Author Topic: The symmetric Sheet bend  (Read 30421 times)

roo

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Re: The symmetric Sheet bend
« Reply #60 on: December 21, 2011, 10:08:03 PM »
Willful blindness is a bit dramatic in this particular post, don't you think? You're being a bit specious with me considering I do not give advise to use this bend. I believe you are making a exceedingly large issue of it by your continuing to pound away at the keys on it. It has been said already.
You keep wrongly calling it secure despite several people noting what happens to the bend when a free end (working end) sees force, by snagging for example.

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I have written that I loaded this bend with my own weight(175 lbs.), bounced on it using a foot loop affair and it held.
Why do you keep going back to this while ignoring the easiest mode of failure?  It sure looks like willful blindness so you don't have to retract your security claim.
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I have just now repeated the simple foot loop test and while suspended I gave one tail (longer now so I could wrap it around my hand) a tug and I stayed above ground.
ibid.  You know the easier mode of failure.  Pull one standing part while pulling a tail.  When the parent line tension resumes or starts, say goodbye.

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I kicked and rolled of my own volition. Sort of didn't think I needed clearance on that.
More avoidance of the elephant in the room.

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I like the fact that it can be spilled relatively with some ease when its load is released, just the same as the bell ringer loop can once you're done with, let's say, a truckers hitch use. Both hold while under loading.
And nobody uses a bell-ringers loop like a bend or describes it as a secure bend. 

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I would not be using it for life endangering/rescue work!
But you keep insisting that it is secure.

« Last Edit: December 21, 2011, 10:30:15 PM by roo »
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Hrungnir

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Re: The symmetric Sheet bend
« Reply #61 on: December 21, 2011, 10:53:14 PM »
I've tied it in cordage with different sized diameters and different materials. The dark cordage is made of polypropylene and is thicker than the white cordage. The white cordage is polyester.

It seems to hold well, but further testing is needed.

xarax

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Re: The symmetric Sheet bend
« Reply #62 on: December 21, 2011, 11:11:46 PM »
 
I've tied it in cordage with different sized diameters and different materials.

  I hope not as soft and of such a small diameter as the ones shown in your pictures ! :) To clearly see what you are doing, and to be able to handle the strands with the care and the precision required, I suggest that you start from rather stiff, incompresseble materials, with LARGE diameters ( not much thiner than your fingers... :)). When you will be accustomed to such ropes, then you can proceed and try to tie it with ropes of smaller diameter. Anyway, as I have said many times, this bend is obviously begging for large diameters, and hard,  solid ( not hollow braided, for example ) ropes.( My tests were mostly done with 9 -12.5 mm climbing kernmantle ropes, and 1/2 inch nylon solid braid rope. Static kermantle climbing ropes, being so stiff and able to retain their round cross section when they are subject to shear forces, are probably the easier and safer material which one can use, when he starts learning this bend.
« Last Edit: December 21, 2011, 11:20:30 PM by xarax »
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TMCD

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Re: The symmetric Sheet bend
« Reply #63 on: December 21, 2011, 11:40:36 PM »
Xarax,

Is there anyway you could post a video of your tying method for this particular bend because I can't seem to consistently get it set properly. I think it's a good looking bend but the security issues AND tying issues are a concern, a video would be appreciated.

xarax

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Re: The symmetric Sheet bend
« Reply #64 on: December 21, 2011, 11:53:00 PM »
The sheet bend is also tried and tested for different sized diameters, different types of materials, one tuck simpler to tie [and] harder to tie wrong

  All very true...but does the common Sheet bend slip LESS than this bend ? I think not, because the tails there are not as effectively interrupted, in their effort to slip and free themselves out of the knot s nub, as it happens in this bend. Here we have both tails squeezed in between two  strands of rope, and, on top of that, each  tail is most effectively squeezed by a rope strand at a right angle (perpendicular) to it... That is, we have strands that bite other strands hard, and so make deep 'dents" in the skin of the tails, that penetrate deep into their body - and those dents act as obstacles that block/prevent slippage.
   Does the common Sheet bend is stronger a knot than this bend ? I think not, because the common Sheet bend is a highly asymetric bend, and one of the two links will be loaded more and will break first, long before the other reaches the same limit. Symmetric bends are better suited to equalize the forces and achieve higher breaking strengths than asymmetric ones.
   
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xarax

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Re: The symmetric Sheet bend
« Reply #65 on: December 22, 2011, 12:09:34 AM »
Is there anyway you could post a video of your tying method for this particular bend

  Oh, my dear TMCD, my method is dumb! ( I can not even tie a f... Sheet bend quickly enough !) You have to ask SS369 to do this, ( I already did ... :)), because his method is clever - and I see that Hrungrir already uses it, and has good results....Although I think that the tying method is of much importance here, I also strongly believe that the problem people have has more to do with an inadequate understanding of the mechanism that prevents the tails to slip out of the knot s nub. Also, it is recommended that you better start from a stiff, hard, solid core rope, with as large a diameter as you can handle :) ( It also depends upon the size of your fingers and your corrective lenses... :)
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Hrungnir

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Re: The symmetric Sheet bend
« Reply #66 on: December 22, 2011, 12:23:01 AM »
 
I've tied it in cordage with different sized diameters and different materials.

  I hope not as soft and of such a small diameter as the ones shown in your pictures ! :) To clearly see what you are doing, and to be able to handle the strands with the care and the precision required, I suggest that you start from rather stiff, incompresseble materials, with LARGE diameters ( not much thiner than your fingers... :))
Hei xarax!

By using the tying method of SS369, I was able to tie your knot in 2mm polyester in my very first attempt. By using his tying method, the working ends fall correctly in place when pulling the standing parts. The bend seems to hold well in this form.

When it comes to diameters, the cordage in the picture is the thickest I have at hand right now. I'm not sure what the diameter is, but you get an idea when you see my fingers. The polyester is somewhat soft yes, but you won't find cordage which is much stiffer than polypropylene.

Hrungnir

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Re: The symmetric Sheet bend
« Reply #67 on: December 22, 2011, 12:28:36 AM »
Is there anyway you could post a video of your tying method for this particular bend because I can't seem to consistently get it set properly.
I don't have a video, but I have a picture of the tying method.

I tie a sheet bend. The white cordage is parallell and the dark cordage is making the half hitch.

Then I retuck the working end of the white cordage as described by SS369 and shown in the picture. Tighten the knot by pulling the standing parts only.
« Last Edit: December 22, 2011, 12:29:24 AM by Hrungnir »

SS369

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Re: The symmetric Sheet bend
« Reply #68 on: December 22, 2011, 12:40:07 AM »
Willful blindness is a bit dramatic in this particular post, don't you think? You're being a bit specious with me considering I do not give advise to use this bend. I believe you are making a exceedingly large issue of it by your continuing to pound away at the keys on it. It has been said already.
You keep wrongly calling it secure despite several people noting what happens to the bend when a free end (working end) sees force, by snagging for example.

Quote
I have written that I loaded this bend with my own weight(175 lbs.), bounced on it using a foot loop affair and it held.
Why do you keep going back to this while ignoring the easiest mode of failure?  It sure looks like willful blindness so you don't have to retract your security claim.
Quote
I have just now repeated the simple foot loop test and while suspended I gave one tail (longer now so I could wrap it around my hand) a tug and I stayed above ground.
ibid.  You know the easier mode of failure.  Pull one standing part while pulling a tail.  When the parent line tension resumes or starts, say goodbye.

Quote
I kicked and rolled of my own volition. Sort of didn't think I needed clearance on that.
More avoidance of the elephant in the room.

Quote
I like the fact that it can be spilled relatively with some ease when its load is released, just the same as the bell ringer loop can once you're done with, let's say, a truckers hitch use. Both hold while under loading.
And nobody uses a bell-ringers loop like a bend or describes it as a secure bend. 

Quote
I would not be using it for life endangering/rescue work!
But you keep insisting that it is secure.

roo, I don't know why you are being so semantically inclined here. Yes, I said the knot was secure and I described my method of arriving at that conclusion. No, it did not take into account every possible scenario that could cause it to spill. That is one of the things a forum discourse can be helpful with.

Care in rope work is a must and always will be and you can load this page with all manner of what ifs and whatnots, so if you drag and snag during your testing that is fine. I did not, though I did do a second test as I wrote and tried to pull one free end (working end) to cause it to spill. It didn't.

You are taking one-liners and making a case where there is no case to make. I said that this knot was secure in My tests. Get it through your head that I have no intention nor am I recommending this to anyone for use in anyway. Capishe??

With your attempt at bullying here to force an admission from me I believe it is you who are behaving like the elephant in the room.

The analogy of the bell ringer loop was to indicate, not to you only, that it can be a helpful thing that one could easily untie a bend such as this. Not that I am suggesting that the BRL be used as a bend. But there may be some-such a thing in the future.

The original poster and another forum member has indicated that he has tied it and found it to hold and not slip one bit using his arm power.

I still think that in the scenario of my test/evaluation that my statement holds.

No, I won't be using it for life saving or anything like that, there are better knots, but I have said this repeatedly for the sake of the reader who may misinterpret anything. Or a member who reads only what he wants to so he can bully and argue.

The whole thing has been blown out of proportion, by you, considering that from the get-go this has been a discussion about the workings of the offered bend. If you didn't take the stance you do most often there might be more contributors to these discussions. And they might learn something useful.

If you want to be right, you're right, but I am not wrong.

Please consider no more clever rejoinders and join the discussion in the way it was meant to be because you are seriously derailing the intent of the topic.

If you have anything else to say to me personally, I would appreciate that you do so by the personal message option. Thank you.

SS


xarax

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Re: The symmetric Sheet bend
« Reply #69 on: December 22, 2011, 12:41:49 AM »
you won't find cordage which is much stiffer than polypropylene.

  That is why I have recommended a kermantle climbing rope...
  Also, I suspect that this bend is sensitive to the helicity of the laid rope, in a quite subtle way, with possible consequences I can not predict... It would behave somewhat differently if tied with an S or with a Z rope - but I myself do not know yet which would be more secure and/or strong, and why...
« Last Edit: December 22, 2011, 12:52:31 AM by xarax »
This is not a knot.

SS369

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Re: The symmetric Sheet bend
« Reply #70 on: December 22, 2011, 12:51:11 AM »
Thank you Hrungnir for the picture and the better way of describing "my" method. ;-) After reading my own post describing how I did it, it made sense to me and I hoped it would be useful for someone else. Sometimes it goes like that with verbal descriptions.

And yes you may be correct that one could use a better knot to save their car or truck from damage, but for me I can not think of a time when I have had to use a bend during that kind of activity. Just my experience.

SS

roo

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Re: The symmetric Sheet bend
« Reply #71 on: December 22, 2011, 12:58:02 AM »
No, it did not take into account every possible scenario that could cause it to spill.
This is some progress.

Acknowledging these scenarios as security problems will help others from learning them the hard way.

The second, less obvious security problem arises from slack shaking that causes looseness that can again cause the bend to assume its free-rolling form.
« Last Edit: December 22, 2011, 01:10:24 AM by roo »
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xarax

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Re: The symmetric Sheet bend
« Reply #72 on: December 22, 2011, 01:19:26 AM »
   The analogy of the bell ringer loop was to indicate... that it can be a helpful thing that one could easily untie a bend such as this.
the BRL be used as a bend. But there may be some-such a thing in the future.

   Perhaps the bend shown in (1), and a reply to it in (2) , were somehow lost in the exchange of opinions- or of what else is exchanged here  :) . Have a look at it. It is a secure bend, it can be tied and untied easily, and also has an additional advantage, that might be proven to be useful/practical : One can keep the slipped overhand knots tied on the ends of the two ropes, and hook and then un-hook them, the one with the other, using their tails as pivots. In shorts, another rope-made hinge, just as the Zeppelin bend - but not as economical in material use. I think that it works in a way similar to the symmetric Sheet bend ( or "ABoK#1406 b', if you like... ), that is, it is depending upon the resistance of the tails - that, taken together, play the role of a rope-made pivot - to the shear  forces, induced on them by the tension of the perpendicularly placed bights.

1. http://igkt.net/sm/index.php?topic=3716.msg21527#msg21527
2. http://igkt.net/sm/index.php?topic=3716.msg21543#msg21543


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knot4u

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Re: The symmetric Sheet bend
« Reply #73 on: December 22, 2011, 01:19:45 AM »
This thread proves this bend is not simple.

xarax

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Re: The symmetric Sheet bend
« Reply #74 on: December 22, 2011, 02:03:11 AM »
this bend is not simple.

  We enter into a very complex subject here, knot4u !  :) What is "simplicity' is debatable, and it is not a simple matter at all, that is for sure ... I use the word in a restricted, quantitative sense, that has to do with the number of elements , and the number of relations between elements, an entity has. You know Newton universal gravitation equation, Maxwell s equations, ( in their antisymmetric tensor form), Einstein gravitational field equations... They are "simple", in that they relate a few quantities with a few relations, yet, in a broader sense they are not simple, not at all !
   We can easily say that a tetrahedron or a cube, for example, are the simpler Archimedes polyhedra. However, our evaluation might depend upon the machine and the language we use to describe them. We can actually count simplicity, by counting the number of bits and bytes a particular computer, with a particular program that is able to describe a thing, will use. (Computational complexity :  A relevant web book, at (1) , and a simple article, at (2)). But what happens with another computer, and with another compute language ? In some computers and some computer languages a thing can be described with a shorter, more economical in bits and bytes program than another thing, so we can argue that the former is simpler than the later... but, in some others, the order of simplicity count can well be reversed ! And the matter can be vastly more complicated than that, because brains evolved to understand the difference between a cow and a tiger, not between the symmetric sheet bend and the ABoK#1406 ! For a cat, a mouse is a much simpler thing than either a tetrahedron or a cube, that is for sure.  :)
  In the field of knots, to count complexity in an objective way, should we include only the geometrical elements of a knot, or also the steps - tucks or whatelse -,  we have to follow to tie this knot ? Should we count only the 3D geometrical elements of the tied knot, or also the physical mechanisms needed to keep this 3D machine in a static equilibrium ? A knot simple in geometrical elements count, but complex in physical mechanisms count, is it a simple or a complex knot ? You tell me... :) At the end of the day, what counts are not semantics, but our lives... and lives, being so short, should better be interesting to live. This bend is an interesting thing, and when we learn interesting things, we feel we live longer... :)

 
1) http://www.cs.princeton.edu/theory/complexity/bookWebNov06.pdf
2) http://pespmc1.vub.ac.be/COMPLEXI.html
   
« Last Edit: December 22, 2011, 02:07:02 AM by xarax »
This is not a knot.