There's more Replying here than reading & thinking,
and some comments that call for redress.
To one central point --i.e., relative strength of Rosendahl's bend--,
there is some evidence that the Grapevine Bend (aka Dbl.Fish) is
considerably stronger. A decade ago or so, one fellow did some
homebrew, truck-pulls-knotted-rope-with-knots_A_vs_B in a sort
of competition. With a few trials for most, he came out with the
Blood knot as a champion, and the Grapevine was also strong;
Rosendahl's Zep. bend was around the middle, not quite so strong
as Ashley's #1452, IIRC. About these, we can wonder at the exact
geometry taking the force. (The ends of each specimen were tied
w/Fig.8 eyeknots: these never failed!!)
((Roo should recall this: initiated by interest in a presumed invention
of the "Bulldog Bend", which turned out to be Ashley's #1425, which
indeed is a neat knot.))
And from the Treebuzz thread cited by Roo, we have another view:
When I tested the F8 bend against the ZB, I got 66% and 63% respectfully,
in 9mm PMI rope. I don't even consider 3% enough to claim a difference.
The DFB, however, held to a significantly higher loading and I finally ran
out of room on the machine before it failed.
This is not all so surprising, and quite contrary to
It seems that that the Zeppelin Bend doesn't put as much stress on a rope as does the Double Fisherman. The angles in the Zeppelin Bend are not as extreme.
To my eye --and to one commenter in the Treebuzz thread--,
the initial bends in Rosendahl's bend are relatively hard, around
one diameter, whereas those in the Grapevine are more gradual
AND each SPart gets gripped pretty firmly by the other. (E.g.,
in one test of 8mm low-elongation (caving) kernmantle where
a Strangle noose-hitch was tested (i.e., rope turned around a
'biner, and then a "half a Dbl.Fish" was tied to itself), the break
came in the SPart
of the noose-hitch, not the knot --so tight
was the knot's choke on the highly loaded line! (This might not
occur with every rope, though.)
To Roo's dismissal of the witnessed slippage "post rupture" of
the Grapevine:
When a knot breaks, it breaks. I'm interested in what the strength percentage is,
not what dance the rope does or does not do afterward.
I'm done trying to think of different ways to explain this.
Security issues only apply before rupture. It shouldn't need to be said.
...
This is not a security issue with slippage, it's what happens after the rope ruptures.
But this behavior
is significant, indicating the internal
slippage occurred prior to and so led to the rupture
of the mantleand not the (very strong) core. Consider that at rupture HMPE
stretches about 4%, but polyester about 10%: why would the
PES mantle be first to break, then? --unless the kern's slippage
has left the mantle to do the work (or more than it should)!?
That's my conjecture, anyway.
So, it's not simply some behavior occurring after rupture, IMO;
it has occurred during loading and led to rupture.
Moreover, re
As I said before, the security issue with slick stiff rope and this knot
is the possibility of things springing open, not slither or slipping.
while I'm unsure of "this knot" --Rosendahl's?--, stiff rope can be
problematic re slipping as turns don't become sharp and nip,
enabling the rope to slip. (This might explain Richards's results.)
I'd like to throw into the comparison the Albright Special, the Double Uni,
the Double San Diego Jam, etc. Let's stack the Fisherman Bends up against those knots.
Firstly, let's forget we even thought about some "Dbl.SDJam"
-- hitching to a hitch is an obviously severe weakening, worse
than eye-in-eye: 1dia turns of highly loaded line vs. line, AND
moving (with force increase).
Secondly, somewhere above I asked if anyone had actually tied the Uni;
my point was that the just-prior-to-tightening images that are commonly
shown present a markedly different form of a multiple-Overhand knot
than seems to be expected to obtain from setting (which would be
the Dlb./Trpl./Quad Fisherman's/Grapevine (and Strangle) form.
So comparing a Uni to the Fisherman's is working with mirrors.
That this isn't recognized speaks to the level of familiarity with
these knots (which to some degree speaks to their presentations).
But I don't think certain rope users choose these knots because they jam.
Oh, they do. And they do more: they tape or hog-ring staple or
tuck-through-the-lay or otherwise secure tails of knots, even of
ones we conclude jam (such as the Fisherman's, noting here though
that Richards's testing found them to slip at high loads). And
I've read remarks that jamming (well, what would pretty much
be tantamount to this aspect) is deemed good to limit movement
of material within the knot, under load. (Think *frictional heat*.)
--dl*
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