Author Topic: ITRS report on Bowline testing  (Read 3588 times)

agent_smith

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ITRS report on Bowline testing
« on: November 23, 2019, 06:20:06 AM »
Link to ITRS test report on some different 'Bowlines'.

http://itrsonline.org/wordpress/wp-content/uploads/2019/10/Byrne_Boutique-Bowlines.2019.pdf

Test report details:
Author: Kelly Byrne
Dated: Nov 01, 2019

Of interest to me is that he tested #1074 Bowline with a bight - which is a type of Bowline that is TIB and can be biaxially loaded.
It also has 4 rope diameters inside the nipping loop.

Mr Byrne did obtain my paper on Bowlines and he has attempted to extract a definition of what a 'Bowline' is.
He attempted to cite 3 criteria for determining if a knot structure can be deserving of the title of 'Bowline' but, with some deviation.

The 2 legs of the collar do not need to project along a parallel trajectory when entering the 'nipping loop'.
What I think he was trying to write was the the 2 legs of the collar should enter the nipping loop from the same side (as per #1010 simple Bowline).
But, this is not a requirement - because the 2 legs of the collar can enter the nipping loop from opposite directions (per 'Myrtle' type structures and indeed #1033 Carrick loop Bowline).

In any case, he has gone down the same well trodden path as virtually all of his predecessors with the default mindset of 'slowly-pull-it-till-it-breaks' mentality.
There doesn't appear to be any original thought patterns that deviate from this type of thinking.

A 'control' is glaringly missing from his test data.

I my opinion, he ought to have used #1010 Simple Bowline as the experimental control.
The absence of any declared 'control' is a common theme with virtually all knot testers.

In any case, his test results on #1074 'Bowline with a bight' are of great interest.

Future testers should investigate the effect of increasing the number of rope diameters inside the nipping loop.
Examples of a sequence:
[ ] #1010 simple Bowline - 2 rope diameters inside nipping loop.
[ ] #1010 simple Bowline (slipped) - 3 rope diameters inside nipping loop.
[ ] #1074 Bowline with a bight - 4 rope diameters inside nipping loop.
and so on...


Based on Mr Byrne's test results, a Bowline with 4 rope diameters inside the nipping loop boosted the MBS yield by approximately 76% as compared to a nominal 2 rope diameters with a 'Yosemite Bowline'.
Follow up testing needs to be done to confirm if the number of rope diameters inside the nipping loop consistently boosts the MBS yield.
Mr Byrne's results constitute a statistical sample of just one person's report...we need more people doing follow up tests.

EDIT NOTE:
There is something peculiar in some of the reported results...with the triple Bowline being reported as having a MBS yield higher than the actual MBS of the rope it was tied in!
Also, the test configuration is somewhat of a mystery...would have been helpful to have clear photos or diagrams showing precisely how the knots were tested.
« Last Edit: November 24, 2019, 02:41:42 AM by agent_smith »

SS369

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Re: ITRS report on Bowline testing
« Reply #1 on: November 23, 2019, 07:34:02 PM »
Thanks Mark.

"Conclusions
The group of bowlines tested appear to be suitable for rescue work in regards to breaking strength as well as cyclic loading.  Three broad generalizations that can be made in observing the test data:

1.When loaded from the fixed loop to the standing end of the rope, the bowlines tested showed ≈ 30 - 40% strength reduction; which is in line with available results on bowline tests.  Having more strands inside of the nipping loop, such as with the Triple Bowline with a bight, do increase the strength a bit when pulled from fixed loop to standing end.

2.   When loaded from fixed loop to a forward facing bight from a Yosemite, there is almost always a higher breaking strength than unknotted rope. This makes as the force of the load is more evenly distributed across more strands of rope.

3.Well set bowlines that get loaded, appear to have very minimal slippage."

I am confused by the Second conclusion. Firstly, the arrangement described?
Secondly, is the knotted rope truly stronger than the unknotted rope??\

I kind of wished there had been some photos of the test, not just the equipment doing nothing.

For my own cyclic tests, I generally take a rope with the knot(s) to be examined, stretched between two anchors (trees in my case, can be around the tree or to carabiner /slings) and bounce on the middle. I know this is not scientific,but for my personal use, this tells me if I can trust or not.

Not sure that I am impressed by the test report/conclusions, but at least it was done.

SS

agent_smith

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Re: ITRS report on Bowline testing
« Reply #2 on: November 24, 2019, 02:33:35 AM »
per Scott:

I agree in that there is something peculiar with the way in which some tests were conducted.
Also,  it is very peculiar that a triple Bowline ended up having an MBS yield higher than the actual MBS yield of the rope itself! This can't be correct.
[ ] MBS of Sterling HTP 11mm rope = 7568 lbs (33.7kN)
[ ] MBS yield of triple Bowline (as reported) = 10,750 lbs !
I have never known any knot to have a higher MBS yield than the actual MBS of the rope it was tied in.

Also, I am somewhat confused about the loading profile stated as:
"pulled from fixed loop to forward facing bight"

As with most knot test reports, there is no clear photo or diagram showing precisely how that knots were tested.
It appears that some Bowlines were loaded from the fixed eye at one end, and the other end was loaded at the bight which forms the tail end. In other words, they attached the connector of the force generating machine to the 'tail'.
If so, this is most peculiar and in my opinion, 'wrong' (see attached photo for a more appropriate type of knot which enables multi-directional loading profiles).
Another alternative is to use a termination knot such as a tensionless hitch tied directly to the anchorage point.

Loading profile should be:
[ ] attach connector/pin to the fixed eye of the knot
[ ] attach the SPart to a pin/bollard using a tensionless hitch
« Last Edit: November 26, 2019, 03:24:30 AM by agent_smith »

Dan_Lehman

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Re: ITRS report on Bowline testing
« Reply #3 on: November 26, 2019, 02:54:50 AM »
Also, I am somewhat confused about the loading profile stated as:
"pulled from fixed loop to forward facing bight"
It is : the BWL WITH a bight (hence, all doubled parts)
and the tail (i.e., the bight end) does the "Yosemite"
finish (i.e., makes a Fig.8),
and this bight end is loaded opposite the knot eye
--or, to put it per intended use, eye-vs-eye (which
makes me wonder what the SPart is doing, but I
guess some other task).

So, yes, each end of the specimen is an eye,
each leg of eye holds 50%,
and then these parts go into a knot :: and one
should expect that this is stronger than were
some single strand isolated in the tensioned item.
(Kinda akin to folding rope into an ends-overlapping
round sling and knotting the overlapping area.)


 - - - - - - -

Now, to the question of knotted cordage being "stronger...",
there was a case where some guy who did a lot of angling
knots testing had results where Bimini Twists tested higher
than the pure line.  I'm unsure where the breaks came:
e.g., did the knots break, but at (surprise!) higher force,
or did the line-outside of knot break, and at higher force!?
And where did "pure" line break (at pins?).

PURE MUSING :: If specimens are same length, and eye
substantial of that length, and test device has constant
DISTANCE rate of movement,
then the lesser and more elastic (than doubled parts)
pure line will later see high force than in the knotted
specimen; if lonnnnger rise brings on fatigue, maybe
an unknotted line could break at a lower --but longer
experienced?-- load?!?!
AGAIN, PURE MUSING.
This angler guy did have the wit to recognize the
oddity of his results, not just report them w/o remark.


--dl*
====

agent_smith

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Re: ITRS report on Bowline testing
« Reply #4 on: November 26, 2019, 03:32:26 AM »
In my view, the use of the 'forward facing bight' (eye) of a Bowline seems to be redundant and dare I suggest it...non-sensical!
I say this because there are more effective anchoring solutions for vertical rescue teams.
For example, a 'wrap 3-pull 2' is very effective because it enables multi-directional loading and due to the capstan effect, it resists jamming.

The concept of attaching to a 'forward facing eye' is essentially creating a 'soft chain' / 'soft link'.
It seems redundant to do this when alternatives such as a 'rigging plate' and/or a wrap 3-pull 2 is available.

In vertical rescue, rigging plates are common and universal in application.
« Last Edit: November 26, 2019, 03:33:43 AM by agent_smith »