Welcome, back, Paul! Happy 007.
I’ve had a project on my action item list for some time at work to test the strength of various common knots,
using at least a couple of different types of rope. These need to be knots useful for the hanging of suspended
scaffolding, or the rigging of vertical or horizontal lifelines.
I’ll have to use soft lay ¾ inch three strand twisted nylon.
I will probably also use a marine kernmantle.
I’m considering also using static and dynamic kernmantle rope from a rock-climbing source.
How about some polypropylene or coextruded ("copolymer") PP & polyethylene (e.g., Ultra Blue,
PolySteel)? What is typically used for this hanging scaffolding (seems polyester or some
combo rope of that with PP or coextruded fibres in the core would be used)?
Perhaps for a good compromise of shock absorption and durability, less stretch,
some of the recently conceived "gym ropes" used by rock climbers might work?
They area designed with thicker sheaths to endure repeated use in climbing
gyms, and sacrifice the full capability to hold a UIAA-defined severe fall with
the low impact forces of typical climbing rope. They might be more beneficial
in "fall arrest" than some of what I've seen advertised for that--which tend to
be substantial (5/8" dia.) ropes of fairly inelastic material! (Though one can
use a special, shock-absorbing lanyard to attach to such a line.)
At the very least, I need to test the following:
Bowline (left and right handed versions)
Clove hitch (Backed up with single and double half hitches)
You can get as much variation in dressing/setting ONE type of Bowline
as you might in variants--and that might be a good thing to test, too.
E.g., one can dress the knot such that the end is pulled away from where
it will be drawn by loading, and one can set the collar tighter/looser.
Ditto for the Fig.8 (and Gordon's suggested Overhand) loopknot: for
starters, which of its two ends will you load? --might see if that makes
a difference (cf. Lyon Equipment's testing for the UK's HSE).
Though if few test cases are done, well, less can be concluded (Lyon's
few tests exemplify this, unfortunately).
There is a Bowline variation below--rightmost, "Janus"--which you might
try (and it would be nice to try an extension of this one where the end is
brought a 2nd time around the SPart and through the "rabbit hole"--it's
a matter of both further securing but of one more diameter of rope that
the loaded SPart wil bend around.
and a precise/specific orientation for the Fig.8 loopknot can be found here:www.iland.net/~jbritton/KnotPhotoContributions.htmlUpdated Link > www.pssurvival.com/PS/Knots/Knot_Knowledge_Photo_Illustrations_2004.pdf
(This knot is tied in so many various dressings, it's amazing that folks think
some test results for "Fig.8" mean anything w/o knowing the details!)
Btw, what are the circumstances for use of the loopknots? I.p., are there
some applications where the knot will be (or can be) tied completely
before being put in place (e.g., tying the Fig.8 in the bight rather than
"re-weaving" it)? If so, that gives me some ideas for replacing the Fig.8!
(And I think I sent some of them to you--derivatives of #1425, sort of
Also, try backing up the Clove with an Overhand stopper.
Since my boss is paying for the test, I need to limit the scope to what meets his objectives.
He is interested in making sure that our scaffolding and fall protection riggers are using the
correct and the safest knots with the correct rope type. I’ve got access to all sorts of test data
compiled by other testing agencies, and have come to the conclusion that none of it really
applies to our business.
... have all the equipment we need to do this correctly.
What other suggestions would you make?
I suspect that although you have "all sorts of test data," there isn't sufficient specification
about the structure of the knots for you to assuredly replicate the testing! --that's typical.
I thus strongly suggest that you photograph the test specimens at the start and mid-way
to rupture, and ruptured, if sensible
. It's the only way others can see into exactly what
your testing might mean. Where feasible, it would also be wise to e.g. tie TWO loopknots
in a line, so to ensure that after the test you have one broken and one in the form that
it got from nearly breaking (which can be compared to the "mid-way" image to see what
changes in structure occurred). Such information might lead to insights into how to dress
and set knots in particular ropes.
Also, what sort of loading do you expect in practice? Slow-pull destruction testing is
probably not such a good model of expected use.