UKC

I've been playing with bunny ears (not the Hugh Hefner ones) and noticed if you pull on one of the loops, it gets bigger, eventually leading to the knot undoing. I took some photos and chucked them on the igkt forum but didn't really get an answer to the questions I raised.
Here's the series of photos:

1) http://www.flickr.com/photos/42853948@N06/3949503460/

2) http://www.flickr.com/photos/42853948@N06/3948726261/in/photostream/

3) http://www.flickr.com/photos/42853948@N06/3949508704/in/photostream/

4) http://www.flickr.com/photos/42853948@N06/3948719359/in/photostream/

OK, so I experimented on a loosely tied knot (so I could see the whole mechanics of it) but if only one loop was connected to, say, a climber toproping, will the knot tighten sufficiently on a fall or lower to stop this slippage? Is this never really going to happen? Is there any research on this sort of knot being put under these conditions?

Or am I being totally paranoid?

Thanks,
matt

Oh, it's tied on prusik cord

In reply to climberfranksie: I imagine that even if it does maintain itself if it is tight ( I have no idea - watching to find out) the safety would still depend on what use it had.

What uses can you foresee for it/have you used if for before?

Would you leave a novice at a belay where they could misunderstand the knot's dynamics?

In reply to EZ: I've seen it used in an indoor wall instead of a normal fig 8 so people can clip into it with a krab. It's used purely coz it's easier to undo at the end of the day than a fig 8. The climbers back this krab up with a rethreaded fig 8 (?!). I'm not so much looking at the use of this indoor climbing system, just looking at the bunny ears itself.
I believe novices should be exposed to knots which have a purpose, are easy to use and easy to tie/recognise.
So, any answers? Safe? Or am I losing the plot...

In reply to climberfranksie:
why not clip both loops as thats what the knot is for ?

In reply to climberfranksie:

I can't quite see the point of using it at an indoor wall. A normal figure 8 would be much better for what you describe surely? if you want them to attach with a karabiner then just tie it on the bite.

I've seen the knot in SPA training, but will leave someone more experienced than me to comment on it's usefulness and safety.

cheers

N

In reply to climberfranksie:

is it tied right, i looked at it and thought it was wrong
but maybe on closer inspection its ok ? it says it should be stable
(and on my experience is)

http://www.animatedknots.com/fig8loopdoublerescue/index.php

In reply to lithos:

It looks ok. It's just missing the friction you'd get with a dressed knot, most knots will pull apart if tied loosely enough in slick cord.

OP: The normal use is with something clipped in both loops (often with both loaded). While I'm sure a well dressed knot would be fine loaded on just the one loop the problem seems to be one you've created since they're very rarely used that way. Used normally it can't pull apart.

jk

In reply to climberfranksie:

I think you may have tied an overhand bunny's ears knot rather than a figure of eight bunny's ears knot. Best bet is to ask a caver, it's their knot. It is a bit overused in climbing particularly on SPA courses when one or two fig of 8 knots would be just as good and simpler (and simpler is often safer). Is there anything on YouTube?

In reply to climberfranksie:

youtube.com/watch?v=vYS6Wvn7dDI&

In reply to Mike Raine:

or look at the animated knots site (like wot i linked) Mike, very good site

In reply to koolkat:

The hope is that people will clip both loops, but I've seen some crazy things happen in indoor walls before so I'm exploring all options before I try to encourage this wall to stop using bunny ears. I guess I'd like more ammunition than just "it's a complicated knot which should be kept for the rope access boys".
So I'm on the quest for research on this knot and if there's any evidence of slippage. If not then I guess I'm just paranoid and I'll keep taking the pills. But if you get some rope or cord and play about with it, it's surprisingly easy to pop out - go on, try it!!

In reply to Mike Raine:

It's definitely a fig 8 bunny ears knot, just opened up and flattened out so you can see what's happening. There are other really good bunny ears knots which don't slip (as described on the igkt forum) but are complicated as buggery or hard to undo.

In reply to climberfranksie:
If you're using a bunny ears knot, you will presumably have a use for both loops, so one pulling out shouldn't really be possible, surely?

In reply to climberfranksie:

WARNING: Simple but blunt answer ahead

If you have to ask a bunch of random forum punters in order to justify your thinking you probably shouldn't be trying to advise walls on things like this.

Why are you trying to "encourage this wall to stop using bunny ears" and in what way are you qualified to do this?

In reply to timjones:
< applause >

In reply to climberfranksie:

So you're telling us that a climbing wall is clipping novice climbers to the rope with a bunny ears figure of eight, backed up with a rethreaded figure of eight? Hmm, smells of troll to me...

In reply to climberfranksie:

I don't know what the name of the knot you tied is, but the bunny ears knot I know and the one taught by the MLTE and the Joint Services centers, is the one Mike Raines posted a video of. Look at it again, then look at your pictures.

In reply to timjones:

You're right - I'd be stupid to ask a bunch of randoms to justify anything. That's why I asked for any research or evidence for this knot testing. Once I read that, then I can use some scientific evidence to learn about this knot. Until then I like hearing the opinion and experience of others.



I'm really more interested in the bunny ears strength testing, which is why I went to the igkt forum first. The comment on "encouraging" is misleading. I haven't seen this set-up before and want to understand it first.

There's many ways to attach yourself to the end of a rope, and I was taught the less links, the better, and always follow manufacturers guidelines. Using bunny ears here seems odd to me.

In reply to climberfranksie: In over 1,ooo,ooo hours of rope access work i havent heard of one incident of a bunny knot coming un-done. Is that scientific enough ?

In reply to Oceanic:

>

Nope, it's real. WE got told off at a wall in Christchurch, NZ for not clipping in AND tying in at the same time. Was very confusing!

As for the OP - I see what you are saying, but in normal use, wouldn't you have both ears clipped to something, thus meaning that they can't pull through?

In reply to Oceanic:

No, I'm saying the novice climbers are clipping themselves to the rope, hence the possible clipping of just one loop. It's a new system I aint seen before so just wanting to know more.

I do think there are many ways of attaching climbers to topropes but I can't yet see the advantages of this way, only disadvantages, especially as all the safety emphasis is biased towards the krab and bunny ears, not the rethreaded fig 8.

In reply to muppetfilter:

That's good to know. But still like to see tests done on just one loop. There'll be some out there but I haven't found them on any website yet.

Oh, if you pull the other loop it turns into this weird fig 8 with a twist, so it's just one of the loops which undoes the bunny ears (this knot is tied identically to the bunny ears in Grogs knots and how I've been taught how to do it as a rope access worker too)

In reply to climberfranksie: I don't get how you're managing to do this. If I tie a properly dressed bunny ears and put a single loop attached to an anchor and then bounce up and down like mad on the live side of the knot, it doesn't slip at all. Loading the live side tightens the whole knot stopping slippage. Of course it will slip if you hold the knot and pull on a single loop but that's not a situation that will ever happen in a real application.

In reply to AlistairB: As much as you present a fancifull scenario i would hope you are wearing your helmet as being hit on the head by an asteroid is more likely....

In reply to muppetfilter: What? I was agreeing with you, even if 1 anchor fails or only one loop is clipped, it still doesn't slip when dresssed correctly.

In reply to climberfranksie:

I tech rope access. In 2000 I did a series of strength tests on bunny knots which you can read about here:

http://www.hse.gov.uk/research/crr_htm/2001/crr01364.htm

Your knot is dressed incorrectly. Not easy to explain in words, but the loop connecting the two loops should sit around the waist of the knot, not around the base as you have. When dressed correctly either loop will hold to failure of the rope without slipping.

As you've shown the knot is not reliable when incorrectly dressed. For this reason I wouldn't recommend this knot for uses other than static loads with both loops weighted.

In reply to AlistairB: I know I was suggesting that asteroid impact to the head was more likely an occurance than a bunny failing in use.

sorry fot the confusion

In reply to AlistairB:
As just an SPA trained numpty I'm not qualified to advise but for what it's worth I also wasn't happy with the Bummies Ears for the same reason -
it slips 'when tied a certain way'.
I know it's designed to have both loops clipped but if it slips when only one is clipped then at some point that's going to happen.
I've found that if the final loop is laid at the bottom of the knot(where the Ears are) and everything is cynched up, the loops won't slip even if only 1 is loaded.

If the final loop is laid at the top (anchor side) then the loops can slip.
Just my opinion.

In reply to muppetfilter:
"In over 1,ooo,ooo hours of rope access work i havent heard of one incident of a bunny knot coming un-done"
Are your number correct? working 300 days a year 8 hours a day that's 416 years of work. Or are you a supervisor of a team of rope access workers?

In reply to gethin_allen:
"

or answer ..

c. The total number of hours now exceeded worked useing rope access worldwide as a method of access.

(I only have 5000 hours logged over 9 years)

In reply to climberfranksie:

I've also done many years in rope access (IRATA) and I've never seen a Bunny Ears tied like this
http://www.flickr.com/photos/42853948@N06/3949503460/

Enty

In reply to Adam L:

Thanks for that - I know the knot isn't exactly dressed properly in the photos so the strength of the knot is compromised if not tied properly.
It's good to see some research on it and it's also good to see there's other walls using this set up, also in the southern hemisphere.

Maybe i should start thread of what set up would be best for a climber to attach themselves to a top-rope WITH A BACKUP. Or maybe not

In reply to timjones:

He's not asking "a bunch of random forum punters", he's asking on a forum which seems appropriate to ask the question. He also seems bright enough to sort the wheat from the chaff.


When considering safety it's better to say "what if" than "if only".

The simple fact of him considering that it may not be a good idea qualifies him to encourage the wall to stop using the knot in this way.

To the OP.

I've used a bunny ears when running a group abseil with the ab rope on one loop and safety on the other. Although both loops are clipped, often only the loop with the ab rope actually gets loaded and I've not seen any evidence of a properly dressed and tightened knot slipping.
Having said that, I can't see any justification in using a knot which makes two loops and only using one of them. Poor choice of knot? If they're using it because it is easier to undo, perhaps that a reason NOT to use it in this way.

Mike

In reply to climberfranksie:

Hi mate,
only my tuppence worth!
Thats not a set of properly tied bunnies ears. When it is tied correctly and you have pulled the "ears" tight, they shouldn't come undone.

I use them all the time for setting up group abseils when teaching as a few have mentioned, one for the ab rope and the other for the safety rope.

Not too sure why you would want to tie bunnies ears for a bottom rope situation?

In reply to mike swann:


Oh I don't know I think we're a pretty random bunch of punters on here, some of us hold qualifications and some are very experienced but in how many cases do we really know just how qualified and expewrinced other posters are beyond the claims they make. This isn't a criticism of anyone it's just the reaility of the virtual world you find in forums, newsgroups etc.

It's very common to find people on forums raising this sort of question, the reality is that if the OP has the authority to change working practices at this wall then it should be backed up by a level of knowledge and experience that would allow him to implement a simpler and more robust operating procedure without needing to ask questions here.

As for the knot itself I use it on abseils as you suggest where I have two or more bombproof anchors. One of the strangest suggestions in this thread seems to be Mike Raines theory that two Fo8s would be just as good, surely this would make it a lot harder and more fiddly to ensure that the anchors were correctly equalised?

In reply to climberfranksie:

Really? You didn't pursue it much, then. Checking that forum, we find you saying
>>> 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.

If even you have to guess at what you're asking, maybe it's to be expected
that the answers didn't really give you what you wanted.

But one answer did point to Dave Merchant's _Life on a Line_ e-book
presenting the knot as a worthwhile tool, as secure and non-slipping.

In fact, what LoaL states is that slippage is minor on single-eye
SLOW-pull loading (and we might guess that slippage occurs only
at higher loads than usually seen); but he cautions against shock
loading one eye -- which I think is more to what seems to be your
issue with some suspected single-eye clipping at a gym?

YES, you tied the knot correctly. It's dismaying that so many here
have replied to the contrary, apparently not recognizing the knot
or bothering to follow your image with rope, et cetera. Yes, you
presented a *exploded* view to clarify the structure, and suffered
the irony that the undressed-&-set image did the opposite.
tsk, tsk.

I concur in others' sense that the use of this/any 2-eyed knot
seems to be misguided, irrespective of the merits of the knot
-- but all the more so given Merchant's caution.

*kN*

ps: It should be noted that your "one loop" is "one but not the other"
-- were the other left unloaded, it would not come untied but result
in a wierd single-eye Fig.8 (but sliding friction would still be a concern).

In reply to timjones:

Tell us, if you truly believe the premise re "bombproof",
what is your point in using two or more?
Otherwise, if the two-eyed knot is done for the sake of having one
eye hold alone in some eventuality, it begs the OP's question, doesn't it?!
(Granted, this indulges the *theoretical*, but, it's worth asking: bombproof
yet duplicated ?)

*kN*

In reply to Adam L:
>

Ah, Adam!
Firstly, note that your assertion above clashes with that by Merchant's
_LoaLine_ e-book, in which he recommends the dressing you decry
as "This doesn't have a huge effect on strength but does help prevent the knot binding under load."
We might presume that he at least found no untoward results from
dressing it that way, unlike you?

And re that 2001 report, the published data in it really give no
basis for your assertion, esp. as this aspect of the knot isn't mentioned
in distinguishing between tested orientations of the knots -- only the
aspect of which end of the knot was loaded (given in data footnote).
But even presuming that the footnote is wrong in this knot's case
and that your "a" v. "b" distinction was on the aspect of this dressing,
the data are inconclusive, esp. with so few tests.
So, was there much more testing than what is presented in the report?

Btw, in your 2001 knots test report you describe the particular
loading of the with-a-bight eye knots (Overhand-8-9-10)
with the phrases "above/below"; sadly, that is not very clear, and
the illustrations in the report don't indicate what is meant.
Can you please clarify this? E.g., in the case of these knots,
the twin lines enter the knot, curve a bit, and ultimately turn
around the legs of the eye and come back to further build the
knot; at the turn, ONE part will be nearer the eye than the
other (were you to try to pull the eye open, this part's turn
would be the first to resist that opening). Perhaps that part
is what you'd call "on top of" and also "above" the other?

Or refer to the report itself: Fig.2 shows Overhand, Fig.3 the F8,
Fig.4 the F9 (perhaps not so definitely!), Fig. 5 the F10 (also with
much hidden, where ends could cross). How does "on top of" or
"above" apply to these images?
My guesses:
The Overhand has loaded end "below" the "rope end".
The Fig.8 has the loaded/"working rope" "above"... .
The Fig.9 ... "below" ... .
The Fig.10 ... "above" ... (but, again, too much is hidden under wraps).

Thanks for the work -- finally, someone realized that there were
such differences! (But, ditto for the Butterfly, and others, which were
missed.)

*knudeNoggin*

In reply to knudeNoggin:

Christ on a bike

In reply to knudeNoggin:



I hope that you don't really need to answer this because you laready know a number of answers for yourself! The world isn't perfect and neither are we.

In the first instance should you assume that your judgement of both the anchors strength and the other links in the chain is totally infallible? When working with groups a backup is always wise IMO. It's not only the anchor itself that may fail. Is there any excuse for relying 100% on a single anchor and the equipment that links you to that anchor when a mere couple of minutes allows you to use a second? Don't forget that you're also reducing the load on each ancher and all the links back to it.

Even if you're naive enough to believe in you're totally infallible, how often is there a "bombproof" anchor in exactly the right place, a second anchor allows you to equalise your centre point to the optimum position. By adjusting this position by as little as a few feet you have the ability to make the experience more pleasant for the abseiler AND make your own job easier, less fatiguing and therefore a lot safer for the people you are looking after.

We're not perfect and neither is the environment we climb in, so why not invest a couple of extra minutes in the safety of those who trust us to be "bombproof"?

In reply to timjones:

This is the point I was making: if you are using multiple anchors
on the caution that, *who-knows*, things might go wrong, then
it seems that the same caution -- to be consistent -- must be put
to the knot, and you cannot use a bunny ears knot that you don't
trust for loading just the one eye (which goes hand-in-hand with
the failing of an anchor).

Yes, if you're positioning and seeing "bombproof" in the greater
confidence that the anchors cannot fail (any more likely than the
odd meteor visiting you), then you're putting confidence in the
knot only so long as both eyes are loaded.

*kN*

In reply to knudeNoggin:

You're the one that appears not to trust the knot. I think it's fine in these circumstances.


The bunny ears don't go back to the anchors. You take a V from the anchors towards the crag edge, then tie a bunny ears knot in the centre of the V using one ear for the abseil line and the second for a safety rope. Both eyes are loaded and both a have a krab and rope clipped into them which unless I'm missing something makes it almost impossible for them to pass through the know and come ynthreaded even if they do slip.

In reply to timjones: It is a very effective method of equalising two anchors, the ears can be tied at different lengths.

In reply to muppetfilter:


It certainly could be used that way. However in most of the locations where I could use it for this purpose the ears would need to be well over 10 feet long

In reply to timjones: Agreed , not as easy to rig as an alpine butterfly and figure of 8 to link anchors.

In reply to climberfranksie:

Am I missing something here - what's the point of a climbing wall insisting on this knot? If they want you to clip into the belay loop via a crab rather than tie in, then surely a single figure eight would be the easiest way - it's easier to teach for a start. I can't see that two loops makes the system any safer - you will still be climbing on one strand of rope.

In reply to timjones:

Well, I'm taking D. Merchant's caution as my assumption: do not
shock-load the knot w/one eye. Now, note that the loading that
you describe is likely different in one way than what he tested:
you load BOTH ENDS + one eye (in case of use of safety: that
it comes into play --is loaded-- only upon something going wrong
with the abseil line?). And likely Merchant's loading was with just
one end loaded and with a pretty severe drop (FF1 or greater).
I'm just following that assumption to conclusions.
Here, too, we can remark at the different orientation of Merchant's
from AdamL's orientation and from the alternative twin-eye Fig.8
shown here (from IGKT thread): www.postimage.org/image.php?v=Pq2M0G7A
And recall that the OP's feared use by others was undesirable.

In the situation you present BUT with BOTH eyes clipped by whatever
might deliver load to the system (e.g., both abseil & safety line),
I'd favor a Bowline WITH a Bight here, for ease of tying/untying,
and probably equal strength (it will also be crunching upon 4 diameters
with minor deflection from the twin collar). But that knot does some
major slipping in certain cases of one eye being unloaded.

As for using bunny ears in the opposite orientation --i.e., ears going to
the anchors--, unless the reach is pretty short, it is as noted easier to
rig a Butterfly with its tail tied off.

Thanks, *kN*

In reply to Alan_2468:

The OP says a couple of posts down:
"I've seen it used in an indoor wall instead of a normal fig 8 so people can clip into it with a krab. It's used purely coz it's easier to undo at the end of the day than a fig 8. The climbers back this krab up with a rethreaded fig 8 (?!)"

Bizarre!

In reply to deepsoup:

If the idea is to (a) use a quick'n'easy clip with easily untied knot,
but (b) have the tail tied of with a won't-come-untied-knot 2 B sure
(which however will seldom take load, so will untie when desired),
I think it would be best to use a Bowline, whose tail is pointing in
the right direction (towards harness) to be then tied off however.
Let the Bowline take the falls, as it's very easy to untie after loading,
and have the back-up in place all along.

Though for all that trouble, one could as quickly, and with as much
security, tie a more secure Bowline (e.g., making a full 2nd pass of
threading through the harness loops) and skip the krab attachment.

*kN*

In reply to deepsoup:

Struggling with my memory a bit but..A few years ago in NZ a young person fell at a climbing wall because the krab used for clipping on came undone (for whatever reason). In court they said they used a krab rather than tying on with a knot because a knot would be hard to undo after loading.

After due consideration the judge decided that they should clip on, but back it up with a knot which would only be loaded if the krab failed.

Astounding!

In reply to knudeNoggin:

Apologies for the slow reply, forgot about this thread.

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.

Most of my tests (and all of the published results on the bunny) were on a single loop. I found dressing the loop around the waist enabled the knot to be loaded on a single loop to breaking without slippage. This wasn't possible with the other way of dressing - the other loop slipped at forces well below (~<5Kn)the breaking strength of the other configuration (>15Kn).


Yes, there were some preliminary trials. They got me interested in this dressing aspect and I then incorporated variations into the main test programme.

Due to the difficulty of terminating a rope so as to preserve its ultimate strength, each test consisted of tying two knots in each end of a short piece of rope, then pulling it to breaking.

What I did was to tie the same knot in each end, but to dress them slightly differently. So although each test only resulted in one figure, actually two were being tested with the 'loser' of each little tug-o-war becoming the published result. I relied pretty quickly that although tying messy knots gave varied results, I wasn't going to learn much with the small number of tests we had scheduled. So I stuck to testing neat, dressed knots (as IRATA techs should be tying anyway) and investigated the variations in them.

I appreciate this wasn't brilliantly explained, partly intentionally as outlined below. Shame we can't include photos in these posts...

Consider a perfectly dressed double overhand or eight -ie the ropes remain prefectly parallel throughout knot, no crossing over. Where the working line and rope end enter the knot, they are parallel. The end can either be to the outside or the inside. In our tests breakage always occurred where the working line makes the first major turn, ie where it goes behind the attachment loop. So on an overhand, if the end was on the inside, it would be 'on top' where the ropes round the loop. If its not making sense, get some rope and try it.

For the published results, first I tested the two variations against each other ('a' vs 'b'). Then I tested two type 'a', then two type 'b'. So if in the first test 'a' beat 'b', I could expect 'a' vs 'a' to give a higher figure than 'b' vs 'b'. This was borne out by my results almost perfectly - I the fig-10 may have not shown such a clear pattern.

In the end, the bunny was the only knot where the difference was sufficient to require full explanation - and the result is all IRATA training now teaches dressing the loop around the waist.

For the simpler, single loop knots, although the pattern was absolutely clear and repeatable (ie in a fig 8 'a' always beat 'b') we decided the variation was not sufficient to require explaining in depth - and also because the pattern was not consistent across all the knots (ie I think overhands and eights were the same, but nines the opposite - I think the effect was strongest on nines for which the stronger dressing was with the working line below the end on the top bend. If you really want to know more I could delve into the files...).

Plus 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.


Actually, for the butterfly, the normal 'correct' dressing is only stable when it is mid-rope, ie both ends loaded. When the loop is pulled against one end it collapses into another configuration whose dressing I gave up trying to control... rest assured I didn't miss it though!

In reply to Adam L:
Thanks much for the further insights, Adam -- apologies understood
re delay (no problem: the thread endures .


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.


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.)


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.)

>([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.


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).


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.

In reply to deepsoup:

It is not quite like that.
TH eset up is for top ropes of course rigged through a top anchor and back to a GriGri attached to the floor with an adjustable lanyard, which also has a krad to cli into the belayers belay loop.
The general principle is outlined correctly in that the climber ties in with a fig 8 and then the fixed krab slightly back up the rope. This is not necessarily a "Bunnyears knot" http://www.chockstone.org/TechTips/BunnyEars.htm per s but is often a captive eye kran and the knot cinched up tight onto the twistlock. Having not been to the wall for a while I can't recall exactly what the knot is but I am pretty sure it is tight.

In reply to nz Cragrat:
Oh, well, if you put it like that I guess its not bizarre.
Its *beyond* bizarre. Ludicrous!

In reply to deepsoup:

Why?

In reply to climberfranksie:
Purely out of interest, when did the Figure-of-eight-on-the-bight start being called the "bunny knot"? Or is it a generic term for any knot which provides two loops? Personally I use a bowline-on-the-bight in the rare instances when I need this, probably because I'm a dedicated bowline man.

In reply to Andy Long:

It didn't


No

The knot the OP is discussing is distinct from a F8 on the bight by having two loops that are easily adjustable for length.

In reply to Andy Long:

It's one of those confusing things with knot names. A bowline on a bight gives 2 loops, but a fig-8 tied in a bight only gives one loop.

The confusion is caused by the bunny ears (what Ashley calls a double figure-eight loop) is tied in a similar manner to a bowline on a bight and provides 2 loops.

In reply to knudeNoggin:


Sorry, thought I made that clear - all knots were 'perfectly' dressed with no crossed strands.


Yes.


I'd agree our sample sizes were too small for anything but tentative conclusions. But for each knot we tested four ropes, with three tests on each, each comprising a lanyard with two knots. So 24 knots in total, even if only 12 were broken...

My suspicion is if we did a hundred tests on each, you'd find a normal distribution/ bell curve would result for each 'a' and 'b', comparison of which would show a fair degree of overlap - ie proof that one was 'stronger', but not a 100% guarantee that in a single test one would always beat the other.


In equal diameter ropes, I'd expect one which follows the rabbits path around the tree - because the bend is formed around a single strand and is therfore tighter in diameter than the other rope, which wraps around two strands (this is where our bowlines broke). I think the received wisdom is in uneven ropes, to use the thicker as the rabbit and the thinner as the tree. I'd guess the thinner tree(tighter bend) is outweighed by the greater strength of the rabbit...



Got a link? If he missed the dressing effect there's not much can be drawn - either they were all the same or a random mix.


Yeah, its nice to be aware of its potential but not worth using unless it is the weakest link in the chain...


Yeah, I always teach the crosses on the back of the knot, ie the standing legs lie parallel between the 'wings' on the front of the knot, as it is much easier to untie.



Dynamic rope is much softer than low-stretch - ours was brand new 11mm. Doesn't suprise me - the best general conclusion I drew was that clove hitches are unpredictable...



I'd caution that that was simply my best guess. Its a plasusable theory but untested. Our static pull rig was limited to a 1m range of movement so couldn't accomodate much stretch - trying to isolate a double fisherman's in the middle of a rope requires terminating the ends with either knots (too much stretch) or other methods eg sewn which we didn't have access to.

In reply to nz Cragrat:

Sorry about the v slow reply. Initially I couldn't be bothered (sorry), but then another thread just popped up which illustrates it nicely.

You said:
The general principle is outlined correctly in that the climber ties in with a fig 8 and then the fixed krab slightly back up the rope.

I replied:

I said that because I already thought the business of both tying in *and* clipping in with a krab was bizarre. I'd never heard of the ground-anchored Gri-gri thing before your post, and doing that on 'safety' grounds seemed equally bizarre. (On the grounds that its expensive, cumbersome, and not actually any safer than a conventional belay device anchored to a conventional belayer.)

Here's the other thread:
http://www.ukclimbing.com/forums/t.php?n=376199