This post is directed at Derek:
# Also - apologies, my post is off-topic. But since Derek has chosen to direct his intentions toward me, I am choosing to respond in kind.
In reply:
Your fixation with "basic '101' rules of testing" seems to have led you to missing the point of the work which is encapsulated by the term 'Comparative'.
I'm unclear of the underlying intent behind the typed word "fixation".
Maybe you are
fixated on something else?
One of the so called '101' rules that you allude to is
repeatability.
As 'Ben' was publishing his test to the 'world', he does a have a basic duty to get the 101 rules correct.
No one can repeat his tests with certainty and be confident of their results - partly because we have no idea of the type of test article and the force he generated.
It is a 101 basic concept that a force is being generated - and there is a level of force which triggers the initial threshold jamming state of a #1047 F8 knot.
I would also point out that the definition of 'jamming' was not fully described/quantified (see below at end of my post).
No load cell was needed because both knots were subject to the same loading.
?
This statement is non-sensical.
Presumably, I could conclude from your premise that any type of knot test setup that involves 2 knots doesn't require measurement of force.
eg test on say #1053 derived Butterfly bend to probe threshold jamming state requires no measurement - we could just guess the loads generated?
It raises the the question; what is the point of measurement? Testing normally involves measurement of some type - so it is repeatable by others.
And; what is the
difference in level of force require to reach threshold jamming state of knot 'A' versus knot 'B'? Is the difference statistically significant?
Again,no additional value is obtained from knowing the value of the drop mass, nor it's fall, nor any initial velocity imparted at dispatch, nor the elasticity of the attaching connections
?
As above.
It raises the question: What is the value of measuring force? In other words - anyone can publish test results without specifying the peak loads they reached.
I of course think this would create an odd situation - if all testers published their results without specifying force.
eg "I picked up a mass in my hands and dropped it...now all of you other testers around the world can try and repeat my results! And by the way, try and guess what type of rope i used!"
Unless I have missed something
Your fixation on me has misled you, and caused you to miss many basic 101 rules of testing.
eg... What type of rope was used in the test? What was the drop mass? What was the peak load?
And, he should have tied identical knots at each end (not mix 2 different geometries).
This a completely legitimate first order comparison and will yield unambiguous data. However, had the system under study needed to reflect two interacting variables...
I disagree.
As a rule, only one variable should be tested.
With identically tied knot specimens at each end, you have the ability to compare each knot.
One is attached to a fixed anchor point, and the other is attached to a moving mass of unknown quantity.
We are robbed from seeing the comparison between the 2 identical knots - in terms of their individual response to load.
Again, you have missed the point that it is the knot configuration that is under test, not its substrate.
Again - I think you have missed some basic rules of testing. That is, specify the parameters of the test article. Why make it a guessing game?
It seems that you have no concept that climbing ropes are highly variable in their performance?
I am quite shocked by your apparent lack of knowledge.
For example, are you are aware of the EN892 specification? Are you aware that in each of the 3 sub-categories of dynamic rope, there is great variance in rope diameter, core construction, sheath construction, stiffness and elongation?
therefore any climbing rope should have sufficed.
This is a nonsensical statement.
See above - there is huge variance between climbing ropes.
Furthermore, in the case of 'twin' or 'half' ropes, it is a requirement that 2 ropes are tied into the climbers harness.
That is, there are 2 ropes which are each subject to load.
Presumably, the tester 'assumed' the case of a 'single' category - and ignored the other 2 cases?
Even if he ignored the other 2 cases, there is still the fact that a climbing rope is tied directly into the harness - which captures the bridge of the leg loops and the waist loop - which provides both stretch and a larger contact angle.
............
Overall, on the surface it appears as a seemingly odd post by Derek.
But what is the underlying intent?
What kind of message does it send to knot testers around the world?
In a general browse of the myriad of knot test papers and videos, it is very rare to find published work that omits things such as the type of test article, the loads that were achieved and the mass that was used to achieve those loads.
My own theory is that it is youtube phenomena - anyone can become a tester and 'publish'.
Note: I do encourage people to test! Testing is good.
Just try to test in a way that makes it easy for others to try to
repeat the results.
And at least try to give an indication of the type of rope that was tested and the force that was generated.
Here's 2 really simple questions:1. What is the magnitude of the force required to reach the threshold jamming state of a #1047 F8 knot tied in EN892 (single category) rope of 9.1mm nominal diameter - tied in specific way
#1 (image given to reveal precise geometry)?
2. What is the magnitude of the force required to reach the threshold jamming state of a #1047 F8 knot tied in EN892 (single category) rope of 9.1mm nominal diameter - tied in specific way
#2 (image given to reveal precise geometry)?
NOTE: 9.1mm diameter dynamic rope is the average (mean) diameter in common use with rock climbers.
Although I have to admit that Beal (France) are great innovators in rope technology - take for example their 'Opera' EN892 8.5mm diameter rope - which is certified across all 3 categories of EN892. Such a thin rope (8.5mm) is pushing the envelope - and it also uses bonded 'unicore' which would be interesting to test and compere to a non-bonded sheath/core interface. Again - we don't have any peer reviewed test data on how these unicore ropes compare to non unicore copes (in terms of jamming threshold). I have no clue as to what type of rope 'Ben' tested in his video - its a guessing game (unless he's updated his video or added commentary since I last checked??).
Jamming definitions given as follows:[ ] Threshold jamming state: The knot can eventually be loosened and untied by hand (without the use of tools) - but only after
considerable effort and time.
[ ] Maximal jamming state: Loosening the knot is beyond the level of human hand strength - tools are required to loosen the knot (but damage will be
negligible/trivial).
[ ] Irreversible jamming state: The knot is fused/welded and cannot be loosened and untied without causing severe and permanent damage (due to the use of tools and considerable force)