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fresh
Sep 9, 2007, 10:04 PM
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I read in long's "climbing anchors" that most modern belay devices slip at 2-3 kn. this should imply that the force put on the top piece of protection shouldn't go higher than 7ish kn (some force will be absorbed by friction on the top piece). is this a reasonable conclusion? how much force will a regular atc, a reverso, and a gri gri absorb before slipping?
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coastal_climber
Sep 9, 2007, 10:37 PM
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Well, since with an ATC the only thing holding the rope is you, I'd say before 2-3kn.
>Cam
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papounet
Sep 9, 2007, 10:56 PM
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belay device are force amplifier.
With a belay device, such as a fig-8 , studies have found 2kn, with a munter hitch (better than any manualdevice ) belay device, 2,75 kn
grigri is a assisted block system that slip at 7kn
(figures ar from the top of my head, go to the petzl fall simulator for the figures Petzl got from its own study).
Friction on the top aluminium carabiner = 60% of the fore is transmitted,
so if there was only the belay device, the maximum force would be 5 to 6 kn for a manual device
But the belay device is just one part of the equation. a lot of energy is absorbed by the movment of the arm and body of the belayer. as well as in friction against the rock and the other biner. so the maximum force on teh top pro is higher.
Search for the Italian Alpine club real-world test (i posted links to them several times) for both actual mesures and a rather fine mathematical model.
Part of this was published in the UIAA magazine 2000 3rd quarter
http://www.lancs.ac.uk/...c/uiaa_equipment.pdf
which contains many nuggets of safety information
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fresh
Sep 10, 2007, 2:12 AM
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papounet wrote: belay device are force amplifier. With a belay device, such as a fig-8 , studies have found 2kn, with a munter hitch (better than any manualdevice ) belay device, 2,75 kn grigri is a assisted block system that slip at 7kn (figures ar from the top of my head, go to the petzl fall simulator for the figures Petzl got from its own study). Friction on the top aluminium carabiner = 60% of the fore is transmitted, so if there was only the belay device, the maximum force would be 5 to 6 kn for a manual device But the belay device is just one part of the equation. a lot of energy is absorbed by the movment of the arm and body of the belayer. as well as in friction against the rock and the other biner. so the maximum force on teh top pro is higher. Search for the Italian Alpine club real-world test (i posted links to them several times) for both actual mesures and a rather fine mathematical model. Part of this was published in the UIAA magazine 2000 3rd quarter http://www.lancs.ac.uk/...c/uiaa_equipment.pdf which contains many nuggets of safety information
what I was hoping to discover was that a simpler belay device like an ATC would be safer for trad climbing because it limits the force that can be put on the top piece due to slippage. if these numbers are right then I'm out of luck.
does anyone see this as a reason to not use a grigri for sketchy trad climbing?
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shockabuku
Sep 10, 2007, 2:52 AM
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Belay devices don't absorb force. I don't think "absorb force" really means anything.
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greenketch
Sep 10, 2007, 4:26 AM
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fresh wrote: what I was hoping to discover was that a simpler belay device like an ATC would be safer for trad climbing because it limits the force that can be put on the top piece due to slippage. if these numbers are right then I'm out of luck. does anyone see this as a reason to not use a grigri for sketchy trad climbing?
I'm not sure how you arrrived at the conclusion you did. You are correct in assuming that a device such as an ATC will disapate force at a lower rate than a GriGri. That will help in keeping sketchy trad pro in place. Even more than the device is belayer skill. How did the numbers lead you to think this is not the case?
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flint
Sep 10, 2007, 5:33 AM
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fresh wrote: papounet wrote: belay device are force amplifier. With a belay device, such as a fig-8 , studies have found 2kn, with a munter hitch (better than any manualdevice ) belay device, 2,75 kn grigri is a assisted block system that slip at 7kn (figures ar from the top of my head, go to the petzl fall simulator for the figures Petzl got from its own study). Friction on the top aluminium carabiner = 60% of the fore is transmitted, so if there was only the belay device, the maximum force would be 5 to 6 kn for a manual device But the belay device is just one part of the equation. a lot of energy is absorbed by the movment of the arm and body of the belayer. as well as in friction against the rock and the other biner. so the maximum force on teh top pro is higher. Search for the Italian Alpine club real-world test (i posted links to them several times) for both actual mesures and a rather fine mathematical model. Part of this was published in the UIAA magazine 2000 3rd quarter http://www.lancs.ac.uk/...c/uiaa_equipment.pdf which contains many nuggets of safety information 60% seems high for friction on the top piece of protection (not that I have a good reason to question it, haha). I guess I'd believe it if it were spread through a bunch of biners but one seems like too little. I'll take a look at your stuff though. what I was hoping to discover was that a simpler belay device like an ATC would be safer for trad climbing because it limits the force that can be put on the top piece due to slippage. if these numbers are right then I'm out of luck. does anyone see this as a reason to not use a grigri for sketchy trad climbing?
Like what was said above, the belayer is the most important part here. All in all, for sketchy trad, I would far prefer an atc over a grigri. I allows for a better catch due to all the tech. aspects in those articles that you didn't read before posting.
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majid_sabet
Sep 10, 2007, 6:38 AM
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papounet wrote: belay device are force amplifier. With a belay device, such as a fig-8 , studies have found 2kn, with a munter hitch (better than any manualdevice ) belay device, 2,75 kn grigri is a assisted block system that slip at 7kn (figures ar from the top of my head, go to the petzl fall simulator for the figures Petzl got from its own study). Friction on the top aluminium carabiner = 60% of the fore is transmitted, so if there was only the belay device, the maximum force would be 5 to 6 kn for a manual device But the belay device is just one part of the equation. a lot of energy is absorbed by the movment of the arm and body of the belayer. as well as in friction against the rock and the other biner. so the maximum force on teh top pro is higher. Search for the Italian Alpine club real-world test (i posted links to them several times) for both actual mesures and a rather fine mathematical model. Part of this was published in the UIAA magazine 2000 3rd quarter http://www.lancs.ac.uk/...c/uiaa_equipment.pdf which contains many nuggets of safety information
Where did this 60% came from ( source please)
UIAA testing with cross loading biner on anchor point ?
or may be it is new way of testing
[URL=http://imageshack.us]
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papounet
Sep 10, 2007, 8:36 AM
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majid_sabet wrote: Where did this 60% came from ( source please) UIAA testing with cross loading biner on anchor point ? or may be it is new way of testing
Two way to come at 60%
Theoritical: Coefficient of friction of unlubricated nylon on Aluminium.
Practical, a biner acts as imperfect pulley (takes into account angle, deformation of material, slipperiness of treated weaved nylon,..)
You can double check yourself the impact of the static coefficient of friction at home by testing
attach 10 kg to one side of a rope,
put it in a biner
put just enough weigtht on the the other side of the rope to hold the balance.
you should find something between 6 kg and 7 kg
this gives you an estimate of the force %
(can't remember off-hand the formula to give the coeeficient of friction from the %, though)
Add a tad more weigth, balance is broken.
Once friction has been overcome, the force needed to continue slipping is less.
An anodized biner is slightly more slippery, the value is higher.
I believe 60% to be the value is given in John long Anchors book (2nd ed) as well as in the self rescue book I already recommended.
you see it also expressed as maximum force on acnchor = 1.6 force on the tension side
PS: found back some of pulley test, the figure could rather as high as 70%
One of course could head to the peztl fall simulator where all those values and question of the OP are addressed ;-)
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overlord
Sep 10, 2007, 9:48 AM
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fresh wrote: I read in long's "climbing anchors" that most modern belay devices slip at 2-3 kn. this should imply that the force put on the top piece of protection shouldn't go higher than 7ish kn (some force will be absorbed by friction on the top piece). is this a reasonable conclusion? how much force will a regular atc, a reverso, and a gri gri absorb before slipping?
they do not absorbt the force, they multiply the force you create by braking. they do it by increasing friction.
even if they do slip, this doesnt mean that you loose control of the fall. it just means that the leader will have a tad longer fall.
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cracklover
Sep 10, 2007, 2:31 PM
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fresh wrote: I read in long's "climbing anchors" that most modern belay devices slip at 2-3 kn.
I don't know if he said this or not, but if so, it's pretty dumb. There's a wide variance in the amount of force you can expect to hold with a modern belay device. Among "tube" style devices, the Reverso is near the bottom, then simple tube-style devices like the ATC, with "jaws" style devices (with a "V" slot to pinch the rope) near the high end of the spectrum. But all of these work under the same principle - they multiply the amount of force you can hold with your own hand, by adding friction.
So how much you personally, or your belayer, can hold, is the first part of the equation. Next is the multiplication of that force. The low end is about 6 times, the top end is about 8 times. Just to give you a ballpark, the range here is probably about 1.2kN - 2.5kN before slipping.
A munter hitch will give around the high end of that range (for a given belayer).
Then there are devices which pinch the rope when loaded, such as the Gri-gri, the TRE, and the Cinch. These are not force-multiplying devices. These devices typically need a little bit of force on the brake and the live strand to "engage", and then will hold up to a given force (which varies based on the rope characteristics) before slipping. I'm not aware of the slipping point of the Cinch, but my recollection is that the TRE is about 4kN, and the gri-gri is around 8. I'd expect the Cinch to be similar to the gri-gri, or perhaps even higher, based on its design, but that's pure speculation.
So that tells you that, in fact, "modern devices," operated properly, will slip anywhere from such a low enough point to cause almost certain loss of control (or at least very severe burning) in a hard fall with a non-gloved belayer, to such a high point that a severe fall can rip out any well placed piece of gear aside from a really good pin or bolt. Obviously, a very very wide range!
In reply to: this should imply that the force put on the top piece of protection shouldn't go higher than 7ish kn (some force will be absorbed by friction on the top piece). is this a reasonable conclusion?
No, it's not a reasonable conclusion. See above. Just to go over the math, let's assume a few points, to make sure we're on the same sheet of music. Assume the belayer can hold 60 lbs of force with the break hand before the rope starts to slip. Assume a tube-style device with a force multiplication of 7. This gives you around 1.9kN of stopping force at the belay. Multiply that by 1.6 (pulley and friction over the top 'biner) and you arrive at around 3kN of force. But a lot of things can affect that. With rope drag, (rope running against corners/overhangs, bulges in the rock, rope making angles through protection biners) the belayer could hold *much* more force before slipping. How much more, I don't know, but probably at least double. That's pushing your 7kN figure right there. Now how about a tube device that offers more friction? How about a belayer who can hold more than 60 lbs of force? How about an old fuzzy, fat rope, that creates a lot more friction? How about a cinch, TRE, gri-gri, etc?
Let's look at the upper limit. Most ropes give as their rating for hard falls a force of 8-9 kN. With a device like a gri-gri, you should expect no rope slipping in such a fall. With no intermediate protection points, you should expect such a fall to generate around 14kN of force on the top piece. This would be higher if the rope was running through intermediate protection pieces, or around overhangs or corners. At any rate, we're now clearly way above the 7kN you were assuming.
In reply to: how much force will a regular atc, a reverso, and a gri gri absorb before slipping?
See above.
GO
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majid_sabet
Sep 10, 2007, 4:09 PM
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papounet wrote: majid_sabet wrote: Where did this 60% came from ( source please) UIAA testing with cross loading biner on anchor point ? or may be it is new way of testing
Theoritical: Coefficient of friction of unlubricated nylon on Aluminium.
Practical, a biner acts as imperfect pulley (takes into account angle, deformation of material, slipperiness of treated weaved nylon,..) You can double check yourself the impact of the static coefficient of friction at home by testing attach 10 kg to one side of a rope, put it in a biner put just enough weigtht on the the other side of the rope to hold the balance. you should find something between 6 kg and 7 kg this gives you an estimate of the force % (can't remember off-hand the formula to give the coeeficient of friction from the %, though) Add a tad more weigth, balance is broken. Once friction has been overcome, the force needed to continue slipping is less. An anodized biner is slightly more slippery, the value is higher. I believe 60% to be the value is given in John long Anchors book (2nd ed) as well as in the self rescue book I already recommended. you see it also expressed as maximum force on acnchor = 1.6 force on the tension side PS: found back some of pulley test, the figure could rather as high as 70% One of course could head to the peztl fall simulator where all those values and question of the OP are addressed ;-)
I know most pulleys can deliver up to 95% efficiency and biners can deliver up to 60% efficiency by loosing 40% due to frication caused by nylon over aluminum.
Are you sure you are not mixing 40% friction with 60 % efficiency?
I mean that 60% sounds pretty high and if it came from a reasonable source, (not your backyard testing) please provide a link.
(This post was edited by majid_sabet on Sep 10, 2007, 4:15 PM)
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fresh
Sep 10, 2007, 11:40 PM
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greenketch wrote: fresh wrote: what I was hoping to discover was that a simpler belay device like an ATC would be safer for trad climbing because it limits the force that can be put on the top piece due to slippage. if these numbers are right then I'm out of luck. does anyone see this as a reason to not use a grigri for sketchy trad climbing? I'm not sure how you arrrived at the conclusion you did. You are correct in assuming that a device such as an ATC will disapate force at a lower rate than a GriGri. That will help in keeping sketchy trad pro in place. Even more than the device is belayer skill. How did the numbers lead you to think this is not the case?
please point it out if I'm mistaken, I don't care if I'm wrong or not I just want to learn haha.
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fresh
Sep 10, 2007, 11:44 PM
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cracklover,
thanks for the excellent reply. note to self: read whole thread before replying at all? whatevs!
long states what I referred to on on page 104 of climbing anchors.
thanks to everyone else.
(This post was edited by fresh on Sep 10, 2007, 11:51 PM)
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fresh
Sep 10, 2007, 11:49 PM
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overlord wrote: fresh wrote: I read in long's "climbing anchors" that most modern belay devices slip at 2-3 kn. this should imply that the force put on the top piece of protection shouldn't go higher than 7ish kn (some force will be absorbed by friction on the top piece). is this a reasonable conclusion? how much force will a regular atc, a reverso, and a gri gri absorb before slipping? they do not absorbt the force, they multiply the force you create by braking. they do it by increasing friction. even if they do slip, this doesnt mean that you loose control of the fall. it just means that the leader will have a tad longer fall.
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overlord
Sep 11, 2007, 7:38 AM
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fresh wrote: overlord wrote: fresh wrote: I read in long's "climbing anchors" that most modern belay devices slip at 2-3 kn. this should imply that the force put on the top piece of protection shouldn't go higher than 7ish kn (some force will be absorbed by friction on the top piece). is this a reasonable conclusion? how much force will a regular atc, a reverso, and a gri gri absorb before slipping? they do not absorbt the force, they multiply the force you create by braking. they do it by increasing friction. even if they do slip, this doesnt mean that you loose control of the fall. it just means that the leader will have a tad longer fall. I think I may have phrased my question poorly; losing control of the fall isn't the issue here, what I'm concerned with is whether or not a belay device that slips more easily is superior on routes with sketchy pro because it limits the load that can be put on the whole system.
oh, in that case, yes, especially on MP when you belay from a hanging belay (hard to make a dynamic belay in such a situation).
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microbarn
Sep 11, 2007, 10:28 AM
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majid_sabet wrote: papounet wrote: majid_sabet wrote: Where did this 60% came from ( source please) UIAA testing with cross loading biner on anchor point ? or may be it is new way of testing
Theoritical: Coefficient of friction of unlubricated nylon on Aluminium.
Practical, a biner acts as imperfect pulley (takes into account angle, deformation of material, slipperiness of treated weaved nylon,..) You can double check yourself the impact of the static coefficient of friction at home by testing attach 10 kg to one side of a rope, put it in a biner put just enough weigtht on the the other side of the rope to hold the balance. you should find something between 6 kg and 7 kg this gives you an estimate of the force % (can't remember off-hand the formula to give the coeeficient of friction from the %, though) Add a tad more weigth, balance is broken. Once friction has been overcome, the force needed to continue slipping is less. An anodized biner is slightly more slippery, the value is higher. I believe 60% to be the value is given in John long Anchors book (2nd ed) as well as in the self rescue book I already recommended. you see it also expressed as maximum force on acnchor = 1.6 force on the tension side PS: found back some of pulley test, the figure could rather as high as 70% One of course could head to the peztl fall simulator where all those values and question of the OP are addressed ;-) I know most pulleys can deliver up to 95% efficiency and biners can deliver up to 60% efficiency by loosing 40% due to frication caused by nylon over aluminum. Are you sure you are not mixing 40% friction with 60 % efficiency? I mean that 60% sounds pretty high and if it came from a reasonable source, (not your backyard testing) please provide a link.
He is saying 60% is transmitted. That means that 40% is accounted for by friction. You are agreeing with him.
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cracklover
Sep 11, 2007, 2:43 PM
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Hey Fresh, no problem, happy to help.
microbarn wrote: He is saying 60% is transmitted. That means that 40% is accounted for by friction. You are agreeing with him.
No, actually, he's not. He is (was?) confused. He clarified his understanding here: In reply to: the highest level of force that should be created by a fall is something around 8-9 kn. if 60% of the force is absorbed by friction at the top piece of the carabiner, then something around 3-4 kn will be transfered to the belayer.
Fresh, 60% of the force is not absorbed by the top piece, the figure is more like 40%.
But there's another issue here.
In reply to: losing control of the fall isn't the issue here, what I'm concerned with is whether or not a belay device that slips more easily is superior on routes with sketchy pro because it limits the load that can be put on the whole system.
I understand that your concern is with limiting the load on the top piece. And that's a valid concern. But you must understand the tradeoffs involved in trying to limit that load merely with a belay device that doesn't provide much friction: losing control of the belay is a very real concern in a serious fall. Using a low-friction device, could you actually catch a factor two fall (that means leader falls on your harness) at all?
Consider buying a screamer or two, and using those on sketchy and/or very important pieces. Then use a device of your choice that offers sufficient friction to give you a reasonable chance of catching a very serious fall.
Cheers!
GO
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papounet
Sep 11, 2007, 10:25 PM
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majid_sabet wrote: papounet wrote: majid_sabet wrote: Where did this 60% came from ( source please) UIAA testing with cross loading biner on anchor point ? or may be it is new way of testing
Theoritical: Coefficient of friction of unlubricated nylon on Aluminium.
Practical, a biner acts as imperfect pulley (takes into account angle, deformation of material, slipperiness of treated weaved nylon,..) You can double check yourself the impact of the static coefficient of friction at home by testing attach 10 kg to one side of a rope, put it in a biner put just enough weigtht on the the other side of the rope to hold the balance. you should find something between 6 kg and 7 kg this gives you an estimate of the force % (can't remember off-hand the formula to give the coeeficient of friction from the %, though) Add a tad more weigth, balance is broken. Once friction has been overcome, the force needed to continue slipping is less. An anodized biner is slightly more slippery, the value is higher. I believe 60% to be the value is given in John long Anchors book (2nd ed) as well as in the self rescue book I already recommended. you see it also expressed as maximum force on acnchor = 1.6 force on the tension side PS: found back some of pulley test, the figure could rather as high as 70% One of course could head to the peztl fall simulator where all those values and question of the OP are addressed ;-) I know most pulleys can deliver up to 95% efficiency and biners can deliver up to 60% efficiency by loosing 40% due to frication caused by nylon over aluminum. Are you sure you are not mixing 40% friction with 60 % efficiency? I mean that 60% sounds pretty high and if it came from a reasonable source, (not your backyard testing) please provide a link.
Well, I'll put it to the fact that we both are not native english speaker.
I wrote: "Friction on the top aluminium carabiner = 60% of the fore is transmitted, "
It should have been
"Friction on the top aluminium carabiner => 60% of the force is transmitted,
I suggest you consider next time why you think that what you KNOW is more reliable that what others write (when in fact, it may well be that we say the same thing)
OK my sources :
Beal puts the pulley effect at 60%, which is the figure I rememberedhttp://www.bealplanet.com/...rce_choc&lang=us
Petzl used to put the pulley effect to 60% (in a top rope situation if 100 was hanging on one side, the holding side only saw 60)
in the latest simulator,it is 50% of the force (see simulator)
page 136 of "climbing self rescue" by Tyson and Loomis efficiency of biner = 70%
http://oberon.ses.nsw.gov.au/...iction%20Testing.pdf
with the diversity of values, I ended up doing a check which is easy to reproduce and is consistent with the litterature.
So, what we you saying, Majid ????
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