UKC

/ Fall factor 2 - what is the reality?

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rockface - on 10 Jul 2018

Has anyone here ever experienced a fall factor 2? Can you describe the experience? I've been reading about it and wonder how it would go down in reality?

Dave Garnett - on 11 Jul 2018
In reply to rockface:

I’ve held one: my partner fell off the hard pitch of Suicide Wall before getting anything in. The belay was a low peg.  I occasionally think that we were lucky not to have both been killed.

Martin Bennett - on 11 Jul 2018
In reply to rockface:

I've taken one and held one, both in Winter. On both occasions the faller fell with no effective protection and thus ended up falling twice the length of rope out and needing a downward catch from the belayer. 

My fall was when a cornice collapsed on me. I fell about 40 - 50 metres finishing 25m below  my second. the funny thing was as I left the belay he'd said "don't fall off, I've little confidence in this dead man belay"! It held though; sliced into the snow exactly as designed to. Took ages to dig it out. The sling was half cut through where my crampon had hit it as I shot past.

The fall I held was on (well alright then, off) Vanishing Gully. I was belayed in the wrong place, out on the edge on a single in situ rock piton. My leader encountered rotten ice on the crux pitch when about 20 metres above me and out to one side, his ice tool (Terrordactyl) cut through as he was trying with the other hand to get gear and off he came. Both ice screws below him ripped out and he accelerated past me and disappeared over a bulge below. As Tom Patey wrote in his account of Crab Crawl: "the peg had to hold . . .. . . .  and it did!  This was in the days before belay plates so I was using a waist belay and ended up upside down staring wide eyed past my feet at the peg, willing it to stay in place long enough for Rob to take the weight off the rope, assuming he wasn't injured or worse. (He wasn't).

It might be argued that the first fall described was to some extent a slide, being in a snow gully, but it was mighty steep and it didn't feel like a slide to me as I tumbled over and over. The second fall described was undoubtedly through the air.

So you tell me - is it all hot air and we've nothing to worry about because this proves these things can be held safely? Or were we just very fortunate? I know what I think.

Post edited at 00:40
Blue Straggler - on 11 Jul 2018
In reply to Dave Garnett:

Which Suicide Wall? Guessing not Cratcliffe...

 

ChrisBrooke - on 11 Jul 2018
In reply to Blue Straggler:

I’m assuming Bosigran. I remember the move and being pretty pleased not to fluff it. 

FactorXXX - on 11 Jul 2018
In reply to rockface:

One thing to bear in mind is that a true FF2 would only be possible if there was no rope slack and/or no belay slippage.  Conversely, it's entirely possible to exceed FF2 by taking in rope during a fall when there's no gear placed.
 

Baron Weasel - on 11 Jul 2018
In reply to Martin Bennett:

Great post!

Michael Gordon - on 11 Jul 2018
In reply to Dave Garnett:

If Bosigran, I can understand how the situation could happen, though it also seems like a good example of a route where clipping the top piece in the belay is a good tactic.

Michael Gordon - on 11 Jul 2018
In reply to Martin Bennett:

That Vanishing Gully one sounds scary as anything. 20m above the belay!

Sputnick - on 11 Jul 2018
In reply to rockface:

Iv held one from an hanging belay on the last pitch of the E2 traverse at Stoney. my mate set off rising upwards on easy slabby ground, about 15feet out , a scream, and then a massive wack as i was smashed into the face. I was glad to have backed up the rusty pegs. our problems were only just begining though. the faller hit a 3 inch ledge and broke his leg. would there be enough rope to get to windy ledge? there was.

Jim Lancs on 11 Jul 2018
In reply to rockface:

In the early 70s, Klaus Swartz had a 'belay machine' rigged on the fire escape of the Loch Eil Centre. He was an passionate proponent of the Sticht plate and one of his evangelising techniques was to let you experience how 'easy' it was to hold a FF2 fall of a large 12 stone concrete filled lorry tyre with one.

It was such a profound experience that you immediately lost what little confidence you ever had in a waist belay, stumped up the cash there and then for a sticht plate, but mainly learnt that you never wanted to experience a FF2 ever again.

Dave Garnett - on 11 Jul 2018
In reply to Michael Gordon:

> If Bosigran, I can understand how the situation could happen, though it also seems like a good example of a route where clipping the top piece in the belay is a good tactic.

It was Bosigran and now a long time ago (New Year 1979).  My diary refers to 'pegs', but I can't remember what else (if anything) we had in.  Obviously I know better now, but our main mistake was not to get a wire in immediately above the belay.

I do recall ending up very nearly pulled off the ledge, looking down into the waves in the gathering gloom, as it snowed lightly.  

I very recently discovered (through UKC) that we are both still climbing, so we must have learned something... 

Jim 1003 - on 11 Jul 2018
In reply to rockface:

I held one on Scawfell when the leader fell 30 off Moss Gyhll which we were climbing in pouring rain. He pulled a huge block out above tennis court wall, no runners in, fortunately I was belayed out to the right, and I have a vision of him flying through the air still holding the block. When the block came out a large quantity of other rocks also came out, the fact I was belayed to the right saved us both. I had a large Hex and a friend in as the belay. I was belaying for an upward pull and was whipped round by the force, he was  heavy guy, 6'4'' and there was a fair jolt as I held the fall. I remember being curious as to wither the main belay would hold. My main concern was the fate of my dog, from the rockfall, left under the route. It was sheltered from it as it only seemed to be curious when we eventually returned to our rucksacks. I remember thinking, I was glad there was no slack in the belay system, otherwise it might have not had a happy ending.

Post edited at 10:15
profitofdoom on 11 Jul 2018
In reply to rockface:

I fell 80 feet off Krapps Last Tape at Avon when I went off route near the top of it [trying to straighten it out by mistake], ending up just above my belayer. I stripped runner/s [they popped immediately] then was held by one. I hit nothing on the way down luckily and the fall was not scary though my second said I was shouting the whole way down [probably to alert him]. He held the fall beautifully, and no damage done. The scary part was desperately scrabbling at the rock with my fingers, and ultimately failing to hold on, before lobbing

rogerwebb - on 11 Jul 2018
In reply to rockface:

A good friend of mine fell on Orion Face (windslab) just after I had called 5m to go, so about 45m out with no runners. He was airborne when he passed me.  I was surprised that there was no massive pull but a steady build up of immense pressure. That allowed me to react and take some of the strain onto my legs before eventually being dragged into a hanging position. I suspect that mitigating of the impact onto the belay preserved it. Conversely I fell on steep mixed about 5m above the belay. That put an immediate hard pull on the belayer and only the quality of that belay kept us both on.

Get that early runner! 

Kid Spatula - on 11 Jul 2018
In reply to rockface:

I would have experienced a fall factor 2 when I fell off the top of Cotton Terror, luckily the ground stopped me before it could happen.

Post edited at 10:51
jon on 11 Jul 2018
In reply to Dave Garnett:

> It was Bosigran and now a long time ago (New Year 1979).  My diary refers to 'pegs'

I was there over Christmas New Year that year. My diary for NYD refers to climbing the grade 1 snow gully that Ash Can Gully on Chair Ladder had become that morning!

 

Michael Hood - on 11 Jul 2018
In reply to Dave Garnett:

Would the best thing not be to run the traverse and crux pitches together (careful double rope management required) so that there's no chance of a high fall factor on the crux.

That's what I intend to do if I ever get back there to reverse my previous failure (on the traverse).

Michael Gordon - on 11 Jul 2018
In reply to Michael Hood:

> Would the best thing not be to run the traverse and crux pitches together (careful double rope management required) so that there's no chance of a high fall factor on the crux.

> That's what I intend to do if I ever get back there to reverse my previous failure (on the traverse).

I wouldn't say so - good to have the belayer close at hand with minimal slack in the system to save hitting the ledge in a fall. I think the best option is clip the high piece in the belay, then get something in as soon as you move up a bit. Also good for confidence having them watching you, considering it's hard moves (pushing 6a) above gear; no way is it E1 if climbed free - check out the success rate in the logbooks!

Gordon Stainforth - on 11 Jul 2018
In reply to rockface:

I held quite a few big falls in my early days of climbing, particularly with my bold climbing partner Tim James from c.1969-71. The biggest impact I remember was when he fell of the crux of Cobweb Crack on the Cromlech in January 1970 ... it was snowing. Whatever gear he had came out and the impact came straight onto my waist - using a waist belay with leather gardening gloves. He went about 40', ending up about 25 feet below me, and the impact on my waist I remember was colossal. He was more or less unhurt.

Robert Durran - on 11 Jul 2018
In reply to FactorXXX:

> It's entirely possible to exceed FF2 by taking in rope during a fall when there's no gear placed.

I've not got paper and pencil handy, but I don't think that would increase the force.

 

3
Robert Durran - on 11 Jul 2018
In reply to rockface:

I held a fifty foot or so one high on the NE spur of the Droites. It did involve a bit of bouncing which no doubt decreased the still condiderable shock somewhat on me and the single red camalot belay but the resulting injuries (along with incoming storm) did result in a somewhat stressful couple of days until we made it back down to the glacier......

Post edited at 18:30
FactorXXX - on 11 Jul 2018
In reply to Robert Durran:

> I've not got paper and pencil handy, but I don't think that would increase the force.

It might not in a totally static situation, but with dynamic ropes you have to factor in the extra cushioning effect of having more rope available to stretch in relation to the length of fall.
 

Robert Durran - on 11 Jul 2018
In reply to FactorXXX:

> It might not in a totally static situation, but with dynamic ropes you have to factor in the extra cushioning effect of having more rope available to stretch in relation to the length of fall.

Yes, but the fall will be shorter.......

Edit: You may be right, but without doing the maths, I don't think it's obvious either way.

New edit: actually a rough calculation on my head suggests you probably are right....

Post edited at 20:00
1
Toby_W on 11 Jul 2018
In reply to rockface:

One minute I'm on a ledge saying I've got you, the next I'm hanging upside down looking down at my friend trying to work out which way is up and which way I need to move my hands to lower him to a small ledge so I can pull my way back up on the single sling holding us to discover what's left of my belay.  Let's just say we were lucky.

Cheers

Toby

teh_mark on 11 Jul 2018
In reply to Robert Durran:

> actually a rough calculation on my head suggests you probably are right....

I'm guessing you found a pen, but paper eluded you?

 

Robert Durran - on 11 Jul 2018
In reply to teh_mark:

> I'm guessing you found a pen, but paper eluded you?

Baldness has many advantages.

TheGeneralist - on 11 Jul 2018
In reply to OP:

I saw someone take a factor two off quartz vein scoop on beinn ulaidh. He was in a team of three. The belay pulled and his belayer took to the air too. The third man took the weight of both of them on his two ice tools, and held them.

Sounds completely bullshit but it did happen. Unbelievable 

Post edited at 21:21
Dave Garnett - on 11 Jul 2018
In reply to jon:

> I was there over Christmas New Year that year. My diary for NYD refers to climbing the grade 1 snow gully that Ash Can Gully on Chair Ladder had become that morning!

The sea and the snowflakes was such a vivid image as we hung from the belay that I wondered whether I might have imagined it, so good to have the weather confirmed!  We aided up that pitch and finished the route pretty much in the dark, which I think was a good effort in the circumstances.

rgold - on 12 Jul 2018
In reply to Robert Durran:

> Yes, but the fall will be shorter.......

> Edit: You may be right, but without doing the maths, I don't think it's obvious either way.

> New edit: actually a rough calculation on my head suggests you probably are right....


If we use the classical rope equation, the question becomes whether the fall factor H/L goes up or down when the belayer takes the rope in.  The answer is...it depends.

The question asks for the behavior of (H-x)/(L-x).  The derivative of this expression is (H-L)/(L-x)^2 and so has the sign of H-L.  It follows that (H-x)/(L-x) is a decreasing function for H<L (so for FF<1) and an increasing function for H>L (so for FF>1).

Consequently, taking in rope will decrease the fall factor if the initial situation has a fall factor less than one, and will increase the fall factor if the initial situation has a fall factor greater than 1.

In particular, for a situation that  initially has  FF=2, taking in rope will raise the fall factor.  Moreover, because of the vertical asymptote at x=L, there is no upper limit to how big the that fall factor can get.  (Generally speaking, you don’t get near this asymptote because you can only reel in at most H/2 of the rope in any climbing situation and usually H/2 is much less than L.  But for FF=2, we have H/2=L,  so you could theoretically pull in all the rope and stop the falling leader at the belay, at the expense of an infinite peak load…)

Michael Gordon - on 12 Jul 2018
In reply to rgold:

> Consequently, taking in rope will decrease the fall factor if the initial situation has a fall factor less than one, and will increase the fall factor if the initial situation has a fall factor greater than 1.>

You'll have to remind me. In a normal fall onto gear, isn't the fall factor greater than 1 anyway? I would have thought taking in rope would always increase the force on a runner (though usually not significantly).

Luke90 on 12 Jul 2018
In reply to Michael Gordon:

Fall factor is distance fallen divided by the amount of rope available to absorb energy. That means a normal fall onto gear should generally be significantly less than one. A fall factor of one would be falling the same distance as the amount of rope out, e.g. if you had gear 5m above the belay and fell from another 5m above the gear. You'd theoretically fall 10m with 10m of rope out and start to be caught by the rope when back level with the belay.

Barring weird edge cases, you could generally only exceed factor one on a multipitch route because you'd have to fall past the belay. Fall factor two requires you to fall twice as far as the amount of paid out rope i.e. to fall past the belay before you've placed any gear at all.

In all of this, bear in mind that fall factor is not a direct measure of the impact force, nor is it even proportional to impact force. It's a useful way of considering the severity of the fall but there are vast numbers of other factors involved. Whether or not taking in rope increases the force on the gear is really a different question from whether or not it increases the fall factor. They're related but not in a simple fashion.

In this sense, Robert Durran and those he's debating could both be right when he says "taking in rope might not increase the force" and they say "taking in rope increases the fall factor". Though his more recent posts seem to be referring more to fall factor after all.

Even if fall factor did relate directly to the impact on the gear, there are other considerations too. Taking in rope during a conventional fall of less than factor one definitely decreases the fall factor. I'm not clear what effect it has on real-world impact force. Regardless, it often amplifies the extent to which you slam into the wall which is generally a good reason not to do it (and is possibly the effect that makes you think of those falls as more violent).

Andy Gamisou - on 12 Jul 2018
In reply to all:

Is there any data available which rates the various belay devices according to how effective they are in holding a high fall-factor?

Stefan Jacobsen - on 12 Jul 2018
In reply to rgold:

Thanks, I was hoping for a response like that from you. For my own  curiosity/education, could you provide a link to a resource showing the classical rope equation ?

Robert Durran - on 12 Jul 2018
In reply to rgold:

All this is more or less what I came to last night writing backwards with a mirror on  my bald head while also drinking Guinness and trying to watch the football post climbing in an Irish pub....... 

My concern is that the conclusions might only be "first order" since they don't take into account the stretching of the rope. H/L is proportional to the energy absorbed per unit length of rope ignoring the extra gravitational energy absorbed due to the stretch. I'm not sure whether this affects the general conclusions or not. I now have paper and pencil available, so might work it out. I seem to remember from a previous thread that having extra slack in the system (the equivalent of paying out rather than taking in rope during the fall) didn't affect the conclusions, so I suspect this won't either.

cb294 - on 12 Jul 2018
In reply to Luke90:

The only realistic case of getting very high fall factors (>2) is not rapid taking in of rope during a fall, but slipping on a vertical bit of via ferrata: The lanyard and harness will give you roughly a meter, slipping down 2m of steel cable before the carabiners arrest at the next bolt will therefore already give you a fall factor of 3. 

This is extremely dangerous despite screamer or plate like rope brakes in the VF kit.

CB

FactorXXX - on 12 Jul 2018
In reply to Andy Gamisou:

> Is there any data available which rates the various belay devices according to how effective they are in holding a high fall-factor?

Depends on your definition of best.
The best one would be one with a high 'grab' factor such as a GriGri.
However, it would also be the worst one because the last thing you want is a device that locks up before energy can be dissipated by allowing the rope to slip through it, etc.

Gordon Stainforth - on 12 Jul 2018
In reply to Stefan Jacobsen:

> Thanks, I was hoping for a response like that from you. For my own  curiosity/education, could you provide a link to a resource showing the classical rope equation ?

Nice article here from way back:

https://www.ukclimbing.com/articles/skills/fall_factors_explained-647

jimtitt - on 12 Jul 2018
In reply to Andy Gamisou:

GriGri/Edelrid Eddy (and possibly the vrious clones) would hold any fall no matter what you did. The AlpineUp and ClickUp provide enough braking force but are not to be used in a FF2 situation according to the manufacturers and you need to be prepared to change your braking action if a FF2 occurs.

The Italian Hitch works irrespective of ones hand position and is the only conventional device to do so, it provides comparble brakingforce to a conventional device. Normal plates it´s the ATC XP a the most powerful I´ve tested and things like the DMM Mantis/Reverso coming in second place but you need to change hand position if a FF2 occurs, some extra karabiners with these bring the friction level up to a reasonable level where one should be able to stop at least moderate falls (my definition of "moderate" and "severe" falls is far higher than the usual as I work from worst case i.e falling the entire rope length).

Howard J - on 12 Jul 2018
In reply to rockface:

My mate fell just a few metres above the belay on some winter route in Glencoe, after I'd specifically warned him the belay wasn't up to much. It was mostly a slide, so maybe not a proper FF2, but pretty scary. The belay held (or I wouldn't be writing this) but my stance collapsed. He stopped on the edge of the drop, and more than 30 years later I can still picture the look in his eyes. That was with a waist belay.

Stefan Jacobsen - on 12 Jul 2018
In reply to Gordon Stainforth:

Indeed a nice article, but I'm after the "classical rope equation" rgold mentioned, because it might tell something interesting about the physics behind the fall factor.

FactorXXX - on 12 Jul 2018
In reply to Stefan Jacobsen:

> Indeed a nice article, but I'm after the "classical rope equation" rgold mentioned, because it might tell something interesting about the physics behind the fall factor.

Wikipedia has a page about Fall Factor:

https://en.wikipedia.org/wiki/Fall_factor

captain paranoia - on 12 Jul 2018
In reply to Stefan Jacobsen:

This may not be the 'classical rope equation's, but it is one of the best analyses of rope falls I've seen:

http://lamountaineers.org/pdf/xRopes.pdf

rgold - on 12 Jul 2018
In reply to Stefan Jacobsen:

> Thanks, I was hoping for a response like that from you. For my own  curiosity/education, could you provide a link to a resource showing the classical rope equation ?

The equation goes back to an article entitled Belaying the Leader, by Richard M. Leonard and Arnold Wexler, in the Sierra Club Bulletin 31 (1946), later reprinted with Leonard as editor in the book Belaying the Leader: An Omnibus on Climbing Safety, Sierra Club (1956).  In the days before modern dynamic climbing ropes, these guys invented the dynamic belay (in which rope was allowed to run through the belay in order to absorb some of the fall energy).  The term has now been redefined to refer to having the belayer jump at the moment of impact, which has nothing to do with the original concept.

Taking no credit for the ideas and the approach, I wrote up a modern simplified account for undergraduate math, physics, and engineering majors at my institution.  This somehow found its way to the internet, and can be downloaded from http://4sport.ua/_upl/2/1404/StandardEqn.pdf .  It should go without saying that any errors there are mine and not Leonard and Wexler's.

You can get a whole lot more information in condensed form from David Custer's article at https://arxiv.org/pdf/1611.04327 .  (He refers to the classical equation as the Wexler equation.)

The classic equation is a first approximation in which the rope is modeled as a spring.  The model can be improved by introducing viscous damping, which however I did not write up.  The CAI has a sophisticated computer model for what happens based on applying the viscous damping model sectionally to the various components of the belay system. 

There are other models that take into account the non-elastic elements of rope behavior.  I think the first of these is by Pavier http://4sport.ua/stuff/mn1001/2012-12/13171/files/Pavier.pdf , who uses a  hybrid spring-dashpot model used for studying non-elastic deformation.  Pavier gets good agreement with experimental results, but there is no underlying physical explanation for the relevance of the model he uses.

An internet search will turn up references to other models as well.  Once past the classical equation, these models all involve systems of differential equations that require a some kind of numerical solver to get answers from, rendering Robert Durran's bald head inadequate for obtaining any answers.

Post edited at 16:02
rgold - on 12 Jul 2018
In reply to Robert Durran:

> My concern is that the conclusions might only be "first order" since they don't take into account the stretching of the rope. H/L is proportional to the energy absorbed per unit length of rope ignoring the extra gravitational energy absorbed due to the stretch...

Yes, but in the classical equation, which is fundamentally a calculation of maximum rope stretch (then converted via Hooke's Law to peak load), H/L appears and, keeping the climber's weight and the rope modulus constant, H/L determines the peak load via an equation of the form w+sqrt(w^2+cw(H/L)), where w is the climber's weight and c is a constant calculated from the rope modulus.  From this we can see that changes in the fall factor produce changes (in the same direction) in the maximum peak load.

Of course the whole equation is at best a first-order approximation, the only point being that the use of H/L in reasoning about the severity of the fall ignores neither rope stretch nor the extra fall distance it imposes.

 

Post edited at 17:57
Robert Durran - on 12 Jul 2018
In reply to rgold:

Yes, I agree. My point was that you really do need that formula to establish that max force increases with fall factor rather than using H/L as an approximation proportional to energy absorbed per unit length of rope.

cb294 - on 12 Jul 2018
In reply to rgold:

Interesting post, just to add that Wexler and Leonard almost certainly did not invent dynamic belaying. There is an old saying in German climbing about a rope having to run ("Seil muss laufen") that was in use both in the Elbe sandstone and the Alpine areas and definitely predates WW II (at least according  to books as I am old but not that old!).

These guys also held massive whippers using hemp rope with direct tie ins and waist belays, which only had a chance of working if the rope was initially allowed to run and then gradually slowed down.

CB

rgold - on 12 Jul 2018
In reply to cb294:

Thanks for that info...I won't credit Wexler and Leonard with the invention any more.  They may or may not have been the first to analyze the situation mathematically and derive guidelines for the optimal amount of rope that should slide (around a hip belay) for various sizes of falls.

oldie - on 12 Jul 2018
In reply to rockface:

I have held and been held, quite easily as far as I can remember, on short factor 2 falls (waist belays). Both myself and my main climbing partner at the time would have been under 10 stone (64 Kg) which must have helped! Probably there was some rope slippage involved so as FactorXXX says in an earlier reply  neither would be true factor 2.


I have little understanding of the physics involved but assume there is a difference in severity between factor 2 falls dependent on their length: although the fall factor theory (as I possibly misunderstand it) seems to imply the opposite I have never been able to believe that a severe 0.5m fall is as hard to hold as 50m. I think the difference between falls of the same factor but of increasing length is often explained as same force but of increased duration. 
Incidentally, although perhaps not relevant to this point, surely in actuality during a severe fall a rope will have progressively less stretch available (shock absorbing ability) and start approaching the properties of a "static" rope (itself having some elasticity). This fact sems to be recognized when recommending a rope is rested after a fall to regain elasticity.
Hope this is not all rubbish and that someone can clarify for me.

rgold - on 12 Jul 2018
In reply to oldie:

> I...assume there is a difference in severity between factor 2 falls dependent on their length: although the fall factor theory (as I possibly misunderstand it) seems to imply the opposite I have never been able to believe that a severe 0.5m fall is as hard to hold as 50m...

Well, in theory anyway, the peak force, which occurs at the moment of maximal rope elongation, is the same for big and small falls with the same H/L ratio.  But here's the catch: once the rope starts slipping, you change to a different energy-absorbing mechanism (you are no longer doing work stretching the rope but instead are doing work against belay device friction).  Unlike the rope, which there is more of for bigger falls, this second mechanism is not scalable (your device doesn't magically develop higher friction if the fall is longer), which means that more, and possibly a lot more, rope is going to have to run through the device in order to absorb the remaining potential energy of the fall.  Your ability to maintain your grip over this longer run time with everything getting burning hot is a big if, and so holding a big factor 2 fall is going to be a lot more intense than holding a small one.

> Incidentally, although perhaps not relevant to this point, surely in actuality during a severe fall a rope will have progressively less stretch available (shock absorbing ability) and start approaching the properties of a "static" rope (itself having some elasticity). This fact sems to be recognized when recommending a rope is rested after a fall to regain elasticity.

Are you suggesting that actual loads will be greater than the elastic model predicts because the rope is stiffening as it elongates (so the rope elasticity modulus is not constant but increasing over time)?  I guess this is possible, but don't know anything about it.  (To be clear, I'm just a lowly mathematician, not an engineer or physicist who might be expected to have specialized knowledge on the subject.)

Dave Cundy - on 12 Jul 2018
In reply to oldie:

I seem to remember reading an article that looked at the loads imposed on cow's tails when doing SRT in a cave.  I can't remember the source of the work (twas in the internet somewhere) but I clearly remember the conclusions.  If you are clipped into something using a cow's tail and then climb above it and then fall onto the belay, a highly significant effect on peak load is the slippage of the knot.  If you have a tight knot, there's no give in the system, so you can approach FF2.  If the knots in the cow's tail are a little bit loose, the rope slips a little as the knot tightens, thus absorbing some of the strain energy and reducing the load.  The study's conclusion was that if you fall onto your cow's tails with any force, get to a stance where you can undo and retie them - otherwise you might not be so lucky a second time.

In terms of relevance to the current thread, it suggests that any MOVEMENT of the belayer / belay system (where resisted) has some importance for very short falls (i.e. where the movement is a significant fraction of the rope length).  On long falls, the additional distance gained by that movement (and the resistance that goes with it) will be negligible, relative to the rope length, so will have no impact on the outcome.  That kind of backs up what Oldie (amd Martin B) were saying about waist belays and/or short falls.

Suicide Wall at Bosi - me and Christian got there just as it started raining, so we never got to tackle the 5c bit.  I think someone dropped us a rope and we fudged our way past it.  I s'pose that ought to be listed as unfinished business??

When I was rather younger, I used to reckon that letting the rope slip through your ATC was a kind of dynamic belay and ought to be useful (in principle).  The Ilearned that once the rope starts slipping, it burns your fingers which then involuntarily let go.  So don't try that at home, kids.  Just grip the rope like there's no tomorrow..

oldie - on 13 Jul 2018
In reply to rgold:

I'm struggling to understand the rope slippage explanation but it sounds good.....I think I was held on a short F2 fall where my second was not wearing gloves but was not burnt which supports it. Dave Cundy's knot absorbing energy might also have played a part. Certainly worth considering using grippy gloves as was discussed in a recent thread.

oldie - on 13 Jul 2018
In reply to Dave Cundy:

Thanks for that explanation.

  However re the deliberate dynamic manipulation of the device and burning fingers surely one should consider using grippy gloves (the recent Summit article warned that they also reduced grip strength however). Though because really severe falls are rare in modern rock climbing I don't expect many people would bother anyway.

Andy Gamisou - on 13 Jul 2018
In reply to jimtitt:

> GriGri/Edelrid Eddy (and possibly the vrious clones) would hold any fall no matter what you did. [other good stuff truncated]

Thanks for that Jim.  I'm thinking that something like the megajul would be pretty good too, and more practical in a multipitch situation than something bulkier like a grigri?  Normally when trad climbing I tend to use an old fashioned sticht plate - how do you think this would compare with newer ATC devices?

 

jimtitt - on 13 Jul 2018
In reply to Andy Gamisou:

Sticht plates are alright but nothing else really, their braking performance isn´t terrible and one can increase it with extra karabiners. The extra height of the tube style device increases the braking power and the vee-grooves add a bit more which allows the designer to make the slots a bit more generously sized to improve the rope handling. I used one for years but most modern devices are better in every way.

The MegaJul has such poor braking performance AND it cannot be improved by adding karabiners that I wouldn´t contemplate using one, if it was the only device available I would just use an Italian hitch instead.

There are theories that an advantage of the MJ and others of it´s type is that in the event the belayer burning their hands and releasing the rope the device will continue to brake the faller. There are two drawbacks to this, firstly as the braking force is so low the chances of rope slip are increased and which of the climbing party is injured is irrelevant in a safety context, using a device which reduces the likelyhood of injury to either is the sensible option. The second issue is whether when the belayer releases the rope the residual braking force is sufficient to stop the faller. We normally consider a braking force of 2.5kN sufficient for "normal" falls and around 4kN for large falls and a MegaJul achieves nothing like this, with no belayer and a 9mm rope we see about 0.7kN and the Smart Alpine even worse at 0.5kN. With thin ropes the braking force is effectively zero.

The exception are the two devices from Climbing Technology which once locked give exemplary braking force up in the 5kN region.

Post edited at 07:40
Stefan Jacobsen - on 13 Jul 2018
In reply to captain paranoia:

Aye, good article. Thanks!

Stefan Jacobsen - on 13 Jul 2018
In reply to rgold:

Thank you professor! This will take me some time to work through as calculus wasn't really my strongest subject.

Andy Gamisou - on 13 Jul 2018
In reply to jimtitt:

Thanks!

Luke90 on 13 Jul 2018
In reply to jimtitt:

Thanks for the detailed information, your posts on belay devices are always fascinating.

Have you seen the new GigaJul? Do you have any thoughts about whether it looks likely to address the weakness of the MegaJul?

jimtitt - on 13 Jul 2018
In reply to Luke90:

Well no, since Edelrid don´t mention anything about improving the braking power I have my doubts. I´ll wait a few years before looking closely, gotta wait for the first few rounds of recalls and some long-term experience before it´s worth actually testing one.

The Smart is supposedly improved but not the Alpine version yet, we shall see


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