Your question's particulars suggest that the situation you're interested in is one
of joining a rockclimbing (dynamic) rope to a haul line (low-elongation)?
And the point of doing this is most commonly to abseil the full length of the
climbing rope (but to not bear the load of two such ropes). --one argument
for using
twin (8mm) climbing ropes! (-;
--and the knot preferred for the above-guessed situation is the Offset Overhand Bend
(aka "European Death Knot (EDK)", "(dbl) Overhand Bend", "Thumb Bend").
For the case of the offset knots (even for the Flemish, aka Fig.
, the difference you
state should be no problem; but those asymmetric offset knots should then
have the thinner rope first wrapping the SParts (so that it would have to be
pushed up arouund the thicker rope to flype/capsize, which is harder than
pushing the elastic thicker rope around the thinner).
As for the intended-to-be (but scrutinize presented images and see how often
it is NOT) symmetric Fig.8 bend, that gets problematic as ropes differ.
MOREOVER, please note that a definite orientation of this knot is ALMOST
NEVER PRESENTED: in a symmetric form, which two ends are you loading?
(Test data is inconsistent re how much this matters.)
Cf.
www.iland.net/~jbritton/KnotPhotoContributions.html Updated Link > www.pssurvival.com/PS/Knots/Knot_Knowledge_Photo_Illustrations_2004.pdfand about the 4th
knot down the page for a
perfect form of the Fig.8 trace knot; the bends
corresponding to this loopknot would be those loading either the two dashed
parts ("A-B" vs. "H-I", or "S-Q" vs. "G-FE"). Usually, the exact form or the knot
is not known/reported in discussions about it. E.g., in some testing done by
Tom Moyer, in which such loopknots in 7mm nylon kernmantle broke quite
consistently around 92% (!!!--of his tested tensile!), he had a couple of slightly
asymmetric forms (and his images are a bit ambiguous). YMMV.
In the case of mis-matched sizes, the former version indicated above seems
to work better (more secure/tight). But here's an argument for using the
Grapevine, where the component Strangle knots are somewhat independent
of each other, abutting to jam tight.
--dl*
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