Author Topic: Non slipping bend in Dyneema  (Read 67188 times)

allene

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Re: Non slipping bend in Dyneema
« Reply #45 on: January 24, 2014, 06:14:39 PM »

The end-2-end knot I recommended above (post #47),
Ashley's #1408 (and simiarly his #1452, which is
more commonly presented) with the extended tucking
I describe
should hold.

It slips.  I also did a little extra tugging on this knot to try and lock it.  I was pulling against my knot and also did a little extra tugging on it.

I used the Ashley Bend in animated knots as a starting point and tucked exch working end along the exit path of the other working end.

Allen

allene

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Re: Non slipping bend in Dyneema
« Reply #46 on: January 24, 2014, 06:18:02 PM »
I found a knot that did not slip.  It is the knot I opened this thread with but with an extra hard pull on the ends before testing.  I put the ends in a vice and pulled with hand pressure on the loop that had the knot in it.  One could also use pliers and pull on the ends themselves.  This locks the knot and it does not slip.  I tested a loop with two of my knots in it.  This is a very easy knot to tie and now with the extra locking it does not slip.


Allen

PS.  After breaking the loop, I untied the surviving knot with the aid of a marlin spike.  I pressed the spike through the center of the knot, and after that it is easy to remove the two ends and untie the knot.  The knot has a natural detent where the marlin spike needs to go so not that difficult.
« Last Edit: January 24, 2014, 06:26:16 PM by allene »

SS369

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Re: Non slipping bend in Dyneema
« Reply #47 on: January 24, 2014, 08:13:52 PM »
Hi Allen.

I found a knot that did not slip.  It is the knot I opened this thread with but with an extra hard pull on the ends before testing.  I put the ends in a vice and pulled with hand pressure on the loop that had the knot in it.  One could also use pliers and pull on the ends themselves.  This locks the knot and it does not slip.  I tested a loop with two of my knots in it.  This is a very easy knot to tie and now with the extra locking it does not slip.

Do you think that if the same tightening of all the parts of other offered possible candidates were to be employed, it could alter the outcome somewhat? Not that I think a knot has to be super-tightened necessarily, but if the mod carrick is done that way and it helps then it may stand to reason that another may fare better too in your testing.


Quote
PS.  After breaking the loop, I untied the surviving knot with the aid of a marlin spike.  I pressed the spike through the center of the knot, and after that it is easy to remove the two ends and untie the knot.  The knot has a natural detent where the marlin spike needs to go so not that difficult.

So did you find that the specimen exhibited detrimental qualities that might be inhibiting the reuse of the rope?

SS

allene

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Re: Non slipping bend in Dyneema
« Reply #48 on: January 24, 2014, 08:50:11 PM »
^^ I did the tightning on the modified Ashlet bend but pulling on a tail tends to open, not close, that knot so the answer is, it would depend on the knot.  I do think it would change the results.  Consider the test where one knot slipped, then the other, then the first stopped and the other one broke.  Clearaly something strange was going on there.

In terms of was the line damaged.   It is definatley flatter where it was in the knot I took apart.  But remember that the force I applied was just about to break the line at that knot so one would expect some damage.  I mean, an identical knot in the same line broke on the other side of the loop.

Allen

allene

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Re: Non slipping bend in Dyneema
« Reply #49 on: January 24, 2014, 10:59:51 PM »
Estar did some testing on one of the earlier knots and tied a half hitch on the tail.  My knot does not slip if you do this but one that, in my words, "slipped easily", just pulled the half hitch into the knot and continue to slip.  I would assume the extended figure of eight, which is the strongest knot I tested, could be tightened and would respond well to a half hitch in the tail.

That said, I added another tuck to my knot and now that combination does not slip.  It may be much more difficult to untie however.

To tie it, just do the knot I started this post with then tuck the tail out the opposite leg.  Be careful to maintain the over2-under-0ver-under arrangement when you do the second tail.

It is more complicated but still easy to tie.


xarax

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Re: Non slipping bend in Dyneema
« Reply #50 on: January 25, 2014, 05:09:16 AM »
  I do not know if it is "still easy to tie", but it is still asymmetric - without any particular reason, except from the fact that it had happened to be born so in the first place... 
  After the side-by-side "8" shaped links bend, it was expected that you would tie a side-by-side Pretzel links bend... :).  A more symmetric ( although still not perfectly so...) solution to the problem of interweaving two Pretzel-shaped links in a end-to-end knot, is shown at the attached pictures. ( To interweave symmetric Pretzel shaped links you have to orient them face-to-face, as in the many such bends you can find in the Forum, if you search for the word "Pretzel" - see, for example, the bends at (1)-(5), Some of them were described as "decorative" bends (6),(7), but they might serve as practical bends, too, if all simpler solutions will be proved inadequate when tied in Dyneema... However, with so few bends that were tested till now, I believe it is too early to jump into such conclusions. )
  There is only a thin line separating the practical knots from the decorative ones, which seem something in between knotting and knitting. Personally, I do not like any knot which needs more than two tucks - if I will have to decide between a tuck-tuck-tuck knot and a spin-spin-spin one, perhaps I will decide in favour of the later, as suggested by roo... :). After all, it is easier to spin the end of a line, than to drive it through the correct openings - while you are " in your shower, standing on one of those exercise balls - with the water on, of course :-)". I have to repeat once more that a symmetric knot is much easier to inspect, because even one wrong tuck will "break the symmetry", so it will be spotted at a glance. Especially if/when we are forced to tie complicated knots, symmetry is a safety factor - and divides the information we need to remember to tie the knot by two !  :)
   Although you do not follow any particular method, you start to point higher  :). Go on !   

1. http://igkt.net/sm/index.php?topic=3585.msg20496#msg20496
2. http://igkt.net/sm/index.php?topic=4188.msg25686#msg25686
3. http://igkt.net/sm/index.php?topic=4203.msg25704#msg25704
4. http://igkt.net/sm/index.php?topic=4293
5. http://igkt.net/sm/index.php?topic=4705.msg30503#msg30503
6. http://igkt.net/sm/index.php?topic=3671
7. http://igkt.net/sm/index.php?topic=4215
« Last Edit: January 25, 2014, 05:13:18 AM by xarax »
This is not a knot.

allene

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Re: Non slipping bend in Dyneema
« Reply #51 on: January 25, 2014, 05:31:36 AM »
I tried a symmetric version first but it slipped easily.  Seemed to lose something.  But the bad part is that the knot slipped for Estar at 40%,  which us pretty good but still disappointing.

Dan_Lehman

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Re: Non slipping bend in Dyneema
« Reply #52 on: January 25, 2014, 05:55:56 AM »
The end-2-end knot I recommended above (post #47),
Ashley's #1408 (and simiarly his #1452, which is
more commonly presented) with the extended tucking
I describe
should hold.  Or else it will exhibit a new level
of rope fluidity, I think!

Well, then you will be able to learn something today . . . it slipped at 630lbs,
about the same as the double fisherman I just tested (post above).
630lbs (27% of rated line tensile)  was the 'loop load',
so the knot load would be (very roughly) half of that.
I have pictures . . . but they just show the tails sucking into the knot.
Actually, they show more : they show that the
knot wasn't correctly tied --there should be equally
two turns of end tucks showing on either side
of the line, but there are three on our/viewer's side
(only the leftmost turn runs behind the line, the
others are over).  Still, you have extra tucks
one way or another, and that they can all slip
--and so evenly, as seen in both tails--
is indeed a(nother) eye-opener!  Egadz!!   :o
One throws away the old playbook!

> Just FYI . . . The knot as shown in your picture,
> without the extra tucks, slipped at 295lbs.

I thank you very much for this extra information.


One could endeavor to engineer the knot so
that tail-tucks went in opposite directions,
in hopes that maybe removing *sympathetic*
movement might help, but I want something
simpler and more sure.



I can think of one simple adjustment to the
interlocking of overhand knots such we have
in #1408, Shakehands, #1452, zeppelin :
at the point of the "U-turn" of the overhands,
continue turning and make a full loop (as with
a bowline) and then to the collaring, now
thus around the opposing S.Part.  Might this added
surrounding of constricting parts succeed?
(Although in the above cases even though neither
individual S.Part surrounds --they make 180deg turns--,
they jointly surround.  Still, the full turn seems
a significant adjustment.

(And the mirrored bowline held, yes?)


--dl*
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Dan_Lehman

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Re: Non slipping bend in Dyneema
« Reply #53 on: January 25, 2014, 06:38:13 AM »
One thing to ask in this exploration of end-2-end
knots for HMPE is What are the expected purposes
for these knots?
  I.p., I thinking that in general
one won't want to use knots, but there might be
some emergency cases in which they're needed;
and in these cases --some, at least-- aspects of
beauty & compactness might be irrelevant.  E.g.,
it might be that coming up with a simple knot
that works with the tails stoppered will be
a good thing to know.

Beyond this, of course, if we can find something
neater, great.  But if making, say, a blood knot
and tying off the tails in a (joint) overhand stopper
works, that'll be good to know.

--dl*
====

allene

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Re: Non slipping bend in Dyneema
« Reply #54 on: January 25, 2014, 07:16:01 AM »
I wish to make two points.  1) This line is usually spliced.  It is dead easy to splice and very secure when spliced.  However, the recommendation for the bury is 72 diameters so the splice is long.  If both ends need to be spliced, that is 144 diameters so in a 3/16 line that is over 2 feet.  Some applications do not have that kind of room so in these, we are looking for knots.  For example, my halyard goes into a sheave just a few inches from the where it is secured to the headboard.  The sheave cannot take the added diameter that comes with the splice as it was initially made for wire.  I need a line that is as strong as wire and this is the only option.  I used to do something very complicated but have switched to a soft shackle tied to the halyard with the Estar knot.  A nice solution.

Second point.  At this point we know of very few knots that do not slip.  There are more loop knots but there loads are divided so I think non loop knots are more challenging and that is what I am focusing on.  There are basically two and while neither is a bend, I think I can see a characteristic of these that is important.  The simplest of them to analyse is the new knot that Estar discovered that I named the Estar knot in his honor. This is what I observe about that knot.  There is a single loop responsible for the force holding the line.  The basis of the knot is the buntline knot and the loop is basically a clove hitch.  That knot has known good holding power but it slips with this line.  The second point to observe is that the tail is put through this single area of high stress that holds the knot.  The tail has less of a load on it but it needs to be constrained or the knot slips.  Putting it through the high force area gives the holding force on the tail to prevent the slippage.  All the knots that have lots of tucks and turns, including mine, slip.  They lack that point of high concentration of holding power that can keep the tail from slipping.  I think that you have to deform the line to keep it from slipping and beyond that, you have to grab onto a lightly loaded part of the knot and deform that.  You have to grab the tail really hard.  You can also lock knots and they won't slip.  This also deforms the line. If the line is deformed, slipping now involves extruding material or moving the deformed area.  This is much harder than moving a smooth surface against friction (or lack thereof).  Writing this makes me think of ice skates.  If you want to prevent slipping on ice, you need to deform it because doing it with friction takes 72 diameters and you just can't make a knot that long.

I tried yet another knot and am waiting for Estar to test it, if he isn't fed up with testing my slipping knots and ready to get on with life.  It is a bend where the holding force is a clove hitch and the tails go through the opposite strands hitch.  It satisfies the two conditions above.  It looks a lot like both the Estar knot and a double fisherman's.  It held in my testing but then so did some other knots that slipped in Estar's testing.

Allen

Stagehand

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Re: Non slipping bend in Dyneema
« Reply #55 on: January 25, 2014, 07:41:23 AM »
Hello Allen and Estar.  Thank you for your interest in bends on slippery lines.  Thank you for sharing your research capabilities.  I suggest you advance on your successes with Modified Carrick Bend.  The Carrick Bend takes part in the polyhedron geometries of the Turks-head knots.  Seeing Carrick Bend as the incomplete form of the 4 lead x 3 bight Turks-head Knot will then present a path to continue Carrick Bend into sufficient security.  This method is available on any single-line Turks-head knot used correctly as a bend.  In every case, as with Carrick Bend, there is both a path to sufficient security and a standard for correctness, in faithfulness to the polyhedron/Turks-head form.
« Last Edit: January 25, 2014, 06:19:21 PM by Stagehand »

alpineer

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Re: Non slipping bend in Dyneema
« Reply #56 on: January 25, 2014, 03:32:56 PM »
Hi all, I am the guy with the test bench. I am happy to test things that people are interested in, but I don't do a lot of different forums/thread . . . so you may need to e-mail me (estarzinger at gmail dot com) to get my attention.

While we are on this thread . . . I will mention that I have developed a useful and simple sliding loop knot that does not slip and holds relatively high strength and can be easily tied to a fixed padeye (unlike the Polamar).  It is a modification of the buntline . . . picture of how to tie it here: http://www.bethandevans.com/pdf/modifiedbuntline.pdf.  It is a nice looking and relatively simple knot.

I have a page on the same site that is documenting my test results to-date at: http://www.bethandevans.com/load.htm

Greetings estar and allene,

A knot related to the EStar Knot which has the Clove oriented opposite to that of the EStar (i.e. the Clove is rotated around the axes of Standing Part and Tail) may also show good test results. You can tie this knot by taking the Buntline's tail over the Standing Part and continuing as for the EStar on the opposite side of the Standing Part.

Your test results would be appreciated.

alpineer

allene

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Re: Non slipping bend in Dyneema
« Reply #57 on: January 25, 2014, 04:44:05 PM »
^^ That is how I tie it.  I like the flow of the knot and the crossover on the shackle.  I had not noticed that Estar tied it the other way.  That said, my theory on why these knots work would say there would be no difference between the two.  The theory says it is deformation that holds the knots, not friction.  I believe that the Estar holds because there is a stress concentrator in the clove hitch and that deforms the tail and holds it.  Some evidence of that is that a knot like the extended figure of eight slips and yet a much simpler knot like the Estar does not.  Hard to think of a knot with more friction than the extended figure of eight and yet it slips.  My theory is that it takes a mechanism other than friction, or a different friction mode depending on how you look at extrusion, to hold this line.

Allen

xarax

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Re: Non slipping bend in Dyneema
« Reply #58 on: January 25, 2014, 05:48:15 PM »
The theory says it is deformation that holds the knots, not friction. 

  Your theory is good !  :) ( You should only describe it differently, because friction is a consequence of deformation, too, although in a microscopic scale).
  When the one line is squeezed on an other, their surfaces are deformed - the saddle-like shapes that are generated play the role of obstacles, of "dents", which increase the amount of forces required for any lengthwise motion predicted by the theory of friction of solid, non-deformable bodies.
  We can actually see this by measuring the friction between two lines when they meet each other at different angles. When the angle is more acute, so the area of mutual contact is more extended, the lines can slide along each other easier, because the deformations / obstacles on their surface are less pronounced - they are more extended, but less deep. When the angle approaches the right angle, the contact area is smaller, so the same perpendicular force can allow the lines to bite each other harder and deeper - so they can not move lengthwise as easily as it would had been predicted by a theory of friction which does not take account the local deformation on the surfaces of the bodies.
   
This is not a knot.

allene

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Re: Non slipping bend in Dyneema
« Reply #59 on: January 25, 2014, 10:40:26 PM »
I am waiting for Estar to test my latest version but in any event I have more to report.  I started by observing that on the Estar knot, the constriction is a  clove hitch.  I then tied a knot a little like a fisherman't knot except clove hitches and then took the tails and tucked them back through the opposite clove hitch.  This knot was tested and did not slip, but it was not strong.  So why the difference between the strength in the Estar and this latest knot?  The answer was obvious once I looked at the Estar knot.  The Estar is a loop and the load on the clove hitch was half the line load. 

I tried a couple of variations but the one I am about to describe was stronger than back to back Estar knots and dead easy to tie.  Tie interlocked Buntline hitches and tuck the tails through the center.  No slip and in a loop, stronger in the test I did than back to back Estar knots.  I await confirmation testing from Estar.  I tucked the tails through in opposite directions and in a way that looped around the clove hitches.  There are probably 4 ways to tuck the tails.

Allen