Like you, I have seen a video of a heavy duty Dyneema rope simply pulling through a knot - too strong to break and too slippery to hold.
One should note that although HMPE is quite strong, as measured
in standard pull testing, it isn't "too strong to break" in many cases,
and does so arguably at about the same load as other like-knotted
materials --but which absolute load is a much smaller portion of its
tensile strength as compared with those of other materials.
I have to disagree with Dan in his statement that some tried and trusted knots have been with us for so long it is unthinkable that they would fail, and lean towards Roo's warning that we must consider the nature of the cordage.
Before too long, someone is going to abseil using one of the new hyper strong ropes (with super low cf) and will rely on one of these tried and trusted knots which will promptly slide through itself as if someone had greased its surface.
Whoa, you're over-reaching on what I said. In the world of
abseiling, the conditions are pretty well established and real-world
tested. Now, the point about using HMPE ropes is worth noting,
especially for canyon(eer)ing, where that material is working into
the main (non-"accessory") lines. Still, for these, someone should
find out an *easy* (as opposed to the unwanted "hard") way how
the ropes perform, as it's a simple matter to load such and end-2-end
knot with real-world loads.
(BTW, FYI, after reading Brion Toss's long-back SAIL article about
bowlines slipping, I tried with a 5:1 (poor, actually) pulley to see
such slippage in pure Spectra & Vectran (maybe also Technora), w/o
success; my figuring was that I'd generated the force (around 20%
tensile, IIRC) at which he reported slippage, but ... . (ca. 900#))
Today in the ultra slippery kite lines, most of our arsenal of knots are useless, given enough load, they simply pull though without breaking.
Maybe we should start a separate thread to explore what the
state of the art was prior --name knots!-- and what it has become
after the advent of these HMPE lines. I remain skeptical that some
solutions can't be found, though in rope, well, breaking strength
too much suffers --but none of my 6 tested eyeknots slipped.
At the rate that technology is developing, it is conceivable that we will soon have access to cordage which is essentially unknottable in that it will always pull though before breaking.
Again, slippage is a factor but the real problem with the current
group is more of weakness relative to tensile strength, no slippage
--that even
holding, the knot doesn't meet the need.
Btw, the J. Walker paper I guess copies images from Bayman,
for which I note that their "constrictor" is (a) not that, but the
structure of #1674 (a better behaving kin to the
ground-line hitch),
but (b) is loaded on that hitch's
tail, so inferior in working!?
.:. strange that?!
--dl*
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