Which knots for Y hangs?
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Mark Wright
Active member
Jon said:
Things will only change when a new knot or technique is proven beyond doubt to be significantly safer than that currently used. I doubt very much that a Fusion Knot is a game changer. As MarkS points out, it does look as though the knot is being misloaded in the 'Y' hang configuration.
As I said before, any saving in rope will be negligible. You wouldn't be using a Bunny Knot for wide 'Y' hangs anyway as a Fig. 8 or 9 and an Alpine Butterfly would be the most appropriate knots to use in this situation. A Bunny Knot is for use when anchors are relatively close together.
I would have thought if you were taking 'clients' on an SRT course/trip it would be paramount that they have a good understanding of what they are looking at in terms of safe rigging.
Mark
Mark Wright
Active member
maxf said:
A Fig. 9 is a little stronger than an 8 though negligible really. The main advantage, as you say, is its ease of untying. Mind you, It'll still be hard to untie if a lot of people have been using it and bouncing on it as they invariably do.
Mark
Mike Hopley
New member
Yeah, this is another less-than-ideal aspect. Jon -- this issue will still be there if you substitute the Diju for the Fusion, although perhaps less worrying due to the Diju being more "solid".
Well I generally would, because I don't like creating a section of rope that is unsafe to clip into -- especially when it's a wide Y hang, because then it might be hard to reach the next section (the traverse) with a cowstail.
While this can be negotiated safely with a jammer, I rarely see people actually do that. That's not to say the rigging is unsafe in itself, it's just less user-friendly. The amount of rope saved is small, so I'd rather just make the rigging nicer for people. And accurately measuring a wide double-loop knot is easy when you know how, so both methods take about the same amount of time.
Chocolate fireguard
Active member
Well I generally would, because I don't like creating a section of rope that is unsafe to clip into -- especially when it's a wide Y hang, because then it might be hard to reach the next section (the traverse) with a cowstail.
While this can be negotiated safely with a jammer, I rarely see people actually do that. That's not to say the rigging is unsafe in itself, it's just less user-friendly. The amount of rope saved is small, so I'd rather just make the rigging nicer for people. And accurately measuring a wide double-loop knot is easy when you know how, so both methods take about the same amount of time.
[/quote]
Yes.
I don't understand why this isn't said more often. When passing a wide Y-hang on the way up, especially when carrying a heavy bag, it's so much easier if it has been rigged with a bunny-ears or similar, when the next rope comes to the bottom of the Y. It can be passed easily and safely.
And with a free hanging Y-hang re-belay to make it as easy with a Fig. whatever and an alpine butterfly the loop that has to be left is such that no rope will be saved.
Mark Wright
Active member
Mike Hopley said:
What section of a Fig. 8/9 and Alpine Butterfly wide 'Y' hang is unsafe to clip that is any different to clipping into a wide 'Y' hang tied with a Bunny Knot? I've certainly used an ascender attached to the single rope part of a 'Y' hang in order to reach a traverse but you obviously wouldn't be able to use an ascender to do that with a Bunny Knot or the rope would simply pull through the anchor point.
I have absolutely no issues at all with using a Bunny Knot for wide 'Y' hangs, it just uses more rope. There aren't many situations I can think of where transferring from the rope to a traverse line is that difficult to achieve. If it is such a big reach why not put some slack in the traverse line so your cow's tail will reach.
Every pitch head has its own peculiarities but can generally always be safely rigged with a combination of the traditional knots as previously mentioned.
Mark
Surely the bottom of the fusion knot should have both strands hanging down in the same way that a figure 8 should, otherwise the bottom of the knot will deform.
Maybe the BFK is what you are looking for, the double loops go to the anchors & the single can be used as clip in (if made smaller than shown)....
https://youtu.be/jN1LtSu61Xo
Maybe the BFK is what you are looking for, the double loops go to the anchors & the single can be used as clip in (if made smaller than shown)....
https://youtu.be/jN1LtSu61Xo
Mark Wright
Active member
The BFK, or Big Fucking Knot to give it it's full name, is another one of those knots that comes and go's.
The main issue with it is that when loaded it seriously deforms and becomes almost impossible to see whether it's tied correctly. There is so much rope in the knot that if you tested it 10 times you would likely get 10 significantly different test results.
Some tried to introduce this into the industrial environment about 20 odd years ago. After considering the points above it was not adopted as a suitable knot for industrial use.
Mark
The main issue with it is that when loaded it seriously deforms and becomes almost impossible to see whether it's tied correctly. There is so much rope in the knot that if you tested it 10 times you would likely get 10 significantly different test results.
Some tried to introduce this into the industrial environment about 20 odd years ago. After considering the points above it was not adopted as a suitable knot for industrial use.
Mark
andrewmcleod
Well-known member
Mark Wright said:
I think you are being slightly disingenuous by saying you don't know which bit it is unsafe to clip (the single strand, obviously) and then saying you have used your ascender on it - which doesn't count as 'clipping' it.
I would argue any traverse line approach you have to put an ascender on is awkward. Ideally traverse line should be fairly tight, which precludes using your descender to approach the pitch head and makes ascending tricky. If the pitch head is that much lower than the traverse bolts, then possibly a short rebelay from the traverse bolt/bolts would be easier anyway, but it is often much easier if the traverse line goes straight to the pitch head.
Leaving the traverse line slack enough so that you can reach means you don't have a tight traverse line and you use extra rope anyway.
The single strand isn't unsafe to clip, as it is coming from a traverse line. It's when it is coming from a single bolt that it is risky (although modern bolts are much less likely to fail than spits were, so maybe rock fall is now the greatest potential problem outside the control of the caver).
There are numerous traverses that come in above the level of the Y hang & having the line go straight there would mean a higher fall factor on your cowstails if you slipped...
There are numerous traverses that come in above the level of the Y hang & having the line go straight there would mean a higher fall factor on your cowstails if you slipped...
Mark Wright
Active member
I wouldn't consider the single strand as being unsafe to clip into with a cow's tail. We are all happy enough to be attached to a single rope with a toothed ascender that will probably break the rope sheath at +/- 450kg. This could easily be achieved with a 100kg caver falling just 45cm regardless of the Fall Factor.
The first drop going from the right-hand wall at the top of Aldo's in the Berger is where I have regularly used an ascender just to give me that extra 25cm or so to reach the traverse line on the left-hand wall. I totally agree this is not ideal rigging and can be quite awkward but the traverse is higher than the pitch head so there isn't much choice. We just need to be sure we are being as safe as is reasonably practicable.
I would argue that a tight traverse line is unsafe due to the significant Vector forces which could be applied to the traverse line and its anchors. If a tight traverse line gave a 160 degree angle at the point of suspension then the resulting load at each anchor point would be +/- 288kg with a 100kg mass. If your cow's tail reduced the potential falling forces on you to, e.g. 4.5kN then the traverse lines and their anchor points would be subjected to a force which could be alarmingly close to the breaking strength of a typical 9mm rope with Fig. 8 termination knots!
The forces applied to traverse lines and their anchors rigged tighter than this will increase exponentially. A 100kg mass hanging (not falling) on a traverse line with an angle of, e.g. 179 degrees could result in anchor point loads of +/- 5,747kg!!! This figure would be halved with a 178 degree angle but still way in excess of the rope's breaking strength.
In an industrial environment, and professional caving would come into that category, traverse lines should never allow angles greater than 120 degrees. 10% sag between anchors would usually achieve the 120 degrees. Safety nets should always be rigged with 10% sag for this reason.
I would argue that time constraints are irrelevant in a professional SRT instructional caving situation and whether 'clients' are interested in rigging or not is no excuse for disregarding best practice. I'm not the one who would be stood in front of the judge trying to explain why the 'client' died, I would more likely be the expert witness for the prosecution.
I sat as the IRATA representative on the HSE Advisory Committee for Work at Height Training prior to the introduction of the 2005 Work at Height Regulations. When the 2007 amendment was introduced allowing the outdoor pursuits industry to use single ropes, the author of the above regulation made very clear to me that the full force of the law would bear down on the person in charge should that single rope fail. In effect, outdoor pursuits instructors have an obligation to be extra-extra careful. This means the following of 'best practice' to the book.
Having recently seen an example of the supposedly professional caving 'best practice' documents, I would suggest the best place to find out about industry best practice would be from the IRATA International Code of Practice, freely available from the IRATA website, www.irata.org.
Mark
andrewmc said:
The first drop going from the right-hand wall at the top of Aldo's in the Berger is where I have regularly used an ascender just to give me that extra 25cm or so to reach the traverse line on the left-hand wall. I totally agree this is not ideal rigging and can be quite awkward but the traverse is higher than the pitch head so there isn't much choice. We just need to be sure we are being as safe as is reasonably practicable.
I would argue that a tight traverse line is unsafe due to the significant Vector forces which could be applied to the traverse line and its anchors. If a tight traverse line gave a 160 degree angle at the point of suspension then the resulting load at each anchor point would be +/- 288kg with a 100kg mass. If your cow's tail reduced the potential falling forces on you to, e.g. 4.5kN then the traverse lines and their anchor points would be subjected to a force which could be alarmingly close to the breaking strength of a typical 9mm rope with Fig. 8 termination knots!
The forces applied to traverse lines and their anchors rigged tighter than this will increase exponentially. A 100kg mass hanging (not falling) on a traverse line with an angle of, e.g. 179 degrees could result in anchor point loads of +/- 5,747kg!!! This figure would be halved with a 178 degree angle but still way in excess of the rope's breaking strength.
In an industrial environment, and professional caving would come into that category, traverse lines should never allow angles greater than 120 degrees. 10% sag between anchors would usually achieve the 120 degrees. Safety nets should always be rigged with 10% sag for this reason.
Jon said:
I would argue that time constraints are irrelevant in a professional SRT instructional caving situation and whether 'clients' are interested in rigging or not is no excuse for disregarding best practice. I'm not the one who would be stood in front of the judge trying to explain why the 'client' died, I would more likely be the expert witness for the prosecution.
I sat as the IRATA representative on the HSE Advisory Committee for Work at Height Training prior to the introduction of the 2005 Work at Height Regulations. When the 2007 amendment was introduced allowing the outdoor pursuits industry to use single ropes, the author of the above regulation made very clear to me that the full force of the law would bear down on the person in charge should that single rope fail. In effect, outdoor pursuits instructors have an obligation to be extra-extra careful. This means the following of 'best practice' to the book.
Having recently seen an example of the supposedly professional caving 'best practice' documents, I would suggest the best place to find out about industry best practice would be from the IRATA International Code of Practice, freely available from the IRATA website, www.irata.org.
Mark
Jon
Member
Mark Wright said:
The rest of your post is really useful and thought provoking but I don't understand how you've leapt from an instructor teaching a client SRT but not rigging and then taking then caving to the client dying because they haven't been taught rigging. It's perfectly possible to teach SRT but not how to rig a cave and then take that person caving safely.
andrewmcleod
Well-known member
Mark Wright said:
Because if the other bolt (the one with the double loop) fails there is every chance that your nice big cowstail carabiner will slide over the central knot and other stuff and send you down the pitch.
Have you got a reference for that? (The physicist in me says you mean 450kg-force, but that doesn't really matter).
And happy is a relative term - unless I've got two bolts with minimal extension on failure or a bucket load of rope above me, I am not happy about being on ascenders...
andrewmcleod
Well-known member
Mark Wright said:
A tight traverse line doesn't mean it has to be a large angle, and in any event large angles are actually really quite hard to do anyway since you might start at 120 degrees for a (small e.g. 1 foot spaced bolts) but once you've actually loaded it it's nearly always less than 90 degrees anyway.
Has anyone ever damaged a rope from overloaded at a tied Y-hang style anchor system with no hauling or mechanical advantage? I think even for a Tyrolean from one wall to another, just tying into anchors on opposite sides of the wall will always end up with so much stretch and slack from the knots that you never end up breaking the rope. I could be wrong on that though.
Having a taut (maybe a better word than 'tight' traverse line reduces the size of a fall from a slip as there is less slack and the attachment point is higher.
The traverse line also only needs a very small amount of slack in it to not take most of the force as well.
Chocolate fireguard
Active member
Mark Wright said:
The numbers are correct but misleading in a caving situation.
Caving ropes stretch. A typical figure for 9mm rope is 3.9% for a 150kg load (about 1500N tension in the rope).
Someone with a firm footing and muscles like Garth might get to a third of that if they really tried to rig a tight line (I believe 300N is taken as a good personal contribution on a haul line, but I am willing to be corrected).
So they get perhaps 1.3% stretch. And that's a really tight line!
Someone coming along and putting a little weight on the centre of the line is going to increase the tension considerably - as Mark has pointed out with an included angle of 179 degrees the tension in the rope is over 50 times the weight placed at the middle.
So on the face of it a 20N weight (sack with a few metres of rope in it?) will increase the rope tension by 1kN.
Just as, on the face of it, a heavy person would snap the rope.
The reason these things don't happen is because the rope stretches and the included angle decreases, so allowing the weight to be supported by a much lower rope tension.
In the tight line above an increase in rope tension of 1kN to 1500N would increase the stretch by about 2.5% so the load point at the centre would fall by 22% of the span and the included angle would fall to 155 degrees. At which point the tension in the rope is just over twice the weight being supported.
But coming up with accurate figures for exactly what the tension is in a loaded traverse line is very complicated, and I don't know how it can be done. I have put in quite a few hours on the problem.
