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Assisted belay devices for trad, the force on the top piece

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 David Coley 20 Sep 2021

Following on from some earlier threads.

In http://theundercling.com/wp-content/uploads/2014/03/PetzlDynamicRopeExperience.pdf

we see that a grigri increases the force on the top piece quite a bit once the force on the belayer reaches 2kN. That there is little difference between assisted and non assisted for lower forces on the belayer makes sense as they do not lead to enough force to over ride the belayer's arm and hence the rope to slide (I'm guessing it is the hand that moves, on not the rope through the fingers - see various videos on the web).

So, question 1: is 2kN+ on the belayer normal or not? In a trad situation. The end of the document has some pointers to this, once drag is introduced, possibly not. Also worth noting is that in the first fall (at the top of the doc) the belayer is lifted a considerable distance (see text) requiring the first bolt to be unclipped for safety reasons. With the higher FF the belayer is tethered. And I assume hits the end of the tether. For the trad falls I've held, I have not been lifted up much, so I assume I have probably only been exposed to 1kN or so? And the grigri would have imparted little if any extra force.

Question 2: if extra force on the top piece from using an assisted device mainly shows itself in agressive falls where the belayer is lifted  or slammed against the rock, or pulled up sharp above the anchor in multipitch, then do we have a bit of an issue, in that the falls most likely to cause the belayer to let go, are exactly those where one would want to be using a non assisted device in minimise forces?

Question 3: In sports climbing I believe I give a softer catch with a gri gri than a reverso. I think this is because I'm willing to move more, possibly even jump a little with a gri gri, because I know the fall will be held whatever happens - even if I hit something or trip, whereas with a plate I kind of just hold on as tight as I can and try not to move. Hence, with single pitch trad with the leader in sight, with known marginal gear might I, out of instinct, give a softer catch with an assisted device? 

Question 4. Imagine a fall forceful enough at the belayer to make a difference to the force on the top piece if using a grigri. (a) this only matters if this then causes the top piece to rip, but this would not have ripped if a plate had been used. This seems a narrow window. (b) as the Petzl doc suggests we are talking about falls where the belayer is lifted a considerable distance (2kN at the be;ayer), if the piece then fails, the belayer will be dropped a considerable distance - to the deck. I'm guessing there is a reasonable chance they might let go of the brake strand - although with the plate they might not be so far off the ground.  So might everyone be better off with the assisted device when marginal gear is in place, especially if it makes them willing to instigate a soft catch? Or does the rope slide before 0.8kN (the point you are lifted up)? I think there was some test date (not Petzl) with a high time res series comparing grigri to plate but I can't find it.

Question 5. What do we mean by marginal? The document shows that with some friction in the system, to get 2kN at the belayer we need way more than 5kN on the top piece. This isn't marginal in the normal sense of the word. So the issue is not around those slab test pieces on the culm coast when you are above 6 RPs. It is when a long way above more average, but not bomber gear; or when there is little friction, i.e. near the ground with two bits in and no drag. Does this make sense?

 PaulJepson 20 Sep 2021
In reply to David Coley:

youtube.com/watch?v=m8z6adEqaOs&

This is also a really good demo of where the force from a fall goes in different scenarios.

 gravy 20 Sep 2021
In reply to PaulJepson:

Sick!

In reply to David Coley:

This video is probably the best explanation of the forces in a fall I've seen:

https://www.youtube.com/watch?v=WyExE2qH4Fs&t=1076s

Your questions seem to assume that the belayer and top gear piece forces will be proportional. In reality, more rope drag means a lower the force on the belayer, but often higher force on the top piece, as the lower parts of the rope aren't able to act as effectively as a shock absorber. The hownot2 video linked by Paul shows this well! 

Question 3 is a really good point, and in the hard is easy video he makes a similar point that it's really difficult in reality to provide a meaningful amount of rope slip to give a soft catch, but it's potentially a lot easier to time a jump just before the rope goes tight to soften the catch. 

 MischaHY 20 Sep 2021
In reply to David Coley:

If you're belaying correctly (dynamically, jumping into the rope as the climber weights it), then rope slip through the device has a negligible effect. The longer the fall, the more dynamic the catch in order to soften it sufficiently. 

 galpinos 20 Sep 2021
In reply to David Coley:

I think it's easiest to think of the scenarios separately to understand the forces and mechanisms involved then use that knowledge to understand what happens in your chosen scenario.

Firstly:

> we see that a grigri increases the force on the top piece quite a bit once the force on the belayer reaches 2kN.

I think this statement is misleading. The forces in the system are proportional* to the fall factor. As the fall factor increases, so does the force at the top piece**. It is not a factor of the force at the belayer***.

The second scenario to consider is drag. The more drag in the system, the more force on the top piece. This is due to the "effective" fall factor increasing as the drag prevents the full length of the rope of "absorbing" the force. This scenario could lead to a high force on the top piece and a <1kN force on the belayer.

The third scenario to consider is the belay device. For this, we have less "real world data" to go on but from the testing Petzl have done, it would appear that the forces in the system for a manual device catch are less than those for an assisted device catch, all other factors being equal.

The last think to consider is the force at the belayer. "Real world testing" has shown is it is mostly <2kN.

So, what conclusion to draw from this?

Q1 - Most trad falls I have experienced would give ~1kN at the belayer. I would be very suprised if the had ever been >2kN.

Q2 - Even the most aggressive falls don't put a force on the belayer large enough that holding the fall would be too hard, regardless of the device.

Q3 - Maybe, but I would wager you would be as attentive/non-attentive regardless of device used and your "catch" would be similar if caught unawares

Q4 - a) this does seem a narrow window and b) having taken "big" sport falls on an ATC Guide where I have been lifted there was no "issue" with me letting go.

Q5 - I don't understand the question. Factors that increase the force at the top piece are:

  1. Fall Factor
  2. Drag
  3. Belay Device Used

The biggest force on top piece scenarios are:

  1. Big Fall Factor and assisted belay device (with low drag)
  2. Big Fall Factor and High Drag (drag reduces effect of belay device choice )

I would imagine that Option 2 is the worst case scenario and in the real life tests, option 1 is not going to exceed 5kN even at FF1.

Your best scenario for minimising force on your top piece is minimal drag and a manual device......... Whether that's the best set up having climbed 20 pitches in the alpine with a snoozy belayer is a different matter!

*not strictly true i know but it's a start.....

**Also, this does not hold true for the Petzl pdf as 0.7FF fall on a reverso has a top piece force as lower then a 0.3FF and 1FF fall. Bizarre.

***As the force at the belayer is affected by other factors, e.g. drag.

 David Coley 21 Sep 2021
In reply to galpinos:

Thanks for the extensive reply. What I'm mulling over is the following. Petzl and others have shown that in some falls using a grigri increases the forces on the top piece. But looking at their graphs I'm left wondering of what fraction of falls this is true, and when it is true, what fraction it really matters (if the gear is super solid I'm not sure it really matters).

A. From the graphs it would appear that if the force on the belayer is small, there is little or no additional force on the top piece. This makes sense, as if the FF is low or friction is involved the rope is unlikely to slip through the plate, and if it doesn't slip it offers no advantage. The graphs also show that once the rope zigzags even a bit the force on the belay can be very low.

B. (And this was my Q5) So, for the device to make much difference we need to have a fall that puts quite a lot of force on the belayer (enough to, "lift them a considerable distance", around 2kN?). In turn, this means a considerable force on the top piece (around 5kN). I would suggest pieces that can take such a force are not normally termed marginal. Let's say the top runner is marginal (3kN?). Looking at the graph, if the force on the top runner was 2.9kN then with modest friction the belayer would feel very little force and no slippage through the plate, and hence using an assisted device would not add to the force on the top piece and it would still hold.

I think what I'm concluding is that the times where device choice can make a difference is a rather small window: The forces must be forceful enough to cause slippage, the gear not marginal (in the normal sense of the word), the gear not good either. 

Why this might matter? If we make the assumption that assisted devices might add safety for those new to belaying or holding falls or double ropes or weak hands or light of weight or on long routes or loose rock or where one needs to belay out from the face because of the terrain, then using one makes a lot more sense if the window of falls where they are a bad idea is narrow. Devices like the alpine up are interesting, because they allow assisted or non assisted. So one could make a simple choice at the start of the pitch. Unlike a grigri an alpine up uses the same hand motion as a plate (so it builds those skills). It also uses the same hand motion in assisted and non assisted mode (again building the right skills and muscle memory).

There will be times when slippage is a good idea: a vertical limestone route protected by two not confidence inspiring, but okay-ish, threads comes to mind!

The reason for the post was an attempted to see if there is an error in my logic. All comments very much welcomed.

Thanks again.

Post edited at 09:31
In reply to David Coley:

Looking at the Petzl tests, one thing to note is that the fall factor 0.7 and 1 tests (which show the significant difference between devices) the belayer is tethered, so there is minimal belayer movement which is probably why the forces on the belayer are so high and the effect of the belay device is amplified. To combine your scenarios with these falls would represent a marginal gear piece soon after the belay on a multipitch with the leader taking an early fall. 

I agree with your conclusions, especially in the situation with a belayer who is much lighter than the climber. With heavy, experienced belayers it may be better to have a device that allows some more slip? 

 galpinos 21 Sep 2021
In reply to David Coley:

I think your logic is sound in that the scenarios that an assisted device would dangerously increase the force on your top piece are very rare. I think this is evident by the fact many other nations use grigris etc for trad any they don't have cases of top pieces popping regularly. Accidents in North America* isn't full of those kind of reports.

My concern with assisted belay devices is that they are not all equal and the current work being done to devise a performance test for the new EN 15151-3 is showing that they all perform very differently. This could lead to problems with belayers putting more faith in the device than their technique. 

*Yes, I do get and read this every year. I make no apologies!

 Cobra_Head 21 Sep 2021
In reply to David Coley:

> For the trad falls I've held, I have not been lifted up much, so I assume I have probably only been exposed to 1kN or so? And the grigri would have imparted little if any extra force.

I was practising falling the other week, on top rope at our local wall, I was surprised to be lifted off my feet, and lifted my belayer when I fell.

We were both at about the 4-5 clip so 5 or 6m above, I had an arms length of rope out extra to the clip in point!!

We both weigh the same 85kg.

I never thought, he'd lift me off the ground, I held loads of lead falls and with bigger blokes than me, I've been climbing for 20 years, and as I said this was a big surprise.

Maybe it was the old tope rope having not stretch left in it, I'm not sure.

 galpinos 21 Sep 2021
In reply to Cobra_Head:

I don't understand? Were you taking lead or top rope falls?

In reply to Cobra_Head:

> We were both at about the 4-5 clip so 5 or 6m above, I had an arms length of rope out extra to the clip in point!!

> We both weigh the same 85kg.

> I never thought, he'd lift me off the ground, I held loads of lead falls and with bigger blokes than me, I've been climbing for 20 years, and as I said this was a big susurprise.

Even just a metre of fall generates enough extra energy to lift your partner, you don't need to fall far before these forces really increase. That's why you don't just use slings for say via ferrata. 

If you do multiple falls on the same rope without resting it, untying knots, then the force on the belayer will be higher, than the first fall, as there's less in the system to absorb the load. 

In reply to Cobra_Head:

> I was practising falling the other week, on top rope at our local wall, I was surprised to be lifted off my feet, and lifted my belayer when I fell.

> We were both at about the 4-5 clip so 5 or 6m above, I had an arms length of rope out extra to the clip in point!!

Most top rope anchors are more substantial than a normal carabiner and there is only one of them in the system. So I would imagine the friction is a lot less than most trad falls 

 David Coley 21 Sep 2021
In reply to galpinos:

>  Accidents in North America* isn't full of those kind of reports.

> *Yes, I do get and read this every year. I make no apologies!

Nice to know I'm not the only nerd in town

 David Coley 21 Sep 2021
In reply to Cobra_Head:

I'm well used to being lifted up at the wall. Less so outdoors with trad. Looking at the petzl graphs, even modest friction in the system takes much of the force from the belayer and trad routes are often not straight lines with the rope not in contact with the rock

In reply to David Coley:

On a related matter, you might find this interesting/informative about belaying. ENSA have a lot of good resources, worth taking a look at what they have there

https://www.youtube.com/watch?v=eqZQnCGl24A&t=201s

See the test at 1:19 to catch your attention!

Post edited at 13:10
 HeMa 21 Sep 2021
In reply to David Coley:

> Unlike a grigri an alpine up uses the same hand motion as a plate (so it builds those skills). It also uses the same hand motion in assisted and non assisted mode (again building the right skills and muscle memory).

actually, if you belay well… you belay with a grigri just like you belay with an ATC. So the point you make is only valid if you’re bad at belaying.

have a look at Hard is Easy videos on YouTube (he has two, for grigri in his masterclass series).

so the only real con for grigri on majority of the time, is the fact that you can only belay on single ropes.

as for the original ponderings. Well a grigri might be a problem if the route in question has only a few marginal pieces high off the ground and then you fluff the runout top portion. The gear need to be marginal, and as said a few pieces max (no rope drag), with a big whipper. But to be honest, such a line well not sure if using a tube or heck even a fig eight would stack the favours in your side… I thing for such lines falling simply is not an option.

now with good gear, sure you might get some safety buffer with ATC, or not (too much slippage -> belayer burns hands and lets go -> crater). But a dynamic belay (belayer jumps) might actually result in a nice soft catch…

Post edited at 14:24
 David Coley 21 Sep 2021
In reply to HeMa:

> Well a grigri might be a problem if the route in question has only a few marginal pieces high off the ground and then you fluff the runout top portion. The gear need to be marginal, and as said a few pieces max (no rope drag), with a big whipper.

Hi. I'm not sure this is true and was one of my points on why people might be getting the story wrong. The gear needs to be quite good, but not too good. Rather than marginal. It needs to be strong enough to ensure enough force is passed to the belayer to slip the rope through the plate. Unless the force is great enough the choice of device doesn't matter. Or at least that's what I'm thinking, which might be wrong 

 HeMa 22 Sep 2021
In reply to David Coley:

Yes, it needs to be good enough to get past 2kN to the belay device (not sure I'd call that even marginally good gear) where the slippage on ATC occurs. 

But honest, lets think about the scenario (runout start with pretty much no gear) to a gear cluster, followed by no gear upper part with big fall potential. Sure, some harder grit routes are like that and I'm sure almost anyone can think of an example outside of grit (I can't, but I don't climb in the UK).  Which is my point. 

ATC vs. GriGri, it can matter, but it needs special circumstances which are actually rather rare.  For majority of the time and people, a GriGri seems to be just fine for trad.

In reply to HeMa:

One hazard of Grigri and trad, is dropping the Grigri when wearing thick gloves/mits. There's something about the shape that makes them easier to drop than other kit. If only they could be captive on one side and swivel and click shut like a petzl stop etc?

Also they don't perform predictably with icy ropes, or very wet and muddy ones for that matter, whereas a tube style device fares better  (or Italian/munter hitch if conditions are really hideous) but then you have no assistance

Post edited at 08:30
 David Coley 22 Sep 2021
In reply to HeMa:

Thanks for the reply. Yep I'm sure for a testing grit route one would opt for a non assisted device.

I'm more thinking about when some of the following are true:

 for those new to belaying or holding falls or double ropes or weak hands or light of weight or on long routes or loose rock or where one needs to belay out from the face because of the terrain

The ability to move from assisted to non assisted of the alpine up is a great attraction. I just wish it liked slightly fatter ropes and was less chunky to feed ropes into and hang on the harness

 Ciro 22 Sep 2021
In reply to David Coley:

> Hi. I'm not sure this is true and was one of my points on why people might be getting the story wrong. The gear needs to be quite good, but not too good. Rather than marginal. It needs to be strong enough to ensure enough force is passed to the belayer to slip the rope through the plate. Unless the force is great enough the choice of device doesn't matter. Or at least that's what I'm thinking, which might be wrong 

It doesn't require a high force to slip the rope through the plate - with practice you can add in rope slip on any fall with a tube device.

To my mind it's safer to use rope slip (assuming we'll practiced) than jumping up into the wall when you're climbing on trad gear.

Jumping will almost always be the best approach on sport, where you know the bolts are going to hold*, the belayer will end up under the first bolt, and the top piece will comfortably hold the weight of both climbers.

What happens if you've jumped on trad, and the top piece does blow?

Both the climber and the belayer are now falling towards the ground - the belayer is effectively a passenger and no longer in control of any aspect of the catch.

If neither hits the ground before the rope tightens, the next piece experiences the highest possible peak force. 

If the belayer had stayed on their feet they would be in a position to give another soft catch on the next piece, move backwards to reduce rope length or even attempt to spot the climber, depending on the situation.

In addition to staying in control, if you use the device to soften the catch, the peak force at the belayer is *always* below the force required to lift their weight - as the peak force on the top gear is a function of the peak force on the belayer this means the force on the gear is also limited. 

If you don't use the device to soften the catch, that limit no longer applies.

* OK, bolts do fail occasionally, but it's very rare so for practical purposes we assume they don't and belay accordingly.

 David Coley 22 Sep 2021
In reply to Ciro:

Excellent input. Thanks. That all makes a lot of sense. If I may, I'm going to put that into the very experienced belayers category and possibly for when the climber is in view and tumbles off the crux type event.

I'd count myself as reasonably experienced, but I've never been brave enough to try slipping the room. However I have had it done to me and it was so soft a catch it was unbelievable. Something I need to practice. Any tips? 

 HeMa 22 Sep 2021
In reply to CantClimbTom:

> One hazard of Grigri and trad, is dropping the Grigri when wearing thick gloves/mits. There's something about the shape that makes them easier to drop than other kit. If only they could be captive on one side and swivel and click shut like a petzl stop etc?

 

That is true, there are ways to manage this (how you do things, and also an easy hack).  But other devices are better in that regard. N.b. I've never dropped a grigri, but I also generally don't use mittens when belaying.

> Also they don't perform predictably with icy ropes, or very wet and muddy ones for that matter, whereas a tube style device fares better  (or Italian/munter hitch if conditions are really hideous) but then you have no assistance

Yes, cam based assisted braking devices and muddy, icy ropes are not a good combo. But I don't climb when it's raining or muddy... and don't use a grigri in the winter, whilst ice or mixed climbing.

 Ciro 22 Sep 2021
In reply to David Coley:

> Excellent input. Thanks. That all makes a lot of sense. If I may, I'm going to put that into the very experienced belayers category and possibly for when the climber is in view and tumbles off the crux type event.

> I'd count myself as reasonably experienced, but I've never been brave enough to try slipping the room. However I have had it done to me and it was so soft a catch it was unbelievable. Something I need to practice. Any tips? 

Whether or not you want to practice it is a decision for you, and you alone. There will be lots of people along shortly to tell you that you should never do what I've described.

I certainly feel safer when I'm climbing with someone I know had spent a lot of time thinking about, and practicing, loss of different belaying techniques - and there are a couple of occasions I can think of where I would have been injured if it wasn't for a belayer employing this technique.

If you do want to practice it, do it at the wall, start with a light climber and short falls,  and with a second belayer keeping the climber on an emergency top rope that's short enough to keep them off the ground but long enough not to interfere with your ability to give a soft catch.

Keep your break hand low and use the angle of the rope and your hip/buttocks to increase friction rather than trying to squeeze the rope harder to stop the climber - the latter will result in rope burn and dropping the climber.

With practice you can get to the point where you don't actually actually stop the climber until they have almost reached the ground - you just gradually slow them down the whole way.

This obviously gets harder the heavier the climber and the longer the fall though. Back when I used to practice this regularly at the wall I had one partner who was 95kg - if he took a long fall I would just lock off and let the rope take me off my feet to ensure I didn't lose control of the rope - the device and my hip wouldn't provide enough friction to stop him and as I say you can't compensate with increased grip without burning yourself.

I never actually went trad climbing with him, but I'd be very wary of employing this technique to any great extent with someone of that size. 


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