Mike, my questions are simple, and can be answered simply, verbally.
But you posted more photos; they answer one question–viz., Where’s
the eye. They don’t answer Which end is loaded? This is a question
left unanswered by most people for such knot-in-a-bight loopknots.
Lyon recognizes the difference, and makes some effort to determine
it effect (if any), with mixed (per knot) results. (Actually, as limited as
their testing was–in test cases, e.g.–, one shouldn’t make any con-
clusions based upon it, other than that there is something worth
pursuing in further testing.)
Bob says that Lyon didn’t dress their Fig.10 LK so neatly, but I see
it as they worked in stiffer rope (for what is pictured, at least), which
shows evidence of apparent torsion in the eye, e.g.; I think that they
got it pretty well dressed, and the same, re crossing strands (none).
But they might have not forced the wrapping as far as could be done,
letting it come over the earlier turn more than is necessary.
The effects of dressing (and even orientation vis-a-vis loading of
which end) might matter and matter differently in different materials.
I think that it’s conceivable that in a material with greater friction
that one might see some friction-gripping of the wraps, whereas
in a slicker rope this wouldn’t happen, and so for it, another dressing
might work as well or better.
Then there is the question of How to measure strength?
–with slow-pull loading?
–with sudden (“shock”) loading?
–over time of useage & battering and sustained loading?
I know that Bob likes to dismiss “shock loading” as mythical, but
Dave Merchant asserts (if not in Life on a Line then on the NSS’s
forums.caves.org OnRope forum) that it makes a significant difference
in these very loopknots, with the more complex ones (Fig.9, 10?)
losing strength from presumed greater frictional heat (perhaps from
there being more material to be drawn out of the knot on compression
at the high loads). Re the third mused strength measure above, what
I’m wondering at is there being a chafing penalty for some knots that
don’t jam and hence see movement of material on loading/unloading,
and which though maybe testing stronger on a device in a lab would
fail sooner in the rigors of repetitive practice vs. a knot that gets tight
and holds its position, without such movement. (OTOH, one might
see the latter as preserving tension that weakens over time, whereas
the former, loosening, enables some recovery!?)
March’s 70% & 55% seem somewhat out of line w/other soundings
(i.p., Lyon’s), especially compared to the big difference between 8 & 9
(i.e.,the difference of the relative strengths of the two knots is too great).
The Fig.8’s strength is just too low, here.
I’ll recall that one person doing crude break tests with a truck and
small stuff (quarter to three-eighths inches PP (mostly) rope) of different
bends, used Fig.8 loopknots for the connections to the anchors
and they NEVER broke (Blood knot, fyi, won vs. other bends)!
(A perplexing aspect of this sort of testing is that the technocrats
will decry it for not being done w/laboratory controls; and yet it
might well be more like the actual use–and so more relevant,
as real life tends to occur outside of laboratories.)
–dl*
