Author Topic: Best gripping hitch around a tensioned rope  (Read 43346 times)

xarax

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Re: Rat-Tail stopper
« Reply #45 on: January 21, 2012, 11:32:21 AM »
   I've put to some test... upon ONE of the versions of the "ww hitch"
shown.

   If you wish to comtinue your tests - for which I am greatfull ! - you can try the other 7 (seven) variations of it, posted back at (1) ! It shows two interlinked half hitches, but the situation is similar with the two free ends of the rat-tail stopper, of which we want to pull only the one. We have four ends in total. We have  two ends going "up", towards the rat-tail stopper s main body - going around helical paths, while, at the same time, they cross each other - and we have two other ends, of which we want to use only the one as a standing end, and leave the other as a tail. So we have two lines coming into / and going out of the end point, in all the possible endings/variations of the rat-tail stopper.  The task is to figure out which ending secures that the two limbs would nip the main line at this end point hard enough - so we will not need many crossed coils and much elognation of the whole hitch, and manage to keep it as short as possible - AND which ending ensures that the two limbs would be adequatelly entangled, so they will work as one, and distribute the tension evenly on the main line. At (1) I have tied all the possible simple variations I could think of, but I may have missed something...Try them, and report your findings here, please.

1) http://igkt.net/sm/index.php?topic=2948.msg17512#msg17512
« Last Edit: January 21, 2012, 12:03:25 PM by xarax »
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xarax

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Re: Best gripping hitch around a tensioned rope
« Reply #46 on: January 21, 2012, 08:53:02 PM »
That explains why my posts above are a little off.  I'll delete those posts now.  It's too bad.  This thread had potential.  Now, it's a tangled mess.

Xarax got me again.  I keep falling for it.  LOL

 On the contrary, to separate the "ww hitch"/ rat-tail stopper from the "BB hitch" / series of half hitches, was absolutely the right thing for me to do. I did not do it for me, because I know those knots very well, but for the benefit of the other members, to help them not be confused. I have seen that there were some misunderstandings, because it was not clear about which of the two quite different hitches one was talking about each time. Of course, I have posted the reasons of this re-arrangement immediately, but it seems that some members read only a very small fraction of what I write, and missed the relevant post ( posted at ; Reply #28 on: 2011-07-28, 12:14:03 . i.e. before 6 (six)  months !  :))
  This thread s potential, any thread s potential, is not depending on mine s or your posts, my dear knot4u ! It is depending upon the CONTENT, i.e. the knot presented ! We can easily delete any post we wish, but we can not delete the knot, can we ?  :) The rat-tail stopper is here to stay, and it really does not matter if we like it or not... And the same happens with all the (hundreds) other knots that have been presented in this forum. It should be better perhaps for me to present only their pictures - but I have thought that a little honest discussion will make no harm. I might have been mistaken on this... but not on the usefulness or beauty of the knots themselves I have met and presented here !  :)
   
« Last Edit: January 21, 2012, 08:55:56 PM by xarax »
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Dan_Lehman

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Re: Best gripping hitch around a tensioned rope
« Reply #47 on: January 25, 2012, 05:06:29 AM »
[NB:  This post is *reconstituted* from memory --it was largely
quoting of fixed sources-- after the system glitch that resulted
in an editing session erasing the text on Xarax's reply (which he
promptly posted an alert about --#50, below--, so we redress it).]


... I think that, nevertheless, climbers should have known / should better learn this hitch, because it can obviously be used as a security device, to fix their position on a vertical tensioned line, for example...

I'm abashed to have forgotten that this general structure
earlier surfaced to my awareness --viz., in Dave Merchant's
e-book (2nd edition), Life on a Line , as his #18 "Dog & Tails".
This book is aimed at cavers, but with general application also
especially to SAR, and to other users of similar kermantle ropes.

He confirms Xarax's surmise, saying :
Quote
The Dog & Tails is an anchor system specifically designed for securing a line
to a fixed belay point ... .  The knot does not usually cause damage to the
main line if shock-loaded[,] as the gripping action is distributed along the rope ...
//
The center of a long length (2m+) of cord or webbing is fixed to the anchor point
with a Fig.9 [eyeknot], then a series of alternating under- and over-crosses are [sic]
taken around the main line, ending in a slipped Reef knot ... or something similarly easy
to release.  ...  For 9mm accessory cord and 11mm kernmantel [sic] rope, 10 to 12 crosses
are sufficient.
Under load, the crosses kink and grip the main line, with the friction concentrated
in the centre third of the chain of crosses.  [my underscoring]
//
The Dog & Tails tied in 8mm accessory cord on 11mm rope and using 10 crosses
has been tested and shown to reliably arrest a 200kg FF-0.33 fall event {sounds seasonal  ;D  }
with 50 cm, although the rope and cord will both be damaged by friction.

He adds that the D&T works well also on hoses & electrical cord,
but not on solid objects such as steel cable or pipe,
because they cannot be impressed by the wraps.
(One should remark at this contradicting Derek's finding with a
like structure, though he had relatively small hitching line to
the large, hard, smooth object.)


--dl*
====
« Last Edit: January 29, 2012, 05:09:49 AM by Dan_Lehman »

xarax

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Re: Best gripping hitch around a tensioned rope
« Reply #48 on: January 25, 2012, 06:05:49 PM »
   Thank you, dan Lehman.

  I must also admit, that from the time I saw this rat-tail stopper published, I keep asking all my friends sailors/fishermen if they knew it...What can I say ? They look at me with a sad face, tap-tap me at my back, and tell me that EVERYBODY knows this stopper, ( except me !), and I should better find another field to try to discover anything, than the field of marine knots... :'( Total humiliation !
   Here in my country-  that has a really big commercial ships fleet- not knowing this knot is a joke...that almost proves you are a shepherd !  :) I feel ashamed I have not met this knot before in my  life... or that I have never paid any attention on it ( because it is only the last 3 years that I have a certain interest in knotting, although I sail the last half century or so...)

   As I have mentioned somewhere, my preliminary tests with 1/2 nylon kernmantle climbing ropes gave me some evidence that 4, ot at most 5 pairs of crossings would be enough ( 8 or 10 crossing points). And that this configuration is safer than a similar-number series of half hitches ( "BB" hitches, as I used to call them)- which IS known by climbers.
   However, I understand the slightly greater number reported in your reference, because the endings I use are much more effective, as nipping structures, than the reef knots used in the common rat-tail stopper. I have already provided enough information about them, and you can try them to see my point : If you use two interlinked half hitches instead of a reef knot, you probably need at least one crossed pair less than the common rat-tail stopper - so your knot iwill be at least 20 -25 % shorter, for the same gripping power.
   
« Last Edit: January 25, 2012, 06:07:53 PM by xarax »
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Dan_Lehman

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Re: Best gripping hitch around a tensioned rope
« Reply #50 on: January 30, 2012, 06:04:48 PM »
Note that the first-given URLink'd resource in SS369's post
has a structure much like the Dog & Tails but the ends are
seized as well as 2-3 points along the wrapping structure.

With the YaleGrip(s), each *arm* is put on completely and
separately from the others --i.e., there is no alternating
over/under relationship : successive arms are entirely over
the preceding ones.  Surprisingly and sadly, that information
page doesn't clearly show how each arm is tied off.  I recommend
the reverse groundline hitch --a half-hitch which aims
the tail back towards the wrapping and a 2nd h-h which
then reverses that direction and locks the structure.

(I'm about to employ similar working in repairing a breaking
plastic 4gal. pail handle --it's cracked about 3/4 the width of
the flat handle at one point.  I'll employ (planning to...) some
cable-hauling polyester tape by seizing that to the handle
near the sides, and somewhere along the handle, AND THEN
wrap over that in this D&G manner (probably alternating
over/under) with the flat, stiff BAILING TAPE frequently used
on e.g. bundles of newspapers, boxes of copier paper, and so on.
This wrapping should keep the polyester tape in place, and add
security & strength to that.  --not sure how I'll tension & tie-off.)


--dl*
====

xarax

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Re: Best gripping hitch around a tensioned rope
« Reply #51 on: January 31, 2012, 02:03:50 AM »
   I have not found many pictures of the rat-tail stopper in the internet, but perhaps I have not searched long enough...See the attached pictures.

I would like to repeat a few points here :

1. I think that it is of paramount importance to load the two lines ( that go around the main line in those helical, crossed over/under paths), in as a symmetric way as possible.
2. A proper interlinked-half-hitches ending can help to shorten the overall length of the knot, because it replaces at least one node, and connects the two lines firmly together - so the pull from the one is transferred to both, and the symmetric loading is retained intact.
3. We do not know yet what is the optimum angle for the crossings.
4. Around poles, the multi-coil hitch based upon the "simple hitch a la Gleipnir" is superior.
« Last Edit: January 31, 2012, 03:08:26 AM by xarax »
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xarax

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Re: Best gripping hitch around a tensioned rope
« Reply #52 on: February 02, 2012, 07:59:49 PM »
   I am afraid I have to return to the subject, because something I keep saying for a looong time now is not heard, evidently.
  The rat-tail stopper ( and the "ww hitch", as I have named this knot, -with a minor addition/modification by me - when I was not aware of its existence), is symmetric in relation to the two segments/legs of the rope that are encircling the main line, while crossing each other at the same time ( at 8 or 10 points) .That means, that each segment /leg goes over and then goes under the other, in succession, so the distribution of loads is as even as possible. First the one coil presses the other and force it to "bite" the main line, then the order is reversed, and so on. We had an argument about this with SS369, and we have not reached any conclusion, but we have pinpointed the difference clearly ( and I have reported this argument in this thread).
   The "Dog and Tail" hitch presented in Dave Merchant s ( wonderful ! ) book "Life on a line " , is not like this. The one segment/leg of the hitch tied by the attached line around the main line, is always over the other - so , at the crossing points, there is always one and the same leg that does the job of pressing the other, and always one and the same leg that bites hard into the main line s body.This is just as in the original SS hitch, which made me think about the "ww hitch" at the first place.
   Is it of such importance I think it is ? I can not be sure, but my understanding of the "ww mechanism", and my preliminary tests persuaded me that it is, indeed. The main line remains more aligned with the axis of the hitch, if each leg plays both roles, the one after the other. And this axial, even distribution of forces is very important to the total gripping power of the hitch.
   The second - obvious - thing about the D&T hitch is that it is reversed, in relation to the rat-tail stopper ( and the ww hitch ). I am not sure that this is irelevant or rrelevant to the final result - but, not having the possibility of an additional nipping ending/closure, the D&T hitch is condemned to be longer, for the same overall gripping power, than a rat-tail stopper, that is for sure.
   See the attached picture of the D & T hitch, as presented in the Dave Merchant's e-book (2nd edition), "Life on a Line" .
 
   P.S. Does those differences prove that the mechanism of the rat-tail stopper was not known to the climbers ? Nooo... :) On the contrary, they prove that the climbers knew about the essence of the mechanism, but they have not explored it much, because they have all those climbing friction hitches at their quivers. The sailors knew better,  perhaps because the had fewer possibilities, or they do not know so much as the climbers do ... :) ( exactly as it had happened with me. )
   
« Last Edit: February 02, 2012, 08:35:37 PM by xarax »
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SS369

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Re: Best gripping hitch around a tensioned rope
« Reply #53 on: February 02, 2012, 08:18:30 PM »
I have a suspicion that the main line material and/or construction method will have influence on which orientation that will be most effective in keeping slippage the least.
Also the line size being used for the stopper is a consideration as well, imho.

As I have seen, the rat tail stopper on laid lines, the first "leg" goes parallel, in the lay of the rope. The following "leg" goes over, crossing the first to press it in place. (Sometimes the loose ends twisted by hand and held, since it is very temporary till the hawser is wrapped around the bollards/bitts.)

With braided rope, if it is of hard density, then there will be little bite as the stopper cord can not penetrate and it is my opinion that there be more crossings and the first leg be wound first (as in the picture xarax just posted). Soft rope -  I would think the opposite would be better. Just an opinion formed by my few unscientific backyard tests using static and dynamic climbing ropes.

SS

xarax

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Re: Best gripping hitch around a tensioned rope
« Reply #54 on: February 02, 2012, 08:53:25 PM »
With braided rope, if it is of hard density, then there will be little bite as the stopper cord can not penetrate

   I do not agree on this. I have used hard, kernmantle ropes, and I have seen this "bite" there, too - so it must be even more pronounced in the case of braided ropes.
   Let me try to describe the situation, the great difference between the friction hitches based on parallel coils ( like the climbing hitches ), and the rat-tail stopper. In the former case, at the helical lines of contact between the main line and the legs of the attached lines, the compression forces are gradually increasing or decreasing. In the later case, alongside those lines, the compression forces are varying in an alternating way . If you were the main line, you would feel been pressed much harder at the points the coils are crossing each other,  rather than squeezed alongside the whole helical path that nips your neck ! Irrespectively of the degree that the surface of the main line retreat under the compression forces, the generated friction forces are more localized, with many minima and maxima, in the case of the rat-tail stopper than in the case of the climbing hitches.
 
« Last Edit: February 04, 2012, 03:05:14 AM by xarax »
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Dan_Lehman

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Re: Best gripping hitch around a tensioned rope
« Reply #55 on: February 05, 2012, 03:52:51 AM »
The "Dog and Tail" hitch presented in Dave Merchant s ( wonderful ! ) book "Life on a line " , is not like this.
The one segment/leg of the hitch tied by the attached line around the main line, is always over the other -
I suggest that you get the proper document to cite
--you've apparently copied from the first edition; the
2nd edition shows the structure with the two tails
alternating respective over/under crossings.  Frankly,
I don't think that this will matter much, but I've not
tested it.  (The pinching of the object line comes at
points between the hitching line's crossings.)

--dl*
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xarax

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Re: Best gripping hitch around a tensioned rope
« Reply #56 on: February 05, 2012, 11:52:19 AM »
The "Dog and Tail" hitch presented in Dave Merchant s ( wonderful ! ) book "Life on a line " , is not like this.
The one segment/leg of the hitch tied by the attached line around the main line, is always over the other -
I suggest that you get the proper document to cite--you've apparently copied from the first edition; the2nd edition shows the structure with the two tails
alternating respective over/under crossings.

I have copied and posted the free electronic version - the 2nd edition is not for free, and, even if I had bought it, I do not know if I could legally copy and post an image of it here...
The interested reader should visit the relevant site :
http://www.lifeonaline.com/
I am happy that the author has understood the difference and corrected the mistake.

The pinching of the object line comes at points between the hitching line's crossings.)

Nooope. The "pinching" of the main line comes mainly underneath the crossing points. It is there that the "UNDER" leg - that is on contact with the main line at that point- is more forcefully pressed upon the main line - and "bites" it harder -by the "OVER" leg. Of course, both legs are squeezing the main line at their almost uninterrupted helical contact lines, but this squeeze is not uniform, has minima and maxima, as I have tried to explain. And the maxima are preciselly underneath the crossing points. At a climbing friction hitch, the situation is totally different ! there are no minima and maxima, the coils are nipping the main line with a uniform force alonside their contact line . We can not even talk about "pinching" in this case, I believe.
   I understand that people mis-tie the rat-tail stopper, by first wrapping a helical path with the one leg around the main line, and then wrapping again both, the main line and this first helical wrapped leg, with a second leg.  ( GREAT mistake ! Or, A DIFFERENT hitch, different from the one I am talking about all this time, and more like the original SS hitch. ) That is probably the easiest thing one can do - otherwise he has to use both hands at the same time, so he can pull both legs evenly as he crosses them and put the one over and the other under, alternatively, at each crossing. If one is tying the wrong hitch, with the wrong way, it is expected that he will not load the two legs of the hitch evenly at the first place, and also that the hitch as a knot will not be self loaded evenly afterwards - with detrimental effects in its overall gripping power. 
   
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xarax

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Re: Best gripping hitch around a tensioned rope
« Reply #57 on: February 06, 2012, 01:27:45 AM »
we've seen a quartet of somewhat similar gripping hitches :
  • YaleGrips-like "stoppers" that alternate direction of complete wraps (4 strands);

  • D&T that has just alternating-over/-under wrapping (2 strands);

  • D&T with a leading *guard* nipping/gripping structure (which you've shown);

  • D&T with a trailing gripping structure (valdotain).

   The rat-tail stopper, with a square knot (as the mooring line stopper described more often ) or a two-interlinked-half-hitches ( as the "ww hitch" described in this thread ) closure/ending at its lower end, should better be called a "Tail & Dog" rather than a "Dog & Tail" hitch...  :)
    See the hitch at Reply#25 (1)(and attached picture) , for a "Dog & Tail & Dog" hitch. There I have tried to add some nipping "opening" at the other, upper end of a ww hitch, but that complicated the knot without any niticeable benefit. I remember that it was not clear to me, at any given instance, which one of the three different segments of the hitch was gripping harder, and was doing the main part of the job - so I decided to abandon that line of exploration. ( I have not thought of a "Dog & Tail"- like hitch, because this type of "reversed", upside-down ww hitch needs a carabiner at its lower end  - and I was not searching for a climbing hitch.)

1   http://igkt.net/sm/index.php?topic=2849.msg17439#msg17439
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Dan_Lehman

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Re: Best gripping hitch around a tensioned rope
« Reply #58 on: February 06, 2012, 06:54:09 AM »
I am happy that the author has
 understood the difference
   and
 corrected the mistake.

Rather, you're presumptive in believing either
--that images are necessarily chosen & understood
by authors (!),
and that this one in particular regards either form
as a mistake to be corrected.
(But I'd bet on your side of this assertion, if forced;
though it might be *stability* more than anything
that appeals of the alternating over/under.)

Quote
The pinching of the object line comes at points between the hitching line's crossings.)

Nooope. The "pinching" of the main line comes mainly underneath the crossing points. It is there that the "UNDER" leg - that is on contact with the main line at that point- is more forcefully pressed upon the main line - and "bites" it harder -by the "OVER" leg.

This seems like nonsense, in that there is no opposition to the
supposed more forceful pressing, so no "bite" can be effected,
as a bite needs teeth on opposite sides (the difference between
a pinch & a poke (which we'd certainly expect esp. European
men to know!  ;D )).  But a quick examination of fat 1/4" laid
CoEx PP/PE rope D&T'd around 11mm dynamic kernmantle
suggests it might be so --i.e., that there might be more
*deflection* of the object line at the doubled points than
there seems to be compression between those points.
.:. We might say that this dog's poke is worse than its bite?!
(I tried once with the as-shown-by-Grog start, and once
with pure wrapping; the former saw a big bite & pinch with
the initial joining of hitch to line.)


--dl*
====

xarax

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Re: Best gripping hitch around a tensioned rope
« Reply #59 on: February 06, 2012, 11:25:32 AM »
it might be *stability* more than anything that appeals of the alternating over/under.)

I have tried to explain that it is "security" which is mostly enhanced by the alternating over/under paths -due to the even distribution of  forces alongside both legs, if the hitch is tied "correctly". However, you are right that "stability" is also an important factor. With the one leg moving around a helical path, in continuous contact with the main line, and the other going over it, I have seen that the position of the crossing points were not stable, i.e. the "over" line was able to slide on top of the "under line", and reposition itself when it was loaded - because, as it was not been kept at its place by the "under" line at any crossing point, it was able to form its own, independent helical path, and the two helices were crossing each other wherever they wished, at unevenly placed crossing points. When we tie the hitch "correctly", by an alternating over/under position of the two legs of the attached line, the crossing points are distributed evenly on the surface of the main line at the first place - and they remain evenly distributed, even when the hitch is loaded afterwards, because both legs hold each other at every second point, and their elongation is even alongside the main line. It is like a normally weaved braid : The threads remain in stable positions, because tensile and compression forces are evenly distributed inside the braid s body.

as a bite needs teeth on opposite sides

  I did not meant this... At each and every crossing point, the "bite" of the upper jaw, the 'over" line, by means of the teeth, the "under' line, was onto the lower lips, the main line.
« Last Edit: February 06, 2012, 11:26:45 AM by xarax »
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