Here’s a new presentation of some test results.
Using 10mm low-elongation rope (maybe the PMI
really is “static”!?) for eye knots (Fig.8, bowline, butterfly),
and 7mm “static” cord for end2end knots (grapevine & water knot).
Interesting to see that they used the fig.8 “strong form” (as
per Rob Chisnall’s assertion, long ago), which seems to
be uncommon, based on images seen. Odd that they also
seem to have tested specimens with knotted eyes at both
ends, and in some cases presumed the fig.8 to be stronger
than the other (or why use it)? IMO, they wasted a chance
to get more information re the others!
http://overtheedgerescue.com/rope-rescue/baseline-testing-lightweight-rope-rescue/
(I see that the ropes appear to have been marked with ink
for some location (perhaps to assess “slippage”?), but I don’t
find an explanation --or pre-testing image to show the mark
then.)
–dl*
Odd that they also
seem to have tested specimens with knotted eyes at both
ends
Although I think the concept of simultaneously testing identical knot specimens at each end termination is a good idea.
Its the mixing of different knots in the same test that is odd.
Also, the testers only focused on the common #1010 Bowline - and none of the secure Bowlines with 3 rope diameters inside the nipping loop. Presumably, the results for the #1010 Bowline will be assumed by the general public to be all encompassing and representative of all Bowlines (which it is not).
And lastly, as is typical for nearly all testers - all they focus on is pure MBS yields and nothing else (which is sad and monotonous). Knots simply don’t break in the field - for example, I know of no arbitrary failing (ie breaking) of eye knots used as a tie-in to a climbing harness. Same goes for highlines (which induce very high loading) - cant recall any instance of a knot breaking due to stress and strain. Anchors have failed and rescue frames have toppled over, but knots don’t just arbitrarily fail (assuming the knot has been correctly tied).
Mark G
[edited my typo in thread Subject]
And the mixed-knots cases mean that possibly
a weaker version of the presumed target knot
could be missed. (Recalling Derek’s objection
to such testing as mussing up pure statistics
and having such lesser-value’d results --although
OTOH it seems preferable to dealing with the least
vs. the most or even average!)
And, yes, break testing --no signs of flogging! :o
In searching for any sort of rope-movement-melting
testing/evidence, I found one yachter’s (also cyclist
& rockclimber!) assertion of a tail-tucked figure 8 eye knot
(tied in “weak form” (interior twin strand loaded),
and tail brought across the SPart opp. collars,
then tucked out by eye legs such that the tail is
the first of these 3 exiting strands to be crossed
by the SPart.
[Blog post dated 2009-11-28, Saturday, of blog
http://sail-delmarva.blogspot.com/ ]
The [i]figure-8 [eye knot][/i] can be improved upon;
take the tail around the standing part again and feed it through the first turn.
This increases the strength, makes it more secure against working loose,
and makes it easier to untie. Three for one!
This has become my favorite mountaineering tie-in,
and I have tested it through more than a few falls,
as well as failure-testing it against both splices and standard figure-8s.
It is less than line strength, but not by very much.
Now, I might guess that his asserted testing
was done using yacht braid and not climbing
rope (and was A-vs-B testing, not calibrated).
Anyway, a good result from one source.
It has been pointed out, though, that such tail-tucking
for this knot can make flyping more easily done, upon
ring-loading. (And, frankly, I forget which way was
suggested in Outdoor Knots by Clyde Soles, for which
I’m partially responsible --though hadn’t myself much
considered this extension.) A short tie-in eye shouldn’t
be getting ring-loaded, except if used qua belay loop
–which some folks do (and I think that BMC even
suggested, or acknowledged?).
–dl*