Author Topic: Best gripping hitch around a tensioned rope  (Read 34616 times)

Dan_Lehman

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Re: Best gripping hitch around a tensioned rope
« Reply #60 on: February 17, 2012, 12:02:55 AM »
It should be remarked that there is conflict between two
of the referenced works of this thread:
Dave Merchant says that the D&T cannot be used for
controlled lowering, as once slippage begins, it will (likely)
run out of control;
but the reference cited by SS369 (the electrical journal,
via Googlebooks), gives instructions for just such controlled
slippage --though, given that they specify using at least TWO
such D&T structures, it's not clear how they are to be
each handled for this (might it be that only one is released
from full grip?); they also specify three points of seizing.


--dl*
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estar

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Re: Best gripping hitch around a tensioned rope
« Reply #61 on: April 23, 2014, 05:10:24 PM »
BTW, I was just doing some gripper testing. 

I choose to test perhaps the most challenging situation - a loaded dyneema main line, being held by a dyneema gripper line.

An icicle will hold about 1500lbs in this test.

However, the rail tail will only hold about 150lbs, before it slips (you can see the mark move in the two pics below).

« Last Edit: April 23, 2014, 05:11:42 PM by estar »

Dan_Lehman

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Re: Best gripping hitch around a tensioned rope
« Reply #62 on: April 23, 2014, 05:32:42 PM »
BTW, I was just doing some gripper testing. 

I choose to test perhaps the most challenging situation
--a loaded dyneema main line, being held by a dyneema gripper line.

An icicle will hold about 1500lbs in this test.

However, the rail tail will only hold about 150lbs, before it slips (you can see the mark move in the two pics below).

Hi, EStar!  If the middle photo shows the state of
things prior to loading (mark being at right end
of the structure), then you have way too much
slack in the rat tail : by the time it achieves the
sort of open helical angles you show, it should've
been heavily loaded (and thus making severe
compression to have such open angles) --and at
this much openness, there is not much further
tightening/gripping that it could do, but just
deliver force to the endmost securing knot.

Also, I've read one instruction (for the application
of a pre-made, 4-leg helical gripper) that specifies
that each leg ("arm"?) is to be put on entirely,
after/before others --so, over all that precede,
under all that follow (no alternating over/under);
I see that you do this BUT for one crossing,
near the right (pulling) side.  --for what it's worth.

But you have chosen difficult materials!
(What are their respective diameters?)

Thanks,
--dl*
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xarax

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Re: Best gripping hitch around a tensioned rope
« Reply #63 on: April 23, 2014, 07:33:18 PM »
BTW, I was just doing some gripper testing.

   Fine - but, please, do them PROPERLY !

  You had not said how much loaded is the main line itself ! AND, In the picture with the icile hitch, we clearly see that, contrary to what is happening in the picture with the rat-tail-stopper, the man line is bent  - so it presents a HUGE obstacle to ANY hitch that tries to slide along it...
  If one can force such a pronounced deflexion in the main line, he can use MANY other, less gripping hitches... And, if he can make a whole turn on this main line, he can tie a bowline instead !  :)
   Have you ever seen a mooring or anchor line of a boat stopped by this stopper ? There are only a few pictures in the web, but, even in those, you can see that the main line is supposed to remain STRAIGHT ! ( Trying to achieve this, I had used the MA of a Trucker s hitch - and there I had (re-) discovered the locking of the tail between opposed bights...(1))
   In short, the cross-gartered segments of the rat-tail-stopper tied on his stockings, are meant to encircle Malvolio s STRAIGHT leg   :).
   On the plus side, it is good that you test gripping hitches with the same number of wraps / turns. We should compare apples to apples - with a sufficiently large number of wraps / turns, ANY hitch will grip around ANY main line...

1. http://igkt.net/sm/index.php?topic=1870.msg17364#msg17364

P.S.
 On the very first post of this thread, I had said that :

The tensioned rope, the "Main line", is of the same material and same thickness with the one used for the gripping hitch. The loading/direction of the end is close and parallel to the Main line s axis.

  All my tests were done with same-size ropes. However, it would be interesting, indeed, if you differentiate the sizes, as you have already done, but in a more systematic way. So, you should better first keep a standard-size main line, and then vary the size of the hitching knot in equal increments of the area of the cross section, in order to see if/how those variations alter the results one takes when he tests the hitch with same-size ropes.
   AND, do not forget, the main line is meant to be much-much more loaded than the hitching line, so it would remain STRAIGHT, more or less - I should had included this "Straight", explicitly, in the title of the thread...
   
   
« Last Edit: April 23, 2014, 08:06:00 PM by xarax »
This is not a knot.

TheTreeSpyder

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Re: Best gripping hitch around a tensioned rope
« Reply #64 on: April 24, 2014, 12:07:43 AM »
i'd always and all ways favour Icicle / or variant.

Friction hitches not designed to lower thru; especially higher loads.

Mixed materials best, generally hitchcord would be ~2mm smaller than host line for better grip, maintain more strength % around tight line of host line etc..
Also, by design it would be best; if line below hitch is not loaded, so is 'fatter' than loaded/ gripped line; offering shelf mechanic to hitch.

Would try flat Tenex for hitch cord for greater grip area. 
Would try 3strand as cord too.
Such rough friction duty demands quality materials; maintained w/o glazing from friction slides etc.

Some of this comes down to style of setting and usage, so mileage can vary per user!!!
Some choices offered surpass others in the way they can more easily be pushed up the line, then reloaded.

A 2:1(1 line) climbing system is a different animal than single line drop.

xarax

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Re: Best gripping hitch around a tensioned rope
« Reply #65 on: April 24, 2014, 01:16:02 AM »
by design it would be best if the line below hitch is not loaded

   That is for sure - and THEN, only then, it might be the case that the Icicle hitch might be better than the rat-tai-stopper, indeed !  :)
   However, this subject, the "Best gripping hitch around a not-loaded / not-tensioned rope", belongs to another thread...
   I now know ( because it was revealed and proved by the posts in this thread ) that most knot tyers do not (yet) know the rat-tail-stopper, and they do not understand clearly how it works, so they do not believe it works better than all the other gripping hitches around tensioned ropes ! It is not the first time , of course, that arm-chair knot tyers do not know or understand an already known, by the practitioners of another occupation, knot - however, I must say that I was embarrassed by the way commercial boat sailors looked at me, when I showed them this knot they knew it existed from the time of their grand-parents... which, by the way, I have since learned that is used every day for securing the mooring or anchor line of big boats. I had never met this knot in small, recreational sailing boats, or, even if I did, it seems that I had not noticed it, and so I had not appreciated it, or tried to understand its working.
   
   I have a theory, that most knot tyers were misled by the classification and the drawings of similar hitches by Ashley, only as hitches around poles ! They had never considered those hitches as hitches around ropes, where they always had preferred the climbing gripping hitches. And they had never really understood and explained the difference between such a cross-gartered hitch tied around a "compressible" material, a rope, where the knobs of the crossing points can "bite" the surface, and so become able to be attached on it easier, and a solid material, a pole, where they can not. So, they had not tried to maximize the effect of the particular property that makes those hitches very efficient : the even distribution of the crossing points on the surface of the main line, where , at each crossing point, the one leg, as a riding turn, pushes the other to "bite" into the flesh of the material.
   Now, regarding tight hitches around poles, I had also tied or learned some "new" ones. FAR better than the Icicle hitch - as the Locked Cow hitch or the recent Alaskian hitch and Bull Clove hitch, for example  - but this is also the subject of another thread !  :)
« Last Edit: April 24, 2014, 01:25:42 AM by xarax »
This is not a knot.