The Butterfly knot or Lineman's Loop/Rider aka "Alpine Butterfly" is fairly commonly
known among users of kernmantle ropes (rockclimbers, cavers, SARescue) and in
knotting circles. That is, the knot name is known, and some method of forming
some version of it is known. It is useful as a mid-line eye knot because it performs
well when loaded by either end and by the ends alone, being generally reportedly
strong and fairly easy to untie. We should remember that Paul Kruze (? IIRC) however
reported testing it in (again, IIRC) thick, flexible, soft-laid nylon rope and finding it
to be weaker than the bowline (and rather weak, absolutely). We should also note
that the knot can be oriented in various ways, and that being asymmetric it is of
a different geometry per end.
Some people (in the caving world, and UK caving world i.p., I think, so far)
have taken to regarding a like knot --viz., Ashley's #501 (fuse arrowed ends
together (I don't readily find the exact eyeknot))-- as "Butterfly" and made
the Lineman's Loop "Alpine" (which fits with one publication source, anyway).
One concern about the Butterfly is that it can jam on certain loadings and
orientations -- the eye leg that feeds into the collar around the unloaded
end can be drawn snug around it, very tightly.
So, here are some *new* knots of the same sort, and ones that can be
oriented in anticipation of a "directional" loading such that they don't jam.
The first knot shown is a simple variation on the Butterfly which I verbally
presented in the "Knot testing - Life support knots - procedures and results"
thread -->
http://igkt.net/sm/index.php?topic=1239.45#msg10158By putting an extra half turn/twist into one half of the knot during tying,
that half will form a Fig.8 and be resistant to jamming. (The red PMI knot
is a bottom view of the knot below.)
The second knot shown is a mid-line eye knot corresponding to Ashley's
bend #1408. The photo shows (crudely, but hey ... !) the knot being
formed, from left rope to right; the thick yellow PP rope serves as a
kind of physical arrow in seizing the inchoate eye and pointing to the
path to tuck it out; the central blue CoExOlefin shows the knot loosely
tied, and then the red PMI E-Z Flex holds a lightly tensioned knot.
Beyond this is a variation of the Butterfly itself with the sort of extra
eye-leg wrap seen for the #1408 variation -- which surprised me, as
I thought that structure was only a penalty to getting the otherwise
symmetric #1408 into mid-line state, and that the Buttefly's asymmetry
was its price; but, in fact there is this other variation. (later)
--dl*
====