UKC

Figure of 8 bunny ears

New Topic
This topic has been archived, and won't accept reply postings.
 zimpara 07 Aug 2016
Is it just me, or is the one loop totally dependant on the other remaining undamaged?

It seems to me, one strand of loop 1 is merely cinched in half of the figure of 8 and then turns into one strand of loop two?


3
 planetmarshall 07 Aug 2016
In reply to zimpara:

> Is it just me, or is the one loop totally dependant on the other remaining undamaged?

It's just you.
4
 Timmd 07 Aug 2016
In reply to zimpara:

I've never heard of the figure of 8 bunny ears?
 andrewmc 07 Aug 2016
In reply to planetmarshall:

I realise this may be hard to believe but I think zimpara is actually right on this one... if you cut one of the loops of a Fig 8 bunny ears there is a good chance it will pull through.

It gets used a lot in caving because you quite often want a two-loop knot for a pair of bolts mid-rope. In caving the rigging is such that the rope will not be rubbing on the rock, and consequently there is no danger of damage to the rope. In climbing this is often not the case, although when would you need it anyway? I never use it because I am rubbish at remembering how to tie the thing and you can always do alpine butterflies anyway.

The double-loop bowline (same as a bowline-on-the-bight/rethreaded bowline) is also used for this, but recently it was shown that one of the loops is unstable and falling onto just that loop will cause the knot to entirely fail and the rope runs through the knot. It is a perfectly good knot if the loops are not used separately.
 andrewmc 07 Aug 2016
In reply to Timmd:
Not commonly used in climbing, but not a rare knot by any means and used quite a bit in some forms of rigging. My SPA assessor brought it up when talking about redundancy in knots (or lack therefore) and therefore why he didn't use it.
Post edited at 21:12
 planetmarshall 07 Aug 2016
In reply to andrewmcleod:
> I realise this may be hard to believe but I think zimpara is actually right on this one... if you cut one of the loops of a Fig 8 bunny ears there is a good chance it will pull through.

This seems extremely unlikely, and cannot reproduce the scenario you're describing. Not that that means it can't happen, mind, but as I first came across this knot while being taught crag rescue for Buxton MRT, I'd be inclined to believe that it's reliable.

...edit: I've tied this a few times now and can't get either of the 'ears' to so much as budge, regardless of whether one of them is cut. Are you sure you're tying it correctly?
Post edited at 21:34
 andrewmc 07 Aug 2016
In reply to planetmarshall:

Part of the 'appeal' of the Fig 8 bunny ears is that it is 'equalising' - that is that it is easy to pull rope from one loop to the other (as it is a fairly simple and short path around the back of the knot). It is this easy equalization that means it can fail if a loop is cut.

It is a totally safe knot if you don't cut a loop. If you are doing rigging/crag rescue etc there should be no way in which the rope should be cut, and so it is safe. In caving, where the rope will not rub with good rigging, I am more than happy for other people to do it and if someone asked me to do it I would. With certain rope types it may not slip anyway. If the knot is pre-tightened it may not slip anyway. If you pull one loop hard enough from a loose-ish knot I would be surprised if it didn't pull through eventually, but it might hold bodyweight or more (or less).

It is reliable partly because having a loop cut is normally just not a concern. It is not a redundant knot in the 'cut-any-one-strand' sense (but many/most of our knots are not).
 planetmarshall 07 Aug 2016
In reply to andrewmcleod:
> Part of the 'appeal' of the Fig 8 bunny ears is that it is 'equalising' - that is that it is easy to pull rope from one loop to the other (as it is a fairly simple and short path around the back of the knot). It is this easy equalization that means it can fail if a loop is cut.

OK on the original point I stand corrected, having now managed to reproduce this in a fairly contrived manner. Let's just say I'll put this somewhere next to clove hitches slipping and EDKs unrolling on the list of knotty things I worry about...

Good spot, though.
Post edited at 21:52
 andrewmc 07 Aug 2016
In reply to planetmarshall:

Edit before posting:

It seems like nature has conspired to prove zimpara wrong.
youtube.com/watch?v=P5qDr3qYZ9o&
It does slip but only at very, very high loads. Your mileage may vary with different rope types.

maybe I should rephrase 'good chance' to 'theoretically'. Further examination of the web has revealed some uncertainty and I have not found any testing... playing around with my big fat fluffy 10.2mm rope seems to confirm that it normally tightens up (a bit like the claim that if you tie a fig 8 then instead of rethreading just poke your rope through a hole it will hold on friction alone).
 Timmd 07 Aug 2016
In reply to andrewmcleod:
I think it's of value that he's posted about it though, as it's lead to you posting the video and more information appearing on the forums.

No such thing as a stupid question...
Post edited at 22:17
 biscuit 07 Aug 2016
In reply to andrewmcleod:

It's not a claim, I've done it. On purpose with a back up rope I hasten to add. Fairly loosely tied fig 8 (just like normal before you double it through) and passed the loose end just through the first return. This left quite a long tail. I sat back on it quickly and the fig 8 tightened up and (after a bit of slippage) grabbed the loose end and held me. I jumped about a bit on it and it didn't budge anymore.

Anecdotal n=1 evidence but quite interesting to me.
 andrewmc 07 Aug 2016
In reply to zimpara:
also, this has been done before...

http://www.ukclimbing.com/forums/t.php?t=374155

with some interesting (but again mixed) results.
Post edited at 22:25
 andrewmc 07 Aug 2016
In reply to biscuit:
I'm pretty sure I've tried it as well but I wouldn't use it in anger :P

this is why you definitely shouldn't use just one loop of a bowline on a bight though...
youtube.com/watch?v=-5-YbRxceiY&

Post edited at 22:35

New Topic
This topic has been archived, and won't accept reply postings.
Loading Notifications...