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想找找多大的力或什么条件下grigri开始起作用，可惜只有定性的分析，没有具体的数据，可能涉及的因素较多，不仅仅是多大力的问题。
tradgirl上整理了一些grigri使用讨论，值得一看。
冲坠时，向导手抓绳子过紧也会妨碍凸轮起作用。
How do I belay safely with a Gri-Gri? / How can a Gri-Gri fail? [back to top] [FAQ contents]
From: Eric Hirst
There are several ways for a GriGri to "fail." The following list should account for most GriGri drops:
1. Threaded backwards
2. Belayer holding it open
3. Rope < 10mm
4. Brake hand off rope
5. Very light climber / rope drag (slow slide, could lead bad belayer to commit sins 2 and 4)
6. Biner unlocked
7. Biner not on harness properly
8. Ice (?)
9. Excess creativity -- new ways to make things fail are being devised every day.
From: Julie Haas
The dichotemy is this: they are indeed often safer than other belay devices. For that reason, they're often found in the hands of beginners or newbies, who haven't the slightest clue of how to 'use it properly'! What they learn, is that they don't really need to worry about belaying properly, this here thingy will do it for them.
From: MadDog
Gri-gris are not foolproof, especially with a fool at the helm.
Belayer holds non-brake side of rope too hard
From: Steven
The gri gri works by locking when the rope goes through the system at a certain speed...I'm no physicist...so I don't know if I mean speed or am referring to force or what...you who have a gri gri know what I mean. If the rope is allowed to fly through the system fast, the device works. However, when someone is used to using an ATC or something else...there enters a problem.
If the belayer is catching a fall, the natural reflex of the BRAKE hand should be to grab a hold of the rope tight and make sure it is in the proper position to brake the fall. The GUIDE hand however should also be holding onto the rope to provide stability etc. BUT, if the GUIDE hand is holding onto the rope so tight (this too is a natural reflex when you have a climber make a sudden fall) that the GUIDE hand actually pulls down on the rope towards the gri gri...the clenched hand actually SLOWS the rope down by providing extreme fear induced friction on the rope ahead of the locking mechanism of the gri gri. By not allowing the rope to reach the spead/acceleration/force necessary for the gri gri to spring into action literally, the rope continues to funnel through the belayers hands (YES, this burns the skin RIGHT DOWN...just ask my belayer) at a very fast but NOT death inducing fall velocity. The reflex of the belayer when seeing their climber falling and not feeling the device kick in...is to grip harder with both hands...this furthers the problem by slowing the rope down even more and freaks the belayer out more...and a vicious cycle continues.
My experience was that I was on a very long, extremely overhanging (horizontal) gym lead climbing wall (Rockhead's in Toronto) and I bailed on a climb. In the blink of an eye, I was about 40' up horizontal, and then I'm sitting on my butt. I look over at my belayer...his eyes were WIIIIIIDDDDE open. A few seconds later...we look at his hands, and the friction burns took about 3 wks to heal before he could climb again. I fell at a quick rate...fast enough to get me down in a surprising hurry...but not fast enough to cause damage (except if I dropped my head on the ground or something like that). A death-inducing speed drop would have caused the gri gri to kick into place.
Bottom line, if you are using a gri gri and catching a fall, grab firmly with the BRAKE hand...or not at all (that is the point of the gri gri...to act as a back up in case the hands are not on), and DO NOT DEATH GRIP THE GUIDE HAND ROPE...if anything let go of the guide hand or grip loosely and allow the device to work.
From: John
I have been on the receiving end of such a belay. It was in the gym and my father was doing the belaying. It must be said that my father is the kind of guy that needs things repeated to him many many times before he actually does it. Anyway I was doing this lead route and was just about at the anchors. I had struggled up since several time I was lifting my belayer as he forgot to feed (the grigri would lock up). With his left hand on the climber side of the rope he was now feeding. I fell and he instinctively tried to hold the fall with this left hand rather than left the grigri work. So here I am watching the draws go by me as the ground gets closer. I was falling ass first so I was kind of horizontal. Eventually the burning sensation made him let go of the rope and I got stopped. I put my feet down and stood up. Had I not been horizontal I probably would've snapped my ankles.
From: Brad Baker
I dropped my partner about 20 feet when he took a lead fall while gym climbing. He didn't deck, but ended up about 5 feet above the ground and I was up in the air next to him. The gri gri didn't fail, it was human error. For some reason, I tightly grabbed with my brake hand and my feeding hand. The tension I applied to the rope prevented the gri gri from locking. I kept trying to stop the fall with both hands, burning the hell out of my upper hand. When the heat got too much, I let go of the upper hand and the gri gri stopped the fall as designed. Ouch.
From: Aaron Rough
So the first time I used a GriGri was on a lead belay of a friend on an easy climb for him, or at least one he didn't expect to fall off of. Needless to say, he did fall off and I did my usual grip with my left hand and lock off with my right. The fall was bad enough to where the rope was ripped through my left hand, but I expected the GriGri to lock off the fall, so I didn't have a super strong grip on my right hand.
What happened though was I took enough of the force of the fall from my grip with my left hand that the GriGri did not cam. The rope started whipping through the device and pulled the rope right out of my right hand. The only thing that saved my partner from decking was I literally clenched my right hand on the running rope and it got sucked part of the way into the device, thus causing it to cam up and stop the fall.
Holding the lever open while lowering
From: Hank Moon, Technical Information Manager, Petzl America
The practice of lowering the climber “using primarily the brake handle” is potentially dangerous and contrary to the technical information which comes with the Grigri:
From Grigri technical notice:
When descending or lowering a climber with this device, control is maintained by the brake hand on the rope, not by the handle. This device can help eliminate some potential belaying errors, but not all of them. Our experience with it indicates that the problem with making a product that tries to make climbing less risky, is that climbers may act as though there's no risk at all. Don't make that mistake: this device is not a substitute for skilled, vigilant belaying.
From Petzl website:
Warning: while descending with the GRIGRI - braking is done with the brake hand on the free end of the rope, just as with any other descending device. The handle is not the brake and the person rappelling must be completely aware of this fact. As with any other rappelling device, its use requires care and proper training.
On the surface, using the handle seems to be a good way to avoid wear and tear on the hands, but the reality is that this practice will generally increase the risk of losing control of the lower or rappel. While Hugh mentions that “the belayer has to have the presence of mind, and the training, to release the brake handle,” most people will never develop this ability and in a panic situation, the normal reaction will be to pull down on the handle and lose control. The tendency of humans to grab harder whatever they're grabbing when surprised or panicked is well documented (see “white-knuckle” in the dictionary).
A good habit to get into when using a Grigri is to use a glove when lowering (and belaying, for that matter). Almost any old leather glove will do, though I prefer fingerless for dexterity. Like developing any new habit, it may seem odd at first, but quickly becomes second nature. If you don’t have a glove, try running the free end of the rope through a carabiner clipped into the harness belay loop and use the ‘biner as an extra friction surface when lowering. CAUTION: do not use the GRIGRI attachment ‘biner to do this; use a second carabiner. Opening the GRIGRI ‘biner while under load is needlessly risky.
From: Loui Clem
One popular misconception is that the GrGri's handle is intended for controlling a descent. The fact of the matter is that regardless of what device you are using, your brake hand is the key element. THe camming action of the GriGri may help catch a fall, but the belayers brake hand is where the buck stops. Even when the cam is opened it works very much like a sticht plate concept where the bend in the rope provides friction and the belayers hand provides braking action. In a lower, the belayers hand is, again, the key element. With the cam held open, a lower can be easily controlled with the belayers brake hand.
From: Stefan Axelsson
Petzl clearly states that you should hold the cam open and control the descent with your brake hand, like every other belay device on the market.
And having tried both ways I can only agree with them, controling with the lever increases the risk of accidentally dropping/hurting someone, and it's a risk that buys you nothing!
Threading it backwards
From: Jason Kester
Last summer I took a fall with a bolt at my waist and ended up on the ground because my belayer had threaded the gri-gri backwards. On the bright side it was the softest 30 foot ground fall of my career.
From: MT
The only time I have seen a Gri-gri come close to 'failing' in stoping the initial part of a fall is when someone had thread it in reverse and did not realise it. Fortunately, they had still used both hands on the rope and were able to control the fall by the technique below. I have never seen a Gri-gri completely fail.
When the Gri-gri is reverse threaded, bending the rope around the side and under can create more than enough friction to control the lowering to rethread or a fall.
Light climber, high rope-drag, icy ropes, thin ropes
From: Petzl Gri-Gri Technical Notice
Attention: the friction
Light falls and featherweight climbers:
Multiple friction points on a long run-out will limit the shock-force transmitted to the device
In a similar way, the weight of a light climber, or the load of a sliding fall, may delay or prevent the locking action of the GRIGRI.
Authorised Uses:
The GRIGRI is a belaying device for the leader or second on a rope. It is for use only on single UIAA ropes from 10 to 11 mm diameter. The GRIGRI can also be used as a descender on ropes of 10 to 11mm.
From: Chris Maytag
before I was educated (the hard way), I used my grigri with a brake hand, but not a particularly *attentive* brake hand. My partner fell, the grigri didn't lock immediately (she was very light and the slab was low angle, so forces were just shy of enough to close it). Thirty-plus feet later, and after finally losing some skin on my brake hand (which should have been there in the forst place), I/we/it stopped her fall. I've since learned how to properly use the device, and take every oportunity to educate people I see misuse it as I did.
From: Bob Harrington
It's not a good idea to rely on the force of the fall to close the cam anyway, because with lots of rope drag or a light leader, it might not close and the rope slips through the device -- you should either close the cam with your braking hand, or move your braking hand to the braking side of the rope.
From: Jon Poulson
I have used the grigri on wet and iced ropes. I have never had a problem. You need to use it like you would any belay/rappel device, keep your hand on the rope applying more/less friction when necessary. If the cam fails to lock, you still have the friction of the rope running over the edge of the grigri to control your decent speed.
Cam held open by a foreign body
From: Bill Yerazunis
The official Petzl propaganda sheet cautions that situations where the cam is pressed open by rock or 'biner can cause the GriGri to fail to work
From: Dave Buchanan
The Gri-Gri slammed into the draw, with the cam taking the brunt of the impact. For whatever reason, I did not get speed-lowered. I'm not quite sure why.
From: Greg Daughtry
There are two reasons why you did not get speed lowered:
1) 11 feet off the ground, your belayer was suspended in air, with the climbing rope under the tension of her full body weight. Provided that your belayer still had her hand on the brake side of the rope, this presents a lot of force for the cam to lock. The device was locked prior to hitting the draw, which is a big distinction to the warning case presented on the Petzl web site about belaying with a bolt clipped just above the gri gri, on the leader side.
2) Even if the cam were completely open, the gri gri is still a pretty reasonable friction device. So long as your belayer doesn't take her hand off the brake side, you've still got a pretty good catch. This is why loading the gri gri backwards isn't the end of the world.
From: Jonas Wiklund
I am well aware of petzl's warnings regarding these matters, but I see no physical reasons for failure of grigri when the belayer gets yanked up to the first draw of a steep route. If the cam is slammed open, whats holding the belayer up in the air, forced againts the draw? Momentum? Magic? An antigravity belt? The grigri is open, hence the belayer start to decent down the rope.
From: Rex Pieper
I took a 60 footer on the Black Tower pitch on Zodiac in '97 when a fixed KB blew a few minutes after I was standing on it. The fall length wasn't caused by more gear ripping as a big alumnihead caught me. Instead, a small pebble got wedged INSIDE the GriGri, not allowing it to lock up in a fall. My partner finally got the rope under control, stopping me 10 feet above the ramp at the base of the Tower.
From: Robert Fonda
Always, always check the cam device BEFORE you get on the rock. Small pebbles and the like can get into the device and cause the cam to fail. I check mine constantly when I am belaying someone (especially at Josh). All it takes is for your partner to kick sand down and jam your device!
Paying out slack
From: John Baker
With a GriGri, one way to feed slack fast is to squeeze the cam with the non-brake hand and use the normal brake hand to yard slack. This may be safe if you develop the habit of releasing both hands after each pull, but still you are squeezing the cam at some point in the operation. What if the leader falls right then ? This is where habits enter the picture. A proper grigri habit might be to just let go with both hands. But that's just not going to happen with an old dog like me after 20 years of body belays and sticht plates. My instinct is to grab that brake side with the brake hand and pull it around towards my tailbone and hunker down with all my might.
And my non-brake hand ? I don't even think about it. I'm probably pulling or squeezing with that too, just as part of the overall hunkering process. So if it started out squeezing the cam, that's probably what it's still doing. Harder than ever. And that's no good.
I dropped a friend in exactly this manner I believe. But it happened so fast that I wasn't really sure what went wrong until thinking it through later. He demanded (over my better judgement) that I use a grigri, even though that's not what I normally use. Luckily he wasn't hurt, but I felt like a very low turd.
From: Eric Coomer
Actually, the best way is to squeeze the cam with the pinky finger on your brake hand(try it, it's a natural grip) while yarding slack with your non-brake hand. This keeps your brake hand closer to the brake side of the rope.
What if the leader falls right then ?
Part of the reason for using just the pinky finger- theoretically you shouldn't be able to apply enough pressure on the cam to keep it open. If you're using your thumb or palm of your hand it is a possibility...
From: Gary Fike
Right. I've learned to feed line this way almost as fast as I can with a tuber. Also, you're much less likely to hold the cam open than you would be dicking around with the lever.
Gri-Gri causes higher impact on climber and gear
From: Lanier Benkard
There are also cases where an ATC is safer, such as anywhere the pro is dicey, a very common situation. I have not ever seen anyone able to safely give a dynamic belay with a Grigri (in such a way as to eliminate risk of dropping the climber), but that doesn't mean it isn't possible, it just means that it is hard.
From: Chris
The reason a gri-gri is not recommended for trad climbing is because it provides too static of a belay. an atc or similar device allows for slightly more rope slippage then a gri-gri, which provides more of a dynamic belay, which lessens the impact on the protection. you can find more about this in petzl's website, in their technichal manual.
From: Gary Foster
GRIGRI's are very controversial do to the fact that they are, for the most part, improperly used. They teach bad habits for beginners and are only recommended sport climbing. The reason for this can be found in any Petzl catalog. All Petzl catalogs contain a technical manual in the back describing the use for all their products. This is what it says about the GRIGRI:
"The locking action of the GRIGRI places great load on the point of reversal of the rope direction (the last point of protection). On crags which have been equipped for sport climbing the UIAA requires anchors to have a strength of 25kn. In this case there is no problem. On the other hand the GRIGRI is not recommended for traditional gear climbing or on ice, where anchors may have strengths less than the value recognized by the UIAA."
From: D. Condit
The only way a Gri Gri would place more load is if the belayer always slipped when using other devices (making a dynamic belay.) This Gri Gri stuff is a bunch of b.s. legalism that some layer thought up...how rediculous. It's the dynamic rope that absorbs the energy, not the belay device.
From: Mike Rawdon
ACCORDING TO PETZL, the Gri gri slips (despite full "lock off") at 9kN vs 2 kN for the other devices you mention.
That's how.
I guess someone may want to argue that THEY can hold more than 2 kN (abot 450 lbs) with their ATC or whatever. That should be easy enough to test ; hang two partners off your haul loop and then do a controlled one-strand rappel. I'd pay to see that!
From: Jay Tanzman
The question is not whether belaying with a gri-gri is dynamic or not, it is whether it is sufficiently dynamic to protect the leader. There is at least one case where it is not: steep sport routes. We have discussed this in considerable detail recently. When a leader falls from above his protection on a steep route he will swing into the wall if the belay is not sufficiently dynamic. The force can be bone shatterring. Sport climbers who use gri-gris routinely jump up as the leader's weight comes onto the rope to dampen the swing into the wall. |
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