Author Topic: The symmetric Sheet bend  (Read 30424 times)

xarax

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Re: The symmetric Sheet bend
« Reply #30 on: December 18, 2011, 08:45:04 PM »
It is the resistance of this pivot to shear forces, that ...
   Is no more "shear" than that of most(?) other knots, such as [/i]Ashley's bend #1452[/i] (or #1408).  Making a big thing of this is misleading.  Tails are nipped, hardly a unique quality; they have axial forces on them as well.

   I understand that it is difficult (at least for me) to explain this difference, and it is difficult for a person not trained in engineering to understand it. In the case of this bend, as well as in the ABoK#1406, shear forces, - and the resistance of the pair of tails, functioning as as a rope-made pivot, to them - is paramount. I am not saying that shear forces do not play a role in other bends as well. In fact, they participate in the mechanism of any knot, alongside tensile and compression forces. However, if you manage to see the hinge-like mechanism, you will also see what I mean.  Only in those three bends the principal role of shear forces is so pronounced. ( I can also think of a few other knots, like the Anglers loop, for example, where we have a similar situation). Of course the tails are nipped, like it happens in any knot, we could hardly have a knot without this function ! However, in most other knots, we have entangled bights, and the knots remain knotted because the tails are nipped as they pass through these bights, and they can not slip through. When the tails can not slip through the bights, these bights remain entangled, and the knot remains tied. This is a very different mechanism from the hinge-like mechanism of the symmetric sheet bend ( and the ABoK#1406 and the Zeppelin bend ), where we do not have entangled bights, but bights revolving around a common axis, materialized by the pair of the tails.
   I do not make "a big thing of this", although I admit that I had the hope at least a few people, in this particular forum, would be able to mentally see this difference... Anyway, untill the time we can take pictures of loaded knots made by flexible transparent material ( a flexible plexiglass, perhaps ?), where we can literally see the distribution of forces into the bulk of the material, we can not prove or disprove any of our opposing views, can we ?  :)

« Last Edit: December 18, 2011, 08:48:17 PM by xarax »
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xarax

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Re: The symmetric Sheet bend
« Reply #31 on: December 18, 2011, 09:39:09 PM »
  Thank you Derek. It is always a pleasure for me to discuss with you about simple, fundamental knotting mechanisms.

This is the 'Practical Knots' board, and this is never going to be a 'Practical Knot' and I believe we have a duty not to promote it as such.

  I agree. Let us move it to our brand new Knotting Concepts and Explorations, where it clearly belongs. I see it as an exercise, I could even dare to say a theorem of knotting mechanism. If it would ever be considered a "practical" knot, it would only be in the sense that it can solve a practical knotting problem of an experienced knot tyer, who knows what he is doing and why is he doing this. As I have stressed, it is a difficult knot, suitable for knot tyers only, and it does not take hostages.. :).   

it is one of the few knots which 'dresses itself' to the extent that it won't eat any of the tails as it is loaded

   Oh ! I forgot to mention that advantage !  :) I thank you for reminding it to me. It might be interesting to mention that the other three bends that work in a similar way - using the pair of tails as a rope-made pivot of a rope-made hinge - also do not "eat" much of their tails during further loading. The shear forces are very effective of inducing a large amount of friction, and block the slippage of the tails.

it is none the less only safe as a 'cerebral exercise'.

  May be, but you know how useful have "cerebral exercises" have been , in the course of human history !  :) A cerebral exercise of half a dozen scientists, back at 1964 where most of the knot tyers - indeed, most of the people - in the world were not born, proved to be a hard, material reality a few days ago at CERN...In fact, it was proven to be the reality that gives to all matter its material substance, its mass  :)!
   I have said that this bend is a difficult bend , and should only be tied by people that know what they are doing, and why they are doing it. In fact, it is a very safe knot, in that it can not be even tied by other people, so no week-end knot tyer would ever dare to tie it... (Just kidding...) I have also said that it should be accompanied by the scull and crossed bones sign Ashley uses for ABoK#1406. In fact, it is not more "safe" or more "dangerous" than ABoK#1406, and I have not read anything in this thread that points to even one subtle difference between those two bends. People are alarmed with the security of this bend more than with the security of ABoK#1406, for one simple reason ; They knew the one, but they have not seen the other ! And the one is there, in their holy book, while the other is not. In short, nothing more than the well known knot tyers conservatism.
   The great advantage of this bend is the lessons it offers to us, the widening of our view about bends in particular, and knots in general. I would try to incorporate the mechanism of this bend in more complex, and more easy to tie knots. For me, knots are more a mental game than a practical necessity, so a cerebral exercise is a welcomed thing - and a cerebral theorem, like this bend, is a Knotworld-heavens blessing !  :)
   It is amusing that the knots I present is this forum are criticized as too complex or too simple ! I do not know what is the truth, but I
only hope that they are not too boring...
   Derek, I know you could explain this knot using your elaborated system of fundamental knotting elements, and I would be glad if you will compare it to its evil impostor, and to the ABoK#1406.
   
« Last Edit: December 18, 2011, 09:48:36 PM by xarax »
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xarax

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Re: The symmetric Sheet bend
« Reply #32 on: December 18, 2011, 10:20:12 PM »
   I would like to ask a question, related with matters discussed in this thread.

   We have two knots :
   1. On the one hand , the well known Thief knot. It is very easy to tie, very difficult to tie it wrongly, but it is a very slippery bend.
   2. On the other hand, the relatively unknown symmetric sheet bend. ( It can be considered as a different dressing of the Thief knot ). It is very difficult to tie, very easy to tie it wrongly, but it is not slippery a bend at all.

   The Thief knot is considered to be a "practical" knot, and it is almost never accompanied by the danger/ scull and crossed bones sign of Ashley. The symmetric sheet bend is not a practical knot, and it should always be accompanied by the danger/ scull and crossed bones sign.
   The question is : Which one is really more dangerous ? The one that slips even if tied correctly - but it is easy to tie... or the other, that does not slip when tied correctly - but it is difficult to tie ?
   My answer is this : the Thief knot has already killed -  it will continue to kill, because it slips, and it is an easy to tie bend - many more people than the symmetric sheet bend will ever do... because the symmetric sheet bend does not slip, and it is a difficult to tie bend. So, I conclude that the Thief knot is much more dangerous than the symmetric sheet bend...( and I admit that I have asked this rhetorical question only to intrigue some answers by the (few) participants of this forum... :))
« Last Edit: December 18, 2011, 10:21:59 PM by xarax »
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SS369

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Re: The symmetric Sheet bend
« Reply #33 on: December 18, 2011, 11:33:18 PM »
Although the thief knot is a supposed "practical" knot, the practical-ness of it comes from the trickery it was supposedly used for. It was to potentially indicate that a sailors ditty bag security was violated by the assumption that a reef knot would be tied back instead.
How much it really remains a practical knot is a matter of personal choice.
But if we choose to categorize it as one then in my own opinion a Turks head knot is a practical knot. It has been used as a marker on a ship's wheel.

Just because we talk of it and refer to it in the Practical Board doesn't necessarily make it practical.
I don't use it for anything.

The OP bend could be practical if we found a good use for it in daily life.  ;-) I find it meets the requirements of a good discussion knot, to aid further understanding of the forces in play to arrest/resist the linear material's movement.

For me it is not so much that a knot is dangerous or not,  it is the tyer who could be the dangerous one. Knots don't kill, people do.

SS

xarax

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Re: The symmetric Sheet bend
« Reply #34 on: December 19, 2011, 06:22:42 PM »
It is the resistance of this pivot to shear forces, that ...
...Is no more "shear" than that of most(?) other knots,

   I use this opportunity to show another interesting bend (see the attached picture), that can be used when we want to connect  two pieces of rope in a way that will allow us to disconnect them easily, and then repeat the same cycle many times. Now, this bend works exactly in the same way as the Zeppelin bend, but here the two ends can be separated, yet there remain some untied structures on each of them ( the slipped overhand knots ), ready to be utilized when the ends will be entangled with them again. It is just an example of the few bends that work using the resistance of rope to shear forces more than the other bends do. The symmetric Sheet bend  we are talking about in this thread, its closest relative, the ABoK#1406, the "slipped overhand knot bend"  in its crossed tails variation, shown in this post, the 2 U s  hitches presented at (1), the angler s loop... in all those knots the resistance of the tails, that play the role of a rope-made pivot, is the principle reason those knots, once loaded, remain in one piece.
   The tails working as pivots that keep opposed bights together, even if those bights are not hooked the one by the other, that is what characterizes the symmetric sheet bend - and make it very different from the Thief knot, from which it can be derived by a manipulation / different dressing of the tails. I am sorry that the people I have not been able to convince about this fact - which seems rather obvious, but is proven o be not so easily digestible - will miss some of the marvellous qualities of the symmetric sheet bend...  and of with the Zeppelin bend, and all the other knots I have cited. We can know how to tie a bend, we can use a bend, we can even appreciate it a little bid, but we can still fail to enjoy it mentally, as an example - or even a beautiful theorem - of the wonderful  KnotWorld. 

1) igkt.net/sm/index.php?topic=3104
« Last Edit: December 19, 2011, 06:27:10 PM by xarax »
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DDK

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Re: The symmetric Sheet bend
« Reply #35 on: December 21, 2011, 12:05:19 AM »
   I would like to ask a question, related with matters discussed in this thread.

   We have two knots :
   1. On the one hand , the well known Thief knot. It is very easy to tie, very difficult to tie it wrongly, but it is a very slippery bend.
   2. On the other hand, the relatively unknown symmetric sheet bend. ( It can be considered as a different dressing of the Thief knot ). It is very difficult to tie, very easy to tie it wrongly, but it is not slippery a bend at all.

   The Thief knot is considered to be a "practical" knot, and it is almost never accompanied by the danger/ scull and crossed bones sign of Ashley. The symmetric sheet bend is not a practical knot, and it should always be accompanied by the danger/ scull and crossed bones sign.
   The question is : Which one is really more dangerous ? The one that slips even if tied correctly - but it is easy to tie... or the other, that does not slip when tied correctly - but it is difficult to tie ?
   My answer is this : the Thief knot has already killed -  it will continue to kill, because it slips, and it is an easy to tie bend - many more people than the symmetric sheet bend will ever do... because the symmetric sheet bend does not slip, and it is a difficult to tie bend. So, I conclude that the Thief knot is much more dangerous than the symmetric sheet bend...( and I admit that I have asked this rhetorical question only to intrigue some answers by the (few) participants of this forum... :))

I do not consider the Thief Knot "easy-to-tie" for the inexperienced knot tyer.  Most who will tie it are somewhat experienced and very likely aware of its slippery nature.  Those with experience are also likely aware that it is unwise to use a "binding knot" as a bend.  Thus, we have the "Reef Knot" or "Thief Knot" and not the "Reef Bend" or "Thief Bend".  I find it unlikely that the Thief Knot will often be used as a bend and equally unlikely that it is much of a "killer" or very dangerous.  I also do not find the OP knot to be very dangerous for the same reasons.

DDK

roo

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Re: The symmetric Sheet bend
« Reply #36 on: December 21, 2011, 12:14:04 AM »
  I find it unlikely that the Thief Knot will often be used as a bend and equally unlikely that it is much of a "killer" or very dangerous.  I also do not find the OP knot to be very dangerous for the same reasons.
I thought the same thing of this insecure "bend" for much the same reasons until SS369 started calling it secure.
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SS369

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Re: The symmetric Sheet bend
« Reply #37 on: December 21, 2011, 12:44:24 AM »
Hello roo,
I'll stand by that statement I made about the OP bend being secure, at least for me. I would not use it for rappelling because there are more secure bends for this and > I don't recommend it for any life threatening activities.

But, I was able to bounce my weight using this bend in a foot loop affair and it did not slip or come undone. I doubt seriously that while it was loaded with my weight that I or another would have been able to cause it to spill. To me it is no more dangerous than any slipped knot that is going to see loading.

Perhaps I get favorable results due to the qualities of the ropes and cords I use.

I see it as no more insecure than the standard sheet bend once dressed and tightened. < My humble opinion, based on my own personal experience.
Heck, even a Zeppelin bend can be flailed loose.

I recommend anyone interested, to get a feel for the mechanics of how it works,  to tie it and load it however you see fit and see for themselves.

SS369

roo

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Re: The symmetric Sheet bend
« Reply #38 on: December 21, 2011, 01:00:36 AM »
Hello roo,
I'll stand by that statement I made about the OP bend being secure, at least for me. I would not use it for rappelling because there are more secure bends for this and > I don't recommend it for any life threatening activities.
It's secure as long as you disregard all the modes by which it is horribly insecure?  That is exactly the kind of muddled and flatly misleading message that is going to confuse and endanger casual observers.

I have a very non-exotic cord in front of me that bounces out of the bend in question almost immediately, even when tightened.  Maybe you got the bend tighter in a different rope type, but tightening a knot becomes radically more difficult as rope diameter increases.

Let's set aside rope size and type for a moment.  I don't know how you can dismiss the security issue of the bend falling to pieces if either or both of the free ends are so much as touched.  The free ends get snagged, stepped on, and dragged on terrain in real life.  This is an integral part of security.  Even if you naively think the free ends will never see any force, you'd better hope no other person ever tries to tighten your bend for you, because most people tighten bends by pulling all four ends... an act that will eliminate what little security this bend ever possessed.



« Last Edit: December 21, 2011, 01:15:39 AM by roo »
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xarax

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Re: The symmetric Sheet bend
« Reply #39 on: December 21, 2011, 01:04:32 AM »
   I do not consider the Thief Knot "easy-to-tie" for the inexperienced knot tyer.

 :)

   Most who will tie it are somewhat experienced and very likely aware of its slippery nature.

  Listen what "you" say :  most of the people who is likely to tie the Thief knot are somewhat experienced, so they will not be killed. "I" say that ONLY people that are VERY experienced is likely to tie the symmetric sheet bend - and, moreover, some of them will not try to understand it, and so they will not be able to tie it  :)... So, I say that, in contrast to the Thief knot, only a handful of very experienced people will ever tie this bend, and I an sure no one of them will be killed ... :)

   Those with experience are also likely aware that it is unwise to use a "binding knot" as a bend.


   I like this distinction, but I am not sure I know what is what... Please, elaborate it a little more. There are a number of knots that can be used in either way, I think...This is an interesting discussion by its own right. Have a look at  the binder/bend presented at (1). Is it a bend or a binder ? This is an interesting discussion by its own right.

   Thus, we have There are the "Reef Knot" or "Thief Knot" and not the "Reef Bend" or "Thief Bend". 

  It would be nice if that was the idea behind the selection of the names...but, most of the times, names have little to do with the essentisl characteristics of the knots, they serve as just labels, not descriptions, I am afraid. Is the fisherman knot  NOT a bend ?  :)

1) http://igkt.net/sm/index.php?topic=3656.msg21375#msg21375
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xarax

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Re: The symmetric Sheet bend
« Reply #40 on: December 21, 2011, 01:39:44 AM »
as rope diameter increases.

  As rope diameter increases, it is getting far more easy to tie the knot correctly, so the result is a far more secure knot.  :)

  The issue with the ends is a real issue, of course, and if one is going to actually use this knot as a bend somewhere, I guess that, being an experienced knot tyer, he will be aware of this obvious fact...I have presented this bend as a simple yet difficult to tie bend - even difficult for experienced knot tiers, as I see now, may be because these people are accustomed to handle things the way they know for years, and they are not ready to try and understand something new...I have said that it is depending upon the knowledge and the dexterity of the knot tyer...and that it should better be compared with the ABoK#1406. Unfortunately, ABoK#1406 happens to be in the holy book, so it is a thing made by god, while this symmetric sheet bend is not, so it is, evidently, made by devil.  Brrr... :)
   When I say "secure", I only mean "does not slip as easy as other similar bends, tied on the same material", and when I say "strong", I only mean "it does not break as easy as other, similar bends, tied on the same material". Roo gives a more general meaning to 'knot security", and he may be right. If we include all factors that will determine the outcome of a knotting act, like the inexperience or ignorance of the knot tier, the possible disturbances caused by the environment, ( as the disturbance of the position of the tails roo mentions ), the possible change in the loading pattern, etc, then, of course THIS BEND IS NOT SECURE, NOT AT ALL !  Exactly the same can be said for ABoK#1406, and some other knots, marked in ABoK by the scull and crossed bones DANGER sign.
« Last Edit: December 21, 2011, 01:44:53 AM by xarax »
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SS369

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Re: The symmetric Sheet bend
« Reply #41 on: December 21, 2011, 01:49:44 AM »
Quote
  It's secure as long as you disregard all the modes by which it is horribly insecure?  That is exactly the kind of muddled and flatly misleading message that is going to confuse and endanger casual observers.

I have a very non-exotic cord in front of me that bounces out of the bend in question almost immediately, even when tightened.  Maybe you got the bend tighter in a different rope type, but tightening a knot becomes radically more difficult as rope diameter increases.

Let's set aside rope size and type for a moment.  I don't know how you can dismiss the security issue of the bend falling to pieces if either or both of the free ends are so much as touched.  The free ends get snagged, stepped on, and dragged on terrain in real life.  This is an integral part of security.  Even if you naively think the free ends will never see any force, you'd better hope no other person ever tries to tighten your bend for you, because most people tighten bends by pulling all four ends... an act that will eliminate what little security this bend ever possessed.

Roo, I am am not advocating the use of this exploratory bend to anyone for anything and I have made it clear in two posts now that I don't recommend it for life endangering activities. I am part of a discussion here amongst interested knot tyers and naysayers about the workings of the knot in the original post. I posted that my own method of simple testing this bend disclosed a security (meaning that it did not slip and the connection remained intact) that I would not have thought it had, but it did.

I just now tied it again in 8mm rope( not all that exotic), tightened it up with a yank on both standing parts and then I kicked it and rolled it under my foot. It did not come undone.

So just touching, as you've indicated you can do causing it to explode, does not work for me. Perhaps I am naive in the magic arts.

As for anyone tightening "my bend" for me (!?). I think not.

Beware casual observers. Make sure that you  become advanced knot tyers before you tie any knots.

SS
« Last Edit: December 21, 2011, 01:51:39 AM by SS369 »

TMCD

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Re: The symmetric Sheet bend
« Reply #42 on: December 21, 2011, 04:39:52 AM »
This bend has lots of drawbacks, I can't believe it's even garnered the attention it has on this board. The average person is in MAJOR trouble if they come here and try to find an acceptable bend and run across this one. Please don't say the average person doesn't come here because I was that average person a while back but I've chosen to stick around and have learned virtually every knot that remotely interests me.

I'll say this, if I were to choose a bend to learn for the average person, it would be the Zeppelin Bend. The Zeppelin Bend is a heavy duty performer and checks off well on most of the criteria a keen eye looks for. It's not a fickle bend such as this one presented by xarax. This bend is terribly hard to tie, unloads at the smallest tug of it's WE's and these facets alone, make this a skull and cross bones bend. This bend would spill/unload in harsh, rugged and extreme working environments such as industrial work sites, military operations etc. The WE's scenario is a strange one too, even though a serious knot tier knows not to tamper with the WE's after the bend's set. Roo has exposed this bend as flakey at best.

knot4u

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Re: The symmetric Sheet bend
« Reply #43 on: December 21, 2011, 06:07:54 AM »
I can think of a practical use for this bend.  Imagine you have two ropes.  You want to jump down 5 stories into water.  You want to slow your fall.  You also want to bring at least one rope down into the water with you.

Here's a solution.  You anchor one rope at the top where you are.  You tie this bend in the OP to join the ropes.  You tie the bend such that once tension hits this bend during your fall, the bend will operate to slow your fall.  The bend slows your fall by NOT holding, but rather slipping with some friction.  The bend comes apart as you near the water, and the lower rope comes down into the water with you.

This experiment could go horribly wrong if the bend actually holds!  So, unfortunately, this bend may also be a bad choice for what it does best.

(That's an idea for a new thread:  What are practical applications in which one would intentionally want a knot to slip?)

SS369, may I suggest you experiment with this rope in more types of rope?  Maybe try less expensive ropes that are more likely to be used in everyday tasks outside of climbing.  It seems like you're playing a little bit of the devil's advocate here.  That's useful to have another perspective, but it also makes you sound like you're a bit too far out there.

BOTTOM LINE:  I may like to use this bend in an application where I intentionally want the bend to slip, but never in an application where I want the bend to hold securely.
« Last Edit: December 21, 2011, 06:24:53 AM by knot4u »

xarax

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Re: The symmetric Sheet bend
« Reply #44 on: December 21, 2011, 07:03:36 AM »
I'll say this, if I were to choose a bend to learn for the average person, it would be the Zeppelin Bend.

   We agree  on something !  :)

This bend would spill/unload in harsh...environments such as .. military operations

   Ooos ! Another advantage of this bend I forgot to mention ! :)

   Roo has exposed this bend as flakey at best.

   That was the nail ion the coffin of this bend, indeed  ! :)
   
   My dear TMCD, you had also forgotten - or perhaps "glossed over" (roo s expression)   :) - to mention the same things, when we were talking about the ABoK#1406,  remember ?  ( the ABoK#1406 that, evidently but unfortunatelly, happens to be IN the ABoK... :)
« Last Edit: December 21, 2011, 07:06:52 AM by xarax »
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