Author Topic: Janus Bowline or an equivalent secure bowline for climbing/rescue purposes  (Read 122349 times)

xarax

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Re: Janus Bowline or an equivalent secure bowline for climbing/rescue purposes
« Reply #180 on: September 03, 2015, 05:12:04 AM »
   Even if you use a very stiff rope, under even moderate loading this knot is not stable : it would degenerate into a "Helical loop".
   However, let us, for the moment, suppose that your rope is super-duper stiff, and the segment shown by the green arrow, in the first picture, would not be "swallowed" by the nub. This loop is not a bowline, for two mainly, reasons : 
   1. The  nipping structure / turn/ loop is not a bowline s nipping structure / turn / loop : As shown in the second picture, by the two red arrows, the rim of this nipping loop approaches the continuation of the Standing End two times - it is almost as it has two crossing points. This form characterizes the "crossing-knot-based loops", which are a distinct class of loops. Many of them are very stable loops, which do not need much help from the collar to retain this stability - but this one is not.
   2. The returning / second eyeleg enters into the nipping loop like it enters in the "Eskimo" bowlines - but then it collars the wrong limb, the Standing End ( like it happens in the common bowlines ), and not the ongoing / first eyeleg ( like it should, of it was an Eskimo bowline ). As a consequence, the "collar" can not prevent the nipping loop from degenerating into an open helix.
   Now, as a "helical loop" it is not so remarkable either. The "similar" simple Helical loops shown in (1) and (2) are more secure, in the sense that the knots tied on the Standing End after the eye grips the helical segment more effectively. However, none of those loops can withstand a really strong pull : the knot tied on the Standing Part after the eye will slide towards the tip of the eye. The way to improve this, is to add a second helical turn (3), so the helical segment of Standing Part will be longer, and will encircle and grip the "collar" more - but then your knot loses the simplicity which was its greatest advantage.   
   For other "Helical loops", read the other posts of the relevant thread (4).

1. http://igkt.net/sm/index.php?topic=4965.msg33791#msg33791
2. http://igkt.net/sm/index.php?topic=4965.msg33814#msg33814
3. http://igkt.net/sm/index.php?topic=4949.msg35580#msg35580
4. http://igkt.net/sm/index.php?topic=4949.15
This is not a knot.