Although every time I see yet another "slow-pull-it-till-it-breaks" type test I roll my eyes and yawn.
The yawning is getting deafening these days.
...
The problem is that the vast majority of 'knot testers' are programmed to think in one dimension only - and that is "slow-pull-it-till-it-fails" mindset.
They pull the knot until it yields and then pop the champagne cork and celebrate.
Worse, it is everywhere done poorly or worse,
seldom with a hint of acknowledgement of other
testings --or, if so, of how different those might
be from what is being presented.
The seemingly comprehensive --at least, extensive--
set of testing/etc. listed by SARRR.WEEBLY should be
adequate for me/us to begin building a table of the
*knots* and the many test results,
to show how sometimes stark a contrast there is!
Like it or not --the break values--, one should at
least be concerned about the variance seen in these
results, and the continued void of pertinent information
(e.g. knot geometry) to fill out this information.
I was struck by the comparatively LOW break values
seen in that recent (2015) Yachting Monthly tests of
"Marlowbraid" rope !! --often <50% (!) (though there
wasn't independent testing of the tensile strength,
and maybe Marlow tends to exaggerate that!?).
And an eye splice for that double braid being but 80%?!
(Some standards organization I thought had stipulated
that eye-splice strength BE what is given as tensile,
I suppose reasoning that users want to know useful
not mythical values.)
And he list 'Fig 8 end' and 'Fig 8 bight'... which is amusing to me
(unless its a typo and meant to write #1411 F8 bend).
No, it really IS the case that Richards, and also the
CMC Rope Rescue Manual, 3rd ed., give values for
both tyings --"rethreaded" & TIB-- of a
fig.8 eye knot !
--WITHOUT COMMENT as to why. (And in both cases,
the results of testing 5 specimens for each *knot*
is different by just 1%point, IIRC.)
NOW, **I** can think of reasons for doing this:
1) one tying method (thinking TIB) might induce
some torsion, which can affect strength;
2) or the resulting exact geometry might differ,
of there might be different ends loaded --and, yeah,
the testers don't think to observe & comment on this(!).
An empirical study of what users do and what results
from that doing would be informative. BUT one should
make such points known. Otherwise, we should expect
that once tied by end-reeving or TIB and "dressed & set"
that the same "fig.8" knot will result,
with no significance on behavior.
NB : As also shown for I think later testing, for their
3rd Edition, CMC found that the
fig.8 eye knot loaded
*through*/end-2-end (thus, offset) (eye UNloaded)
was
stronger than the
inline fig.8 so loaded!
--and the point of the latter knot IS supposedly better
through loading (though for which it is essentially a
variation on the
squaREef knot, the infamously
"never use qua bend" entity.
Also eyebrow-lifting : CMC's test of a
wet fig.8 EK =91% !!!
Why so high? Perhaps --conjecture ahead-- the wet line
slipped through the SPart-turn's nip more and thus gave
complementary gripping against the SPart before that
U-turn point, and these combined/broadened areas
of friction enabled the high value?! --plus, as SS369 might
note, maybe some reduction of
heating,
though one can read of heat issues in marine nylon
for cyclical loading!?
The Dave Richards report doesn't even reveal exactly how the knots were tied.
But none do, for the most part --we never know,
and often --forgo exact geometry-- not even merely
which-end-loaded differences or
sheet-bend version
or
butterfly end-loading (as it's asymmetric, but I
think many don't much realize this).
Richards also lists 'Bowline'. Great - another revelation.
Presumably he means #1010 Simple Bowline?
Of course he meant #1010 --what other "bowline"
is known & talked about in the general public?
HE DOES cite "Dutch bowline" as having been
cursorily tested and found roughly equal (though
we can remark that it differs in geometry more
than those diff-tied
fig.8s should!).
As for
butterfly presume eye-loaded; but here, too,
it would've been a better two-tester to do also
*through*/end-2-end loading.
But, yes, in sum, a century of mediocre, un-clever,
and incomplete testing, REPEATEDLY DONE, does
NOT advance our understanding (except for some
hints of things implied by such variances as noted
here and elsewhere).
In my mind, what matters most is resistance to slack shaking, cyclic loading, flogging (now becoming one of my favourites) and circumferential (ir ring) loading (for eye knots).
Ring-loading IMO is of parochial importance
--not something to be concerned with in many
uses, but maybe in some others. (Same as
having an eye knot be TIB : pointless for a
tie-in knot, e.g..)
The security/stability behavior stands in need
of some fairly uniform ways of assessing. But
I think that (increasingly?) many cordage users
realize that "staying tied" is a Really Good Thing,
& nevermind how excessively vs. adequately strong
the knot might be.
(But that Yachting Monthly article sure did imply
that "best" = "strongest". Meanwhile, in doing some
small tasks of late (seizing basketball netting bights,
and other stuff), I value much EASE OF TYING (where
sometimes "ease" seems more like "ability to" than
anything resembling "easy"!
)
--dl*
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