Author Topic: Non slipping bend in Dyneema  (Read 67434 times)

allene

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Non slipping bend in Dyneema
« on: January 22, 2014, 07:39:02 AM »
I will give this new knot thing another try.  This is a bend that does not slip in dyneema. Every conventional bend I have tried slips and I have tried a lot.  It starts life out as a carrick bend but with one of the loops backward so that the two working ends point to opposite sides of the knot.  Then the two working ends are tucked through the center from opposite sides.


allene

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Re: Non slipping bend in Dyneema
« Reply #1 on: January 22, 2014, 05:07:23 PM »
I am the person with the L-36 and the web site L-36.com.  Thank you for the comment.  Estar tested the above knot and in his test, unlike mine, it slipped but it did so at 68% of line strength so he considered it a success as this is a reasonable value.  It is a bulky knot but easy to tie.   By conventional, let's just say all the bends in Animated Knots, knots generally known to sailors, climbing knots, fishing knots, and many knots from Ashley.  It was a great surprise to see that the double fishermen's bend slips.

We are looking for a bend that does not slip in Dyneema and I welcome links to any candidates.  I will test them and any that do not slip in my setup will go to Estar so he can put some efficiency numbers on them.  His setup can test up to 10,000 pounds and is calibrated.

Allen

allene

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Re: Non slipping bend in Dyneema
« Reply #2 on: January 22, 2014, 05:58:32 PM »
Estar posted how to tie the knot

http://www.bethandevans.com/pdf/modified%20Carrick.pdf

I might add that all the knots we have found or "invented/discovered" have been complicated knots with lots of twists.  What we like about them is that they are easy to tie and don't slip in Dyneema.  The fact that they are complicated knots with lots of twists seems to be a requirement.  I would love for someone to prove this wrong.  I am willing to test any candidates.  Any that pass the slip test can be tested to failure and have the efficiency rated.

Allen
« Last Edit: January 22, 2014, 06:01:28 PM by allene »

estar

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Re: Non slipping bend in Dyneema
« Reply #3 on: January 22, 2014, 06:28:44 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

allene

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Re: Non slipping bend in Dyneema
« Reply #4 on: January 22, 2014, 09:53:33 PM »
I would like to defend my knot.  But first, I tried the tweedledee knot and it slipped easily, hardly any force compared to knots that do not slip.  Thinking I might have tied it wrong I did a second sample taking extra care.  Same result, slipped easily.

If you look at my knot from what I can the front, you may notice that going from either standing end, that the line goes through three loops before it experiences a bend.  We know that this is a feature of a strong knot and this knot has been shown to be strong.  If you look at the back of the knot, you see that there is a twist structure where the two lines cross each other.  This structure should experience a fair force under load which creates a lot of holding friction.  In addition, the two working ends exit the knot in opposite directions so there is friction between them.  On knots where the strands exit the knot together, they can pull out without the friction between resisting the slipping.

But I go back to the main points.  It is easy to tie and doesn't slip, or at least if it slips, it is at a very high load.



Allen


PS.  The triple fisherman's knot slips.  It was tested.
« Last Edit: January 22, 2014, 10:34:38 PM by allene »

allene

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Re: Non slipping bend in Dyneema
« Reply #5 on: January 22, 2014, 10:56:01 PM »
If you wish to find candidates as substitudes of the triple fisherman s knot, you came to the right place !  :)  - although, as written in Mozilla < about:config > page , Here be Dragons:)

Just to clarify, the triple fisherman's knot slipped in our testing.  We did not consider it a satisfactory knot.  I am, however, looking for bends that are strong and do not slip.  I guess since the testing showed that the knot I submitted slipped at 68%, perhaps I should just say a strong bend that will hold up to a high efficiency.

So, please give candidates and we will test them.

Allen

estar

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Re: Non slipping bend in Dyneema
« Reply #6 on: January 22, 2014, 11:20:37 PM »
I was e-mailed some pictures of the "Hunter S Bend".

I just pulled it in 1/8" amsteel.  It slipped at 910lbs, which is 36% of tensile.

« Last Edit: January 22, 2014, 11:21:19 PM by estar »

estar

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Re: Non slipping bend in Dyneema
« Reply #7 on: January 22, 2014, 11:41:27 PM »
And I pulled a "Bowline B Bend" which slipped at 1450lbs. 

I should note that the pull numbers I am quoting here are for the loop.  So the bends are only carrying half that load.

estar

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Re: Non slipping bend in Dyneema
« Reply #8 on: January 22, 2014, 11:46:10 PM »
Just for reference, the triple fisherman slips at 1840lbs.
« Last Edit: January 22, 2014, 11:49:19 PM by estar »

estar

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Re: Non slipping bend in Dyneema
« Reply #9 on: January 23, 2014, 12:06:49 AM »
^^ do realize the rope I am testing is dyneema "Single braid" - pure dyneema - that is there is no polyester cover.

I believe most climbing accessory cords/slings have a polyester jacket, which is much less slippery. And all these bends would hold and not slip in it.

However, the Dacron cover does create another problem/weakness, which is (at least for the similar sailing lines I have tested) that the polyester jacket breaks at about half the rated line strength and then the dyneema core pulls out.

Just for reference, the tweedledee slips at 890lbs in this rope . . . we don't need to debate whether that is 'easy' or not.
« Last Edit: January 23, 2014, 12:16:24 AM by estar »

estar

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Re: Non slipping bend in Dyneema
« Reply #10 on: January 23, 2014, 12:23:24 AM »
^^ in sailing, unlike in climbing, we do not have the 'human body breaking' limit, and we like to use really small lines with high loads.  We also like lines that don't stretch and don't adsorb water.  This dyneema single braid is "perfect" except it is so damn slippery.  fortunately it is about the easiest stuff in the world to splice, and that is usually the answer, but occasionally we need knots.  We have found fixed loops that will hold (water bowline and figure 8/9), compact sliding loops (Polamar and EStar). For gripper hitches, the icicle hitch and prussic 'sort of' work/hold in it. But no excellent bends so far - right now if we need a bend the only simple secure answer we have is to put two loops together - the modified carrick that started the thread is the best holder I have tested.

xarax

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Re: Non slipping bend in Dyneema
« Reply #11 on: January 23, 2014, 12:32:31 AM »
^^ do realize the rope I am testing is dyneema "Single braid" - pure dyneema - that is there is no polyester cover.

  I an GLAD we can test our bends in such clear, pure one-material rope - because this shows the characteristics of the knot per se, as a shape made of some material, and not as a knotted material ! When we will find a knot that does not slip, then we can consider the same knot tied on a less slippery material, or with a cover of a different material, etc. If we do not study the knots when tied on slippery materials, but only the knots when tied on ropes covered with Velcro, or immersed in glue, we would nt learn much about the geometry of the knots themselves, would we ?  To test the bends I was tying, I often used some amount of oil or another lubricant, because this can reveal the weakness of a bend which can otherwise remain hidden. I do not doubt that the industry will find a not-so-pure way to conceal the weakness of the knots tied on such materials - but I, for one, I will never use a bend that depends on a cover which could possibly be detached at any time under a fraction of the force required to break or even to slip..
  I have a theory, which can/will be tested some time, I guess/hope. If a knot slips more than another, when it is tied on a most slippery material, it will still slip more than the other, when it will be tied on a less slippery material. I believe that the main property that makes a knot slip is its 3D shape - ceteris paribus, it is the geometrical shape of a knot that mostly determines its knotting properties, so, the same knots tied on two different materials will retain the same hierarchy, regarding their ability to hold, on both of them. It is a theory, that should be, and it is, falsifiable, of course ! Hic Rhodus hic saltus !  :)
   
« Last Edit: January 30, 2014, 02:59:57 AM by xarax »
This is not a knot.

roo

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Re: Non slipping bend in Dyneema
« Reply #12 on: January 23, 2014, 01:16:55 AM »
I am the person with the L-36 and the web site L-36.com.  Thank you for the comment.  Estar tested the above knot and in his test, unlike mine, it slipped but it did so at 68% of line strength so he considered it a success as this is a reasonable value.  It is a bulky knot but easy to tie.   By conventional, let's just say all the bends in Animated Knots, knots generally known to sailors, climbing knots, fishing knots, and many knots from Ashley.  It was a great surprise to see that the double fishermen's bend slips.

We are looking for a bend that does not slip in Dyneema and I welcome links to any candidates.  I will test them and any that do not slip in my setup will go to Estar so he can put some efficiency numbers on them.  His setup can test up to 10,000 pounds and is calibrated.

Allen

A solution for very low friction line was found in this thread:

http://igkt.net/sm/index.php?topic=2013.msg14229#msg14229

It may not be the prettiest thing in larger line, but it's drop-dead easy to tie.
If you wish to add a troll to your ignore list, click "Profile" then "Buddies/Ignore List".


allene

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Re: Non slipping bend in Dyneema
« Reply #13 on: January 23, 2014, 02:00:04 AM »
^^ it is unclear what solution is being suggested here but we do have experience with the Alpine Butterfly knot.  That knot can be tied as a loop or as a bend (cut the loop after tying and it is a bend).  As a loop, it does not slip.  As a bend, it slips.

In the other thread Estar suggested that the full extend of the slipperiness of this line may not be appreciated.  I think the general feeling in the industry is that you cannot tie knots in it.  I have not seen any recommendations on knots, except the diamond knot but the efficiency there in a soft shackle is something above 25% which, while fine as a soft shackle, is nothing to write home about as a knot.

I continue to think the knot I posted is a significant new knot.

Allen

allene

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Re: Non slipping bend in Dyneema
« Reply #14 on: January 23, 2014, 05:13:57 AM »
I am happy to test any knot but you need to know that we have already tested quite a few.  This is not a complete list but I know these have been tested:  Hunter, Zepplin, Sheet, Fisherman's (2 and 3), and Alpine Butterfly or Strait bend.  I just added the tweedledee bend to the list.  They all slip.

What would you suggest we test next?

In terms of triple fisherman's and its recommendation, I do see that.  I also followed the chain of references in the article and could not find any that came back to the kind of line we are using.  For example, the vague reference to the climbing and rescue community left me cold as they would never use this kind of rope.  That said, I did find research in the climbing community recommending triple fisherman's knot on dyneema.  Perhaps that research is what was being refereed to.  However, that was climbing webbing, not 12 strand single braid.  The reference you site from Blue Water is also not anything like the line we are using.  That  TITAN CORD is a combination Dyneema and Nylon and appears to have a tightly woven cover.  Not near the same line.

Just to be clear, this is the line we are talking about  http://www.samsonrope.com/Pages/Product.aspx?ProductID=872

Estar found a knot that doesn't slip at all.  http://www.bethandevans.com/pdf/bend.pdf  It looks very strong but I have not heard numbers yet.


Allen
« Last Edit: January 23, 2014, 05:45:16 AM by allene »