Quote from: Dan_Lehman on Today at 06:36:12
sometimes it is the damage done by movement that can so weaken a SPart part that, even when it lies outside of the nub, it is what breaks
You mean, "even when the damage lies NOW outside the nub" - that is, the damage was done at a point that was once inside the nub, but the movement/flow of material has now transported this point outside the nub ? Because this damage (of a straight segment) can only be damage of fibers, done by other fibers at contact with them, is nt it that so ?
Yes. The drawing out of material *scraped* it against
some taut collar or other part, heated/abraded-damaged
fibres, and now it is weakened such that it breaks, though
no longer in contact with anything but air. (Here we should
be aware of the lack of such good, pinpoint-placement of
the rupture points --something I've tried to determine by
means of marking points in a knot and photographing the
knot pre-testing/post-testing (survivor specimen).)
Quote from: Dan_Lehman on Today at 06:36:12
I will still argue that we needn't put "all the known knots" to the test
(and that we are hoping to be able to replace testing with informed analysis!).
Frankly, as I grow older in this field 
, I do not believe that this "informed analysis" is going to help beyond a starting point...I see the "Oval bend" I have met recently, and I say that I would like to compare it with all the other bends --and especially with the Zeppelin bend to which it bears some resemblance--, and I do not see how one could really predict if this bend will be weaker or stronger, and how much...
Yes, but you can't ... , because you don't have the basis
of intelligent testing to support theories. Given the advance
of understanding got by some attentive, intelligent analysis
of test cases, AND a good look at a
well-tensioned knot
of interest, you should be able to conjecture results; and as
each such conjecture meets actual testing, (y)our skill should
grow! THAT is my hope. Otherwise, it becomes a funny thing
like rolling dice or cranking slot machines, just waiting to be
entertained/surprised by whatever value pops up, by chance.
("God does not roll dice" --challenged, yes, by quantum mechanics,
but good enuff for knotting!)
We do not have sooo many bends and end-of-line bowline-like loops
( certainly, not a "vast" number of them ),
and testing them will take a much shorter time than analyzing them !
We have enough to be wondering by what magical blessing
a cordage maker might decide to gift some mountain of material
for y/our purposes --esp. at 20 cases per knot! And says you, who
wanted to "test all known knots" ?! My, I can count some 2_000
"new" knots to whatever bundle comes before that, I think. By
your criteria, that's (only) 40_000 test cases to do!
Quote from: Dan_Lehman on Today at 06:36:12
To think that practicality is measured "by numbers" is to have too much a bent for quantification.
For what it's worth, the Fig.10 & Fig.9 eye knots have been somewhat shown to be stronger than the popular fig.8 eyeknot --but that has had no huge effect on things
Well, if have to lift somebody s still living body from somewhere by a rope, and if I have enough time, I will always tie the stronger knot, because I want to sleep at nights.
You must have my current restless nights, then
--knowing you don't know what this "strongest"
knot is! But it's outright stupid to make this insistence,
and an understanding in "numbers" --i.p., in statistical
significance (cases to failure) of the strength difference
to practical safety/success-failure (there is NONE).
There simply isn't a way to tie likely SAR rope in such
a way that one would endanger anyone by rope rupture.
that the bend A is 5 or even 10 % stronger than the bend B,
you will do the same, believe me.
No; I'm as likely to try something novel, perhaps
(though that's a real SAR no-no), or vary, between
cases. Most likely, I'll tie something comfortable and
natural to effect, at the time; and maybe something
quite UNnovel to "do as Romans do" and not ruffle feathers.
The enbolded phrase is one needing attention : typically,
it is a mis-use of language where what should be said
is "10 %-pt.s stronger" --say, between 55% & 65%,
a difference of roughly one fifth of the former value,
so "20% stronger", but more-easily-figured "10 %-pt.s" so.
If that is not "practicality", I wonder what is it...Of course, all the other factors
Bingo, as you illustrate. In a short-duration, constantly loaded
situation, a bowline might suit best, for sake of untying; were
the knot to be left unattended ... , one might seek something
w/greater security. Strength, per se, would have no real bearing,
plain and simple --none : there is zero chance of rupture by force.
However, numbers will put everything on some objective perspective
--and I think that someday we would be able to quantify all those other factors, too.
I know that "most" people will keep tying only what they have parroted in a young age
--I have seen this conservatism in this Forum...
That conservatism is if anything a bent in your direction,
of thinking "stronger is better"; and the pathetic tested
results are parroted much more than analyzed/critiqued!
It's naive to think that somehow "numbers will put everything on
some objective perspective" unless you're going to admit that,
as I'm arguing, strength is an unlikely key criterion, and also
remark that
particular, case-at-hand "strength" is going
to be a matter of conjecture, not a readily indexed-on-my-iPad
value to be learned! (And then you have to acknowledge how
various are the tying, dressing, & setting circumstances, beyond
real-life loading vs. test-bed loading, and actual vs. tested materials.
Quote from: Dan_Lehman on Today at 06:36:12
some results for the fig.8 eyeknot putting it near 90%
1. I do not believe in those results, for "plenty" of reasons...
2. Even if that is so 990%), indeed, I want to see those results repeated, by an independent experimentalist.
3. I will never be sure that the same large numbers will not occur for other bends, too - until/unless ALL the known bends are tested....
4. ...and, first of all, the other 4 (four) dressings of the same fig. 8 eyeknot !
I can only say that Tom, too, was impressed by that;
that the values fell with little stnd.deviation (well, hard
to be much lower, for there's not much higher with which
to counter-balance a low value!), and the orientations
where the break occurred were, hmmm, similar, and
not exactly in the pure "perfect" forms of symmetry.
AND that the "%" values were figured NOT from the
manufacturer's
rated tensile strength but from
(IIRC) Tom's own, 5-cases? testing.
AND, I too acknowledge that this is --however done--
an apparent outstanding/outlier case, not replicated
elsewhere (though much of elsewhere relies on rated
tensile for figuring percentage (but one might suspect
ratings to be conservatively low, so % should be high).)
--dl*
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