It should be with some question that one reads quoted test data
for knots, as figures are all over the place, but detailed information
about testing is hard to find. The 80% figure for slings in a choke
orientation is a rule of thumb I’d expect to differ with the material
and the closing part of the sling–an eye in tape normally or specially
formed, or metal of some sort, or … . Angle is important–what I
sometimes consider the deflection )(from straight) of the part
in question.
Yes, there have been reports of knots testing above 80%, in rope
(TMoyer had Fig.8 loopknots at 92% !! --highest I’ve seen.). (I
forget if Lyon Equip did a good job of figuring actual tensile, but
they have some strong loopknots as well. Also CMC Rope Rescue
Manual, and Dave Richards’s recent testing of kernmantle ropes
got up to just about that mused limit of 80%, though not in the Fig.8!)
But the angle of the SPart into the knot I don’t see as needed to be
as hard as it is for a choke sling.
Roo muses that the Bimini Twist is a good counter example, and KnotNow!
echoes the old quotes of high percentage for anglers knots. But where’s
the data? (And who are these fisher people with WWWeb site claims?)
Here’s some actual data re the Bimini Twist, which is I think raising some
controversy in the angling world:
±-----------12-turn Bimimi Twist (avg. breaks paired per vendor line)
| ±-----20-turn
101 69
96 90
80 81
49 58
71 53
97 66
92 84
102 98
101 100
Now in the above, if I’m reading right, are some mixed types of lines–both
trad. monofilament and newfangled “braid”, which I take as a keywork for
HMPE (Spectra/Dyneema)–also “gel-spun polyethylene”. And there are
more tests with the Bimini tops at 81% & 80%, 88 & 77%, but then as low
as 33&37%, 27&38% (20#, 50# lines; 40-&60-turns per knot). !?
Oh, and here are a few examples of “rated” vs actual strengths of braided lines
(which helps explain how some test results are so high vs. rated strength!):
actual as % of rated: in 16 “20#” lines, ranged from: 117%, 138%, 150%, … to 273% (!!!)
and in “50#” lines: 94%, 110%, 112%, … to 167% (!!!)
(Now, if I can find my way back to the discussion list re this, I might see how
the dust has settled.) Oh, reference: magazine Sport Fishing, 2006-08,
pp.62ff, by Doug Olander.
Meanwhile, we have a tester reporting rockclimbing tape slings “girth hitched”
together breaking at (in both nylon & HMPE) about 50%; and yet elsewhere
similar testing (of each, and of mixed) got 70%–a whopping difference!
–might wonder at the knot tying (I always do). :
As for breaking twine the Ashley way (which, for those w/o ABOK, is
holding firmly a bight and drawing through the bight the line near to where you
want to break it, and it running around one’s hand to form the bight (so a sort
of Crossing Knot around one’s hand), where would you expect the break to
come? --at the bight which seems to be getting cut through, or in the line
moving through, attempting to cut, this bight? Well, it surprised ME!
(Ashley’s comments about strength there are a bit silly. Also, somewhere
I have a bit of test report on different ways to interlock two bowline eyes,
and there was a difference in results, which shows that for THEM the break
didn’t occur in the bowlines (else it wouldn’t matter how … interlocked).
And breaking “just outside of the bowline”–nahhhhhh. --wonder how he
tied those knots!