Author Topic: Knot test video (From How Not to Highline Youtube)  (Read 580 times)

agent_smith

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Knot test video (From How Not to Highline Youtube)
« on: August 30, 2021, 04:21:19 AM »
Video link: https://www.youtube.com/watch?v=dagg2-If4h8
Release date: August 25, 2021

Author / principle tester: Ryan Jenks
Youtube channel: How not to Highline

I've already posted my feedback directly on his youtube channel.

Critical feedback commentary:


Hello Ryan - thanks for the effort and time to produce this video - it is appreciated.
I've got some technical feedback for you - all given in good faith.

Giving technical feedback is risky - because it may be perceived as insulting and calculated to cause offense.
No matter what you say or write, there will always be individuals who will retaliate.
I am hoping that you will receive this in the spirit in which it is intended - in good faith :)

For clarity, listed in point form.

1. The principle concept behind your knot tests is the default mindset of 'pull-it-till-it-breaks'.
What do these types of tests actually prove?
What insights did it reveal?
All knot testers around the world appear to have a default mindset of 'pull-it-till-it-breaks' - and then pop the champagne cork, publish the results and celebrate.
I am not sure if this mindset will ever change in my lifetime?
Although there was a refreshing change with the 'Hard is Easy' Youtube video on #1047 F8 jamming tests (although he made many mistakes - and never used a load cell to measure the peak loads he achieved).

If you insist on pure MBS yield tests (ie 'pull-it-till-breaks' default mindset) - you should be examining just one variable against a 'control' - and the purpose should be to investigate the effect of a geometric change in the knot structure (particularly with 'Bowlines' - and the effect of increasing the number of rope diameters inside the 'nipping loop')

2. You need to let your viewers fully identify the knot specimens - and in particular - exactly how you tied them (ie, the precise geometry and dressing state).
from 4:15 - 5:40 we get a preview of the knot specimens. I found it too quick and the camera movements too fast to actually be able to check the precise geometry you tied with each specimen. I tried pausing your video and going full screen with a large monitor - and it still wasn't easy.
Slow it down - give the viewer time to verify your knot geometries (at least so we can pause and go full screen).
It also appears that you didn't pay close attention to the dressing states of the F8 eye knots - but the camera movement was too fast - and pausing the video still didn't give me a chance to verify exactly how you tied the F8 knots. I had to go back and do forensics on your Zeppelin eye knots (ie 'loops') - I wasn't able to check all of your Zepplin eye knot specimens.

3. The Sheet bend at 5:39 is tied incorrectly.

4. At 5:41 - the load testing commences.

5. From 5:41 - 7:15 was all Zeppelin eye knot MBS yield tests. Camera movements too fast to check knot geometries.
At 6:14 the camera finally stopped moving just long enough to pause and examine the knot specimen.
At 6:26 - after another MBS yield test, the 'half-hitch 'stopper' knot is shown - which is a completely worthless addition (stop adding this worthless hitch - it serves no useful role).

What did you learn from the Zep eye knot tests?
It is good that you test 2 Zep eye knots simultaneously (one at each end termination).
You missed an opportunity to show the audience that the surviving Zep eye knot did not jam - ie, that it can be untied by hand (no tools required to loosen the knot).
When testing 2 knots simultaneously, you will always have one 'survivor'. You need to carefully examine the surviving knot specimen - because it will have been loaded right up to its MBS yield point.

6. Next comes the #1053 Butterfly eye knot tests at 7:16.
The loading profile is off nominal for this knot.
The way in which you are loading the 'eye' of the Butterfly is not how it was intended to be used.
If you are going to tie a Butterfly eye knot as a fixed eye knot end-of-line, you should use the 'Mobius Butterfly' or one of the other derived Butterfly eye knots (they are derived from the Butterfly bend).

All 'bends' have 4 corresponding eye knots (within a chiral domain).
For example, the Butterfly bend has 4 corresponding eye knots - one of which is the #1053 Butterfly (drop the use of the prefix 'Alpine').

The #1053 Butterfly perform best in a BTL (biaxial through loading) profile. That is, load passes through the knot core from SPart-to-Spart. In this loading profile, the eye is isolated from load.
Eye loading is not so good - in fact, once a certain load threshold is reached - the Butterfly jams. In a 'BTL' loading profile, the Butterfly is jam resistant.
It would have been good to demonstrate this to your audience.
Also, keep in mind that the Butterfly is a TIB knot (Tiable In the Bight).
The Zeppelin eye knot is not 'TIB'.

7. At 8:20, MBS yield testing of #1047 F8 eye knot commences.
You missed an opportunity to test 2 different geometries (per 'Hard is Easy' F8 jamming video).
Pulling a knot till it breaks proves nothing... what you could have done is probed the jamming threshold of the F8 in different geometries.
I would also point out that there is no load that a sole rock climber can achieve that will ever reach a knots MBS yield point. For example, tying-in with a #1047 F8 is perfectly 'safe' - there is no fall that will ever break the tie-in knot. So why bother doing the default mindset of 'pull-it-till-it-breaks'? Better investment of your time and money to is to investigate jamming thresholds.
And again, forget the half-hitch 'backup knots' - they are pointless - and in fact interfere with your tests. For example, you could investigate tail slippage (ie mark the tail position - and measure any creep/slippage as load is increased - and report this).

I would also point out that there are in fact 4 different axial through loading profiles for the #1411 F8 bend (refer image below).
It would have been instructive to load test each of these profiles and draw conclusions from the results (eg jamming thresholds, stability, and yes, MBS yield comparison).

8. At 9:59 the 'Bowline' tests commence.
You are testing the #1010 Simple Bowline.
Note that this really should be the 'control'.
You missed an opportunity to test the 'inherently secure' Bowlines (eg EBSB Bowline, Lees Link Bowline and Harry Butlers Yosemite Bowline).
Furthermore, you missed the opportunity to test the effect of adding more rope diameters inside the nipping loop.

At 10:13, we see why it is important to mark your test specimens (with a marker pen).
There was no way to accurately determine what occurred - because there are no reference marks to reference against.
Mark your knots specimens - and then you can carefully observe the 'surviving' knot specimen - to see what has happened.
All you are doing is 'pulling-it-till-it-breaks' - and any real science is simply lost.

9. At 11:33 it appears that the #1415 Double fishermans bend is tied incorrectly (but again - there is little opportunity for viewers to check the geometry carefully.
Furthermore, you should test 2 knots specimens in this round sling configuration (one either side). This tactic also helps to alleviate unequal movement of the rope (the knot compresses and the rate of rope movement on one side of the round sling is different to the opposite side).

10. At 11:49 the Zeppelin bend is tested.
Once again, you need to tie 2 Zeppelin bend knots - one either side of the round sling.
And remember, you will always have a survivor knot specimen to examine.
Furthermore, you can show the viewers that the surviving knot can still be untied - even though it was loaded right up to its MBS yield point!
So this is another missed opportunity. (due to the 'pull-it-till-it-breaks' mindset).

11. At 12:16 you commence testing the Butterfly bend (again tied as a round sling).
Same issues as before (need 2 identically tied Butterfly bend knots - one either side).
At 12:30 - we get to see the knot from the 'overlapping' side. All Butterfly knots have a 'S' side and a 'Z' side.
Look closely, and you will see different rates of slippage on one side of the bend compared to the opposite side.
In the video - 'S' is on the left and 'Z' is on the right.
Unfortunately, its all over too quickly and the opportunity was missed (because the mindset is only on 'pull-it-till-it-breaks').

At 12:41 we can see that the knot is sloppily tied.
At 13:01 - this is not a 'Butterfly bend' - it is some kind of variation - and you need to let the viewer scrutinize the exact geometry.

12. At 14:29 you commence testing the #1411 F8 bend (don't call it a Flemish bend - the history of this is unclear and dubious). It is an F8 bend.
The geometry is asymmetric - could have been dressed to ideal symmetry.
Once again - you missed an opportunity to alter the relative position of the SPart rope segments (per 'Hard is Easy' F8 jam test videos).
You could have tied a 'control' #1411 and compared it to another #1411 with the SParts re-arranged.

13. At 15:08 you commence testing the Sheet bend (#1431).
It is tied incorrectly.
You could tie the correct Sheet bend and use it as a 'control' to compare against the version you tied.

14: At 16:20 you test the #1053 Butterfly tied within a round sling.
The #1415 Double Fishermans is tied incorrectly.
We see that the eye of the Butterfly slips - should have marked each side with a marker pen to compare rates of rope slippage. You could report the any differences observed (there is always a 'S' side and a 'Z' side with all Butterfly knots).
Would be good to see eye loading of a Butterfly (on both 'S' side and 'Z' side - and compare against 'control').

...

There's a lot of feedback here for you Ryan.
I think you are missing a lot of valuable science because of the narrow focus of MBS yield testing (ie pull-it-till-it-breaks).
There are so many other more interesting aspects to examine (eg jamming thresholds, instability thresholds, tail slippage/security, etc).

I'm hoping that you can take onboard some of my feedback for future knot testing?
« Last Edit: September 01, 2021, 04:40:37 AM by agent_smith »