Author Topic: Non slipping bend in Dyneema  (Read 67051 times)

xarax

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Re: Non slipping bend in Dyneema
« Reply #105 on: January 29, 2014, 03:21:25 PM »
   Why does the Twedledee bend slips "easily", while the 88 bend does not ? I believe that this is due to the fact that the oblique elements of the two 8-shaped links meet each other at an almost right angle, so the surface of the one bites hard and deep into the body of the other - a condition that deforms the two lines, and prevents their mutual lengthwise displacement more effectively than the increase of the pressure they are hold together. So, just constricting two lines is a less efficient mechanism than preventing them to slide on each other, by paying attention to the angle they follow as they reach to their contact point.
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allene

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Re: Non slipping bend in Dyneema
« Reply #106 on: January 29, 2014, 05:33:48 PM »
  You "First" bend is nothing but a symmetrically ( = good ! ) re-tucked through the central opening ( = not so good, I am afraid...) Carrick bend.

No it isn't.  I started trying that but it had all the bad qualities you innumerate.  The first bend is a very stable bend, look more carefully.

Allen

xarax

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Re: Non slipping bend in Dyneema
« Reply #107 on: January 29, 2014, 05:41:51 PM »
   Yes, I will, because after last night, I do not see very well... :)
   It is the bend that starts from this stage ( shown at the attached picture), is nt it ?
   Perhaps I should had written "alternative" Carrick bend ( ABoK#1428, M. A5), to distinguish It from the "classic" Carrick bend ( ABoK#1439, #1551, M. A6 ) you are familiar with.
« Last Edit: January 29, 2014, 06:05:10 PM by xarax »
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allene

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Re: Non slipping bend in Dyneema
« Reply #108 on: January 29, 2014, 06:09:57 PM »
Yes, that is it.  A carrice bend can be seen here http://upload.wikimedia.org/wikipedia/commons/8/8e/Knife-lanyard-knot-ABOK-787-Carrick-start.jpg and as you can see the tails go in opposite directions and on the first knot, they go in the same direction.  That makes the knot, after the tucks, act completely differently.  It has none of the bad properties you mentioned.  I believe you are talking about a tucked carrick bend.  This is a different knot.  I have never taken pains to dress it properly and it always forms itself into its proper shape.  I just tied one in StaSet and no problem.

A carrick bend tucked has both tails going out the same side of the knot and the pull as a bend is not good.  The standing end goes into the knot and immediately takes a sharp bend.  On the first knot, the standing ends go in and are constrained by three loops which they pass through before turning around the third of the loops.  As you know, having the entry line constrained by multiple loops before making a sharp turn is a good thing.  On top of it not making a turn until it passes the third loop, the bend is not tight but rather goes around a bundle of three diameters.

Then on top if it being stronger than a triple fisherman's knot, it can be untied.

But I get it you don't value those qualities.

Allen

xarax

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Re: Non slipping bend in Dyneema
« Reply #109 on: January 29, 2014, 07:09:49 PM »
  A Carrick bend can be seen here...

  Beautiful picture !  :)

  As you know, having the entry line constrained by multiple loops before making a sharp turn is a good thing.

  It would be a good thing, if it could be constrained=nipped by "multiple loops"= nipping turns - but it can not. The continuations of the Standing ends which still carry the 100% of the loading, can only be forced to have some deflexions from a straight path, before they enter into a constricting = nipping loop. The good thing for the Standing part is first to make the sharp turn, and then only, at the second line of defence against slippage, to be constrained=nipped into/by multiple nipping loops. Any premature constriction of the Standing part before a sharp turn = a collar, is only a waste of the knot s constricting / nipping ability.
  However, this is a subtle issue that should not be discussed at this point. If the bend holds, and if it is strong, we will see why... 
 
« Last Edit: January 29, 2014, 09:38:44 PM by xarax »
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allene

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Re: Non slipping bend in Dyneema
« Reply #110 on: January 29, 2014, 09:35:37 PM »
I feel like I cannot make my points, which has a tendency to piss me off.  I apologize for the sentence you ignored, which should have been deleted so consider it an error.

I see Ashley calls both variations Carrick bends.  I have tied it both ways and it is obviously more secure the normal way.   However, when tucked, it is more secure and much better behaved the way I tie it.  The end knots have no resemblance to each other when tucked.   My first bend has no resemblance to a Carrick bend when tightened up.  It is a completely different animal.

I tied it just now with StaSet and I do not see how it would be possible for it to cinch up in other than the proper way.  The carrick bend tucked looked like it could form up any which way, it is an ugly knot.

Have you tied my first bend and looked at it?

xarax

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Re: Non slipping bend in Dyneema
« Reply #111 on: January 29, 2014, 09:57:37 PM »
... it is obviously more secure the normal way. However, when tucked, it is more secure and much better behaved the [ alternative way ]

  So, you say that the re-tucked-through-the central-opening ABoK#1428 / "alternative" Carrick bend is more secure ( = slips less ) than the re-tucked "Classic" Carrick bend - when tied on Dyneema lines of this size.
  This may well be your most important contribution on this subject.
  I hope you will test this on different sizes, and you will measure the maximum loads re. slippage and strength.

  I have tied all the re-tucked-through-the-central-opening Carrick mats - and I consider that the bends generated by the re-tucking of the particular Carrick mat-like "base" shown at (1) belong in this class. However, I did nt like the fact that all the generated knots should be dressed very carefully, in order to not become "ugly knots", as you say. They do not seem to be self-dressing to me, not at all ! I have not noticed any difference between the Classick and the Alternative Carrick bend - but you should realize that I had tied them on stiff climbing ropes, which are not even close to be as slippery as a Dyneema line. Tied on such ropes, it is very difficult even to "clinch" to a compact knot - too much friction... So, your observation is very interesting - indeed, important news to me !

1. http://igkt.net/sm/index.php?topic=3086.msg18601#msg18601
« Last Edit: January 29, 2014, 10:04:21 PM by xarax »
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allene

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Re: Non slipping bend in Dyneema
« Reply #112 on: January 29, 2014, 10:04:55 PM »
I tied them on double yacht braid.

allene

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Re: Non slipping bend in Dyneema
« Reply #113 on: January 29, 2014, 10:08:36 PM »
I might add.  The tucked carrick bend not only is ugly but the two standing ends are not collinear, which bothered me.  On the first bend, they are collinear.  I think that might help them to dress themselves correctly.  I will try it on heavy line later and report.

Sweeney

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Re: Non slipping bend in Dyneema
« Reply #114 on: January 29, 2014, 10:27:01 PM »
I must say when I tried the carrick bend ABoK #1428, tucking the tails through the centre and pulling on the standing parts did set the knot inevitably into the form shown. A bit of a lump but function takes precedence over appearance in a case like this I think. I tried the bend in:

550 paracord
1 mm polyester
10.5 mm semi-static climbing rope and in
plastic coated washing line (a tube of plastic with a polypropylene (?) core)

the result in each case was the same in that the bend drew up into its final form by pulling on the standing parts. Because I have no HMPE I cannot comment on the bend in this material BUT I tried the washing line because although it is not actually very slippery (unless wet) it is very springy and a large number of bends simply come apart unless kept under constant tension. Normally I would use a double fisherman's pulled tight but this new bend is a possible alternative and although it may weaken already pretty feeble line too much, a bend is normally only used as a short term fix when a line breaks. I also managed to undo it (just about impossible with a double fisherman's) so whilst it's not a bend for everyday use I'll keep a note of it on a just in case basis.

Barry

allene

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Re: Non slipping bend in Dyneema
« Reply #115 on: January 29, 2014, 10:36:00 PM »
I tried it on both 1/4 accessory cord and  50 year old 1/2 inch yacht braid.  I always get the same knot but I do see that if you pull the knot tight from the tails instead of from the standing ends, you get a completely different knot.  It looks more like a ball of tangles than the knot I like.  So it is important how you dress it and you have a good point.  But the way I tie it, it is stable.  The other way, I don't really know, but it does not look stable.

Allen

xarax

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Re: Non slipping bend in Dyneema
« Reply #116 on: January 29, 2014, 10:44:17 PM »
   That is the form I get with only a moderate ( 1 kg ) pull of the Tail ends... :) . A side-by-side Pretzel-to-Pretzel bend - no relation whatsoever with what you show...
   Edit : Wrong ! It is the very same knot - I had just not submitted it to an adequate loading, re. the stiffness and the thickness of the rope, which would elongate it a little more, and it would make it look less "flattened". I am now convinced that this is the only stable form of this knot, so we do not have to worry about any dressing instability.
« Last Edit: January 30, 2014, 04:36:00 AM by xarax »
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allene

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Re: Non slipping bend in Dyneema
« Reply #117 on: January 29, 2014, 11:01:44 PM »
That isn't the knot. 

When you get the general knot formed and everything tucked, insure that you dress things so that the standing ends go into the know straight past three loops but with the tail loops snug.  Then pull on the standing ends. I will add this to my instructions.  Try it.

Allen

Stagehand

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Re: Non slipping bend in Dyneema
« Reply #118 on: January 29, 2014, 11:19:18 PM »
Allan, Thanks for your effort in forums and your promotion of Anarchism.  Will You consider these two bends.  I would like to test if the continued bend is more secure than the bend not continued.

allene

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Re: Non slipping bend in Dyneema
« Reply #119 on: January 29, 2014, 11:37:38 PM »
You did not tie my knot.  Try again.  My instructions clearly said if it doesn't look like the picture, start over.  Look, you gave me knots to tie that were almost impossible to follow with the instructions given.  I give you reasonably clear step by step instructions, others can tie it successfully in multiple type of line.  The knot is stable in the form shown.  Maybe there is a better way to instruct to tie it but I think it is clear what it should look like and a smart knot guy like yourself should be able to tie it.