Giga Jul Initial Impressions

Regarding rope slippage and intentionality. The ENSA PDF on the direct-belay testing has a box at the end, highlighted in orange(ish), that explains the lowest peak forces were obtained with the Munter on the anchor....and they specifically state the belayer must be wearing gloves and does in fact let rope slip through his hands. As Jim and Rich testify, this sort of "dynamic" belaying used to be a skill, now mostly lost! I can't find the damn PDF right now, and I'm supposed to be writing other stuff.....I know Rich and I discussed this at some point....maybe he has it?! RC

Jim Titt wrote:

There are a number of issues that confuse things especially when you start comparing belaying direct off an anchor with off the harness and when you compare FF2 with lesser fall factors, additionally complicated when the falls become larger. 

With small falls we know from testing that briefly we can grip the rope considerably more than we see from longer duration tests so short falls on a drop tower or in the climbing gym we can produce more braking force than longer falls. For working out belay device power we use the lower grip force as these are the only accurate ones we have AND no-one knows exactly how long this brief higher grip force can be held for or how high it is.
Using the normal values we know that achieving a braking force of 2.5-3.5kN is in the normal good range which invevitably means, as the CAI say, the slip must be ca. 1/3rd of the fall distance in a FF2 for any fall where slip occurs (a short fall it may not, or it may only be through the device but not through the belayers hand). Small amounts of slip aren´t normally noticed unless you are marking the rope to measure it (or taking it off the read-out´s) and half a metre or so would be of little interest, much more and it will be felt (the limit is generally thought to be around 1.6m before you get rope burns).
The initial slip through the device is usually at a fairly low force, it´s actually hard to hold your hand down and back against our normal grip force it´s not until the hand gets higher and nearer the device we are strong enough (or the hand hits the device).

In normal circumstances the fail-safe element is belayer lift, since we are all easily capable of holding our own weight when abseiling the extra grip force we normally impose when belaying means we can roughly speaking cope with producing an acceleration of about 3g on our bodies or actually produce 2.5-3kN force on the rope and lift the belayer to stop the faller before the rope will start to slip and for most falls this is enough. Take a FF2 and this safeguard goes out of the window as there is no belayer movement so the braking force of the device is quickly overwhelmed and the rope starts to slip through the belayers hand. And more than say 5m or so fall they may well get rope burns.

People who regularly use controlled slip through the hand generally wear gloves!

Jim, in a fall with FF>=1 there is no redirect (runners) and the fall loads the anchor directly, as a FF2 fall. The CAI rule says "for a fall directly on the the Munter (on a fixed point) the slippage is around 1/3 of the fall length" so I think they are no exclusively addressing FF2 falls.

Or are you considering a harness belay in the second paragraph?

Thanks for all the insights

Fran M wrote:

Jim, in a fall with FF>=1 there is no redirect (runners) and the fall loads the anchor directly, as a FF2 fall. The CAI rule says "for a fall directly on the the Munter (on a fixed point) the slippage is around 1/3 of the fall length" so I think they are no exclusively addressing FF2 falls.

Or are you considering a harness belay in the second paragraph?

Thanks for all the insights

Well obviously you can have a FF of less than 2 directly onto the anchor if you were seconding or traversing but they (and I) are discussing more normal lead falls an using FF2 as a term to differentiate between falls directly on the anchor compared with falls where there is an intermediate piece.

Does anyone have a video for how to use the giga jul rappelling in assisted brake mode? It feels like it would be fairly straightforward but I don't want to be wrong!

Fran M wrote:

Jim, in a fall with FF>=1 there is no redirect (runners) and the fall loads the anchor directly, as a FF2 fall. 

This isn't true!

rgold wrote:

This isn't true!

Ops, you are right! It is possible to climb high enough above the last runner so that that distance is larger than the distance between the last runner and the anchor. More likely to happen close to the anchor.

With that out of the way, re-reading Jim Titt's comment I understand it better now:

For a high-energy fall, belayed off the harness, hand-grip force is enough to avoid slippage because the belayer is holding his body weight (and not the fall) as he is displaced upwards.
However, if there is not enough clearance (or long enough tether) for the belayer to move freely, the belayer's displacement will be abruptly stopped, as he hits his the rock; his belaying device hits the master point where the climber is redirected; or his tether tightens. The climber is still falling, so slippage will take over because the belayer can't move anymore.

Now, is it possible to come up with a rule for belayer's displacement for falls directly onto the anchor as CAI's one for the Munter?

Assuming:
climber's weight = belayer's weight = W
fall distance = FD
Belayer's pull on climber as he is displaced = 3*W (Jim says "we can cope with 3g acceleration")
friction at redirect = 0.5
belayer's displacement = BD

Climber's Energy = Belayer's Energy +  Friction Energy
        W*FD            =         3*W*BD        +  0.5*(3*W*BD)
        W*FD            =    1.5*(3*W*BD)
              FD           =     4.5*BD

so, belayer's displacement is roughly 1/4 of the falling distance? (if they happen to be the same weight)

I think there is a complication in the belayer-displacement calculation problem, and that is that reaching an energy equilibrium only means that the belayer-climber system is moving at constant veloiocity, not that all motion has stopped.  If this is true, then only a certain amount of belayer lift goes into reducing fall energy, and the effect of friction thereafter slows the moving system to zero , without much further effect on the peak loads.  The plausibility  of this supposition is reinforced by CAI tests and their mathematical model of belay-chain loads that suggest that after a relatively small lift, no further lifting reduces the peak load to the top anchor.

rgold wrote: I think there is a complication in the belayer-displacement calculation problem, and that is that reaching an energy equilibrium only means that the belayer-climber system is moving at constant veloiocity, not that all motion has stopped.  If this is true, then only a certain amount of belayer lift goes into reducing fall energy, and the effect of friction thereafter slows the moving system to zero , without much further effect on the peak loads.  The plausibility  of this supposition is reinforced by CAI tests and their mathematical model of belay-chain loads that suggest that after a relatively small lift, no further lifting reduces the peak load to the top anchor.

It's one of those things that to model effectively we need to know a lot more than we do and the data would only suit one particular set of parameters anyway. Since knowing more precisely wouldn't help anyway the CAI opinion is as valid as it gets since it was derived by throwing a weight off the top of a high cliff and seeing what happened to the belayer.

Fran M wrote: With that out of the way, re-reading Jim Titt's comment I understand it better now:

For a high-energy fall, belayed off the harness, hand-grip force is enough to avoid slippage because the belayer is holding his body weight (and not the fall) as he is displaced upwards.
However, if there is not enough clearance (or long enough tether) for the belayer to move freely, the belayer's displacement will be abruptly stopped, as he hits his the rock; his belaying device hits the master point where the climber is redirected; or his tether tightens. The climber is still falling, so slippage will take over because the belayer can't move anymore.

Now, is it possible to come up with a rule for belayer's displacement for falls directly onto the anchor as CAI's one for the Munter?

Assuming:
climber's weight = belayer's weight = W
fall distance = FD
Belayer's pull on climber as he is displaced = 3*W (Jim says "we can cope with 3g acceleration")
friction at redirect = 0.5
belayer's displacement = BD

Climber's Energy = Belayer's Energy +  Friction Energy
        W*FD            =         3*W*BD        +  0.5*(3*W*BD)
        W*FD            =    1.5*(3*W*BD)
              FD           =     4.5*BD

so, belayer's displacement is roughly 1/4 of the falling distance? (if they happen to be the same weight)

This is all confusing, if the fall is directly on the anchor there will be no belayer displacement

Natasja Ysambart wrote: Does anyone have a video for how to use the giga jul rappelling in assisted brake mode? It feels like it would be fairly straightforward but I don't want to be wrong!

https://youtu.be/8Ir1AL778V0

At around 17:40 he shows the assisted technique with the Mega Jul. Which is basically the same. He says he doesn't like to use the assisted breaking rappel technique but I used it a lot already with the Giga and don't have any issues with it. 

Jim Titt wrote:

This is all confusing, if the fall is directly on the anchor there will be no belayer displacement

There will still be a little bit - in field application. The vacuum that is formulas and equations may not account for all outcomes in an applied setting. Having caught falls off the anchor in a fixed-point belay configuration, I was still pulled up and inwards even if slightly - enough the force my focus to keep a brake hand on. 

Jim Titt wrote:

This is all confusing, if the fall is directly on the anchor there will be no belayer displacement

Yes, I think this has to be for a harness belay in order to have anything beyond negligible belayer lift.  Even so, the primary source of fall energy absorbtion, which is rope stretch, doesn't seem to be present.

Kevin Shon wrote:

There will still be a little bit - in field application. The vacuum that is formulas and equations may not account for all outcomes in an applied setting. Having caught falls off the anchor in a fixed-point belay configuration, I was still pulled up and inwards even if slightly - enough the force my focus to keep a brake hand on. 

The formulas and equations, which of course have to be properly constructed and then verified against results from the field, are useful because there is so much noise in the field results that it is impossible to tell which aspects of the system are responsible for which effects.

That said, the effects you are speaking of are incorporated into the CAI model under the heading of the inertial phase of the belay action.

Kevin Shon wrote:

There will still be a little bit - in field application. The vacuum that is formulas and equations may not account for all outcomes in an applied setting. Having caught falls off the anchor in a fixed-point belay configuration, I was still pulled up and inwards even if slightly - enough the force my focus to keep a brake hand on. 

It's confusing because the previous posts were about belaying off the anchor with a Munter and suddenly in the formula it changed to through a re-direct and appears to have the Munter on the belayers harness.

Hello! Does anyone have experience using these devices (Giga, Mega, Micro Jul) with twin-rope? Between 8-9 mm.  Do they have any particular difference?

Peter Piperwrote: Hello! Does anyone have experience using these devices (Giga, Mega, Micro Jul) with twin-rope? Between 8-9 mm.  Do they have any particular difference?

microjul is for twins/doubles 6.9 - 8 mm  megajul is for twins/doubles greater than 7.5 mm so really the right choice between these two for your ropes is the megajul.  Because of the design of these devices they work very poorly providing little friction on ropes smaller than the recommended size.

The gigajul is for from 7.1 mm to 10 mm.  The gigajul's design is far superior with a tapered slot that allows the device to provide adequate friction for a wider range of ropes and progressively more friction as the force increases.  

I think the gigajul is far better than the microjul or megajul.

climber patwrote:

microjul is for twins/doubles 6.9 - 8 mm  megajul is for twins/doubles greater than 7.5 mm so really the right choice between these two for your ropes is the megajul.  Because of the design of these devices they work very poorly providing little friction on ropes smaller than the recommended size.

The gigajul is for from 7.1 mm to 10 mm.  The gigajul's design is far superior with a tapered slot that allows the device to provide adequate friction for a wider range of ropes and progressively more friction as the force increases.  

I think the gigajul is far better than the microjul or megajul.

They all work for twin ropes, but not so much for half-ropes. 

GigaJul can be used as an atc. Other than that, the gigajul does _not_ perform better than the mega or micro in autolock mode.

Neither the giga or mega is reliable for thin half-ropes. Use gloves, you will burn your hand unless there is eanough friction in the rest of the system..

I’ve used all three with ropes rates both twin and half...the Micro is really a specialist tool, can’t imagine most people need it. (I brought it today , for example, on a traverse for which we had a 6mm tag line for a single rappel.) The Mega works fine with my 7.9 Apus ropes, both as twins and halfs (halves?) and just fine with my 8.9 single rope...thé Giga works super on my 7.9s, and the 8.9 as a single rope....I don’t care for any of them in guide mode, though they seem to work fine...I like à Gigi for how easily it takes in rope, so I bring that thing...

used the Giga on a single 9mm today, in guide mode too (Sterling 9mm, triple-rated rope).....works well! not as easy to pull as a Gigi, but totally fine........