I thought, when I originally posted, that I should mention the sources, but I didn't have them on hand at the time to quote accurately... As you probably guessed, my two sources are the same as yours. Merchant's Life on a Line proposing that there is a stronger and weaker way, and Smith and Padgett's On Rope stating that there is no difference.
You're being ambiguous,
except by content of assertion --which pins both
claims I think to 2nd versions :
On Rope, 1st ed.carries the assertion of difference (and the incredibly
stupid illustration (that "flat" impossible '8') with
guidance to "dress & set" but how the devil is one
to know
how to do that, devoid of specifics?!
(typical rubbish, I'm afraid)
And Merchant I think had an earlier version that was
publicly available for free and which has less interesting
knotty information --I think.
And, while it's on my mind, noting that you must be
with OR-2nd, let me point out to you its mistaken
presentation --and to some danger, IMO-- of those
"3- / 4- / 5-coil Prusik [hitches]" : the 2nd edition
turned them upside-down, and it's possible that they
will not grip at all, and otherwise do so poorly --for
the single-turn half then being on "top" will press
down upon the multi-coils beneath, and cause the
hitch to slide (just as Ashley remarks for the
rolling
hitch) !! (I see that "after Thrun" is cited, and
IIRC Bob & I --or him alone?-- tried to contact Bruce
Smith about this (or else whom?), w/o acknowledgement
for the effort. There had to be some matching alteration
of the wording, which I recall discussing --and had thought
it pretty simple--; and that should belie a claim of pure
innocence for whoever made the unjustified change :
i.e., if you confront an assertion of needing coils on TOP
and you're putting them on the bottom, you must know
that you're going against the rationale! And I believe
that the words ARE changed.
[Perhaps Bob can chime in re this.]
Any idea where I can find a copy of Rob Chisnall's Reference manual?
Not of any official source. It's dated (ca. 1984, from memory?),
and in full might be about a $60 copying fee alone (for much
more than just knots, of course). It didn't as I recall have
anything beyond the "10%" claim; not sure where I might
have gotten the thought that ORCA did their own testing.
Merchant does indeed state that the "weaker" method "can" reduce the breaking strength by 10%, but he doesn't cite any particular study or data. He also says of this 10% difference in strength: "in tests it can be difficult to prove this reliably" How about that for a caveat!
The first thing to ask about such claims is what the
"10%" (or whatever) means --"10 %-points" or purely
"10%". It won't amount to a huge difference, but, still,
one should speak clearly. The
easy and IMO more useful
value is %-points --what one can see between test values,
and which works in *both directions* (if I'm 50% bigger than
you --by your weight, x 1.5--, you're not 50% but 33%
smaller than I by my weight :: the two "*directions*").
Again, with Smith unable to get a decent image of the
orientations, I have no confidence that he knows what
he's talking about. AND, to those at least with the right
orientations, recall my thoughts on
setting --i.e.,
to set with hard force on the TAILS, to try to give that
curvature in them against which the SPart will bear,
and have them tight so that they don't (so easily) get
pushed out of the way (and allow the SPart to straighten).
I think that Dr. Merchant's book is the best text available on the subject
of rope rescue, and in the top five texts for rigging with knots.
I can take him to task for dismissing the existence of
mid-line/directional "
fig.9 knots", but such things
are the natives of minds like mine or Xarax and hardly
commonplace. There are actually a batch of directional
eye knots to be played with!
http://igkt.net/sm/index.php?topic=2198
Xarax's version C is what Merchant shows as the "correct" dressing, whereas I believe Xarax's version A is the "correct" dressing of the figure 8 loop knot. (thanks for the pics Xarax)
X. posted some images more recently, too --adding
the version-A after I remarked of the missing "perfect form".
But here's another ambiguity (your 3rd : back to the bench!),
for X. doesn't give loading. To match D.M., it would be white
on right, orange left, of version-C.
Smith and Padgett site Neil Montgomery's Single Rope Techniques as saying that it is possible to tie the fig 8 loop incorrectly, and that the weaker version is 10% weaker (same as Merchant) but they go on to discredit this notion.
They [c]ite "knot destruction tests and Ashley" as sources.
Which begs the question of how that really "discredits"
anything --as you note re Ashley, and I re their understanding
of the actual orientations (as they cannot illustrate it).
I don't know of Montgomery's work, and so cannot comment
on what he might show (or verbally illustrate) as dressings.
Do you have that?
... this notion that there is a 10% weaker version of the fig 8 is NOT widely known, or taught.
The common wisdom is that there is no important difference in the two ways of tying the fig 8 loop.
?? Common wisdom? I don't see evidence of what I'd
call "wisdom" --it would have to be inferred by absence of
counter statements--, but rather a common ignorance
of the difference : mostly, there is no discussion of it,
and many times there is no indication of which end to
load, for the eye knot (and maybe also the end-2-ender,
which is less frequent in presentation, the
grapevinehaving much of that knotting domain).
And note that we are discussing more than "two ways"
of that knot : there are two
loadings --i.e., choice of
Which End?-- per images Xarax gives, so that's six.
Personally, I agree with the common wisdom, but I have been tying 8s
Merchant's way since I read his book. His way certainly can't be worse!
Why not?
But as he notes the differences (in contrast to Smith & P),
one can give to him (as for Chisnall) some hope of credibility!
We might note simply that "ropes don't break at knots"
and that the vast usage of all sorts of slop suggests at least
their practical safety. Still, for our finer understanding,
we'd like intelligent testing! (Here is a good point to remark
at the testing of both "tied in the bight" and "rewoven"
fig.8 eyeknots by both CMC & the no-longer-easily
available Dave Richards testing (which, alas, Smith got
booted off of its host, on account of some simply explained
inconsistencies (misreading data sets between two of the
three ropes tested --i.e., reading A's for B and vice versa).
Last thought about the figure 8: In the 4th edition of the CMC rope rescue field guide
(I just own the field guide, currently not the full text) they state that the efficiency of
the figure 8 bend is 51%, and they state this 51% is much lower efficiency that in their
previous tests (which I believe are widely cited by other sources). There are certainly
stronger bends out there (like the double fisherman) and also more jam-resistant bends
(like the zeppelin bend).
Now you scare me : how can CMC come out with such
nonsense?!!! I mean that in the sense that LOTS of
testing has put its strength well higher than 50% !!
--i.p., their own, as pub'd in their 3rd version : it gives
the
fig.8 end-2-end knot (of some loading (they
use the easy-for-artist-but-impossible-for-rope image))
as 81% which is stronger than their
grapevine!!
How do they explain this
drastic revisionism?!?!?
(Oh, <groan>, they don't actually say '81%' : no, they
indulge the nonsense of talking about "strength lost",
so write '19%' and leave the needed arithmetic for the
reader --bugs me, for its the other value that one uses
in figuring systems and so on, grrrr.)
Do they, e.g., claim to have been doing "youthful
indiscretions" / "taking drugs" when they put out the
test results in the 3rd edition?? (I forget, but think that
Dave Richards didn't test the end-2-ender, but only the
eye knot (tied both ways!).)
Since I mentioned it, here are my top five texts for working with knots (in no particular order)
I could suggest
Outdoor Knots by Clyde Soles
(and w/help from ...
) as a fresh, different treatment.
Last thought (more thread drift!): On Class 2 double braids (HMPE core, conventional synthetic jacket). On a show I worked on we used a class two double braid as guy lines, which were tensioned, and then subjected to cyclical dynamic loading (swinging of a trapeze). We found that the core would bird cage, causing bumps in the line, and eventually break at those bumps! We solved this issue by adding extra slack in the jacket (the lines were spliced either end). We think the friction of the jacket on the core was leading to the issue of the bird caging. On another show (i didn't work on) class 2 line moved a trolley. They were heavily loaded, under constant tension, and dynamically loaded, but the D:d ratio was large. They broke-test a set of used lines and they broke at 50%! of their published breaking strength! My conclusion is that we (all of us) are still learning the behavior of these "new" HMPE ropes.
Okay, not an acronym, but ... what is "birdcage"
qua verb?! And "trapeze" as in the usual thing,
with people swinging? --and then "would eventually
BREAK" ??! What's with the swinger, then?!
As for friction of jacket on HMPE core : I'd think that
there'd be not much --less than for other then HMPE,
anyway.
One can question strength loss, or published accuracy, eh!?
(Angling line seems to often come with WAY understated
tensile strength, so knotted strength is high enough.)
--dl*
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