Author Topic: Knots secure enough to trust with my life  (Read 10586 times)

xarax

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Re: Knots secure enough to trust with my life
« Reply #15 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...

« Last Edit: March 01, 2012, 04:01:51 AM by xarax »
This is not a knot.

Dan_Lehman

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Re: Knots secure enough to trust with my life
« Reply #16 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*
====

xarax

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Re: Knots secure enough to trust with my life
« Reply #17 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 !    :)   :)
   
This is not a knot.

Sweeney

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Re: Knots secure enough to trust with my life
« Reply #18 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

xarax

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Re: Knots secure enough to trust with my life
« Reply #19 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
« Last Edit: March 01, 2012, 02:03:58 PM by xarax »
This is not a knot.

Sweeney

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Re: Knots secure enough to trust with my life
« Reply #20 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

xarax

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Re: Knots secure enough to trust with my life
« Reply #21 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. 



« Last Edit: March 01, 2012, 07:47:21 PM by xarax »
This is not a knot.

Sweeney

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Re: Knots secure enough to trust with my life
« Reply #22 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

xarax

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Re: Knots secure enough to trust with my life
« Reply #23 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.  :)
« Last Edit: March 01, 2012, 11:09:28 PM by xarax »
This is not a knot.

Hrungnir

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Re: Knots secure enough to trust with my life
« Reply #24 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.


Dan_Lehman

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Re: Knots secure enough to trust with my life
« Reply #25 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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