Prussik variation with interesting symmetry

[bushrag]

A while ago I complained about the three wrap prussik being asymmetric and got a few  responses since the three wrap prussik is so perfectly symmetric.

My critique was in regard to the functional symmetry, since each strand of the three wrap in isolation creates a symmetric but inverse form with two different performances when a load direction is chosen. Namely, the secure cinching occurs in the "bottom" three wraps closest to the load direction, and the top/far three wraps become a "spaghetti cinch" where not much additional security is added. The top three wraps unravel if not for the bottom part providing a stop-gap.

So here's a symmetric variation where both strands are "clones" and have the same secure-side features on each strand, the three wraps and collar. Load direction is to the left as the strands are shown. Once you dress the knot, it can be slipped easily by "opening" the collar which draws tight again when loaded.

[agent_smith]

Thanks for your presentation bushrag.
I would not describe your presentation as any type of 'Prusik' (#1763).
It is a type of slide and grip hitch - but not #1763,

All slide and grip hitches can be divided into 2 main categories:
1. Tiable In the Bight (TIB); and
2. Linear (ie, access to either end is essential).

Your presentation is not TIB - it can only be formed from a linear length of cord with access to both ends.
#1763 Prusik hitch is TIB - it can be formed from a round sling (without access to either end).

#1763 Prusik is a symmetric slide and grip hitch.
Your presentation is not 'symmetric'.
All slide and grip hitches distort under load - and the degree of distortion is related to its geometry.
What you have attempted to do is find a way to inhibit or minimize distortion under load (but this doesn't alter a hitches original symmetric or asymmetric designation). In fact, the inherent tendency of a slide and grip hitch to distort under load can actually be beneficial (eg Valdotain Tresse 'VT') - allowing it to be manipulated under load to control the descent.

Loading profiles can be dual leg loading or single leg loading.
#1763 Prusik hitch is an example of dual leg loading.

Blakes/Prohaska hitch is an example of single leg loading.

Would be interesting to load test your presentation to determine:
[ ] jamming threshold
[ ] whether releasable while under load
[ ] utility/ease of use in cyclic loading

Note also that the ratio of hitching cord diameter relative to host is a crucial factor.
[ ] 45% - 73% appears to be the range limit (outside of these ratios has an adverse effect).
For example, 8.0mm cord on 11.0mm host rope = 73%
(eg 9.0mm on 11.0mm host is no longer effective)

There are 2 other factors that also have a significant effect on slide and grip hitch performance:
1. Hitching cord flexibility; and
2. Hitching cord texture (a smooth sheath/cover versus a coarser sheath/cover).

[Dan_Lehman]

My critique was in regard to the functional symmetry,
since each strand of the three wrap in isolation creates a symmetric
but inverse form with two different performances when a load direction is chosen.
...

I feel your pain.  Beware the effect of the away-from-load
half pressing into the nearer-load half --which is what the
coil-away part (which you've reversed, for your "functional
symmetry") must do in order to tighten grip.  There is still
some risk of this coming from coil-to structures; one might
do better with separate --and so spaced apart-- knots of
the two halves!?  --or of twinning the SParts of each half
to be co-SParts of a twinned knot.

Thanks for the nicely labeled images!


--dl*
====

[KC]

i think that if single leg of pull of Friction Hitch of ProGrip, Taut Line, Tarbuck, Adjustable Grip Hitch etc. can have matching diameters and  stiffness.  Of full bodyweight powered hitch rigidity grabbing matching full bodyweight powered rope column grabbed rigidity of lifeline.
.
Problem comes in if hang on dual end Friction Hitch, then host Lifeline is tensioned just as rigid by full bodyweight, but is gripped by Friction Hitch trying to impose, but each leg is only rigid from half bodyweight, not so imposing on greater rigidity especially at matching stiffness and size.
.
Solution is to then reduce size of Friction Hitch cord to lifeline ratio,
To funnel half as loaded into shoe of denser/smaller footprint to compensate to more rigid against full loaded lifeline.
Usually also using stiffer cord to accentuate the effect, this all increases cord wear.
So thinking in terms of tension x stiffness divided by size of dispersed area so smaller cord is greater 
vs. lifeline tension  x stiffness divided by size of lifeline.
.
Textures work in there too:
Rode a 1/2" in 3strand on arbo 12 and 16,  1/2" braids for years for very good grip and very long wearing , 12 strand nubbier, less round like stop sign for better grip but less smooth ride.   Opposite of 16 rounder etc, faster ride.. 
The 3strand contact surface is unique compared to braids for this.
Evolved to 2leg pull varieties in 3/8" Tenex on 16 strand.


.
When noted this was going with cord to be able to fold in half to match lifeline diameter but favored a bit more.  So certainly can go with numbers offered.
.
Always follow the forces,
And may they always be with you...