I was playing around with the bunny ears knot (double loop figure eight) on some 5mm cord and weighted just one loop. The other loop popped out and the knot undid leaving me with a weird fig 8 slip knot thing. I've used this knot for rope access and abseil set-ups to equalise 2 anchor points but was a bit surprised to see the consequences of only one loop being used and weighted. Admittedly, it was a loosely tied bunny ears so I could see how it came apart.
I guess I'm asking if there's any research on this; if I'm tying it wrong (it's the same as animatedknots.com); if it's still seen as a useful knot in the outdoor/rope access industry or what the likelihood of slippage on a fully tightened knot is. I understand this is not supposed to have just one loop weighted, but I'm curious!
There are many factors at work and unspecified, here.
Your 5mm cord was what -- HMPE- or Technora-cored cord
which can be stiffer than usual.
You loaded which of the two ends of the knot (this is almost
always left unspecified in knots literature for these
tied-with-bight knots,
and there's not any good study of the differences. Grog's
Animated Knotsimages are yet ambiguous in geometry & loading: i.p., that bight feeding
the two eyes (which might transfer material from one to the other)
could be pulled (as
A.K. has it) up over or behind under the
adjacent turns of rope (which themselves beg the same question).
Dave Merchant's
Life on a Line (2nd ed.) presents this twin-eye knot
as secure and non-slipping on single-eye loading -- which the knot most
certainly IS intended for, in the case of anchor failure (unlike some
bowlines, where feeding can be quick on certain loadings!). Yes,
one starts with both eyes loaded, but the knot must endure one-eye-only
loading.
In any case, there is a *better* (IMHO) way to get "bunny ears" from
the Fig.8 base, although this knot is trickier to tie *correctly*. The
knot is very easy to untie.
www.postimage.org/image.php?v=Pq2M0G7AHere is an image of the knot, shown in two states, below a Bowline
with a bight whose vulnerable eye has been (pre-)collapsed and
is highlighted with black cord (tied in yachting Sta-Set polyester dbl-braid);
the Fig.8 is in a particular form, which I regard as optimum (and almost
as necessary -- other orientations being awkward at best on setting).
Note the way the ends make a gentle crossing twist on entry (seen
better in lower, exploded image), and how the parallel parts cross
within the knot. Loading either end should be quite strong, and in
any case easy to untie. However, sizing the eyes will be harder to
get right & set, likely, given the curves that the re-tucked bight
makes in reaching its collaring of the ends.
The paper-with-arrows indicates where the eye bight re-enters the
knot, AND DIFFERS between upper/lower knot -- to show that it
can be done either way. (economy of imagery) So, yes, we have
here thus two knots, closely related (times two, for whichever end
is loaded; or THREE, to consider case where both are!).
And here is the same idea manifest in an asymmetric Fig.9 eyeknot,
so show that D. Merchant's dismissal of any "bunny-ears" Fig.9 is
the result of limited vision. The (only) such knot, as D.M. sees it, is the
form at the top, which he found considerable slippage in for single-eye
loading; I find the other forms secure (but have hardly loaded it all so
much -- use body weight and a 5:1 (poor) pulley, so a few hundred pounds).
www.postimage.org/image.php?v=aV2n19M0[Btw, I had to click & re-load some of these URLs more than once in order
to produce an image, after the initial response was "NO INPUT FILE SPECIFIED" ??]
(I might have to repeat the uploading directly to this forum!)
Finally, you should confer the following site, re the Karash knot,
www.karashknot.com/7.htmlfor a bowline-like twin-eye knot that is more secure. Here, again,
the loading isn't specified, but I think that this site implies the
loading of one end, and you can play around with it yourself.
--dl*
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