Author Topic: Bunny ears knot  (Read 7049 times)

climbermatt

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Bunny ears knot
« on: September 23, 2009, 03:21:27 AM »
Hey,
Being new to this forum I'm not sure if this has been talked about (couldn't find it on the search): 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!  Thanks




Dan_Lehman

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Re: Bunny ears knot
« Reply #1 on: September 23, 2009, 05:59:00 PM »
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 Knots
images 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=Pq2M0G7A
Here 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.html
for 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*
====



climbermatt

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Re: Bunny ears knot
« Reply #2 on: September 24, 2009, 03:24:33 AM »
I'm just uploading 4 photos of this knot now so should be ready by the end of this message.  The cord is regular climbing prusik cord, polyester/nylon with sheath and core (technora?). 

OK, the photos.
Photo 1
http://www.flickr.com/photos/42853948@N06/3949503460/

It's a very loosely tied bunny ears based on a fig 8 knot (like Grog's animated knots)

Photo 2
http://www.flickr.com/photos/42853948@N06/3948726261/

I pull on the lower of the two loops causing the upper loop to shrink and lower loop to grow.  This slippage was surprisingly smooth (probably because of the cord used and the looseness of the knot)

Photo 3
http://www.flickr.com/photos/42853948@N06/3949508704/


With continued pull on the lower loop, the upper loop slips out of the fig 8 causing the lower loop to drastically increase in size and put a shock weight on the knot

Photo 4
http://www.flickr.com/photos/42853948@N06/3948719359/

The continued force on the lower loop pulls all the remaining slack from the old upper loop and leaves behind this fig 8 slip knot.

I'd love to look for alternative knots or different ways of tying this knot - a great thing for me personally as I'm always looking for new or better knots for a job.  But this post stems from how certain knots are used in my new place of work, and whether this bunny ears was appropriate in place of a regular fig 8 knot. 

I am a firm believer in keeping things simple and appropriate, and had heard from people in the rope access industry that bunny ears were being used less in favour of a fig 8 and alpine butterfly set up.  I'm wanting to just see whether my paranoia of weighting one loop (the loop as shown in the photos) is in any way dangerous and if there is any research in breaking/slipping strengths of this knot.

I have pulled the other loop and it forms a figure 8 with a random loop around the 2 ends of the tail.  It's safe at least, with failure only coming from shockloading or the heat produced with any slippage (as far as I can see)

Thanks for the replies and hope this makes it clearer what I'm talking about