Author Topic: Pure Unidirectional Prussik  (Read 134 times)

bushrag

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Pure Unidirectional Prussik
« on: April 13, 2020, 01:54:20 AM »
Three wrap prussik, Valdotain Tresse, Schwabisch, Distel, Blake?s Hitch, autoblock, etc.

These friction hitches are essential to the sport climbing and arborist industries, yet for all of their various pros, all of them have the same impurity. The existence of this impurity has resulted in marketability of mechanical devices generally referred to as mechanical prussiks, zigzags, etc. These mechanical devices come with added intricacy and costs.

The industry has worked around this impurity for so long that it probably doesn't expect a solution.

In the primary load direction, these friction hitches are lifesavers.

In the secondary direction, they snag, bind, grab, stop progress, and cause headache. They nearly all require fingers to loosen the hitch to allow the rope to slide freely.

To my knowledge no friction hitch exists that is a a pure prussik that is full friction in one direction but frictionless in the other.

You could spend hundreds of dollars on progress capture devices and mechanical rope grabs like petzl micro traxion, tibloc, kong duck, etc to solve this problem.

Heres my attempt at a solution.

Shown with yellow 5mm accessory cord and a Bluewater VT prussik on green 9mm canyonator rope.



Of course there is some friction, however the backside leg of the rope can be tugged and slides easily through the prussik. No need to touch the prussik.

My solution here has two parts: part one is the typical three-wrap or three round turns, part two is what I refer to as a backstop to nudge the friction turns loose. The backstop part looks like this:



I am looking for suggestions how to simplify this backstop part. The part has two practical characteristics: it has a lasso turn which is a single turn around the rope essentially a fixed loop, and the second characteristic is that load bypasses this lasso directly into the three friction wraps.

It needs careful dressing such that the three wraps are adequately snug to engage, and the lasso turn is sufficiently loose on the rope.

A pure unidirectional prussik could solve current problems and change the ballgame with current rope ascending techniques in caving, rock climbing, canyoneering, etc. It could also be used as a fall preventer on a fixed line, for example you scramble up rocks and the hitch slides upward along a fixed rope, protecting you from downward movement (aka fall).

It could also be used as an arborist hitch, or on an arborist lanyard for positioning. When your hands are occupied, being able to grab the tail end of a loaded rope and pull slack through a friction hitch would be indispensable.
« Last Edit: April 13, 2020, 01:56:32 AM by bushrag »

Dan_Lehman

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Re: Pure Unidirectional Prussik
« Reply #1 on: April 13, 2020, 08:34:35 PM »
Three wrap Prusik, Valdotain Tresse, Schwabisch, Distel, [ProhGrip], autoblock, etc.

... all of them have the same impurity.
...
In the primary load direction, these friction hitches are lifesavers.

In the secondary direction, they snag, bind, grab, stop progress, and cause headache. They nearly all require fingers to loosen the hitch to allow the rope to slide freely.

To my knowledge no friction hitch exists that is a a pure pru[]sik that is full friction in one direction but frictionless in the other.
...

Yes, it's a tricky problem.  Recently, there was some
chatter on www.Treebuzz.com's forum (I forget which
on --Rigging, Climbing, ...) in which a fellow asked
others what EXACTLY they used AND WEIGHED and
IN WHAT CORDAGE (hitch & hitchee) !!!  Yea, these
are important bits of information!

Without testing in hand, your hitch looks to have a problem
in the 2-eye version in that the eye running to the away
end of the coil will not pull on that any more than will
be allowed by the anchored-to 'biner in which the other
eye is attached --i.e., they must go in synch together.
Whereas in the round-sling version you show in yellow
rope, with some loss of movement via friction around
the 'biner, forces can adjust from one end of the hitch
to the other.

Meanwhile I'll note that it seems that some of the cited
hitches work well enough to have "hitch tenders" that
bring them up WITHOUT the manual  fussing you remark at!?


--dl*
====

KC

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Re: Pure Unidirectional Prussik
« Reply #2 on: April 13, 2020, 11:46:10 PM »
Noble pursuit, i think this might be of personal tuning to style, weight, and rope materials used etc.
.

.
This is from my 'bluz' (towel) period!
The Sailor Gripping Hitch and Icicle shown are quoted true to Arborist species name, not Classical
For me personally, the last hitch, counter-intuitively worked for ME in 3/8" Tenex round hollow when straight to flat footprint on arc construction.
(can't find pic of that presently)
To me, also counter intuitively, the widened flat grip seemed to last longer than round
>>also might play with 3 strand hitch to round rope in quest for other unique type of gripping than round tube on round tube.
.



>>i call this self tending, another way to go is to have small pulley or key chain carabiner sized right to comb prussik in one direction (up)
>>while allowing enough free play to pull down.(yellow Tenex on 16strand Tree Pro Red

The blue and yellow tape on end of DBY(Dbl.Bowline w/Yosemtie tie off) are safety markers, and contrasted tape colors on opposite end of rope to id as well which end this or that , and carried to id'ing rigging lines as well
.
in constructions built to 'self tend' more than just work by construction also did this to side D for lanyard,
>>but round seemed to work better here.

modified grip later to pull more evenly to designed geometry of D and intended pull..
.
Back to vertical line support angle, this in Tenex, about worked for ME self tending riding various arbo 12 and 16 braids
>>once again as chased this with others seemed to find weight/style/materials vary results
>>also if riding on SRT of fully loaded hitch or a folded/dual line self adjusting that not all weight is on hitch
>>and thus also has a 'buddy' leg to take loading as move hitch, for a mono line w/o that doesn't release as well.
Eventually the myRide hitch as last item in first pic did better than this
.
This is similar .jpg i found in notes(kinda a .png guy now!):

.
i think Friction Hitch class pushes rope science to 1 limit
>>of hold as faithful as rest, slide, hold again
We don't ask this of any other set of knots
Thus think this high end requires more personal 'tuning' and less global statements can be made.
« Last Edit: April 13, 2020, 11:50:18 PM by KC »
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