In IPatch's pic, does the lower working end (blue rope here) always do the loop around?
Or can the upper working end (yellow rope) do the loop around instead?
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This exploration makes me think there has got to be a widely accepted
improvement to the EDK. ... Are there any rappellers who have used these improvements?
It's pretty simple, except in requiring
understandingof the knot & its dynamics --understanding being not
so simply depended upon. Since we're concerned here
with abseiling, let's try a contrived case involving this,
sort of.
Consider a flag-pole painter who is painting it from the
top, downwards, slowly rappelling (i.e., short lower then
lock-off to paint; repeat); and we see some prankish kids
or maybe it's a playful dog ... take hold of the end of his
line and start to run away with it. You go quickly to
the pole and hug it & line, to keep the line straight
along the pole; I "second your opinion" and likewise
wrap my arms around line & pole, right above you.
Now, when that line is pulled, YOU --but not I--
will feel its tug hard against your hugging arms.
Only as you yield a bit will such forces bear upon me.
This is the aspect of the twin turns of the
"EDK"where the SParts enter : only the "outer" one will
be resisting the pull to pry open the knot, until it
yields and then ... . So, the key to this knot's
security/stability is resisting this prying-open
effect by securing this outermost turn.
The solution best comes in two *steps* with actual
abseiling, recognizing that the joined lines are often
of different natures --a thin and more flexible "haul
line" joined to a climbing rope, or two of the latter
where flexibility & diameters differ. So, a first step
is to orient the knot so that the thinner & more
flexible --let's hope we don't need to choose between
these characteristics(! :: if so, "flexible enough" will
be fine to let the thinner one do the work)--
should be the one that does the "choking"/binding/
securing of the knot. For it should be harder to
pry a thin line out & around a thick one than
vice versa(!); and a more flexible line should be
able to be more tightly set.
The 2nd "step" to orienting different ropes is the
actual knot. The simplest solution IMO is to tie
the
offset water knot / EDK AND THEN tie off
the choking line's (should be thinner...) tail around
the other tail with an
overhand knot set snug against
the main knot --which stopper will prevent material
from being pried out and opening the binding turn.
What Agent_Smith shows with his extra turn in the
outer (blue) line is an additional turn within the nub,
which should also help resist the prying effects. I've
argued with him, though, that this extra turn is best
made at the throat/choke-point (*all-at-once*), and
then the tail traces the twin (yellow) tail in the final
tuck. I think this full/"round" turn makes a sure nip,
and with a closed helix vs. the slightly opened one of
his knot ("open" by having the thicker yellow rope
come between the overlapping parts of the blue).
As for testing : consider the forces that are expected
to be handled --not just anything, in all sorts of sizes
and types of cordage, but specifically YOUR OWN body
weight on YOUR OWN cordage (and with some reasonable
estimate of effects of like weight & cordage). People can
make effective tests, IMO, by simply hanging and bouncing
upon a typical abseil set up, or by exaggerating forces
by doing so on just the single, knotted lines, or even
by making a crude 2:1 pulley with a 'biner and roughly
doubling those already doubled (via single line) forces.
I.e., one expects the knot to see half of the rappeler's
weight, and with simple means, one can impart up
to four times this force.
.:. We do NOT need BREAK TESTS for this knot!!!
.:.' And climbers should see how THEIR PARTICULAR ROPES
behave, not relying solely upon someonElse's testing.
Much of this is laid out already in the posts cited by the
URLink in my reply (#2) above. These include showing
how the knot can assume orientation across about a
180deg range of rotating the knot as though a dial.
--dl*
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