The Tweedledee bowline

[X1]

   The Tweedledee bowline. "The fact that the two identical links, that are interlocked in the [ Tweedledee ] bend, are [ topologically equivalent to the unknot ], makes this bend also suitable for a bowline-like end-of-line loop." (1), (2). A variation of this bend, where the tails pass underneath the diagonal and are crossed / twisted around each other,  is shown at (3).
   This bowline is a rare example, where the nipping loops ( the "nipping structure" ) and the collars ( the "collar structure"), are geometrically identical. Of course, they are different knots, because the nipping structure is loaded through both its limbs ( 100% of the total load from the one, the standing end, and 50% of the total load from the other, the eye-leg-of-the-standing-part), while the collar structure is loaded only from one limb ( the eye-leg-of-the-bight, which bears 50% of the total load). However, this difference in loading is not sufficient to distort the general symmetric aspects of this loop, which is beneficial in its easy inspection.( Something similar happens at the double harness loop, as well as at the other loops mentioned at (4), where the two links are also topologically equivalent to the unknot.) The reader should notice the obvious differences with the ugly so-called "Zeppelin loop", where the two links are topologically equivalent with the overhand knot, ( so the first one - the one tied on the standing part and serves as the nipping structure - will most inconveniently remain tied even after second one - the one tied with the working end after the bight and serves as the collar structure - would have been pulled off ), AND where the loading destroys the beautiful symmetrical aspects of the base bend that is so badly misused here, the genuine Zeppelin bend.

1) http://igkt.net/sm/index.php?topic=1919.msg13267#msg13267
2) http://igkt.net/sm/index.php?topic=1919.msg16218#msg16218
3) http://igkt.net/sm/index.php?topic=3672.msg21244#msg21244
4) http://igkt.net/sm/index.php?topic=3984.0

[Dan_Lehman]

   This bowline is a rare example, where the nipping loops ( the "nipping structure" ) and the collars ( the "collar structure"), are geometrically identical. Of course, they are different knots, because the nipping structure is loaded through both its limbs ( 100% of the total load from the one, the standing end, and 50% of the total load from the other, the eye-leg-of-the-standing-part), ...

Hmmm, one can wonder about the 50% and the (initial)
nipping loop --given that the eye leg's loading goes first
through the companion loop to reach the SPart-loaded
one.

... the ugly so-called "Zeppelin loop", where ... the loading destroys
the beautiful symmetrical aspects of the base bend that is so badly misused here,
the genuine Zeppelin bend.

But one should not limit one's view of what constitutes
a "zeppelin loop" (eyeknot)" --consider the rather nicely
retained Z. symmetry in "twinning* the eye-side's parts :
post #63 in (and rightmost knot presented)
http://igkt.net/sm/index.php?topic=1872.msg12866#msg12866


 

[X1]

one can wonder about the 50% and the (initial) nipping loop --given that the eye leg's loading goes first through the companion loop to reach the SPart-loaded one.

  I was talking about the "nipping structure", the two nipping loops of this "8" shaped knot, taken as a whole. I do not have the slightest idea about the distribution of the tensile forces within the two nipping loops...The same can be said for all the double bowlines - and it might even be the case that the second nipping loop does not add much to the total gripping power imposed upon the penetrating collar legs ! ( So, although we can be sure about the effectiveness of the two collars, we can not be sure about the effectiveness of the two nipping loops...). We have to measure  some things here... but, till then, we can do nothing else than keep talking ! 
   

consider the rather nicely retained Z. symmetry in "twinning* the eye-side's parts

   What I mean is that the original Zeppelin knot, the Zeppelin bend, is such a well balanced knot, that the loading of the former tail, although it does not distort the total symmetry altogether, nevertheless it is a fly in the ointment... If the Zeppelin bend was not such a beautiful and unique rope mechanism, it would nt matter so much, I guess. After a proper dressing and initial tightening of the knots, both the Double harness loop ( this particular version ) and the Tweedledee bowline would also be distorted, albeit not in such a degree that would make them almost unrecognisable, at least to the novice knot tyer s eye.

[X1]

   I should mention a great advantage of this knot, that may remain unnoticed by somebody who is not prepared for this :   
   The ( straight limbs of the ) four ends meet the ( curved rims of the ) four nipping loops at right angles. When two segments of rope are squeezed upon each other at a right angle, they "bite" each other harder and deeper, so their relative motion is blocked very efficiently (1). The interested reader should tie the Tweedledee end-to-end knot (bend) and eyeknot (loop), to see by his own eyes how tight and secure they are, even when tied on very slippery material. Moreover, although the Tweedlelee knot is very compact, it does not seem to jam, even under heavy loading. I believe that the Teedledee bowline is one of the few bowline-like post-eye-tiable eyeknots that can safely replace the retraced fig.8 knot in most demanding, life threatening SAR applications.
     
1. http://igkt.net/sm/index.php?topic=2191.msg25286#msg25286
    http://igkt.net/sm/index.php?topic=2191.msg25358#msg25358

[agent_smith]

Hi X1,

I do like this structure (as I've stated previously).

Can you confirm the differences between this structure and the one from this post: http://igkt.net/sm/index.php?topic=4278.0  ?  I'm checking all of your posts now to find the tying method. Got to fully understand this one...

I believe that the Teedledee bowline is one of the few bowline-like post-eye-tiable eyeknots that can safely replace the retraced fig.8 knot in most demanding, life threatening SAR applications

Hmmm, interesting.

This one is definitely making an appearance in the 'Analysis of Bowlines' paper. I've started to play with this already - but have not yet put it to the ultimate test. Need to run a few more vigorous tests before putting my own life-on-the-line. I still extensively use my own EBSB variant Bowline creation which is solid as a rock secure.

Mark

[X1]

   Thank you, Mark

   The best way to represent the "triple symmetric" Tweedledee knot, is offered by its first explorer, Roger E. Miles, at his book : Symmetric Bends - How to Join two Lengths of Cord - (1995), p. 85.  See the attached picture and open the KM file.
   A great advantage of so symmetric a knot is that it can be inspected at a glance - every mistake can be spotted instantly, like a fly in the ointment ! On the contrary, the less symmetric retraced/rewoven fig.8 knot - which can be tied in a large number of apparently similar but essentially different ways - can not be inspected so easily.
   We have only a few Double nipping loop / Double collar bowline-like post-eye-tiable eyeknots - which I call "Double-Double" eyeknots. I believe that the Tweedledee knot is the best of all, by far. At present, to me, it is the golden standard - because it is easy to tie and inspect, very compact, without dangerous openings that can be caught up somewhere, perfectly balanced between the nipping and the collar structure, does not seem to jam easily, most secure against slippage because of the right angles the segments are squeezed upon each other into the knot s nub... What else can we ask from a secure eyeknot ? I would like to see an experimental comparison of it against the Mirrored bowline, as well as against some other "Double-Double" eyeknots that have been tied recently : the Strangle collar Double bowline (1), the Constrictor x2 (2)(*), the Two collars Girth hitch "Eskimo" bowline (3), and even the most simple Mirrored ( or "anti-mirrored" ) bowline shown at (4).

1.  http://igkt.net/sm/index.php?topic=4300.msg26926#msg26926
2.  http://igkt.net/sm/index.php?topic=19.msg26753#msg26753
3.  http://igkt.net/sm/index.php?topic=4009.msg26872#msg26872
4.  http://igkt.net/sm/index.php?topic=4306.msg26951#msg26951

(*) P.S. 2013-4-21
     About the Constrictor x2 bowline, read
     http://igkt.net/sm/index.php?topic=19.msg27318#msg27318

[X1]

   The symmetric representation of the Tweedledee bowline shown by Roger E. Miles. and at the previous post, is not a tying diagram ! It may lead some knot tyers to believe that this is a very complex knot - it is not. In fact, it is a very simple one - just two shape "8" forms interweaved to each other in the most reasonable, symmetric and simple way. The four bights have to encircle the pairs of the parallel segments of each link, otherwise the knot will fall apart ! If the knot tyer remembers this simple requirement, he can not but tie the Tweedledee knot correctly.
   See the attached pictures for a sequence of moves one can follow, to tie it. Of course, every knot tyer would probably figure out another way, better suited to his dexterity and personal tying "style",  but the one shown can be used as a very simple guide one can begin with. 
   

[X1]

  Before one is going to load his Tweedledee bowline, it is better to pre-tighten it a little bid, by pulling simultaneously first the two ends of the "nipping structure s" link ( the standing end and the standing end s eye leg, and then the two ends of the "collar structure s" link ( the tail and the returning eye leg). This way he would have another opportunity to inspect the knot, and the knot by itself will become more well-formed, symmetric and compact - and it will remain so even after the final loading.
   Let us imagine that, for some reason, by mistake, by evil or by accident, the tail will be untucked, not once, but twice ! Will the knot be untied and the climber s life be endangered ? Nooope ! It will remain functional, at the form of the safe eyeknot shown in the last picture. Compared to the Teedledee bowline, the retraced fig. 8 knot s safety is one collar short ! 

* I have replaced the pictures of the previous post with new ones, where the tying procedure of the Tweedledee bowline is shown in four easy steps.

[Luca]

I do not know anything about the mentality of the climbers, all I know is that with a little patience, as you it seems to me are demonstrating, it is not really  hard to learn how to make this loop,also holding the knot "in the hand".I too (for what it's worth my opinion for that matter) I think it is a very safe loop, even with respect to the intermittent load with slacks, because the tail seems that is not practically affected by this occurrence.