In reply to Adam L:
Thanks much for the further insights, Adam -- apologies understood
re delay (no problem: the thread endures
.
> I've got LOAL, but there isn't enough background info on his tests to compare usefully to mine - I can only assume he tested the bunny with both loops loaded
Well, he gives explicit comment about effects of loading rates,
and notes some little, limited slippage on slow-loading -- that
suggests testing. (Recall the different results you found re the
Clove hitch between the low-elongation ropes (various loads
but all slipped) and the dynamic rope (held to rupture).)
In any case, there is another way to effect bunny ears in the
Fig.8 (which I think I gave a URLink for an image of, above)
that seems more secure, and easier to untie, and good looking
re curvature & strength.
> They got me interested in this dressing aspect ...
It should be noted that "dressing" and "loading" or some other aspect
of [i]orientation[/i] are distinct: both you & [i][u]LoaL[/u][/i] have I think
the same [i]loading[/i] of the Fig.9, e.g., but markedly different [i]dressings[/i]
-- your knot's ends make a fairly straight path to the turn around the
eye legs, whereas Merchant has more elongation in the eye legs' wrap.
The should-be-obvious point that most presentations of these knots
omit is the very simple, basic question of Which End Is Loaded?
Somehow, this just doesn't seem to occur to people -- amazing.
(Yes, it MIGHT be of trifling difference; but if testing, it should be
something to [i]verify[/i] and not assume.)
> Shame we can't include photos in these posts...
Partly, but please note that YOU have photos in your report, and it was
to these that I referred and asked "Which shows 'above'/'on top' ?"
So, if you could just refer to at least your report's photos of the Overhand
and Fig.8 (Fig.9/10 being arguably hard to figure, unless you can confirm
that ends have no twist/crossing hidden beneath the wraps) and state
how those orientations are called by your terms (or see my guesses on
this and confirm or correct), that is all that's needed.
Otherwise, we can find on-line images to refer to easily enough; e.g.,
here's one of what I call "the perfect form" (which points to the same
part as both standing part (mainline) and then as end (tail):
www.treebuzz.com/forum/images/upload/194178-Eights.jpg
Again, my [i]guess[/i] is that you'd describe the upper knot as
having the part "above/on top of" the end being loaded?
(And it is the strand that is first contacted by the eye legs on
their entry into the knot body.)
> I could expect 'a' vs 'a' to give a higher figure than 'b' vs 'b'. This was borne out by my results almost perfectly
>([e.g.] in a fig 8 'a' always beat 'b')
Well, the data don't come with notes about which was the broken one
in the center column, A-vs-B; in some cases, it has the highest value
(e.g., Table 22, Beal dynamic, Fig.9 & Bowline)! If you have only these
3 tests (3 pieces specimens, i.e.), it's too small a basis, esp. where many
values are so close -- a hint, of sorts, maybe. But it's being NOTICED,
that's good to see. (The Fig.8 btw, had B > A in Antipodes, and was
pretty even in the dynamic.
> I suspect the gear freaks of the world would have seized on it and become knot-dressing-nazis, which I was keen to avoid. The level of variation we found was really only of interest on an academic level - in the real world nobody should be working a fig 8 with such tight margins of safety that they need to ensure they have the stronger dressing.
Nor even which of reasonable alternative knots, for that matter.
But it needs to be done, to be specific, so that should differences
be found, they can be examined and a better understanding of
knot mechanics gained. Consider, the Sheet bend has been tied
for ages, but is it anywhere said which of its two, asymmetric halves
(which rope) usually breaks (if...) ? -- whether one should expect
some higher breaking strain if one half is of stronger/larger rope?
FYI, Adam Fox, an AMGA guide had a set of 10 tests in the A-v-B
format, Overhand vs. Fig.8 eye knots, in (presumably) dynamic
rope, and found them equal (5-5 tie in breaks); he reports testing
3 sets of 10 w/like results to the published data from one set;
your data hints otherwise, except perhaps for the Antipodes rope.
But we have no express discussion of dressing/loading by Fox.
The knot nazi reaction can be anticipated with some words to the
effect that such differences are not to be taken as such; I have often
railed against those presuming that Tensionless ("knotless") Hitches
are the cat's meow for anchoring; in practice, for many applications,
it makes no difference (except perhaps causing more gouging of a
tree bark).
> for the Butterfly, the normal 'correct' dressing ...
Wright & Magowan explicitly wanted a crossing eye legs in the knot;
most presentations these days show them not; and there are other
subtleties. For one, which end is loaded, again -- as the knot's symmetric,
and the interlocked Overhands assume different geometries.
Of more interest than effects on knot strength here might be effects
on knot [i]jamming[/i], ease of untying.
Btw, Fox found Clove Hitches slipping in his dynamic rope -- 10mm
tied to a 10mm pin (to simulate a krab) -- ; interestingly, it was ONLY
in dynamic rope that you dependably got breaks. How to generalize
from such conflicting tests, eh?!!
*knudeNoggin*
ps: This insight of yours is one I've tried to share when I can.
It's interesting in that the behavior almost justifies a naive counting
of the strength of each side vs. doubling the weak side. In practice,
though, it's what you get.
[re why the Grapevine (Dbl.Fish.)-tied sling can be so strong,
HSE Contract Report 364/2001 3.3.9 ]
>| This is most likely due to the friction created around the pins at
>| each end of the sling. As the force is applied, the knot tightens,
>| releasing rope into that side of the sling and hence reducing the force.
>| This extra rope must slip around the pins to equalise the forces
>| on either side. Inevitably, friction impedes this process and the
>| side of the sling without the knot is subjected to higher forces.