Author Topic: Alpine Butterfly  (Read 12819 times)

Offline Geoff R

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Alpine Butterfly
« on: March 22, 2006, 12:49:28 pm »
The simple Alpine Butterfly   ??

Alpine Caving Techniques (dont mean to advertise) highlights the way to recognise an Alpine Butterfly and a "false"  Alpine Butterfly.   Both knots look identical apart from how a rope crosses another. They say the false butterfly should only be used as a shock absorbing knot.    

It just happens I've only learnt methods that tie a "true" Alpine Butterfly

But does it really make such difference  -  any thoughts & comment ??
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Offline Cave_Troll

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« Reply #1 on: March 22, 2006, 01:38:28 pm »
yes .
the false buterfly can easily come undone.
Thus if you were to try and use it to tie out a rub point the bottom end of the rope could fall off.

Offline biffa

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« Reply #2 on: March 22, 2006, 04:49:59 pm »
Try tieing both in a rope.  The 'true' alpine butterfly doesn't matter which way it's loaded.  T'other one will stretch out a fair way when incorrectly loaded

Online Rachel

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« Reply #3 on: March 22, 2006, 06:56:17 pm »
Quote from: "Cave_Troll"
yes .
the false buterfly can easily come undone.
Thus if you were to try and use it to tie out a rub point the bottom end of the rope could fall off.


That's a bit worrying. Could someone in the know post some pics?

darkplaces

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« Reply #4 on: March 22, 2006, 07:15:21 pm »

Offline Stuart Anderson

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« Reply #5 on: March 22, 2006, 07:22:39 pm »
Quote from: "c**tplaces"
is this the right one?
http://www.animatedknots.com/fig8loopdouble/


Yes... well it appears to be, it's quite swift even on the slow setting.
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Offline Les W

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« Reply #6 on: March 22, 2006, 07:30:31 pm »
Quote from: "c**tplaces"

http://www.animatedknots.com/fig8loopdouble/

What a really useful website

Most excellent. :D  :D
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Offline AndyF

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« Reply #7 on: March 22, 2006, 08:29:29 pm »
..err....so how do you tie the false butterfly .... :?:
"Life's a pitch, then you fall down one..."

Offline Les W

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« Reply #8 on: March 22, 2006, 08:39:19 pm »
Quote from: "stu"
Quote from: "c**tplaces"
is this the right one?
http://www.animatedknots.com/fig8loopdouble/


Yes... well it appears to be, it's quite swift even on the slow setting.


I don't think that this is the one. The link is for a double Fig 8 on a bight.

The false Alpine butterfly which Geoff R refers to is generally just called the Butterfly Knot (No "Alpine") in the UK. It has been used by cavers for decades with no problems if used in the correct setting.
It is identical in appearance to the Alpine Butterfly Knot except on the rear of the knot the two parts of the rope are parallel and in the Alpine Butterfly they cross over each other. This crossover makes the knot more secure.
Some people have an issue with the Butterfly Knot because "Experts" say that it can slip or deform, this is true, but when used in the correct way it is not an issue and does not compromise saftey. The Butterfly should be used in the middle of a rope for rigging "Y" hangs or tension traverses. It is simple and easy to tie and very easy to adjust> It is absolutely secure in these situations.
It should NOT be tied in the end of a rope (by end I mean not trapped between two other knots) as it could concievably come undone in some situations.

The Alpine Butterfly is slightly more complex to tie (although not by much) It is also harder to untie when it has been loaded. It is more dificult to adjust due to the crossover, this can be an issue when rigging long "Y" hangs, such as the one in Stream Passage Pot, where it is already difficult enough without having to struggle adjusting the rigging any more than necessary. When used in the same setting as the Butterfly it is no more secure.

Perhaps we should start a debate on the most suitable knots...
...on second thoughts it has probabaly already been done here somewhere :)
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Offline Les W

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« Reply #9 on: March 22, 2006, 08:41:14 pm »
Quote from: "AndyF"
..err....so how do you tie the false butterfly .... :?:


For those of you who have had some sort of knot tying training the "False Alpine Butterfly" is the one where you are told to start with "Mickey Mouse Ears" :D
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Offline Stuart Anderson

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« Reply #10 on: March 22, 2006, 08:44:33 pm »
Quote from: "AndyF"
..err....so how do you tie the false butterfly .... :?:


Right... are you paying attention at the back? Good. Then we'll begin.

Take cord and make a loop (as you would when starting to tie a bowline). Pass one of the two strands (it doesn't matter but lets call it strand A) and pass it through the "hole" so you have a slip knot. Take strand B and make a similar "loop" as when you started this whole mess. Strand B must be at the bottom of this new loop. The new loop now goes over the the other loop as if you were crowning it. Set the knot and pull the two strands apart. You have what now looks either like rope noodles or a false butterfly.
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Offline Stuart Anderson

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« Reply #11 on: March 22, 2006, 08:46:46 pm »
Quote from: "Les W"
Quote from: "stu"
Quote from: "c**tplaces"
is this the right one?
http://www.animatedknots.com/fig8loopdouble/


Yes... well it appears to be, it's quite swift even on the slow setting.


I don't think that this is the one. The link is for a double Fig 8 on a bight.

The false Alpine butterfly which Geoff R refers to is generally just called the Butterfly Knot (No "Alpine") in the UK. It has been used by cavers for decades with no problems if used in the correct setting.
It is identical in appearance to the Alpine Butterfly Knot except on the rear of the knot the two parts of the rope are parallel and in the Alpine Butterfly they cross over each other. This crossover makes the knot more secure.
Some people have an issue with the Butterfly Knot because "Experts" say that it can slip or deform, this is true, but when used in the correct way it is not an issue and does not compromise saftey. The Butterfly should be used in the middle of a rope for rigging "Y" hangs or tension traverses. It is simple and easy to tie and very easy to adjust> It is absolutely secure in these situations.
It should NOT be tied in the end of a rope (by end I mean not trapped between two other knots) as it could concievably come undone in some situations.

The Alpine Butterfly is slightly more complex to tie (although not by much) It is also harder to untie when it has been loaded. It is more dificult to adjust due to the crossover, this can be an issue when rigging long "Y" hangs, such as the one in Stream Passage Pot, where it is already difficult enough without having to struggle adjusting the rigging any more than necessary. When used in the same setting as the Butterfly it is no more secure.

Perhaps we should start a debate on the most suitable knots...
...on second thoughts it has probabaly already been done here somewhere :)


Of course. I just went straight to the menu on the left for the Alpine. The link does indeed go to a fig 8.
I've roamed and rambled and I've followed my footsteps
To the sparkling sands of her diamond deserts
And all around me a voice was sounding
This land was made for you and me

Offline Les W

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« Reply #12 on: March 22, 2006, 08:54:54 pm »
There has been a bit of a holy war in our club (Wessex) about the best knot to use. I apply the KISS principle with the addition that anything which is easy to untie after it has been loaded is better.

The point I made about adjustment on a dificult pitch head holds true. Anyone who has rigged the big "Y" hang on the second pitch of Stream will know that you don't want to be fiddling with knots whilst hanging from a sloping ledge over a large drop. I always end up bridged over the pitch and always get "Disco leg" whilst trying to set the hang :D
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Offline Geoff R

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« Reply #13 on: March 23, 2006, 12:06:47 am »
Les W and all,  

thank you very much for your inputs on this. The problem I was having was that although I have only ever tied  Alpine butterfly's,  I could not see why the so called "false" method was apparently so unusable, provided you took a little care of the circumstances.

Seems its not such a black and white subject as certain books make out.

However from all the comments, would it be reasonable to say that if in any doubt, always tie a "true" Alpine Butterfly ??
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Offline Cave_Troll

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« Reply #14 on: March 23, 2006, 12:19:54 pm »
indeed.
most knots that form loops do not actually need the continuity of the loop to maintain the bottom bit of the rope being attached to the top bit.
The exception is the plain butterfly or the "cavers buterfly"
I've always called it the Cavers butterfly when explaining it to rescue types, but have never actually known any cavers that intentionally use it.

MSD

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« Reply #15 on: March 23, 2006, 05:15:26 pm »
According to a nice report proced by the Combined Services
http://www.cs-caving-association.com/Reports/Knots%20A5.pdf
the false butterfly has strengths of

transverse 53%
Longitudinal 67%

The CS report doesn't give a strength for the alpine butterly, but Life on a Line quotes 60-70%, without making a clear distinction about transverse
and longitudinal loading. See  www.draftlight.net/lifeonaline

Obviously these results are not exactly comparable, but a reasonable conclusion is that the false butterfly is very slighty weaker than the alpine butterfly.

I nearly always use the false butterfly, as opposed to the alpine butterfly. It's easier to tie and adjust and easier to untie afterwards. It is a little more sensitive to being set correctly, but I've never found that to be a problem.

Unless you are caving on really lightweight rope, the loss of strength seems a non-issue.

Mark

Offline Brains

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« Reply #16 on: March 23, 2006, 05:36:12 pm »
I habitually use the cavers butterfly rather than the alpine as it is easier to tie, adjust and undo.
My way of tying it? - Tie a slip not in the rope so it will pull undone in the direction of load, then take a bight from this side and pass it back over the slip knot loop to lock it off. Before locking the loop can be easily pulled out to the required length or tension.
I have no worries as to its strength - more than enough.

Offline Les W

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« Reply #17 on: March 23, 2006, 06:27:34 pm »
Quote from: "Brains"
I habitually use the cavers butterfly rather than the alpine as it is easier to tie, adjust and undo.
My way of tying it? - Tie a slip not in the rope so it will pull undone in the direction of load, then take a bight from this side and pass it back over the slip knot loop to lock it off. Before locking the loop can be easily pulled out to the required length or tension.
I have no worries as to its strength - more than enough.


My way of tying it.
Form two loops of opposite hand (Mickey Mouse Ears) put them together and take the lower part of rope (between the loops) and pull it up and through the two loops. Job done, now adjust and set. :)

I always use the "Cavers Butterfly" for the reasons I gave previously and repeated above by others.
It really is much easier to adjust in tricky situations, it has never failed/slipped when set properly (and even if it did it cannot go anywhere or be any less secure if used properly) and it is easier to untie after it has been loaded. It is quite a versatile knot as well. :D
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Offline Les W

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« Reply #18 on: March 23, 2006, 06:30:38 pm »
Quote from: "MSD"
According to a nice report proced by the Combined Services
http://www.cs-caving-association.com/Reports/Knots%20A5.pdf
the false butterfly has strengths of

transverse 53%
Longitudinal 67%

The CS report doesn't give a strength for the alpine butterly, but Life on a Line quotes 60-70%, without making a clear distinction about transverse
and longitudinal loading. See  www.draftlight.net/lifeonaline

Obviously these results are not exactly comparable, but a reasonable conclusion is that the false butterfly is very slighty weaker than the alpine butterfly.

I nearly always use the false butterfly, as opposed to the alpine butterfly. It's easier to tie and adjust and easier to untie afterwards. It is a little more sensitive to being set correctly, but I've never found that to be a problem.

Unless you are caving on really lightweight rope, the loss of strength seems a non-issue.

Mark


I agree, in MOST situations, on MOST ropes, the strength of the knot is a complete red herring. A rope with a breaking strain of around four tonnes when tied with a knot of even 50% strength still has a breaking strength of two tonnes, thats a lot of pies :D
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MSD

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« Reply #19 on: March 23, 2006, 08:16:55 pm »
One issue which nobody has mentioned is that when you tie a Y-hang with a false butterfly, there are two ways of tying it. When you put the loops one on top of the other (before poking the middle loop through), you can have the "upstairs" or "downstairs" loop on top.

In my experience, it s best to have the "downstairs" loop underneath (assuming you are poking the middle loop through from above). This means that the "downstairs" loop presses against the "upstairs" loop. This is more secure because the downhill part of the rope necessarily has a larger force on it (the load is shared between the two arms of the Y-hang). The knot tends to self-set better this way.

It was a while before I worked this out. I always wondered why sometimes the knot seemed to set OK, but other times seemed to pull apart into a less than ideal shape.

Mark

Offline Cave_Troll

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« Reply #20 on: March 24, 2006, 04:06:58 pm »
1) rope strength:
new rope has a strength of about 30kN
Tie in a knot (60%) - 18kN
10:1 safety margin is 1.8kN = 180Kg
ie in an emergency , rescue, hauling or mid rope rescue situation, with two slightly large cavers, you are eroding into your safety margin and hope that you don't shock load the rope.

2) cavers butterflies.
I've just tied one on a bit of rope on my desk. Set it and pulled it tight all three ways.
I then undid it by repeatidly flexing the knot , pushing the rope in, from either side. This is not a good idea and is the reason you always tie a stopper knot on a bowline (unless its in the middle of the rope)
Be aware of this knots limitations. Any cavers i teach are taught to avoid it like the plague.

Dep

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« Reply #21 on: March 25, 2006, 03:22:13 am »
As far as I can see the 'false' or 'cavers' butterfly is horribly like a sheepshank in the way that it uses two half-hitches to lock onto the loop under load.
These are two independant hitches, lose one and you have a simple slipknot. Sometimes this can be a handy feature of this knot - sometimes its downfall.

The AlpineBK has these two locking half hitches not just crossed but more specificially interlocked - each prevents the other from pulling out.

I appreciate the other is quicker and fine for tying on a bag or something non-critical, but for rigging I would use the ABK every time.

Dep

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« Reply #22 on: March 25, 2006, 03:25:38 am »
Quote
GeoffR wrote: Alpine Caving Techniques (dont mean to advertise)


Actually do you have the ISBN no?
This is a nice book, I haven't had much chance to look at it but what I did see was good - I want a copy.

Offline Geoff R

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« Reply #23 on: March 25, 2006, 08:22:00 am »
:)   ISBN = no need, ask any caving shop.  

3-908495-10-5,  Georges Marbach and Bernard Tourte, first ENGLISH edition, 2002.
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MSD

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« Reply #24 on: March 25, 2006, 10:18:42 am »
Quote from: "Cave_Troll"
1) rope strength:
new rope has a strength of about 30kN
Tie in a knot (60%) - 18kN
10:1 safety margin is 1.8kN = 180Kg
ie in an emergency , rescue, hauling or mid rope rescue situation, with two slightly large cavers, you are eroding into your safety margin and hope that you don't shock load the rope.


A safety factor of 10:1 for the rope itself is pretty irrelevant. The reaon being, that most abseiling and prussiking devices will fail at much lower loads. A chain is only as strong as its weakest link.

A new caclulation:

strength (new) of rope ~20kN (I'm assuming 9mm rope here)
strength (worn) of rope ~10kN
tie a knot ~6kN

6kN is about the same order of magnitude as the maximum force you can apply with jammer. You can't actually apply much more force than this, because either the sheath breaks (at which point the jammer slides down the rope) or the entire rope severs at that point.  So the links of the chain are in approximate balance with one another.

Actually, the maximum force you can apply does not vary much with rope diameter. If you look at Petzl's data, an ascension will slip at 5.5kN on 9mm rope and 6kN on 10.5mm rope (for static loading). For an 80kg FF1, maximum force is 5.1kN and 5.4kN respectively. Sheath breakage occurs for all four cases. 8mm rope gets distinctly dodgier, because it severs with the 80kg FF1. It seems that 8mm rope is on the edge of the design envelope for the jammer.

Safety margin with a static rescue load of 180kg in this situation is about three. That's not hugely generous, but if you want more, you are going to have to change all the links in the chain. That's why I cave mostly on 9mm rope, but regard 8mm rope as a bit on the edge (although I have occasionally used it).

I take the points raised about the false butterfly by both Cave_Troll and others. I think I'll do a few experiments in the garden. It's never too late to change your opinion about somethng!

Mark