F8 eye knot geometry and loading profiles

[agent_smith]

Following on from a post by Dennis.
Rather than derailing the other topic post, I have started a new topic based solely on the F8 eye knot (ie F8 ‘loop’ knot).

Images below are illustrating the different geometries of an F8 eye knot.
Also showing a transposition (exchanging the tail with the S.Part).

It is unknown if anyone has tested dual leg loading versus single leg loading
to determine resistance to jamming.

The resistance to jamming in one form of an F8 relative to the other is likely due to the continuation of the
S.Part pressing against its neighbouring segment (refer to image below).

Note:
Chirality and transposition are two different concepts.
A transposition does not alter original chirality.
A transposition occurs when a tail and S.Part exchange identities (but without changing relative position).

Chirality is found everywhere in nature - for example, animals and humans have left and right feet/hands/paws/limbs.
There is nothing you can do to change your left hand into a right hand (or your left foot into a right foot).
When you buy shoes/gloves, there will be a ‘left’ and a ‘right’ version of the product.
In knots, chirality (or ‘handedness’) refers to the particular direction taken by the continuation of the S.Part
as it overlaps (crosses over) itself to form a loop. A ‘loop’ is formed when a rope segment curves
to overlap itself to circularise. All ‘loops’ have a distinct chirality (either left-handed or right-handed).
A ‘bight’ is not a ‘loop’ because there is no overlap or circularisation (typically an open U turn).

Knot book authors typically only show a knot in one chiral form (one chirality).
For example, ‘Bowlines’ are most typically illustrated in right-handed (Z) chirality.
Authors rarely (if ever) show knots in both chiral forms - and this has been an unwritten ‘rule’ since the dawn of publishing.
To the ‘lay’ reader, tie any knot and then hold it up to a plane mirror. The reflected image will be the chiral opposite.
Both chiral forms are equally valid, and perform equally.
The tendency of a person to tie knots with left-handed (‘S’) chirality or right handed (‘Z’) chirality is linked to the following:

1. Whether the person is left-handed or right-handed; and
2. How the particular knot was originally learned ie the tying method that was learned, practiced, and memorised.

Interesting note:
Almost all of the ‘Bowlines’ illustrated by Clifford Ashley are shown in ‘Z’ (right-handed) chirality.

---

[Dennis_Pence]

Thanks Mark for starting another topic.

I first learned about the untying difference this transposition of the Figure Eight Eye makes in the following video (in addition to other small details that make untying easier). https://www.youtube.com/watch?v=QAr-uHd8h8o This was mentioned on some early topic post in this forum, but I do not remember where. Then I learned about the difficulties untying the similar Figure Nine Eye. https://www.youtube.com/watch?v=KsZgZB3oPbc&t=4s That person tying the F8 and F9 eyes was not aware of the above details about the transposition (so some of his are one and some are the other).

That motivated me to do a similar test of the transpositions of the Figure Nine Eye. Just like Mark has shown above for the Figure Eight Eye, it turns out that having the standing part end up on the “inside” of the bottom of the knot causes less jamming (one on the left below) compared to having the standing part end up on the “outside” of the bottom (one on the right below). If you tie all of the Figure Nines perfectly, I found that they are only a little harder to untie after a heavy load in my very limited testing (just my full weight on the line) compared to Figure Eights. I can only guess that the person comparing F8 and F9 in the video above was not so careful when he tied his F9’s (and it is extremely easy not to be perfect, the F9’s are very difficult to get smooth with no tangles inside).

---

[Dan_Lehman]

@Dennis Pence post:2

If you tie all of the Figure Nines perfectly

But what is perfection?!
–judged by ease of untying, of tying, of static strength,
of dynamic strength, of durability (vs. bumps & knots & usage wear)?!

Beyond the dressing (of the “dressing & setting” team)
comes what sort of setting one might do. In Richard Delaney’s
testing of the Fig.8 EKnot in Interior- vs. Exterior-loaded forms,
he didn’t set the knot as I would were I trying to get strength
from the exterior loading --which I figure might come by the
S.Part’s bearing strongly into its interior twin en route to that
rather sharp turn around the eye legs (this is my guess). To
that goal, then, I would set the knot hard to give shape and
resistance to what sadly Richard got in his weakly set Fig.8s,
the exterior strand just pushing aside the way-too-loosely set
interior twin!
.:. One needs to have a reason for things and then testing to
see if it’s true. (I’m guessing that perhaps in SOME ropes
–those w/more friction & less elasticity–
the exterior loading might indeed prove stronger.
Now, does that matter, when? --vs. being able to untie the knot!

–dl*

[agent_smith]

In fairness to Dennis, I think that his use of the word “perfectly” had the intent of
being consistent, accurate, and symmetric, when tying the knot.

Knot geeks approach their knot tying differently relative to user groups such as; climbers, rope access workers, and VR technicians.
Most user groups see knots as a means to an end - to get a job done.

Knot geeks view knots as an art form, and in some ways, a mathematical or geometrical representation of art.

…

With regard to F8 eye knot jam resistance:
There hasn’t been any deep analysis of what is going on with respect to loading profile
and how the particular geometry of an F8 might affect its resistance to jamming.

I think it is universally agreed that an F8 eye knot will eventually jam - regardless of its particular geometry.
That is, regardless of how a person actually ties an F8, its eventually going to jam.
The question is; is there a way to delay jamming?
Answer = I posit that “Yes”, a certain type of geometry will delay jamming.

Now that question becomes: Okay, which geometric form of an F8 is more resistant to jamming?

It is theorised that if the continuation of the S.Part is exterior (relative to) to its neighbouring segment,
it will press against that segment causing greater compression of the core.
The resulting compression means more difficult untying after loading.

If the continuation of the S.Part is interior (relative to) its neighbouring segment, there will
be less compression of the core. This means less difficulty untying after loading.

Unknowns:
We don’t have peer review test data for jamming threshold of F8 eye knot in various human rated ropes.
Human rated ropes are either ‘EN892 dynamic’ or ‘EN 1891 low stretch’.

What is needed is to gather a statistically valid sample of load tests on F8 eye knot to determine
jamming threshold.
This ‘threshold’ can only have meaning for one person, who is not fatigued.
After a period of time untying various tightly set knots, hand fatigue will ensue.
So a suitable rest interval must be allowed for to recover.
Tests need to be done with the same person - because hand/grip strength is relative.

We also need to define what is meant by ‘jammed’.
For example, I know that I can loosen a ‘jammed’ knot with a few hammer blows.
A hammer is a ‘tool’.
So the definition of jammed might be a state where hand strength alone is not sufficient to loosen and untie a knot.

Irreversibly jammed could mean a condition where even the use of tools will not loosen the knot (it is permanently jammed).
To further qualify this condition, it also means that damage occurs when tools are used to loosen and untie a knot.

I therefore distinguish a jammed condition where one or two hammers blows loosens the knot but without resulting in any obvious damage.

I for one am interesting to get some data on the F8 eye knot - to compare one geometric orientation versus the other (response to load).