest slack induced into the knot and the whole thing can fly open if unloaded.  The final embellishment however, of wrapping the end to make another nipping loop (albeit non loaded), makes a significant difference to the knot stability.

I find this ammendment  to the Myrtle loop to be a significant improvement, hence my question to Mark to see if he had similar experience.

Derek

Dan_Lehman

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Re: Analysis of Bowlines paper uploaded for review and comment (PACI website)
« Reply #268 on: December 29, 2015, 08:49:54 PM »
Unless TIB has changed its meaning since last I was on here,
it means tied without access to the ends,
which would totally preclude the ability to make 'the final tuck'.
Then try the reverse : UNtying w/o access to the ends.
I think that you'll be able to do this, and change your mind!
 ;)

Quote
Dependent upon the cordage, the Myrtle can range from the most exquisite simple little knot, to a rather risky beast.  despite having two counter locking nipping loops, it has nothing else to keep the nipping loops working.  The slightest slack induced into the knot and the whole thing can fly open if unloaded.  The final embellishment however, of wrapping the end to make another nipping loop (albeit non loaded), makes a significant difference to the knot stability.

I find this ammendment  to the Myrtle loop to be a significant improvement, hence my question to Mark to see if he had similar experience.
I prefer the anti-bowline similar knot (bring tail
into S.Part's turNip from the opposite side/direction),
and finish by tucking the tail out closer to the eye
--the Myrtle tucking out away ... .
AND put in a 2nd tail-wrap. for added security and that
3rd (better *rounding*) diameter in the turNip's grasp.
(But this isn't TIB..)

And, yes, one can add in a collar to such things (to which
Agent_Smith is bound to Yosemite-tuck the tail!   ;D  ).


--dl*
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DerekSmith

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Re: Analysis of Bowlines paper uploaded for review and comment (PACI website)
« Reply #269 on: December 29, 2015, 11:50:58 PM »
Well, today, thanks to Dan, I was treated to a surprise.

I tied the knot exactly as per the image - a Myrtle plus an extra wrap and tuck.

Then I fixed the ends and started to decompose the knot.  It progressed nicely and rapidly to - The Unknot...

So, I stand corrected - this knot can indeed be TIB.

More research needed...

Thanks Dan - I think!

Derek