Author Topic: Bowline on the Bight - A Method of Failure  (Read 18302 times)

Offline Pete K

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Bowline on the Bight - A Method of Failure
« on: January 10, 2013, 05:45:14 pm »
The Bowline-on-the-Bight is currently being discussed heavily on this forum within the Fusion Knot thread http://ukcaving.com/board/index.php?topic=14580.0 and the Y-hang thread http://ukcaving.com/board/index.php?topic=14594.0.
The reason for discussion is that a film originating from the French Caving School has surfaced thanks to Damian. The film shows a method of failure with the BotB knot. The French have even gone so far as to recommend a replacement knot (Fusion).
Over the last few days myself and colleagues have performed tests on the BotB to better understand the nature and cause of the failures. The reason I have started this new thread is because what comes to light now is something that should really be more widely seen by the caving community and I was worried that the average passer by on the forum would miss the discussion.
I have added the main information to this topic from the others.
I intend to pass all the information about our tests to the relevant groups (BCA, ACI etc..) to make their own choices.

The original film highlighted by Damian in the Fusion Knot thread is here: http://efs.ffspeleo.fr/techniques/noeuds

The FFS have advised against the use of the Bowline on the Bight. This stance has also been adopted by a number of other professional bodies in the French outdoor industry.
Their replacement is under discussion elsewhere on this forum, more from me on that there.

Our original tests from the 8th Jan 2013:
Right, I've been out and done some testing today.
I think it is important to make clear that this failure can happen in caving use and would be serious. I think it is also important to make clear that as a personal and professional caver (CIC) that I do not suggest anyone goes and uses a technique that they have doubts about or are unfamiliar with. This includes the use of new fangled French knot thingies which I have yet to test and have only seen formed when people tie a BotB incorrectly.
I will stop short of giving specific advice on this knot but will say that I will continue to use it for now.
I make no apologies for being slightly self promoting here but this is what I do for a living and it is important to me to know that what I do is spot on.
YouTube film made of today's tests:

Full report to be read with YouTube film here:
http://www.peakinstruction.com/blog/testing-a-method-of-failure-with-a-bowline-on-the-bight-knot/

Today (10-1-2013) I went out with another CIC to test the knot again. In the first test we tried to get a failure by doing things wrong or poorly when we tied or clipped into the knot. Today we were testing a knot that had been tied correctly and was in use exactly as we would do underground*. The results were surprising.

* We would always clip both loops of the knot with our cowstails in real life. The tests were done with one loop clipped.

Today's test film on YouTube:
The written report that should be read with the film on my blog here:
http://www.peakinstruction.com/blog/2nd-round-of-testing-on-the-bowline-on-the-bight-knot/

To summarise for those who have only skim read or do not have time to read it all presently:
We were able to make a failure occur with the BotB tied and dressed correctly. A cowstail connected to the single loop formed by the pitch rope left the caver at a significant risk of a potentially lethal fall. This risk was present in all permutations of the knot we tested, 9 & 10mm, wet & dry, tight & lose, dressed & poorly dressed etc...
The failure was only seen to occur using the one loop, clipped to the lower side. No other failures were noted but we did concentrate on the main risk configuration. The only safe way to use the Bowline-on-the-Bight knot is to have your cowstails attached through BOTH LOOPS. This has always been the advice given to people when being taught the BotB but it is now very important to re-iterate: A cowstail must be clipped through both of the loops on the knot for it to be secure. We did not have a single failure or slip of any kind in any of the test scenarios so long as a cowstail was attached through both loops.

I leave it to cavers to make their own choice as to where to go from here, think of this as a public information broadcast.
I do have a chance to test the French's replacement, the Fusion Knot in the near future. I also plan to look at a knot that we are currently calling the Double Bowline on the Bight, or D-BoB. For anyone who is interested I'll be blogging on that in the near future too. www.peakinstruction.com and click on Pete's Blog at bottom.

I'd like to thank Pindale Farm for their hospitality throughout the testing this week.

Offline Stuart Anderson

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Re: Bowline on the Bight - A Method of Failure
« Reply #1 on: January 10, 2013, 05:59:16 pm »
Well done Pete.

Double Bowline on the Bight would seem to maintain the convention of Ashley's knot naming.

It would also seem logical that this knot would be as easy for people to get to grips with as it's just an extension of a previous skill set.

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Offline Pete K

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Re: Bowline on the Bight - A Method of Failure
« Reply #2 on: January 10, 2013, 06:00:58 pm »
My thoughts exactly.

Offline nickwilliams

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Re: Bowline on the Bight - A Method of Failure
« Reply #3 on: January 10, 2013, 06:10:06 pm »
An excellent, clear and logical presentation and write up. Thank you.

Nick.
"Economics is simply the branch of sociology that deals with people trading items and the fact that they use more numbers does not make it anymore of a science."

Offline mikem

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Re: Bowline on the Bight - A Method of Failure
« Reply #4 on: January 10, 2013, 07:28:48 pm »
Have you done the same test on a single bowline for comparison & what happens if instead of passing the bight over the knot you use a krab to clip it in?

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

Another possibility would be the water bowline on a bight:
http://en.wikipedia.org/wiki/Water_bowline

But I would use a "bunny ears" figure of 8, which doesn't use much more rope:
http://www.animatedknots.com/fig8loopdouble/index.php

cheers Mike

Offline damian

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Re: Bowline on the Bight - A Method of Failure
« Reply #5 on: January 10, 2013, 07:30:54 pm »
I've been wondering about running bowlines, but couldn't make one fail when I tried quickly last night.

Offline Pete K

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Re: Bowline on the Bight - A Method of Failure
« Reply #6 on: January 10, 2013, 07:35:30 pm »
As with Damian, I have had my suspicions about single bowlines but I've never experienced any issues.

I think it prudent for all of us to look at the knots we use and how we use them. They have been made for a purpose and do we ask too much of some knots?

@mikem - I don't follow your question about using a carabiner on the BotB.
"Have you done the same test on a single bowline for comparison & what happens if instead of passing the bight over the knot you use a krab to clip it in?"
« Last Edit: January 10, 2013, 07:57:50 pm by Pete K »

Offline Stuart Anderson

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Re: Bowline on the Bight - A Method of Failure
« Reply #7 on: January 10, 2013, 08:19:50 pm »
"Have you done the same test on a single bowline for comparison & what happens if instead of passing the bight over the knot you use a krab to clip it in?"

 I read it as a two part question:

Will the (single) bowline fail if pulled apart from the loop? Yes, which is why the stopper knot is essential or use a Yosemite finish. It's frowned on by some in mountaineering instructor world as a tie in knot to the harness when that rope loop is then used to belay from.

Second part: no idea what it means...  :shrug:

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Offline mikem

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Re: Bowline on the Bight - A Method of Failure
« Reply #8 on: January 10, 2013, 08:27:31 pm »
Sorry I'm confusing myself as you have to pass the bight over the knot to form the bowline...

& I see you have addressed the issues with "bunny ears" fig 8 now I've read through the fusion knot thread.

All knots work on friction, but the BotB definitely opens up the knot if loaded in a certain way.

Mike

Offline Pete K

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Re: Bowline on the Bight - A Method of Failure
« Reply #9 on: January 30, 2013, 10:42:29 pm »
Just to let everyone know that this has not been forgotten. Some drop tests were done in the Dales today (30/1/13) by Bob Mehew, Roy Rogers and myself.
The BotB, DBotB, Double-Fig8otB, Fusion and standard Fig8 Loop where all looked at. Bob will put out some information as soon as he has had the chance to look over everything and I'll try to put some slo-mo video up on YouTube.

Offline ianball11

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Re: Bowline on the Bight - A Method of Failure
« Reply #10 on: January 31, 2013, 09:12:53 am »
Intriguing.

 :clap2:

Offline Pete K

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Re: Bowline on the Bight - A Method of Failure
« Reply #11 on: February 04, 2013, 06:19:13 pm »
BCA statement now online and out/due in various press:

Warning - correct use of Bowline on the Bight Knots

BCA's Training and Equipment & Techniques Committees would like to highlight the importance of ALWAYS clipping a cowstail through BOTH loops of a Bowline on the Bight knot. Although this has been taught for years by BCA instructors, it appears that many cavers are not aware of the importance.

The problem is that in a fall the knot can slip in such a way that the rope going down the pitch can actually run all the way back through the knot. This means that a caver falling at a pitch head with their cowstail clipped into only ONE of the two loops could potentially plummet all the way to the bottom of the pitch. This cannot happen if they are clipped into BOTH loops.

A useful tip is for the rigger to leave an HMS karabiner clipped between the two loops to make it easier for the rest of the party to clip in and it is always worth remembering that two cowstails are preferable to one.

http://www.british-caving.org.uk/?page=150

Offline Bob Mehew

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Re: Bowline on the Bight - A Method of Failure
« Reply #12 on: February 04, 2013, 07:33:48 pm »
I have posted our initial results from a Preliminary Investigation into Y hang knots at http://british-caving.org.uk/equipment/Initial%20results%20from%20a%20Preliminary%20Investigation%20into%20Y%20hang%20knots.pdf .  Suggestions (polite ones please) for further work are invited.  Confirming the superiority of one knot's dynamic strength over others would take a lot of effort (my estimate would be breaking 10 samples of each knot for each variable such as rope diameter).  Proving no catastrophic loop slip is probably verging on the impossible.  We are hoping to take possession of a static rig which would make testing quicker but at the risk of using an unrepresentative loading method (minutes verses two tenths of a second).

Offline Pete K

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Re: Bowline on the Bight - A Method of Failure
« Reply #13 on: February 04, 2013, 08:01:16 pm »
If anyone is interested in watching the tests (edited down heavily):

http://www.youtube.com/playlist?list=PLCkzBQHq_YaJ4JTDYcVuZAyBgc5-bOnwK

Offline Cave_Troll

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Re: Bowline on the Bight - A Method of Failure
« Reply #14 on: February 04, 2013, 08:29:07 pm »
that play list is private...

Offline Stuart Anderson

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Re: Bowline on the Bight - A Method of Failure
« Reply #15 on: February 04, 2013, 09:09:13 pm »
Good work those men.  :thumbsup:

Slight quibble. The nomenclature is out. Does it matter? I think it does for clarity - especially if you ask me for a particular knot in extremis.

Ashley's Book of Knots is pretty much the Bible. All the knots in this tome are identified thus: ABoK #xxx

You've tested:

Double Fo8 Loop ABoK #1085 (Bunny Ears/Double Fo8 on a bight)

Bowline ABoK #1010 (standard Bowline on a Bight)

Bowline on a Bight ABoK #1080 (double Bowline on the Bight)

Figure 8 loop ABoK #1047 (presume what you refer as Fo8 on the Bight)

Fusion/Karash - newish.

Confusion does arise I agree in that some knots seem to be named after how they are tied and some named on characteristics they take on once formed.

Back to the figures: nothing stands out as particularly weak or worrying.

My criteria when choosing/tying a knot are:

  • ease of tying/untying after load
  • adjust-ability
  • how will the knot react if loaded abnormally in the case of an anchor failure

My thoughts on this are that testing of the last feature will provide a little more "real world" data (which is I guess how all this started). I do however think that now there is a knowledge of the potential problem with the Bowline on a Bight, I'd hate to see a lot of man hours go into investigating it, when there is a solution: clip both loops.

I'd like to see how an Alpine Butterfly acts when loaded as an end loop; mainly for interest as I don't believe modern ropes ever get to the point where, even with the most abhorrently tied knot mess, they are sufficiently weak enough for me to worry.

Thank you all.
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 ianball11

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Re: Bowline on the Bight - A Method of Failure
« Reply #16 on: February 04, 2013, 11:27:33 pm »
I think you may have proved your own point Stu.

I read it as:

Fig 8 on bight (AB#1085 Fig8 Y-hang, bunnyears)

Fusion  (Pete Knight Blog-Fusion )

Double Bowline on the Bight ( Pete Knights Blog-DBotB)

Standard Bowline on Bight (AB#1080, the knot in question)

Fig 8 loop (AB#1047,  Flemish Loop)


Proving how little I understand these things, please could I ask how significant is the spread of values in the Peak force and Max Peak force sections?  For knots that are expected to do very similar jobs, is the spread of 0.5kN over 10kN a small amount or a large enough amount to cause a preference in use due to that value?

And then how significant is the Drops survived column?  Type B static rope should survive 5 factor 1 falls with 80kg mass with fig-8 terminations.  The 100kgs here would make sense that it didn't survive past two with fig-8 loop, but the Double Bowline on Bight, surviving 8 100kg fall factor 1 falls! 

Also I am right in thinking that the breaking of the fusion knot actually in the knot meant both loops were broken?

Having asked all that, I do appreciate the comprehensive body of work hasn't been done to give anything more than indications of areas of question.

thanks Pete, Roy, Bob and the BPC.  :thumbsup:

Offline mikem

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Re: Bowline on the Bight - A Method of Failure
« Reply #17 on: February 05, 2013, 07:49:57 am »
The BotB video:

Difficult to predict why it survived twice as many drops, particularly as it failed at the fig 8 at the other end of the rope, but it would seem that it did a better job of absorbing the impact.

Mike

Offline Jopo

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Re: Bowline on the Bight - A Method of Failure
« Reply #18 on: February 05, 2013, 08:59:46 am »
In the real world the bights are fixed to the anchor points not the falling component. I am curious as to why the test was done upside down.
If you watch carefully the knot becomes unequal which must mean that the strands are moving within the knot, I suspect this causing a increasing unevenness of the load as the test progresses. It may be insignificant but I do wonder why this method was chosen.

Another point which has been raised is the clipping in to both strands of the bight. This of course means that if the anchor fails the crab will fall of the end of the loop (which is the same problem seen with self equalizing anchors once popular in mountain rescue circles).

What would the objections be to introducing a twist in the bight before  attaching to the anchor which would allow the user to clip in over the 'cross' of the twist so that failure of the anchor would at least keep the crab on the rope and still prevent one sided loading of the loop?
Jopo

Offline mikem

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Re: Bowline on the Bight - A Method of Failure
« Reply #19 on: February 05, 2013, 09:16:28 am »
It's that way around because that's where the anchor points are on the rig.

No one has suggested clipping in to both strands of a single bight, they are using the strands from separate loops.

Mike

Offline Pete K

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Re: Bowline on the Bight - A Method of Failure
« Reply #20 on: February 05, 2013, 09:52:33 am »
@Cave_Troll playlist sorted, thanks for spotting that.

As mike says above, the rig has to be set that way. The apparent missalignment of the drop weight as the tests progress with each knot is not a fault of the rig, it is that the bowline variants all acted like a slip knot for the loop formed by the active end and essentially 'unequalised' themselves.

I'm nowhere near as experienced to answer some of these questions as Bob so hopefully he will pop along soon.

@ianball11

The Peak Force is the ammount of force transmitted to the other components in the system (anchors/caver etc...). This figure is relative in these tests, so a lower peak force shown is a greater amount of shock absorbtion through slip etc of the knot. The higher the peak force, the less slip and absorbtion in the knot.
10kN is equivilant to 1000Kg of force. 0.5kN is equivilant to 50Kg of force.

Drops survived give an indicator of the knot's (and rope for that matter) ability to repeatedly absorb shock. The failiure comes when the rope can give no more elasticity to absorb or heat has damaged it enought to make it weak and break.
Essentially a knot with a higher number of drops survived would be a good choice where a shock load risk could occur, i.e. cave bolt failing etc...

@jopo

Clip your cowstail carabiner into a single strand of each loop, thus connecting you to both loops, not entirely around one. Very easy to do on Bowlines, harder on Fig8's.

@stu

I see your point about the Fig8 loop / tied on the bight. I'll pass that on to Bob who wrote the report.

Can I just remind everyone that this was one set of testing only and cannot statictically prove a trend. Yes the DBoB survived mentionably more drops than the others in this test but even Bob thinks we'd need dozens and dozens of tests to be able to make a solid statement.

The BCA have made comment on the BotB. The French have chosen one route. We have provided film and testing. Cavers will choose to continue to use it or not, it is up to them. I hope that the research we have managed to do recently will just allow everyone to make an informed choice on knot selection.
If in doubt speak to an experienced club rigger or a CIC.

Offline mikem

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Re: Bowline on the Bight - A Method of Failure
« Reply #21 on: February 05, 2013, 10:22:30 am »
Has any testing been done on normal bowline versus double bowline to see what effect the second wrap has?

Mike

Offline Jopo

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Re: Bowline on the Bight - A Method of Failure
« Reply #22 on: February 05, 2013, 10:25:53 am »
Quote
No one has suggested clipping in to both strands of a single bight, they are using the strands from separate loops.

Quote
The problem is that in a fall the knot can slip in such a way that the rope going down the pitch can actually run all the way back through the knot. This means that a caver falling at a pitch head with their cowstail clipped into only ONE of the two loops could potentially plummet all the way to the bottom of the pitch. This cannot happen if they are clipped into BOTH loops.

Perhaps it would be much clearer if it the term 'into the loop of each bight' was used.

Jopo

Offline Pete K

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Re: Bowline on the Bight - A Method of Failure
« Reply #23 on: February 05, 2013, 10:39:13 am »
Has any testing been done on normal bowline versus double bowline to see what effect the second wrap has?

Mike
Not by us. The testing is a very long winded and time consuming process. The guys like Bob and Roy are working on their own time in sheds. I think the list of testing that we would have to do alone to give a statistically sound set of data would take months. The number of testable variables is mind boggling. If anyone wants to help they could perhaps convince Lyon to do some testing. DMM are producing caving kit now, they may be up for some fun too.

My gut feeling was correct about the Double Bowline on the Bight and I suspect a Double Bowline would survive more drops than the Standard Bowline. However, in Bob's world of scientific rope testing, I am very much a beginner.

Offline ianball11

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Re: Bowline on the Bight - A Method of Failure
« Reply #24 on: February 05, 2013, 12:01:47 pm »
Thanks Pete, lower the better.

What do you think is indicated if anything on a small sample size, of the fusion knot breaking at the knot, when all the other broke at the other end?