Author Topic: Modifying rigging?  (Read 954 times)

Offline caving_fox

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Modifying rigging?
« on: May 13, 2019, 09:29:40 am »
Are there situations when it's right to do so?

The general 'rule' I've always used is that you leave other people's gear alone, with perhaps two exceptions: a) the trivial one, on ladder pitches rather than double rigging ladders, leave yours coiled at the pitch head use the one that's there, and they'll rig yours if they exit before you do (rig your own lifeline though). b) if you see something obviously unsafe then there is an expectation that you don't just pass on by. The hard bit, and the area I'm interested in people's thoughts is how unsafe* does it need to be, in order to justify altering someone else's ropework?

What sparked these thoughts is a trip at the weekend, passing a popular multi-entrance cave, I observed a line tied off to a single surface p-hanger with a knot I didn't recognise (may have been a fusion, was not bowline or fig8) thrown over a lip to the base of a shaft without other rebelay. I presume without any other evidence, that the party had abseiled on this line intending to exit elsewhere for an easy collection of the rope afterwards.

This is obviously not the safest or best practise. The rigging was clearly dangerous to use for prussicking as it ran directly over the edge. If the party had failed to find their way through or needed to return for any reason they'd have been in trouble. Also being a popular system it's not unknown for other parties to use all available ropes on exiting this way in the assumption (ass U Me) they'd be safely tied at the top, in the same way that in-situ rope is sometimes used.

(As we were planning on exiting this way we just rigged our rope with rebelays for ascent and left that line untouched. It was still there when we exited)

However I'd have been mightily annoyed if I'd returned from a trip to find my rope had been fiddled with, and I'm unsure whether there was sufficient extra length in the rope to rig this pitch 'normally'.

Would you have modified that rope? When would you think it appropriate to do so?


*Bonus marks to anyone who has a justified scale of safeness.
If the world didn't suck, we'd all fall off.

Offline royfellows

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Re: Modifying rigging?
« Reply #1 on: May 13, 2019, 09:56:55 am »
A real dilemma.
I have to point out that if you did go ahead and modify the rigging and there was an accident, probably totally unrelated to the method of rigging, other parties could claim otherwise and so there could be serious legal implications.
Best I can think of is to attempt to make contact with the parties concerned, either by leaving a note or someone stay behind to talk to them.
Glad NAMHO 2019 over.

Offline glyders

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Re: Modifying rigging?
« Reply #2 on: May 13, 2019, 10:49:41 am »
It is a tricky one. Something as simple as doing up a screwgate or reversing it so the gate isn't against a rocky edge I wouldn't think twice about.
One of my big fears on returning to a pitch where I descended someone else's stuff is that whoever rigged my stuff when they left will have made a pigs ear of it and now I'm at the bottom (the worst I had that happen to me was a ladder off one P-hanger and my rope running through one other (I'd left plenty of stuff to easily rig the lifeline off the pair - luckily on a personal trip not leading a group)).

Offline Badlad

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Re: Modifying rigging?
« Reply #3 on: May 13, 2019, 12:31:50 pm »
A lot might depend on our individual interpretation of risk or safe rigging.  It may be that whoever rigged the rope from a single P anger and over an edge thought that was safe enough for the trip they intended (perhaps just a quick ab down), or it may just have been left to pull some kit up.  I'd tend to leave well alone unless it was obvious that something unintentional had happened like the rope getting hooked behind a sharp flake. 

So in the absence of the party who did the rigging only interfere if there is clear danger of injury or misfortune would be my guide.

Offline Mike Hopley

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Re: Modifying rigging?
« Reply #4 on: May 13, 2019, 12:46:03 pm »
It's tricky. I won't interfere unless the rigging looks seriously dangerous. Even then, you have to be careful -- as you said, changing the rigging in that example could have stranded them. Maybe I haven't understood the circumstances that led to that rigging.

Altering dangerous rigging is also a short-term solution to a long-term problem. If they survive their rigging, they'll likely keep doing it. I'd like to find them in the cave and talk with them (nicely!) about their crappy rigging. If not, I'd like to leave a note about it.

And because I can't resist BONUS POINTS...

  • High chance of death:
    • Bad rub point on a longer section of rope (especially thin rope)*
    • Obviously insecure knot (like joining ropes with a reef knot, bowline with no tail at all...)
    • Primary anchor off a really dodgy natural or bolt
    • Open maillons
  • Still dangerous, but high chance of survival:
    • Minor rub point on a shorter section of rope (or very thick rope)
    • Dependent on a single good Spit anchor
    • Lots of slack that could lead to high fall-factors, when rigging off Spits
    • Rigging near significant hazards (loose rock, waterfalls...)
    • Carabiner gate actually loaded against the rock
  • Bad practice but fairly low-risk in reality:
    • Dependent on a single resin anchor
    • Lots of slack that could lead to high fall-factors, but on resin anchors
    • Poorly-tied knots (e.g. end-line bowlines without backup knots)
    • Carabiner (not gate) actually loaded over a rock edge (potential levering force)
    • Carabiner cross-loaded or three-way loaded
    • Carabiner gate opened (usually blocked by the locking barrel)
    • Last rebelay before the ground, off a single Spit
    • Dyneema cord used without extensive knowledge
  • Essentially irrelevant, it just might set off your OCD / scare you:
    • Knots you don't recognise or like
    • Knots badly dressed (no more dangerous than people badly dressed)
    • Knots "loaded wrong", e.g. Alpine Butterfly on a single-anchor hang
    • Carabiners placed/oriented incorrectly, so e.g. could theoretically-maybe press gate against rock
    • Screwgates not done up, or rigging off snapgates
    • Rub point immediately before a rebelay
    • Last rebelay before the ground, off a single resin anchor
    • Al Warild rigging a 1600m deep cave with a couple of ropes and some string

*This is not theoretical. I've seen a rope almost cut by a rub point, with a caver very lucky to be alive. Always look up when you're rigging.
« Last Edit: May 13, 2019, 12:59:09 pm by Mike Hopley »

Offline Alex

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Re: Modifying rigging?
« Reply #5 on: May 13, 2019, 01:05:32 pm »
Quote
Last rebelay before the ground, off a single Spit

True but in some caves that is your only choice? Also sometimes the only anchor can be occasionally be a single spit on small pitches. Thankfully spits are becoming obsolete thanks to CNCC.

Quote
Last rebelay before the ground, off a single resin anchor

Why does it matter if its the last one before the ground or not. I don't understand, it's a fall factor/fall onto ledge should it fail even if it's not the last one before the ground? Spits at least tend fail when you are just below them anyway. Again this may be something you don't have control of as you can only use the bolts you are given, unless you bring a drill which is a whole other ethical ball game.

A note/friendly word is probbably the best option. I suspect they had just rigged it to go down and not intended to go back up and simply did not have enough rope for the pull through. But in that case they should have left a note or something so others did not use it thinking it was safe from the bottom. (p.s. Bonus wezzit from the description, Lancs Hole?)
« Last Edit: May 13, 2019, 01:20:33 pm by Alex »
Anything I say is represents my own opinion and not that of a any club/organisation that I am a member of (unless its good of course)

Offline mikem

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Re: Modifying rigging?
« Reply #6 on: May 13, 2019, 01:57:15 pm »
If there is another exit that doesn't require ascenders then they may not have any to recover the rope if you rebelayed it. Alternatively the pitch may be free climbable, with the rope only there as a handline...

If your interference with the rope will definitely make it safer, then do it - you would be more negligent if you left it alone.

Greatest risk on spits is a single anchor close to previous anchor, as less rope to absorb shock load caused by lower one failing.

Offline topcat

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Re: Modifying rigging?
« Reply #7 on: May 13, 2019, 03:25:26 pm »
Quote

Quote
Last rebelay before the ground, off a single resin anchor

Why does it matter if its the last one before the ground or not. I don't understand, it's a fall factor/fall onto ledge should it fail even if it's not the last one before the ground? Spits at least tend fail when you are just below them anyway.

The explanation is clearly illustrated in 'the books'.............actually it is not so much the last belay before the ground, but when that belay is close to the ground.

There is a pitch in Meregill and one in Lost Johns rigged like this.  Now they are resin bolts, but even so it is bad practise. 

In the above situation the re belay should be a Y hang.

Offline Mike Hopley

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Re: Modifying rigging?
« Reply #8 on: May 13, 2019, 05:22:54 pm »
To explain "last rebelay before the ground":

It (sort of) doesn't matter how high above the ground, because you should assume the bolt could fail at any time. If it fails when you are about 2 metres off the ground, you're going to fall 2 metres and smack your tailbone / neck / whatever. You will not fall "nicely" and land on your feet. You may break something.

Granted the bolt is more likely to fail when you are close to it, and therefore it's more dangerous when the rebelay is close to the ground. That doesn't make higher-up ones safe, just less dangerous.

As Alex said, you often "don't have a choice", because caves are commonly bolted without this in mind. It's even common practice with Spits (I'm thinking more expeditions here), which is really not great when you think about it.

Also this applies not just to "ground" but also "ledge", as Alex mentioned.

Online andrewmc

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Re: Modifying rigging?
« Reply #9 on: May 13, 2019, 05:25:18 pm »
Granted the bolt is more likely to fail when you are close to it, and therefore it's more dangerous when the rebelay is close to the ground. That doesn't make higher-up ones safe, just less dangerous.

Arguably the bolt is also (maybe even most) likely to fail when you have just started prussiking on it. It might have been OK for the lower loads of abseiling, and pop once you start bouncing on it. Which is when you are still close to the ground...

Offline Mike Hopley

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Re: Modifying rigging?
« Reply #10 on: May 13, 2019, 05:27:51 pm »
Arguably the bolt is also (maybe even most) likely to fail when you have just started prussiking on it. It might have been OK for the lower loads of abseiling, and pop once you start bouncing on it. Which is when you are still close to the ground...

Good point.

It's generally reckoned that bolts are more likely to fail as you get close, but in reality we can never be sure what will happen. If a bolt has become weak, it could fail at any time.

Offline Ian Ball

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Re: Modifying rigging?
« Reply #11 on: May 13, 2019, 07:29:31 pm »
I would expect an anchor to suffer greater load on the abseil than on the climb, though I have no source to hand. I think Lyon did some testing.

I have wondered if the Meregill last bolt would  be better as a deviation, or as a multiloop knot to double the rope to bolt connection,  or as a really slippery knot so a fall or similar tightens the knot to reduce peak force.  All thoroughly unproven concepts.

Offline Mike Hopley

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Re: Modifying rigging?
« Reply #12 on: May 14, 2019, 09:01:03 am »
I would expect an anchor to suffer greater load on the abseil than on the climb, though I have no source to hand. I think Lyon did some testing.

Definitely not. "Rough" prusiking can generate forces around 3 times body weight.

Quote
I have wondered if the Meregill last bolt would  be better as a deviation, or as a multiloop knot to double the rope to bolt connection,  or as a really slippery knot so a fall or similar tightens the knot to reduce peak force.  All thoroughly unproven concepts.

Can't recall exactly what it looks like, but I don't think it works as a deviation?

How does "doubling the rope to bolt connection" help? I do this anyway (bowline on the bight) because fig-8s are miserable to untie in thin rope, but I don't see any safety benefit.

A slippery knot is just going to get tightened by body weight. You could add shock-absorbing knots to the rebelay loop, but it's probably a bad idea. They used to be recommended by some texts (ACT) for lightweight rigging, but I believe the idea has fallen out of favour. If they are too loose, they just create more shock; too tight, and they don't work. It's hard to get right.

Offline mikem

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Re: Modifying rigging?
« Reply #13 on: May 14, 2019, 09:47:47 am »
Not sure about 3 times body weight, certainly could be 3 times the difference.

In normal use Lyon found a O.75kN person varied from O.6 to O.9kN (one fifth variation either side) when abseiling & O.35 to 1.O5kN whilst ascending (which is just over half body weight). The reduced loadings are caused by the bounce.

I guess Ian is considering shock loading on the rope, rather than ground impact.

Surely spit is most likely to fail on first loading, which is normally abseil, then may happen to fail on way down or coming back up, but they must be statistically less likely (in above example abseiler loading anchor covers O to O.8, actually abseiling up to O.9 & prussiking from there to 1.O5...)
« Last Edit: May 14, 2019, 10:10:14 am by mikem »

Offline Mike Hopley

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Re: Modifying rigging?
« Reply #14 on: May 14, 2019, 10:07:31 am »
In normal use Lyon found a O.75kN person varied from O.6 to O.9kN (one fifth variation either side) when abseiling & O.35 to 1.O5kN whilst ascending (which is just over half body weight). The reduced loadings are caused by the bounce.

Actually I think you're right -- I may be getting muddled up and recalling that 3 kN number from the EFS lanyard tests, which used cowstails pre-tensioned to that value.

Those Lyon numbers put peak forces at 1.2 times body weight for abseiling and 1.4 for prusiking.

Offline mikem

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Re: Modifying rigging?
« Reply #15 on: May 14, 2019, 11:12:39 am »
Obviously greater forces can be created in both cases by bad technique, but I doubt they are significantly bigger. Equipment failure may cause more of a problem.

If you're particularly worried about an anchor then in most cases it can be changed to a deviation, but the problem is only transferred to the one above.

Offline Mike Hopley

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Re: Modifying rigging?
« Reply #16 on: May 14, 2019, 11:33:26 am »
If you're particularly worried about an anchor then in most cases it can be changed to a deviation

Some rebelays can be turned into deviations, but I'd say it's more exception than rule.

Roughly speaking: if the rebelay is on an opposite wall from the rope, you can often turn it into a deviation (might still be a bad idea, depending on circumstances). If it's on the same wall, you can't.

Offline Ian Ball

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Re: Modifying rigging?
« Reply #17 on: May 14, 2019, 11:59:54 am »
"Industrial rope access - Investigation into items of personal protective equipment"
Prepared by
Lyon Equipment Limited
for the Health and Safety Executive 2001"


Here is the 2001 report.

I was thinking that the most force on a single bolt rebelay would be an arrested clutch plummet, I don't think you could generate the same force prussiking.

Of interest is the rope protector data, that once the pvc of a tackle sack is worn and the fibres of the sack are exposed, the friction is increased.  Don't save your old bags for rope protectors, or I think I'll just stick to my usual approach of never trusting a rope protector.




Offline mikem

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Re: Modifying rigging?
« Reply #18 on: May 14, 2019, 02:38:14 pm »
Roughly speaking: if the rebelay is on an opposite wall from the rope, you can often turn it into a deviation (might still be a bad idea, depending on circumstances). If it's on the same wall, you can't.
True, I was thinking of rebelays on overhanging lips, as they are more likely to pop under downwards loads. Unfortunately, a deviation creates more of an outward pull, so may fail sooner than a rebelay would.

Not sure a lock off from speed would cause as big an increase as you might expect, as you'd have to drop a reasonable distance & then the length of rope will absorb some of the force. Another contender might be failing to move up past the anchor & dropping back onto your cowstail.

The report does say that bags are still preferable to a sharp edge...


Online MJenkinson

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Re: Modifying rigging?
« Reply #19 on: May 14, 2019, 06:22:51 pm »
The other issue Mr Fox is that if we had changed it and thrown in a rebelay, if the persons were just on a pull through mission, would they have the kit (probably “should” do of course) to ascend after dropping in to undo the rebelay?  Would have ended up with their rather pricey rope stuck.