International Guild of Knot Tyers Forum

General => Practical Knots => Topic started by: erizo1 on February 29, 2012, 03:56:33 PM

Title: Knots secure enough to trust with my life
Post by: erizo1 on February 29, 2012, 03:56:33 PM
I'm new to knot tying and eager to learn. After a question on a thread about the security of the Zeppelin bend and loop (http://igkt.net/sm/index.php?topic=1902.45), I got a reply that made me want to pursue this topic more.

I'm very new to knot tying. I'm interested in loops at the moment, and in the zeppelin loop in particular. I'm wondering what others think about the effect of loading one of the ends of the zeppelin bend in forming the loop. Does that make it a less-secure knot than the bend?
...simply that the symmetry of the end-2-end knot's loading is lost in the eye knot (as one overhand part is loaded on both ends, the other not).

Quote
I'm also wondering how the zeppelin bend and loop compare in security to bends and loops typically used in rock climbing.  Is there evidence to say definitively that the zeppelin bend and loop are or are not to be trusted with my life?

Rockclimbers use end-2-end knots in just a couple of cirucumstances : joining ends of a small line or tape to form a closed-loop sling; joining abseil ropes together. In neither of these cases would one have good reason to favor the zeppelin bend.

Eye knots are used for tying in, and the zeppelin eye knot will suffice, as will many many others.  Its ease of UNtying after being loaded is one attractive aspect --but one shared by numerous bowlines and other lesser known knots.

--dl*
====

So here are the follow-up questions to start this thread:

In abseiling, what bend(s) would be preferred and why? What are the reasons not to use a zeppelin bend? I'm interested in what makes a knot worthy of trust with a person's life, as well as in the practicalities of a knot designed for that particular use.

Taking into account ease of both tying and untying, what are a couple of other good eye knots secure enough for tying in? I find the standard rethreaded figure-eight bothersome - takes too long to tie and dress properly. I'd love to know a few of the lesser-known knots you have in mind, and I'm also curious which bowline variations are secure enough for use in climbing. Is the round-turn bowline secure enough for this, as I've seen asserted on one page?
Title: Re: Knots secure enough to trust with my life
Post by: xarax on February 29, 2012, 04:30:44 PM
   Nobody questioned the security of the so-called "Zeppelin loop"...And he could have not done this, without results of properly performed security tests.
   It is is the cleverness of the solution - to just use a secure bend, and transform it to an end-of-line fixed loop knot- that has been questioned. If you really like secure and dumb solutions, the so-called "Zeppelin loop" is fine !
   There is also another reason the so-called "Zeppelin loop" is not-so-clever : It is because the original, authentic Zeppelin knot, the Zeppelin bend,  is SO clever !  :) It is a rope-made hinge, where the pair of tails are used as the pivot. The so-called "Zeppelin loop" is only a pathetic caricature of this, it is just another tangle of ropes that can also work as a knot...The beauty, simplicity, out most symmetry, the even distribution of tensile forces within the knot s nub, the easiness of tying, the easiness of inspecting, all those things so characteristic of the symmetric bends in general, and the Zeppelin bend in particular, are lost in this ugly monster...
   Let us now go one step beyond those obvious facts...In an end-of-line loop knot, the two ends are loaded with approximately 50% of the load, the third with 100%m, and the fourth with 0%.  In a bend, the two ends are loaded with 100%, and the other two with 0%. I guess one should not be a rocket scientist, to see that a fine and clever solution in the later, may be not be so fine and so clever in the former ! A fine and clever loop knot should treat the standing end, with the 100% of the load on its shoulders, DIFFERENTLY than the two ends of the bight - the eye leg of the standing part and the eye leg of the bight - that carry only half of this load. To treat those ends differently,  is not addressing a problem of security, but it might well be a solution of strength - and it is the rational, clever thing one should do.
   
 
Title: Re: Knots secure enough to trust with my life
Post by: xarax on February 29, 2012, 04:53:15 PM
I'm also curious which bowline variations are secure enough for use in climbing. Is the round-turn bowline secure enough for this, as I've seen asserted on one page?
  With convoluted enough knots, and not very slippery materials, I guess that any "secure" bowline would be secure enough - and it might also be helped further by an additional 'lock" - i.e. used as one part of a compound knot. Having said that, nobody should trust a knot that is not tested, and tested properly, and repeatedly. There are many "secure" bowlines presented in this Forum, just search posts with the key-word "bowline". However, none of them is tested as it should - simply because we do not have any willing or capable knot tyers to do the dirty job !  :) Until we have tested ALL those knots, one should probably do what most people do : do what most people do ! Tie a retraced fig. 8 or a retraced 2 fig. 9 knot.
Title: Re: Knots secure enough to trust with my life
Post by: roo on February 29, 2012, 05:39:55 PM
So here are the follow-up questions to start this thread:

In abseiling, what bend(s) would be preferred and why? What are the reasons not to use a zeppelin bend? I'm interested in what makes a knot worthy of trust with a person's life, as well as in the practicalities of a knot designed for that particular use.

Taking into account ease of both tying and untying, what are a couple of other good eye knots secure enough for tying in? I find the standard rethreaded figure-eight bothersome - takes too long to tie and dress properly. I'd love to know a few of the lesser-known knots you have in mind, and I'm also curious which bowline variations are secure enough for use in climbing. Is the round-turn bowline secure enough for this, as I've seen asserted on one page?
I've replied to some of this in the other thread (http://igkt.net/sm/index.php?topic=1902.msg22462#msg22462), so I'll try not to re-hash stuff too much here.  The only reason I can think of for not using the Zeppelin Bend is unfamiliarity.  Just as with any other bend, if you're not comfortable with execution and inspection yet, you should hold off until you have it mastered.

As for loops other than the Zeppelin Loop (http://notableknotindex.webs.com/zeppelinloop.html) for alternatives to the Figure Eight Loop (http://notableknotindex.webs.com/figure8loop.html), I would have you consider the Water Bowline (http://notableknotindex.webs.com/waterbowline.html).  It should be a natural extension for anyone familiar with the quick-tie method of the bowline.  It's more secure than the Double Bowline, although the Double Bowline (http://notableknotindex.webs.com/doublebowline.html) isn't horrible, either.

Test them all in the material and conditions that you expect to see, and go with what you are comfortable.
Title: Re: Knots secure enough to trust with my life
Post by: erizo1 on February 29, 2012, 06:15:12 PM
Thanks very much!
Title: Re: Knots secure enough to trust with my life
Post by: Dan_Lehman on February 29, 2012, 07:18:18 PM
In abseiling, what bend(s) would be preferred and why?
What are the reasons not to use a zeppelin bend?
I'm interested in what makes a knot worthy of trust with a person's life,
as well as in the practicalities of a knot designed for that particular use.

Discussion of abseil-ropes-joining knots can be found (with
images) here:
www.rockclimbing.com/cgi-bin/forum/gforum.cgi?post=2091962;search_string=offset%20fig.9;#2091962 (http://www.rockclimbing.com/cgi-bin/forum/gforum.cgi?post=2091962;search_string=offset%20fig.9;#2091962)

The zeppelin bend can be faulted for two reasons:
1) it is not *offset* and so will not flow over rough surfaces & edges;
2) it is rather *open* in structure --not a compact-tight knot-- and so
suggests vulnerability to further loosening and snagging to be pulled open.

The principal quality for an ARJ knot is security, and then beyond that
are ease of tying (correctly), ability to avoid getting snagged or caught
up on edges, and ease of untying.

Quote
Taking into account ease of both tying and untying,
what are a couple of other good eye knots secure enough for tying in?
I find the standard rethreaded figure-eight bothersome - takes too long to tie and dress properly.
I'd love to know a few of the lesser-known knots you have in mind,
and I'm also curious which bowline variations are secure enough for use in climbing.
Is the round-turn bowline secure enough for this, as I've seen asserted on one page?

One can take the fig.8 start (i.e., tie an 8 in the SPart)
and finish it in ways that are both simpler, definite (almost
nowhere does anyone give express dressing guidance!),
secure, and easy to untie.  I'll attach photos to this post of what
I proudly name the "Lehman8" and --hmmm-- "Collared8"
(to which knots' common mid-state of completion lies what I
call the "Quick8" and then "tucked Quick8" in which the
tail is left, respectively, as-is after its initial insertion & tuck, or else
taken from there and tucked out between the eye legs (by which
one might gain some slack-security in this loop's nipping of the
fig.8's body)).  The design goal of the Lehman8 was to
get the apparently stronger fig.8 "padded-path(tm)" geometry
with the bowline's easy-to-loosen *collar* closure;
I think it meets this pretty well, but have no insight as to actual
strength (but will assert that any difference is likely small &
insignificant, practically!).

(In urethane-coated 5/16" 12-strand Dyneema rope, the
Quick8 proved relatively weaker among a few tested knots,
but did not slip --though it appears that the "tucked" finish
was necessary to prevent slippage (but, hey, that base has only
a 2-nip, pretty straight-through-passage of the tail!).  Please note
that this material is an extraordinary one, unlike common cordage!)

((rupture analysis of Tucked Quick8
The white marker threads were sewn in at points where the rope
parts exited/entered the knot, so to show the degree of knot
compaction/compression or slippage as they are drawn away
(or, for the unloaded tail, sucked in).  The pink thread was sewn
at the point I deemed probable for rupture, AS SET; the gold
was the point  ... probable to come into rupture position, if
not an alternative point.  In this case, we see some compaction
of the knot, with white threads of loaded strands pulled away;
note the slight difference between eye legs (the lower and more
pulled-away leg is that of the tail).

The upper knot equals the ruptured lower knot, and was at the
opposite end of the test speciemen, subjected to equal tension
--hence, it's our insight into geometry changes/effects!

The apparent break point came a little inside the knot, as the
SPart bent around other parts --though the rupture segment
is not all so pointpoint precise, and it COULD be that rupture
began farther *into* the knot (more around the eye leg(s)),
and then got distributed thereafter.  In this photo, the tails
are coming at us and it's hard to gauge how much they
might've been "sucked in;" but other perspectives show that
it was not much (and, I think, to some extent, the turn of
the SPart is working to come back over them!)
))


--dl*
====
Title: Re: Knots secure enough to trust with my life
Post by: xarax on February 29, 2012, 07:19:19 PM
   Do not let the misleading name of the so-called "Zeppelin loop" confuse you, and succeed in making you believe that the quality of the superb Zeppelin knot, the Zeppelin bend, can somehow be "transported" to this ugly dumb monster, the so-called "Zeppelin loop", by sympathetic magic !  :) Because this is a cunning strategy that attempts to sell this end-of-line loop knot, and hide the many other knots we already have. There are many bowline-like loops offering the same, and even superior, security and strength than any eyeknot that needs an overhand knot tied on the standing part before the tip of the bight.
Title: Re: Knots secure enough to trust with my life
Post by: roo on February 29, 2012, 07:26:00 PM
There are many bowline-like loops offering the same, and even superior, security
Name one.

It had better not be an "ugly dumb monster".  You should also let us know what testing you did to determine this, since one of your most common phrases is "I have not tested this".
Title: Re: Knots secure enough to trust with my life
Post by: roo on February 29, 2012, 07:45:56 PM
Quote from: Dan_Lehman link=topic=3810.msg22474#msg22474
The [i
zeppelin bend[/i] can be faulted for two reasons:
1) it is not *offset* and so will not flow over rough surfaces & edges;
2) it is rather *open* in structure --not a compact-tight knot-- and so
suggests vulnerability to further loosening and snagging to be pulled open.
Point 1 is based largely on conjecture.  A European Death Knot that is "supposed" to not get caught on sharp edges may get caught in crevices or other narrowings (branches) due to its bulk which exceeds the Zeppelin Bend.

I don't really see the openness of a properly-set Zeppelin bend (with or without asterisks).  Can you produce any hard evidence of a snag pulling a Zeppelin Bend open?  I doubt it.
Title: Re: Knots secure enough to trust with my life
Post by: Dan_Lehman on February 29, 2012, 08:39:17 PM
Quote from: Dan_Lehman link=topic=3810.msg22474#msg22474
The [i
zeppelin bend[/i] can be faulted for two reasons:
1) it is not *offset* and so will not flow over rough surfaces & edges;
2) it is rather *open* in structure --not a compact-tight knot-- and so
suggests vulnerability to further loosening and snagging to be pulled open.
Point 1 is based largely on conjecture.  A European Death Knot that is "supposed"
to not get caught on sharp edges may get caught in crevices or other narrowings
(branches) due to its bulk which exceeds the Zeppelin Bend.

There is no conjecture about the flow over surfaces,
which is readily demonstrable to any who care to look
--the edge of a desk is often an immediate structure
for testing that.  As for some "V" narrowing, that could
catch any knot, yes.  The "bulk" of the EDK/ORB hardly
much exceeds the zeppelin's --and with parallel tails,
it lacks the poking out of them, as well.

Against the point, though, comes some considerable
user testimony to having successfully used non-offset
knots w/o difficulty, or to having difficulty where an offset
knot wouldn't have helped.

Quote
I don't really see the openness of a properly-set Zeppelin bend (with or without asterisks).
Can you produce any hard evidence of a snag pulling a Zeppelin Bend open?  I doubt it.

(The asterisks indicate a qualified use of the word.)
A zeppelin doesn't get set so snugly as many knots,
and as the ORB ; there are spaces around the collars,
which is why the knot can be untied so easily.  This is
enough to give some concern to me about snagging,
although both unlikely to occur, and then arguably
unlikely IF occurring to be severe?

So, yes, it's more an *apparent* than any confirmed
worry.  But there is no positive quality moving me to
use the knot vice others, for which I haven't even this
concern.


--dl*
====
Title: Re: Knots secure enough to trust with my life
Post by: roo on February 29, 2012, 08:46:35 PM
Quote from: Dan_Lehman link=topic=3810.msg22483#msg22483
   As for some "V" narrowing, that could
catch any knot, yes.  The "bulk" of the EDK/ORB hardly
much exceeds the zeppelin's --and with parallel tails,
it lacks the poking out of them, as well.
Anyone who cares to check (with holes or gaps of various sizes) can see that the European Death Knot gets caught in gaps that the Zeppelin Bend pulls through.  Those tails poking out of the Zeppelin Bend bend back easily.  Throwing a wave down the rope doesn't help much with a size-based interference, compared to a mere sharp edge scenario. 
Title: Re: Knots secure enough to trust with my life
Post by: xarax on March 01, 2012, 12:24:41 AM
One can take the fig.8 start (i.e., tie an 8 in the SPart)

   Now, what if one does not want to have the fig. 8 knot tied on the standing part, "before" the tip of the loop, but "after" the tip, on the tail ? I believe that what can be done on the standing part, can also be done on the tail... so we get a bowline-like loop. I am personally interested on those loops, because I want knots that can be completely untied before the tail gets out of the ring, or bollard, or waist - so, when the tail is released from its entanglement with the standing part, there is no knot left on the line that can be caught somewhere and cause problems.
   Have you tried the same or similar knots with a shape 8 unknot ? I think that what you seek is already given by the geometry of the 8, and not by the topology, so why use a fig. 8, when you can use a shape 8 ?
   Have you bought your new camera, or just decided is about time to let us have a glimpse on your top-secret archives ?  :) ( By the way, I think that the shades in your pictures are somewhere too dark, and somewhere not dark enough...Anyway, at last we have PICTURES as well as words... I hope this trend will continue.)
   
   
Title: Re: Knots secure enough to trust with my life
Post by: knot4u on March 01, 2012, 01:54:37 AM
Videos worth watching about testing the Zeppelin Bend...

http://www.youtube.com/watch?v=Givv9cBB_Hw
http://www.youtube.com/watch?v=_-uQrx7yPYM
Title: Re: Knots secure enough to trust with my life
Post by: xarax on March 01, 2012, 03:03:09 AM
Videos worth watching about testing the Zeppelin Bend...

  I wonder why they almost never put the bends to destructive tests, to measure their ultimum strength...the "absolute" number we were talking about. Also, we should know the ultimum strength of the material used... In short, we want more numbers, and fewer pictures of knot tests - just as we want more pictures, and fewer words of knot structures... :)
 
Title: Re: Knots secure enough to trust with my life
Post by: knot4u on March 01, 2012, 03:35:24 AM
For this thread, I don't think a destruction test would provide information that's more useful. Also, in the first video, you can see the rope used and the load in precise poundage, which is a lot more experimental data than about 99.79% of the posts on this site.
Title: Re: Knots secure enough to trust with my life
Post by: xarax on March 01, 2012, 03:56:55 AM
For this thread, I don't think a destruction test would provide information that's more useful.

   It would provide useful information, that is for sure - and could provide some NUMBERS, too! Strength should always be questioned as much as security, because things fall, and when they fall, people often suffer. The ropes used outdoors are usually over-sized, but also they could have been weakened due to many accidental factors, so, ceteris paribus, the strongest knot is the better.

a lot more experimental data than about 99.9% of the posts on this site.

Sadly, very true...We should start performing experiments, otherwise we are not going anywhere, I am afraid...

Title: Re: Knots secure enough to trust with my life
Post by: Dan_Lehman on March 01, 2012, 05:11:33 AM
For this thread, I don't think a destruction test would provide information that's more useful.

   It would provide useful information, that is for sure - and could provide some NUMBERS, too! Strength should always be questioned as much as security, because things fall ["fail"?], and when they fall, people often suffer. The ropes used outdoors are usually over-sized, but also they could have been weakened due to many accidental factors, so, ceteris paribus, the strongest knot is the better.

But in the world of rockclimbing, things doN'T fail
because of strength, but have done so, because of (in)security.

You have been challenged on this continual clammoring
for "strength" "numbers",
to define both "better" & "strong".

The meaningful numbers for you, which you keep failing
to appreciate, is the probability of "ceteris paribus" and
of any reasonable sense of "strength" having significance
in practical circumstances.  The number you are looking
for is practically zero (raised to the power of how ever
many times you holler for it).

 ;)

--dl*
====
Title: Re: Knots secure enough to trust with my life
Post by: xarax on March 01, 2012, 05:35:34 AM
But in the world of rockclimbing, things doN'T fail

Things fall down, because they can not fall up... :) And then, most of the times, they go straigh up, to heavens...

   So, my dear Dan Lehman, there is no strength of ropes and knots, there is no better or worse knot, and there is no bigger or smaller number...
   Anything goes ! Down with numbers !  Freedom to the people !  Let the climbers - and the bicyclers -  fly !    :)   :)
   
Title: Re: Knots secure enough to trust with my life
Post by: Sweeney on March 01, 2012, 11:02:34 AM
I've seen this first video before - and I find it useful as a real world example since I weigh about 210 lbs! I cannot imagine ever using a rope for an application where I would get close to the breaking load so I'm not convinced that this data is useful other than for knot theory - to understand the transformation of a knot perhaps immediately before it breaks. I am far more interested in knot security because a knot which slips especially suddenly could be at best expensive in terms of damage caused.

Barry
Title: Re: Knots secure enough to trust with my life
Post by: xarax on March 01, 2012, 01:51:25 PM
I cannot imagine ever using a rope for an application where I would get close to the breaking load

The breaking load could change, if the rope has been accidentally weakened due to chemical, UV, etc reasons. And a sudden fall / dynamical load can load the rope with an unpredicted high load.

this data is useful other than for knot theory - to understand the transformation of a knot perhaps immediately before it breaks.

We do not use this misleading term "Knot Theory" any more here, remember ?   :)
The most useful thing in the world ( and in the human history) is "to understand" !
So, who is going to answer to (1) ?  :)

I am far more interested in knot security because a knot which slips especially suddenly could be at best expensive in terms of damage caused.

   You mean, you are not interested in knot strength, because when a knot breaks, all the damage that could have been done, is already done ?  :)
   Security is, in a sense, much easier to achieve, in comparison to strength. A convoluted enough knot will not slip before it will break, but to achieve a high strength knot structure is a very difficult exercise in Nodeology or Desmology, of which we know only a few things...
   On top of this, if you leave strength considerations outside the field of practical knotting, you make the field less rich and less interesting...It is nice if we have more things to talk about, in our lengthy blah blah here... :) A world where any tangle of ropes would not weaken the rope, would be almost as less interesting as a world where no knot slips, ever - or a world where there will be one and only one "knotted material", only one substance to tie any knot on/with.

1)  http://igkt.net/sm/index.php?topic=3811.0
Title: Re: Knots secure enough to trust with my life
Post by: Sweeney on March 01, 2012, 04:09:20 PM
I cannot imagine ever using a rope for an application where I would get close to the breaking load

The breaking load could change, if the rope has been accidentally weakened due to chemical, UV, etc reasons. And a sudden fall / dynamical load can load the rope with an unpredicted high load.

So, who is going to answer to (1) ?  :)

I am far more interested in knot security because a knot which slips especially suddenly could be at best expensive in terms of damage caused.

If the breaking load has changed because of some damage then using this rope for a critical application would be foolhardy if that were known. If the damage were not known then I fail to see what difference knowing knot strength is going to make.

As to who will answer the question re the Alpine Butterfly - that depends on the question!  Although the OP asked about knot strength it seems at least as  likely that slippage (security) is the real issue judging from the later part of that post. It is unfortunately common for people to confuse the 2 quite different measurements. The title of this thread is about security not strength which for practical purposes is hardly ever a consideration.  And although slippage (or collapse) can be reduced, if this at the expense of sheer bulk it is hardly practical in the real world.

Barry
Title: Re: Knots secure enough to trust with my life
Post by: xarax on March 01, 2012, 07:45:48 PM
If the damage were not known then I fail to see what difference knowing knot strength is going to make.

  As the strength of the rope is decreased somewhere, the strength of a knot  tied on it is more comparable to the rope s strength, so it becomes more significant.
   You can say, "I am not interested in the ultimum strength of this knot, because I know beforehand it will be around 50% of the ultimum strength of the rope, and the rope s strength is much more strong than what I need, for the application I will use it." However,
1. You can never predict the force of dynamical loading, or accidental loading.
2. If this supposedly over-marginal strength of the rope has been decreased without you knowing it, it will start to matter - and the ultimum strength of the knot will start to matter as well. It would be always more safe to have tied a strongrer knot, than a weaker one !

strength... for practical purposes is hardly ever a consideration.

THIS is the most unfortunate thing...Knot strength was, is. and will be, always an issue, because the greater disadvantage of ANY knot, is that it reduces the strength of the rope it is tied on. I know this is something knot tyers have long forgotten, or they just prefer to hide, and they do not speak openly about it... And to address this issue blindly, by just choosing a bigger rope, or adding some more wraps and tucks, is not what we wish people to do, is it ?

   I am not happy with the trend I see that is going to establish itself in this Forum lately, that the strength of the knot does not exist, it is not an objective, measurable quantity, it is of no importance, and all this...I have been a witness of another such erroneous trend, where the discussion about the bowline was judged to be only of "pure", "theoretical", and not "practical" importance. Of course, I do not believe that the truth is a matter of votes, and I am sure that prudence will come back, sooner or later. Strength of knots is something that exists, and it is something very important, interesting, and its negligence is not only a lack of understanding, but also a very dangerous omission. 



Title: Re: Knots secure enough to trust with my life
Post by: Sweeney on March 01, 2012, 10:38:54 PM
Strength of knots is crucial in fishing line where the operating load is close to the breaking strain of the line - deliberately so.  But actually we are not talking about "strength of knots" at all but the weakening effect of knots on rope - one knot is not stronger than another, it simply weakens the rope less. In other words it is the reduction in weakening effect rather then the increase in strength (a knot cannot be "stronger" than the rope etc it is tied in).  But knowing how much a knot weakens rope does only matter if the load (be it a static or shock load) is going to come close to the actual rope breaking strength. Hence the use of SWL - safe working load - usually set at about 25% of rope strength but as low as 10% if this is critical or the rope is suspect for some reason.

Being interested in the weakening effect of knots is fine - and avoiding the worst cases may be prudent. No-one is ignoring or hiding this, it just doesn't usually matter other than to a fisherman whose approach is markedly different than someone working with rope etc.

Barry
Title: Re: Knots secure enough to trust with my life
Post by: xarax on March 01, 2012, 11:07:57 PM
actually we are not talking about "strength of knots" at all but the weakening effect of knots on rope - one knot is not stronger than another, it simply weakens the rope less. In other words it is the reduction in weakening effect rather then the increase in strength (a knot cannot be "stronger" than the rope etc it is tied in). 

 :) 
What you describe as "reduction in weakening effect", I simply describe as knot strength - as all people do ! Now, if one wants to split hairs here, I guess he can figure out many other strange ways to do it, too.

But knowing how much a knot weakens rope does only matter if the load (be it a static or shock load) is going to come close to the actual rope breaking strength

As it often does, in many rope applications, as construction, towing vehicles, etc.
I do not see what are you trying to tell...

the weakening effect of knots ...just doesn't usually matter other than to a fisherman whose approach is markedly different than someone working with rope

  An absolutely wrong statement ! Do not tell it to anybody that has something hung over his head, and was forced to use a knot to tie it somewhere...
   There are a lot more at stake in the strength of knots, than a released fish  !  :) 
   I am sensing that this discussion is about a self-evident, common-sense thing, but anything I am trying to say is put under a biased microscope...as it had happened before. So, I am not going to feed this trend I have tasted time and again any more - sorry.  :)
Title: Re: Knots secure enough to trust with my life
Post by: Hrungnir on March 02, 2012, 02:09:41 AM
the weakening effect of knots ...just doesn't usually matter other than to a fisherman whose approach is markedly different than someone working with rope

  An absolutely wrong statement ! Do not tell it to anybody that has something hung over his head, and was forced to use a knot to tie it somewhere...
   There are a lot more at stake in the strength of knots, than a released fish  !  :) 
Then you might ask yourself why the most common bend ever is the Overhand Bend (EDK). Even rock climbers seem to prefer this bend over bends with much higher knot efficiency.

Title: Re: Knots secure enough to trust with my life
Post by: Dan_Lehman on March 02, 2012, 06:38:35 PM
the weakening effect of knots ...just doesn't usually matter ...

  An absolutely wrong statement ! Do not tell it to anybody that has something hung over his head,
and was forced to use a knot to tie it somewhere...
   There are a lot more at stake in the strength of knots, than a released fish  !  :) 

I hope we can move past this debate, with this
understanding : the state-of-the-practice, in various
fields, uses knots without any really good basis for
knowing their strength --as Xarax seems to demand--
other than that this is how things are done .
We might learn, through hands-on, out-in-the-field
surveys, that in fact there are here and there some
wells of experiential knowledge of a *strength* that
belies that got from the test device --one born of
wear & tear and repeated loading cycles rather than
a single slow-pull to rupture!?
.::.  In short, measurements of strength, to my awareness,
have been well short of the degree of thoroughness and
detail and breadth to provide much guidance for use.

Moreover, a review of the history of usage will show that
in many / most cases, knots do not break in normal use
--that just isn't a problem crying out for a solution.  (I'm reminded
of one sailor's remark about docklines surviving a hurricane when
tied in bowlines vs. those w/eye splices --knots didn't break,
though some lines did break, elsewhere (likely over an edge).)
And to hypothesize degrading conditions or extraordinary
loads that might fall just in the small range of forces
that could make a difference between different knots
is to indulge in statistical insignificance & speculation!

Another aspect of knot strength might be that of cumulative
effects on the material : that using a weaker knot will lead
to a greater material weakening over time than using a
stronger knot.  But this is mere speculation, and it might
be that the difference between knots of reasonably good
strength/efficiency (say, 60% vs. 80%) at normal loads
will be so small that one should expect other effects of
material deterioration to be still what determine when
to retire or downgrade that cordage to lesser uses.
(Rockclimbers, e.g., sometimes cut of ends of their
long lines and use the remainder; testing has shown that
the ends of such lines will be more weakened than the
central parts (not necessarily from the knot tying and
compressing, but also the rope being drawn through
a 'biner on each fall --coming more at a small distance
from the end ("run out")). )

Furthermore, I must emphasize my notation " *knot* "
in this : if we are talking purely of the thing represented
by, e.g., ink on paper --schemas for formation--, the general
geometrical form, it is unlikely that such entities are best
for associating with a *strength* value
--in contrast to some particular material so-knotted.
I.e., it might be the case that a bowline is stronger in
some material vis-a-vis some other knot than in another
material.  (I've speculated that HMPE cordage might be much
susceptible to rope movement and generated heat, and so
do better when knotted in ways that restrict movement;
another material --an aramid copolymer, Technora, e.g.--
might do much better when knotted where movement occurs,
vs. HMPE?!)

Then you might ask yourself why the most common bend ever is the [Offset] Overhand Bend (EDK).
Even rock climbers seem to prefer this bend over bends with much higher knot efficiency.

Yes, because strength of any knot here is more than adequate.
(Counting "most common" is tricky : is it what gets tied
the most?  --probably the climber's tie-in knot.
Or what appears in the most cases along a climb?
--maybe the grapevine bend in formed slings
(or the water knot with tape), even though these
knots are pre-tied to the climb.  Even in a multi-pitch
abseil, I suspect the ARJoining bend is tied once and
re-used, not re-tied each pitch.)


--dl*
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