Alpine Butterfly as an end loop

[Wallaby]

  I am trying to find some testing on the strength etc. of an Alpine Butterfly knot (ABK) when the loop is used as an end loop (i.e. only one side is loaded), and I was hoping your collective experience might be able to point me to some.

  It will be for rescue work so strength, lack of slippage etc. is important (when aren't they?).  It will be tied in 11mm static kenmantle rope.

  The ABK is great for creating a mid line loop with minimal strength loss in a line that will be loaded (i.e. both tails are loaded in opposing directions), but for an end loop - e.g. attaching the load line to the anchor - we have traditionally used the tried and true Figure 8 on a bight.  Lately though, someone has started using the ABK as an end loop for attaching the line (I don't know why) and I cannot get comfortable with this.  It looks like there will only be one turn gripping the loop so I suspect slippage will be an issue.

  BWRS have done some tests on the ABK:  http://www.bwrs.org.au/?q=research  but this was using it to join two ropes - i.e. opposed loads, so is not quite what I am after.  Their results do show a lot more slippage than the Figure 8, so this does tend to suggest loading only one side would slip even more.  David Delaney shows it used as an end loop:  http://davidmdelaney.com/alpine-butterfly-loop/Alpine-butterfly-bend-loop.html  and says it "showed no tendency to slip or collapse in my testing" but does give details of the testing or the results. 

  I would like to see some proof to either allay my fears or to show that it is not suitable for this purpose.  Have any of you seen any testing on the strength of the ABK when used in this way - only one side is loaded? 

  (Please turn a blind eye to the tail lengths and reversed wording in the pic - my rope skills are better than my photoshop skills.)

  Thank 'ee.

[Hrungnir]

I really don't like the Butterfly Loop in your image. If you put it under signicant load, it will transform into a jamming version. People which have used the Butterfly Loop in the Versatackle or Truckers Hitch (especially in polypropylen) know what I am talking about, as this happens when you put much load in the mid-line loop.

I don't know about the strength and slipping with the BFL in the image, but as a midline loop it should (by purpose) be able to be loaded at the loop and one (only) of the standing parts. However, you are right when being skeptic as the knot changes form into a jamming one, when loaded in this manner.

Dave Root writes this about the end loop on his website:

From http://daveroot.co.cc/Knots/Knots_SingleLoops.htm#AlpineButterfly
Note: When an Alpine Butterfly is dressed into the end-line loop configuration shown in picture 6 (above), the forces at work within the knot are different than the forces at work within the Alpine Butterfly configuration (picture 7 above). Therefore, the end-line loop configuration is best thought of as a separate knot from the Alpine Butterfly. These two knots are topologically equivalent (see Method #1 above), but they distribute the forces differently and therefore they potentially have different strength/security considerations. Since the end-line loop configuration in picture 6 has never been named (as far as I'm aware), and since it's formed by dressing the Alpine Butterfly a little differently, it seemed simplest to show the two configurations together. For a method of tying the Alpine Butterfly as an end-line loop while preserving the Alpine Butterfly configuration, see Butterfly bend loop.

[roo]

Hi Wallaby,

Just for the record, Wallaby is not my alternate screen name.   

Anyway, I'd be less concerned with rupture strength.  I'd be more wary of the difficulty of tying this correctly if it has to be threaded through or around an object before closing.  With the Butterfly Bend, there are mistakes that can be made that can look like the real thing, and so I'd wonder if a similar problem could creep up when using some end-of-the-rope (close after surrounding an object) tying methods.

For more info:  http://igkt.net/sm/index.php?topic=1892.msg12991#msg12991

Then, there's just the issue of the loop being harder to untie after serious strain when compared to some alternative end loops, such the Water Bowline* or Zeppelin Loop.  Then again, maybe your application won't see much strain.

By the way, the end loop that David Delaney shows is different than the common Butterfly Loop that you're probably asking about.  David's loop tries to more closely imitate the loading of the Butterfly Bend.

*41 diameters

[Dan_Lehman]

I am trying to find some testing on the strength etc. of an Alpine Butterfly knot (ABK)
when the loop is used as an end loop (i.e. only one side is loaded), ... .

It will be for rescue work so strength, lack of slippage etc. is important
(when aren't they?).
It will be tied in 11mm static kenmantle rope.

You can research the history of such usage and come
to a suggested answer to this question : that strength
is poorly understood and unlikely of much significance
in these applications --despite some rhetoric to the contrary.

The ABK is great for creating a mid line loop with minimal strength loss
in a line that will be loaded (i.e. both tails are loaded in opposing directions),
but for an end loop - e.g. attaching the load line to the anchor -

Still, one must realize that some intended uses of this mid-line
eye knot are expecting that it will become effectively just such
an end-line knot --e.g., in anchors where this eye knot forms
a "Y" to attach to a 2nd anchor, in case one fails.

It looks like there will only be one turn gripping the loop so I suspect slippage will be an issue.

You're half right : some slippage of the eye leg leading
to the side that isn't loaded can contract that collar
such that the knot is hard to loosen; but beyond this,
there is no worry.

You have not remarked --nor do most presentations show--
that the butterfly knot is ASYMMETRIC : one half differs
from the other; this implies that one has essentially two
similar but slightly different end-of-line eye knots, depending
upon which end is loaded.  There is also variety in the dressing
of the knot.  (I strongly advise against the supposed end-of-line
orientation shown at the Layhands site.)  Your posted images
are of low resolution, but it seems clear enough that you are
using a commonly shown dressing in which the eye legs (or
tails, if an end-2-end joint) do not cross ; I'll post again
some images in which they do, which I think is better.

Have any of you seen any testing on the strength of the ABK when used in this way - only one side is loaded? 

The CMC Rope Rescue Manual gives test results for both
this and the fig.8 used in both manners --eye knot & mid-line
impediment.  You might be surprised to see the figures for the
latter case!  ("Rhino" low-elongation 12.7mm nylon kernmantle)
qua eye knots :  fig.8 80% ; butterfly 75%
qua mid-line ...:    "    "   65%   ;    "   "    "   69%

to which Dave Richards did --12.7 low-elong., 10.5 dynamic, &
7mm "accessory", resp. --  76%/70%/74% vs. 80%/71%/72%

NB:  we have no good indication of actual DRESSING/orientation
of the tested knots; my guess is that the butterfly was NOT
with crossed legs, and that it would be stronger with them, for CMC;
and maybe Richards's results indeed show this --but we don't know
his orientation, either.

BTW, the directional fig.8 was, resp., 75% & 59% by CMC.
There are some real questions to ask regarding such
mid-line knots as to what values they might have given
certain conditioning --e.g., if first loaded end-2-end,
and THEN loaded qua eye, or vice versa.

(MOST curiously, both of these testers tested the fig.8
eye knot as tied-in-the-bight & re-threaded, as though
the test device should care how it got tied?  --and without
any helpful indication of what actual differences one might
suspect via tying method : e.g., a field survey might show
that dressing corresponds (w/difference) to tying method
(whereas written guidance, such as it is, indicates that
either method should reach the same result --seldom is
that actual geometry specified w/clarity if at all). !!
Ahhh, but at least there are "numbers" to toss around!)

As Roo has suggested, there are knots similar to the butterfly
--i.e., ones of interlocked overhand knots easily untied--
that should perform better; they do so by loading different
parts of the knot --i.e., the butterfly essentially loads both
tails of the end-2-end knot, rather than one pluse the
opposing SPart.  (Compare with bowline & sheet bend .)
I would favor Ashley's bend #1452 here.  Of course, one
could adapt the butterfly similarly --and then it becomes
a choice of which side to load both ends of (the asymmetry).

Then, again, you could bypass this and use some secured
bowline as a means to getting an easily untied eyeknot.


--dl*
====

[knot4u]

Not much to add from me, except I don't like the Butterfly as an end loop. It requires a pre-knot (Overhand) before going around the object. At that point I'd go ahead and tie a Zeppelin Loop - easier to inspect, more secure, less jammy, stronger probably. By the way, the Butterfly Bend is so much different in use and performance than the Butterfly Loop, that it's not really like you're in the same system of knots.

When I can't do a pre-knot and need something more secure than a basic Bowline, then I like the Double Dragon loop. Apparently, this loop is not so popular because some people claim it's difficult to remember. That's not true for me. The DD is easier for me to remember than any Bowline variant. I can tie a DD with my eyes closed. Note the DD can also be tied on the bight, but I typically don't like it is a midline loop.

Regarding the Figure 8, this is a good end loop if the end loop MUST be correct and the people tying the knots aren't knot guys. The Fig 8 loop is difficult to tie wrongly, easy to remember, easy to inspect. I've read it's strong, but I've never brought one to breakage. A downside (or feature) is the Fig. 8 loop is jammy if you put a hard load on it. I view the Fig 8 loop as being a good permanent end loop that you deliberately don't want untied. I'm not saying it'll definitely jam. I'm saying if you want a knot to be untied, there are better options, some of which are mentioned above.

[roo]

Apparently, this loop [double dragon] is not so popular because some people claim it's difficult to remember. That's not true for me.

I'm glad you've found a way that works for you.  I was shaking this loop around in some Bluewater II rope, and found that it came apart a bit quicker than I would prefer for the application discussed here.  More pliable rope would probably be OK with it.