Request for follow up testing of Figure 9 eye knot

Knotting Concepts & Explorations
1

As the title is suggesting…

I am requesting assistance in relation to following up testing of the figure 9 eye knot (F9).
In particular, I am seeking data points for the following:

  1. Jamming threshold
  2. MBS yield

The control would be #1047 F8.

I have already done a round of tests which demonstrated that the F9 is more vulnerable to jamming than the F8.
This needs to be followed up with further testing to either confirm or refute the results.
There has been a long held belief that the F9 has a higher jamming threshold than the F8. My initial tests show otherwise.

Also, another long held belief in the rope access industry (particularly by IRATA - a UK based organisation) that the F9 has a higher MBS yield.
IRATA actively promotes and teaches the F9 to rope access trainees as a better alternative to the F8 - based on the belief that it is both jam resistant and stronger than the F8.

My intent is to do some myth busting…because I am of the view that these beliefs may not hold true.
Further testing is needed to prove or disprove these allegations.

This matter is rather urgent…

EDIT: I have added some images showing various test rig setups… normally, in professional labs, all force is injected from one side.
In the bottom image, I have never seen this type of setup (but I assume it is possible).

Roo’s post leaves me thinking that there are in fact several different test rig setups. And, in most knot test reports, the actual configuration of the test rig is usually omitted (it has always been assumed knowledge). My view is that the default mindset where force is injected only from one side - is a valid method.
However, I am not so sure of the other 2 configurations I have identified…

Knot_Test_Rig.jpg

2

Regarding your requirement to “inject” force on one side only, you are asking the impossible. For any static system to keep from accelerating out of control, the summation of forces in any direction has to be zero. There is a very real reaction force at the restraint.

In free body diagrams for science or engineering, the applied forces are treated no differently than reaction forces that balance them out. If you apply 1000 lbs at one end of rope, the other end will also have to apply 1000 lbs to stay balanced, and it makes no difference if this balancing force is applied by a weight, an immovable object or a mechanism.

I know for some, this isn’t intuitive. Even the act of standing on the ground means that the ground must push up on you equal to the force of you pushing down on the ground, or you will sink into the ground until the forces balance out.

3

per roo:

Regarding your requirement to "inject" force on one side only, you are asking the [b]impossible[/b].

?

Refer my attached image in my original post.

Impossible? Hardly.

You might not fully understand what the word ‘inject’ means.

In knot test rigs, the force generating machine is typically located on one side of the test rig. it ‘injects’ the force from one side.
Imagine a test rig where you have two (2) force generating machines - one at each end.
Now imagine that both force generating machines are injecting force simultaneously from both sides…

In a test rig, a human normally sets it up and commands the force generating machine to commence injecting force.
Enthusiast/Hobbyist testers will normally use a hand operated winch (eg a lever hoist) - and it will be installed on one side.

4

I’m including a sketch of three test rigs pulling a blue rope by expanding the red actuators. In all three cases force is applied equally to both sides. It is unavoidable. Forces must balance to keep the system from accelerating.

5

@ Mark,

You are loosing it on this one. By questioning basic physics you are making yourself out to be an uneducated idiot and putting the data and conclusions you are generating into question. Nobody is going to take your reports seriously if you persist in publicly demonstrating that you do not understand basic physics.

You and I have disagreed on several issues, to the point where I have refused to endorse your reports and insisted that you remove my name from them. Those issues were of a more subjective nature than this. But this is factual physics. You have had this explained to you by several people, yet you still persist in drawing ‘Anchors’ as if they exist in isolation from the other anchor behind the load source.

You have statistically significant evidence that your test rig has a bias towards causing early breakage at the load actuating end of your test rig - but this HAS to be due to some artefact of your test rig design - I urge you to attempt to identify this artefact, or eliminate its relevance, rather than persisting in demonstrating your ignorance of basic school level physics.

I am an Analyst and have spent my career identifying and eliminating testing biases. So here is a suggestion :-

Arrange your test rig so that the loops of both test knots pass over a common bar at your static anchor, then pass the mid point of the connecting cordage around a mandrill attached to your moving anchor. This way, any artefacts induced by the moving end will be applied equally to each knot and will not lead to the generation of a ‘load end’ bias. The downside is that it will double the force you need to be able to apply and measure…

Derek

6

On a separate issue - why are you testing one knot against itself?

http://igkt.net/sm/index.php?action=dlattach;topic=6329.0;attach=23621;image

Do you not realise that you are only testing one of those knots - the weakest. You determine nothing about the other knot other than that it is stronger. Granted, you are creating a ‘reference’ sample that can be used to evaluate jamming prior to the other knot breaking, but this comes at the cost of seriously skewing your data by failing to determine the MBS of the stronger knots and so skewing your measurement of variance in favour of an artificially low standard deviation.

To determine an unbiased MBS you need to test single knots against a standard anchor - the norm is to wrap the cord around a large diameter round bar.

Also, why have you dismissed the option of testing one knot against the other - the ‘8’ against the ‘9’. This would allow you to compare jamming resistance of one knot against the other under identical load conditions - isn’t this the goal of your testing?

Derek

NB - advice on producing valuable analysis data by way of the Parable of the Expert.

It is often said that an Expert is someone who learns more and more about less and less until they reach the pinnacle of knowing everything about bugger all.

The equivalence of this is a test designed so precisely that it gives totally accurate results about a situation that bears no relation to reality., Putting it another way - variance is GOOD. The more variance your test shows the greater the opportunity you have of understanding reality.

7

[/quote]
Well, we’ve been at this debate before.
You determine that TWO tokens of the knot are
as strong as the rupture --and you have one as
an examinable, or further testable knot, in one
run of the gear --all of machine/time/material.

seriously skewing your data by failing to determine the MBS of the stronger knots and so skewing your measurement of variance in favour of an artificially low standard deviation.
Firstly, if my reference values are to be skewed, I'd prefer them to be so in this direction, where one is more sure of "at least..." and not guessing on which side of the mean/median the particular knotted rope at issue might fall. Secondly, if the variance is all so great as to "seriously skew" results, well, maybe there's something seriously wrong with our material or tying skills or ... --why the variance? (In this regard, it's interesting to see in the Dave Richards tests of kernmantle ropes that the least variance (in 5 tests per) came with the [i]grapevine bend[/i] in one of the ropes, and not with the wrapped-around-bollard test to determine a baseline tensile strength!

I think that some testers might have concerns
about test specimen length --that there is a “too
short” length whereby imbalances aren’t able to
get ameliorated over length of material and so
aggravate the weakening --esp. of back-2-back
specimens as we here discuss.

But one needs to take a hard look at what the
presumed purity of testing and running
statistical anaylsis amounts to, in the grand
scheme of things. I will tie my but not your
knots, and in THIS not that material, and …
all in all, some test data from hither & yon
can only mean so much.

.:. In say, X tests of dual-knotted specimens
one will have 2X knots having been put to high
forces, half of them breaking (possibly some of
the survivors will show damage --saw that in
one case of tape knots so tested!).
As opposed to having only X knots tested and broken.
As the breaking point is more the focus,
I think that the 2-specimen test results give
a better view of where that might come.

And among the usually not-recorded, not-noted
data is WHERE the break comes. There was one
testing that put that for the fig.8 eyeknot in the
SPart where eye legs turn around it; and in the
bowline somewhere around the nipping turn
(contrary Dick Chisholm’s assertion, note).

Lyon Equip. testing of OH, F8, F9 eye knots
noted interior/exterior loading for the SPart
(i.e., was it the twin strand that pulled AWAY
from, or bore INTO its twin, resp.),
and concluded --not w/great amount of data–
that :
better to be exterior for OH,
interior for Fig.9,
and either way for Fig.8;
and I think Fig.10 might’ve been there, too,
but now I’m unsure of their conclusion.

Mark shows exterior-8, interior-9, btw.

–dl*

8

What concerns me deeply is that this post has quickly derailed and morphed into a discussion of physics.

Effectively, the point of my original post has been hijacked.

If you stop and think about this for a moment - it is quite sad.

All I had done is ask for some follow up testing of a knot - it isn’t an insurmountable request that defies the laws of physics.

It is hard to actually get work done when you have people hijacking the original posters intent.

Sadly, because of this hijacking and diversion to something completely off-topic - it is likely that my request for follow up testing of the F9 eye knot will likely never happen.
And is so often the case - the wheels keep spinning and nothing gets done (except by a few).

…

With regard to roo - if you want to discuss test rig setup and Newtons laws of physics - please start a new thread - don’t derail this one.

Per Derek:

You are loosing it on this one. By questioning basic physics you are making yourself out to be an uneducated idiot and putting the data and conclusions you are generating into question. Nobody is going to take your reports seriously if you persist in publicly demonstrating that you do not understand basic physics.
Derek, seriously? This is insulting and getting personal - and warrants an apology. While I will not cry foul to the moderators - I will say that you completely misunderstand my intent.

It appears that a single phrase - injection of force - is likely being misunderstood.

Clearly and obviously, all test rigs involve some form of input of force. Every test rig I have ever seen in both a professional lab or from a hobbyist/enthusiast standpoint, all have a single force generation machine located on one side. That is, the force is ‘injected’ (or introduced) from one side. In a professional test rig, the force generation machine is typically a ‘ram’.
There are normally 2 end termination anchors (one at each end)… with one of those anchors being fixed in position.
As soon as force is ‘injected’ - it causes the the knot and rope to s-t-r-e-t-c-h in the direction of the force generation machine (which is effectively a moving anchorage point).
The knot and rope does not s-t-r-e-t-c-h toward the fixed anchorage point.

Anyhow, this is all off-topic and a derailment.

And Derek - I will be seeking an apology from you.
And now that you have revealed the content of your character - I am happy to remove you from any work that I have published.

9

I will remark that there is such a thing as

  1. a symmetric fig.9 eye knot, which resembles
    Ashley’s #1425, one side’s tail following around to
    trace the opposing SPart out (cf. also stopper #523/529?)
    THIS would at least win the jamming contest,
    and should be not too shabby at strength
    –that irrelevant attribute–,
    AND can --in some versions-- be a workable mid-line knot.

  2. Directional Fig.9 --which follows from the
    well-know dir.fig.8! Btw, that f8 isn’t as much
    figure 8 as it could be --there are numerous
    variations on this theme (and more bulky,
    but likely stronger with through loading).

–dl*

10

Actually - this is a call to the moderators.

I am making a formal request to have all of the posts beginning with roo - to be moved to an entirely new thread titled ‘Knot test rig design and setup’.

The entire purpose of my original post has been hijacked and derailed.

This has quickly degenerated into a discussion of Newtons laws of physics, knot test rig design and; insults (per Derek Smith).

It is sad to think that it is now likely that nobody will do any follow up testing of the F9 eye knot.

11

Hold on. I was directly responding to a peculiar requirement of your original post that I found to be misleading and pointless. I have kept my responses brief and to the point. I have made no insults in the least.

12

per roo

Hold on. I was directly responding to a peculiar requirement of your original post that I found to be misleading and pointless.

Hold on roo - I find your comments to be pointless due to gross levels of misunderstanding.

I did not use specific words to declare that you ‘insulted me’. You need to read more carefully.

Your level of misunderstanding is quite profound and alarming to me.

I have started a new thread where you can debate Newtons laws of physics…so as not to derail and divert this topic.

My original intent is to seek assistance in follow-up testing of the F9 eye knot.
Your mind is directed to something else - largely an imagined proposition of knot test rig design - of which you are fixated and confused about the phrase 'injection of force.

I will say no more on this topic because it belongs elsewhere…

13

@ Mark

And now that you have revealed the content of your character - I am happy to remove you from any work that I have published.

As it was some time ago that I requested you to remove my name from citation in your publications, I am surprised to hear that you are only now going to do so. Anyway, thank you for the common courtesy of complying with my request.

Derek

14
As it was some time ago that I requested you to remove my name from citation in your publications, I am surprised to hear that you are only now going to do so. Anyway, thank you for the common courtesy of complying with my request.

Derek

I am surprised that you are still posting on this forum!
I had imagined that after the personal insult you directed at me - that you would have received a ban from this forum (or at least quite a stern warning)?

Am checking through my documents today and tomorrow - and will remove your name from any work that i have published.
Quite frankly, the fact that you seem willing to engage in such heinous behavior - based simply on typed words that you appear to have difficulty in interpreting - somewhat disturbs me..