Author Topic: Knot Test Report: #1425A derived Riggers X bend (resistance to jamming) 1/3  (Read 2876 times)

agent_smith

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TEST REPORT  Part 1 of 3

Knot specimens (test articles):
#1425A derived Riggers X bend (aka Hunters X bend)... hereinafter referred to as 'Riggers X bend'
#1425A Riggers bend (aka Hunters bend)

Test objectives:
1. To determine if an 'X' (crossed tails) modification to #1425A Riggers/Hunters bend will transform it into a jam resistant bend.
2. If Riggers X bend is vulnerable to jamming, to determine the load threshold at which jamming is triggered.
3. To determine if Riggers X bend is less vulnerable to jamming compared to a 'control'  = #1425A Riggers/Hunters bend.

Type of rope/cord material:

3 different types of rope were used as follows...

[ ] Manufacturer: Sterling USA
[ ] Type: EN564 accessory cord
[ ] Diameter: 8.0mm
[ ] Rated MBS: 15.6kN (3506 lbs)
[ ] Condition of cord: near new - had been used only a few times.

[ ] Manufacturer: Bluewater USA
[ ] Type: EN1891 (type A) low stretch abseil rope
[ ] Diameter: 11.4 mm (7/16 inch)
[ ] Rated MBS: 35.3kN (7935 lbs)
[ ] Condition of rope: old (10 years) - had been used many times - had become stiff

[ ] Manufacturer: Edelrid 'Safety Super' (Germany)
[ ] Type: EN1891 (type A) low stretch abseil rope
[ ] Diameter: 11.0 mm (7/16 inch)
[ ] Rated MBS: 30.0kN (6744 lbs)
[ ] Condition of rope: old (10 years) - but rarely used - in excellent condition (not stiff)

Tester: Mark Gommers
Test date: 26 July 2018
Tester classification: Hobbyist/Enthusiast tester

Test Environment:
[ ] Outdoors - in my 'backyard'
[ ] Ambient temperature: 24 degrees C
[ ] Relative Humidity: 50%
[ ] Rope moisture content: Dry
[ ] Townsville weather report: http://www.weatherzone.com.au/qld/lower-burdekin/townsville


Test equipment:
[ ] Load cell (tension type... Dynafor 5 ton)
[ ] 2 ton 'lever hoist' was used to apply force
[ ] 2 sturdy trees were used in my 'backyard' as end termination anchors

Sterling 8.0mm diameter accessory cord (EN564) results:
[ ] At 1.0kN load: no jamming
[ ] At 2.0kN load: no jamming
[ ] At 3.0kN load: no jamming
[ ] At 4.0kN load: no jamming
[ ] At 5.0kN load: no jamming
[ ] At 6.0kN load: no jamming
[ ] At 7.0kN load: no jamming (but some effort to loosen collar on same side as lever hoist)
[ ] At 8.0kN load: no jamming (but some effort to loosen collar on same side as lever hoist)


'Bluewater II' 11.0mm diameter low stretch abseil rope (EN1891 type A) results:
[ ] At 3.0kN load: no jamming
[ ] At 8.0kN load: no jamming
[ ] At 10.0kN load: Bluewater II joined to Edelrid 'Safety Super' rope Jammed!
[ ] At 10.0kN load: Bluewater II-joined to-Bluewater II no jamming
[ ] At 12.0kN load (33% of MBS): Bluewater II-joined to-Bluewater II Jammed!

Control
Knot: #1425A Riggers bend (aka Hunters bend)
Rope: Bluewater II joined to Bluewater II (11.4mm)
[ ] At 1.0kN load: no jamming
[ ] At 2.0kN load: no jamming
[ ] At 3.0kN load: no jamming
[ ] At 4.0kN load (11% of MBS): Jammed


Assumptions:
Two different jamming states are identified as follows:
1. Initial/threshold jammed state: It is not possible to untie the knot by hand - tools are required.
2. Maximally jammed state: Even tools will not loosen the knot - the core has compressed to the point where it is virtually fused.

Observations:
With the Sterling 8.0mm cord, at loads up to 6.0kN, I had no difficulty loosening the knot.
After 7.0kN load (approx. 45% of MBS) - I was able to untie the knot in less than 1 minute without use of tools. I was able to immediately loosen one collar but, the opposite collar on the same side as the lever hoist required some effort to loosen.
After 8.0kN loading, the knot in the Sterling 8.0mm cord had the consistency of 'iron' - but I was able to loosen one collar after a small effort. The opposite collar on the same side as the lever hoist took about 30 seconds of effort to loosen. At no time did I resort to use of tools.

In contrast, with the 11.0mm Bluewater rope, I had no difficulty untying the knot after reaching 8.0kN.
There were some 'creaking' sounds as load was increased - likely due to the stiffness of the rope.
With the dissimilar join created using Bluewater rope joined to Edelrid rope, the knot jammed at 10.0kN load. One collar was easily loosened. The other (opposite) collar on the side of the lever hoist was jammed.
I repeated the test using identical ropes to form the join (Bluewater II joined to Bluewater II) as follows:
[ ] At 10.0kN load: No jamming
[ ] At 12.0kN load: Jammed.

Statistical sampling:
This was a sample of one (1) test at each load milestone for each of the cords/ropes.
The same rope and knot were used for each load milestone.
Load was released after reaching each load milestone to confirm if the knot could be untied.
Load was then re-applied to reach the next higher milestone (rinse and repeat!).

...

Conclusion:
For Sterling 8.0mm cord:
At loads up to 51% MBS, this knot is jam resistant.
Further testing at higher loads is necessary to determine if jamming occurs.

For Bluewater II (11.4mm) low stretch abseil rope:
At loads up to approximately 25% MBS, this knot is jam resistant.
At 10.0kN load (approximately 28% of MBS), the knot jammed when using 2 different ropes of same diameter were used - Bluewater joined to Edelrid).
At 12.0kN load (approximately 33% of MBS), the knot jammed (using Bluewater II joined to Bluewater II).

At only 4.0kN load, #1425A Riggers bend (aka Hunters bend) jammed.
Based on my testing, I can state that crossing the tails of #1425A Riggers bend (to create Riggers X bend) improves its resistance to jamming (but only up to the threshold of 12kN).

Based on these tests, I would like to advance a theory.
It is my view that the tension force expressed as a % of rope MBS is not the key factor.
It is the direct amount of tension force that is key.
In both types of rope material, 8.0kN tension force was insufficient to reach the jamming threshold of Riggers X bend.
At 12.0kN, jamming occurred in the thicker 11mm rope. I suspect the same situation will occur in with the Sterling 8mm cord.

An unexpected observation as a result of my testing indicated that the collar on the same side as the lever hoist (ie force generating machine) was significantly more difficult to loosen and untie - and indeed, one initial/threshold jamming has been reached, it was the collar facing the lever hoist that was jammed.

It is open for other testers to confirm or refute this theory.
« Last Edit: August 20, 2018, 01:29:24 AM by agent_smith »