In particular, the objective is to investigate what effect rotation has on #1410 stability.
It is hypothesized that:
1. The mid-rotation state of #1410 is more vulnerable to instability
2. The anti-clockwise rotation state (with choking turn displaced one rope diameter from axis-of-tension) - raises the threshold of instability (ie the load threshold where instability is triggered).
I don't follow "anti-clockwise", which isn't a full description
of a knot, given mirror images et cetera. --you must have
some reference image/state in mind, to which then this makes sense.
NB: In the given middles state, the
tails generally will run along
the axis of tension (and they are roughly perpendicular to it,
one side or the other, respectively, of the two extreme states).
choking turn is is displaced one rope diameter from axis-of-tension.
I really don't follow this, and won't go into details,
but urge that a perspicuous description is as follows:
"choking
strand makes a forward arc"
& "choking strand makes a backward loop"
& leaving " ... & other strand make lateral arcs".
(Another way to look at this is whether the loop around
the tails is away-most (nearer ends ; in which case the
choking strand is a forward arc) or the other way.)
Any testing should be carried out using human-rated ropes of equal diameter.
The reason for this is four-fold:
1. The class of users of this type of rope joining knot are predominantly climbers and canyoners - and they only use human rated ropes (NOT rope purchased from their local home hardware store) - any knots used in their rigging is life critical - and any error or failure could have catastrophic consequences
2. Consistency and repeatability of testing - if testers are using ropes purchased from ACME Dodgy ropes Pty Ltd or from a home hardware, there will be no consistency and little possibility for other serious testers to try to repeat results.
Although if there are not many testers, having consistency
amounts to having tested very little of possible cordage combos!
4. Equal diameter ropes will ensure consistency - otherwise we have no control over how a tester positions one rope relative to the other - including the myriad arrays of rope diameters currently available which would result in zero consistency from one tester to the next.
As above, and as measuring of diameter sometimes smells
like marketing more than science, and so on. Again, given
the variety of ropes and paucity of testers, consistency like
you are describing amounts to an arguably too parochial
examination of conditions.
While a diversity of test conditions leaves one wondering
... (absent repeated results to verify...), it might be more
helpful in *suggesting* that there *can* be conditions
where things might go amiss. THEN one can try to forus
on that, possibly with some unlikely cordage that can be
seen to aggravate a suspected characteristic (e.g. strechiness,
frictiveness).
Typical rope diameters used by climbers/canyoners:
1. Climbers will use EN892 ropes in the range 8.5mm - 10.2mm
2. Canyoners will use EN1891 ropes typically around 9.0mm diameter.
IMO, it is common enough for "accessory" cord --aka "haul line"--
to be joined to a climbing rope to extend an abseil; and for
the joined ropes to be different in other ways (size, age).
If testers are expected to understand the rotational states,
surely they can understand --per them!-- the significance
of which rope is in which position. ("choking" vs. not is
the choice ; generally, one thinks "thinner & more flexible
should choke --for strength isn't the issue, but rolling!")
This author is of the view that age is not a valid discard criteria (I refer any doubter to Walter Siebert research Link: https://www.facebook.com/SiebertResearch/ )
His is a most dubious assertion; elsewhere, I've read
that (a) age reduces strength by more than he suggests,
and (b) it more significantly reduces ability to absorb force!
(That he makes no reference to dynamic aspects of aged rope
is a warning sign, IMO.)
((For some of us, the old ropes are not only that --aged--,
but they come from a time when ONE FALL was the acceptance
threshold. (But I think that my Goldmantle was a 5-fall time?)
And the loading?
You have a previously posted-in-this-forum test report of
some knots showing various loads, presumably got by
steady increasing of force.
Abseiling can involve more cyclical yet low-level loading.
And most of us won't have calibrated test set-ups; but we
could bounce on various configurations to try to discover
potential vulerabilities.
Btw, I'm reminded that I never really much realized the
supposed vulnerability of an
offset fig.8 e2e joint capsizing
--though I HAVE warned about that. .:. It might be good for
us to try that knot, too, seeing if we are getting bad
results from a supposed known bad knot (!).
Thanks,
(-;
ps: I see I noted my possible cordage, in prior thread.
>>>
Ropes available to me for my crummy 5:1 pulley stressing
--lousy pulley, but bouncing on it surely imparts surges
of force up to what ought to come by good sheaves alone--
are : ancient "Goldmantle' --the name says it all (~40yrs)--,
some old 11mm Mammut dynamic, some other old bit
(discarded top-roping anchor lines), newer 11mm gym
rope, some newer & pretty unused 8mm ropes,
Sta-set 11ish mm yacht rope, 3/8 BW II, and the
incredibly intractable PMI pit rope & some Canadian
stuff that makes the former seem, er, not-so-bad(!!).
(Frankly, these might be unlikely to form an offset knot
that any sane person would actually use!), and other
7mm kernmantle low-elongation ropes, & 6mm.
