Author Topic: Inherently secure knots  (Read 616 times)

mcjtom

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Inherently secure knots
« on: April 27, 2022, 04:40:32 AM »
Hello,

This question is for Mark mostly, and I apologize if it has been answered before.  What is the definition of an 'inherently secure knot', in short?  Is there a clear dividing line between the knots that are deemed to be inherently secure versus those that are not?

Many thanks!

roo

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Re: Inherently secure knots
« Reply #1 on: April 28, 2022, 12:46:24 AM »
Hello,

This question is for Mark mostly, and I apologize if it has been answered before.  What is the definition of an 'inherently secure knot', in short?  Is there a clear dividing line between the knots that are deemed to be inherently secure versus those that are not?

Many thanks!
The more you test knot security, the more you realize that security is situational.  Just for starters, you have to consider rope material, construction, size, age, stiffness, frictional characteristics, motion severity, motion duration, wetness, and the like.  Terms like "inherently secure" have a sense of absolutism that fails to align with reality.

I know "inherently secure" is a term Mark (agent smith) has used before, but I get a sense that he tends to avoid motion-based security trials from some concerning statements that have come up such as:

https://igkt.net/sm/index.php?topic=6773.msg44563#msg44563
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Dan_Lehman

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Re: Inherently secure knots
« Reply #2 on: May 03, 2022, 12:55:18 AM »
What is the definition of an 'inherently secure knot', in short?
Is there a clear dividing line between the knots that are deemed to be inherently secure versus those that are not?
The more you test knot security, the more you realize that security is situational.
Just for starters, you have to consider rope material, construction, size, age, stiffness,
frictional characteristics, motion severity, motion duration, wetness, and the like.

Terms like "inherently secure" have a sense of absolutism that fails to align with reality.
What Roo said, to a point.  Mark Gommers uses the term --defined
(introduced) the term-- in his paper on Bowlines; one may see it
thus as being asserted within some commonly recognized boundaries
of tied material --the importance of which Roo cites.

And one is there taking "knot" to mean "arrangement of material"
but really the assertion goes much to the material so arranged.

And his term denotes those knots for which one should not need
a further knotting to secure.
But, like Roo says, situations can be tricky on effects.  (Duration,
e.g., might be one --a slowwwwwly loosening knot crossing the
boundary w/o easy notice in quick'n'dirty testing --beware ratcheting!)

So, there's not a perspicuous dividing line;
there might be some reasonable classifications.

--dl*
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agent_smith

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Re: Inherently secure knots
« Reply #3 on: May 05, 2022, 04:49:34 AM »
Quote
What is the definition of an 'inherently secure knot', in short? 
Short as possible answer:
Context is important in developing an in-depth understanding.
The term 'inherently secure' exists within the realm of knots used in life critical applications.
You might then ask the natural question: "What is meant by life critical applications'?
The material used to tie a knot is also of paramount importance. And so, there are national/international standards for ropes/cordage used in life critical applications.
And so we are considering only a specific class of rope/cord - for example; human rated EN 892 and EN1891.
If a fisherman loses his fish on account of knot failure - death is not immediate.
You could tender an argument that the fisherman might go hungry... but there are also sporting fisherman who catch and release (ie don't eat their catch).
A mountaineer/rock climber faces the real prospect of death if a knot fails (eg a tie-in knot to the harness).
And so it is highly desirable to select and use a knot that will remain intact for the duration of the activity.
Which by definition requires the knot to be stable and secure - because if it weren't - the knot would be vulnerable to loosening during use.
The base geometric structure of inherently secure knots do not require additions (add-ons) to achieve stability and security.

Slightly longer answer: (Caution: Don't read if you dislike technical detail)
Knots used in life critical applications need to be secure and stable under the conditions encountered during use.
The MBS yield (ie strength) point of a knot is of little importance - security and stability matter more.
Rescue technicians will use ropes that conform to EN1891 or an 'equivalent' standard (eg NFPA 1983).
Rock climbers will use ropes that conform to EN892.
And so this is the material in which the knot is tied and used.
The essential characteristic of knots which are identified to be 'inherently secure' is that they are secure and stable and resistant to the effects of:
[ ] cyclic loading
[ ] slack shaking
[ ] impact loading
[ ] unusual loading profiles such as; transverse loading and circumferential loading (conditional with some knots eg, F8 not so good in transverse loading profile)

An example of an inherently secure knot is #1047 F8.
It is a secure & stable self supporting structure that also requires no additional tail maneuvers to lock down the structure to guard against loosening.
That is, #1047 F8 does not require the addition of a strangled double overhand knot around the SPart.
This particular knot has been used for several decades as a default tie-in knot for rock climbing. There has been no loss of life on account of arbitrary slippage and/or loosening of the F8 knot structure to the extent that it unravels and catastrophically fails while in the act of climbing.
F8 knots fail for other reasons - ie human error (eg the climber failed to tie the knot correctly).
They don't fail for no reason (again - the reason is due to human factors).
Driving a car is an analogy - human error accounts for the majority of road accidents/deaths.
Only a very small % of road accidents can be attributed to a wheel falling off, the brakes malfunctioning, or the engine blowing up (all of which are statistically unlikely).
It is more likely (than not) that human error causes car crashes.

User groups of life critical knots operate in situations that are not static. That is, the knots are employed in situations which are dynamic - in the sense that the knots are always subjected to motion/movement. Loads can be cycling, the knot can be subject to vibration, slack shaking, and sudden impact forces. And so the user needs to exercise care and due diligence when selecting a knot for this type of environment.

In my personal case, I have been rock climbing / mountaineering for more than 30 years. I also work as a rope access technician and a VR technician.
In all of these activities, knots are employed in dynamic situations where nothing is sitting perfectly still or existing in a motionless reference frame.
The consequences of error can be catastrophic - and so ones training, experience, and judgment are routinely called upon to minimize risk as far as reasonably possible.
I might select knot 'A' for a particular application, rather than knot 'B'. The reason behind a choice usually boils down to factors such as resistance to cyclic loads, slack shaking, and impulse/shock loading events (but there are other factors too - such as resistance to jamming - which does weigh on a technicians mind).

Quote
Is there a clear dividing line between the knots that are deemed to be inherently secure versus those that are not?
Short answer:
It depends on how you choose to define the 'dividing line' and how you choose to define the term 'inherently secure'.
As I indicated, the term 'inherently secure' exists within the context of life critical applications.
No rock climber would choose a shoe lace knot as a tie-in to his (and/or her) harness.
In contrast, its a perfectly reasonable proposition to choose a #1047 F8 knot as a tie-in knot to a harness.
We have ample empirical and non empirical evidence which indicates #1047 F8 is secure and stable (and by definition, resistant to slack shaking and cyclic loading).
I would argue that using a shoe lace knot is an unreasonable proposition - and one that could have catastrophic consequences.

Long answer (Caution: Don't read unless you like to dive deeper into technical details):

It is true to state that there are no universally agreed standardized tests to measure a knots resistance to slack shaking, cyclic loading, and vibration.
That is, I can't point you to an EN or ANSI standard which precisely defines how a test must be carried out to measure the effects of these types of loading profiles.
One can however, attempt to subject knots to these loads and observe what happens (in a home brew / backyard type test environment).
We can subject #1047 F8 to a battery of such 'backyard' tests - and observe what happens.
Of course, what is the appropriate duration (ie time frame) that the knot must remain intact to 'pass' such a test?
Is it 5 minutes? 10 minutes? 1 hour? 1 day? 1 year?
Lets say we choose 1 year.
That is, a knot must remain intact after subjecting it to vigorous slack shaking for a period of 1 year. If it loosens and unravels after 364 days, it has, by definition, failed the test.
Is that a reasonable test parameter?
One could then raise the perfectly reasonable question - how long is long enough? eg Is two (2) hours sufficient?
Well - how long is a typical single pitch lead climber on route?
How long is a typical multi pitch lead climber on route? (eg how many pitches constitutes a 'typical' multi pitch route).
How frequently do climbers check their knots while in the act of climbing?
It might be a perfectly reasonable proposition to say that a climber should re-check his knots after every fall - and upon reaching the relative security of a belay station.
And so one could state that climbers should check their knots on an ongoing basis - rather that simply tying a knot at the start of an activity and then completely forgetting about it.
But, to account for human factors and incompetence, we might say that a knot should remain intact for a 'long period of time' - at least for the duration of the activity.
What is a measure of 'vigorous' slack shaking? How vigorous does one need to be to qualify as sufficiently vigorous?
And how many different types/brands of EN892 and EN1891 rope must be tested.
These are all big questions.

I personally have no difficulty declaring #1047 F8 to be an 'inherently secure' knot (when tied in human rated EN rope).
But there are qualifying remarks to this declaration:
[ ] that the knot is consistently and diligently tied to match the geometric detail of a #1047 F8 knot
[ ] that a competent person ties the knot
[ ] that the knot is dressed and cinched tight
[ ] that the knot is checked before absolute reliance is placed upon it
[ ] that the checking process in fact, verifies all of the above!
(Note: this presents challenges for the solo climber - obviously there is no one else to do any checking and/or verifying! A solo climber must be consciously competent).

These qualifiers are perfectly reasonable in my view.
And trainers/assessors apply this doctrine when offering their instructional services.

It is interesting to note that EN892 specifies #1047 F8 in its content.
That is, EN892 requires #1047 F8 knot to used to attach the test mass to the sample rope which is then subjected to quite violent impact forces.

Whilst I have used #1047 F8 as an example in my narrative - there are other knot species which also qualify for the title of 'inherently secure'.
We know (for example) that #1010 simple Bowline is not inherently secure.
Few 'reasonable' people would argue this point.
And so climbers don't tie-in with #1010 simple Bowline.

But, there are some 'Bowlines' that are 'inherently secure'.
One such example is the 'EBSB Bowline'.
I have personally field tested this knot for more than 10 years in lead climbing, rope access, and VR applications.
I therefore have empirically derived evidence that indicates this knot is stable and secure in a variety of loading profiles - it does not unravel and arbitrarily fail.
I will admit that i haven't subjected the EBSB to slack shaking for a continuous period of 365 days (ie 24/7 round the clock continuous slack shaking for 365 days).
I have performed such a test for 10 continuous minutes - until my arm faded from fatigue. After 10 minutes of vigorous shaking, I could detect no loosening or unraveling of the knot.
Should I increase that duration to 20 minutes? (both slack shaking and cyclic loading).
How long is long enough?

I would invite you to perform such a test.
Tie an EBSB Bowline and subject it to vigorous slack shaking for a continuous period of 20 minutes.
Of course, you need to use EN892 or EN1891 rope with a diligently tied knot as a test article.
It would be interesting to see what results you obtain...
« Last Edit: May 06, 2022, 12:38:34 AM by agent_smith »