|
rescueman
Aug 23, 2011, 2:46 PM
Post #101 of 252
(7371 views)
Shortcut
Registered: Mar 1, 2004
Posts: 439
|
mbrd,
Thanks for injecting some common sense into a discussion which veered out into left field.
It's impossible arguing with a climber who thinks that "28 years on the sharp end" gives him a better understanding of the physics of dynamic rope forces than one of the most published researchers in the field. And it's even more impossible to have a rational conversation with a bearbreeder who doesn't understand statistical multivariant analysis and believes that "two opposed biners" is the first commandment of top-roping.
The bottom line, as you so eloquently suggested, is that 6mm cord is fine for slinging your water bottle but dangerous for an extended top rope anchor over an edge, and that two spaced masterpoint knots is more likely to undermine the security of the system than to enhance it.
Masterknot, masterbiner, masterpoint...
Some seem to be here just for mental masterbation.
|
|
|
|
|
bearbreeder
Aug 23, 2011, 2:58 PM
Post #102 of 252
(7359 views)
Shortcut
Registered: Feb 2, 2009
Posts: 1960
|
rescueman wrote: mbrd, Thanks for injecting some common sense into a discussion which veered out into left field. It's impossible arguing with a climber who thinks that "28 years on the sharp end" gives him a better understanding of the physics of dynamic rope forces than one of the most published researchers in the field. And it's even more impossible to have a rational conversation with a bearbreeder who doesn't understand statistical multivariant analysis and believes that "two opposed biners" is the first commandment of top-roping. The bottom line, as you so eloquently suggested, is that 6mm cord is fine for slinging your water bottle but dangerous for an extended top rope anchor over an edge, and that two spaced masterpoint knots is more likely to undermine the security of the system than to enhance it. Masterknot, masterbiner, masterpoint... Some seem to be here just for mental masterbation.
i fell last week on trad ... how far did i fall .. was it 10 or 15 feet? ... i go WHOOSH ... no one took out a meeasuring tape to measure the fall or length of rope out ... how reliable is a survey of climbers where we simply ask "what was yr fall factor?" ....
as to opposed ... every sport climbing area ive been to, the majority of people use 2 opposed biners/draws to top rope and lower ... not to mention every gym around here
i guess we are all dead dodos because we dont do as some "rc expert" demands 
|
|
|
|
|
hugepedro
Aug 23, 2011, 3:00 PM
Post #103 of 252
(7357 views)
Shortcut
Registered: May 28, 2002
Posts: 2875
|
rescueman wrote: It's impossible arguing with a climber who thinks that "28 years on the sharp end" gives him a better understanding of the physics of dynamic rope forces than one of the most published researchers in the field.
I didn't disagree with the findings in that report. YOU are the one that disagrees with them, you just don't know it. As I suggested, try reading it again.
|
|
|
|
|
bearbreeder
Aug 23, 2011, 3:07 PM
Post #104 of 252
(7351 views)
Shortcut
Registered: Feb 2, 2009
Posts: 1960
|
btw ... im still waiting for an explanation on how you can realistically have a factor 1 fall on TR in a normal scenario from the ground up ...
maybe you get the groups you supervise to tie to a bridge and jump off
|
|
|
|
|
Guran
Aug 23, 2011, 3:13 PM
Post #105 of 252
(7349 views)
Shortcut
Registered: Sep 18, 2008
Posts: 220
|
A top rope fall will never exceed fall factor 0.5.
In fact only in rare circumstances would a belayer worth anything let more than a meter of slack build up.
On a really short route (say 10 m) that equals a potential fall factor between 0.05 and 0.1
For those factors, triaxial loading is no concern. HOWEVER, it is a bad practice to ever rig anything in such a configuration, since bad habits tend to travel from top rope rigs to "real" anchors.
|
|
|
|
|
scrapedape
Aug 23, 2011, 3:14 PM
Post #106 of 252
(7348 views)
Shortcut
Registered: Jun 24, 2004
Posts: 2392
|
How on Earth are you going to generate both a FF 1 fall AND a 1.67X load multiplication on the top anchor?
If you are belaying in a slingshot TR system, the max fall factor would be 0.5. That would happen if the climber climbed all the way to the top and fell, without the belayer taking in any slack.
If you are belaying from the top, you could generate a factor one fall if the climber climbed all the way to the top without the belayer taking in any slack. But in this case, why would you be running the slingshot to create the load multiplication on the anchor?
-----
Let's step back for a minute and do a sanity check. Think about the credibility of these claims.
And we'll do it with some math, bitches.
What would a 9kN load at the belay mean for the belayer? Assume the belayer has a mass of 100 kg (fatty fatty fat fat...). The force of gravity on that belayer is 100*9.8 = 980 N. Therefore applying a 9kN upward force from the rope would create a net upward force of 9000-980 = 8020N on the belayer.
Newton's second law tells us F = ma, so that 8000 N force on the 100 kg belayer would generate an upward acceleration of 80 m/s^2. How plausible is this number?
* That's about 8 g's
* It's the equivalent of accelerating from 0-60 mph in a third of a second.
* If applied for one tenth of a second, this acceleration would create an upward velocity of 8 m/s (18 mph)
* to a first approximation, this would launch the belayer up to a height of 3.3 m (11 feet)
So I ask you this: how plausible do you find the idea of a belayer experiencing 8 g's of acceleration when catching a TR fall? The idea of a TR fall yanking a 220 lb belayer hard enough to launch him 10+ feet into the air?
|
|
|
|
|
redlude97
Aug 23, 2011, 3:52 PM
Post #107 of 252
(7331 views)
Shortcut
Registered: Aug 27, 2008
Posts: 990
|
scrapedape wrote: How on Earth are you going to generate both a FF 1 fall AND a 1.67X load multiplication on the top anchor? If you are belaying in a slingshot TR system, the max fall factor would be 0.5. That would happen if the climber climbed all the way to the top and fell, without the belayer taking in any slack. If you are belaying from the top, you could generate a factor one fall if the climber climbed all the way to the top without the belayer taking in any slack. But in this case, why would you be running the slingshot to create the load multiplication on the anchor? ----- Let's step back for a minute and do a sanity check. Think about the credibility of these claims. And we'll do it with some math, bitches. What would a 9kN load at the belay mean for the belayer? Assume the belayer has a mass of 100 kg (fatty fatty fat fat...). The force of gravity on that belayer is 100*9.8 = 980 N. Therefore applying a 9kN upward force from the rope would create a net upward force of 9000-980 = 8020N on the belayer. Newton's second law tells us F = ma, so that 8000 N force on the 100 kg belayer would generate an upward acceleration of 80 m/s^2. How plausible is this number? * That's about 8 g's * It's the equivalent of accelerating from 0-60 mph in a third of a second. * If applied for one tenth of a second, this acceleration would create an upward velocity of 8 m/s (18 mph) * to a first approximation, this would launch the belayer up to a height of 3.3 m (11 feet) So I ask you this: how plausible do you find the idea of a belayer experiencing 8 g's of acceleration when catching a TR fall? The idea of a TR fall yanking a 220 lb belayer hard enough to launch him 10+ feet into the air?
|
|
|
|
|
scrapedape
Aug 23, 2011, 4:07 PM
Post #108 of 252
(7318 views)
Shortcut
Registered: Jun 24, 2004
Posts: 2392
|
redlude97 wrote: scrapedape wrote: How on Earth are you going to generate both a FF 1 fall AND a 1.67X load multiplication on the top anchor? If you are belaying in a slingshot TR system, the max fall factor would be 0.5. That would happen if the climber climbed all the way to the top and fell, without the belayer taking in any slack. If you are belaying from the top, you could generate a factor one fall if the climber climbed all the way to the top without the belayer taking in any slack. But in this case, why would you be running the slingshot to create the load multiplication on the anchor? ----- Let's step back for a minute and do a sanity check. Think about the credibility of these claims. And we'll do it with some math, bitches. What would a 9kN load at the belay mean for the belayer? Assume the belayer has a mass of 100 kg (fatty fatty fat fat...). The force of gravity on that belayer is 100*9.8 = 980 N. Therefore applying a 9kN upward force from the rope would create a net upward force of 9000-980 = 8020N on the belayer. Newton's second law tells us F = ma, so that 8000 N force on the 100 kg belayer would generate an upward acceleration of 80 m/s^2. How plausible is this number? * That's about 8 g's * It's the equivalent of accelerating from 0-60 mph in a third of a second. * If applied for one tenth of a second, this acceleration would create an upward velocity of 8 m/s (18 mph) * to a first approximation, this would launch the belayer up to a height of 3.3 m (11 feet) So I ask you this: how plausible do you find the idea of a belayer experiencing 8 g's of acceleration when catching a TR fall? The idea of a TR fall yanking a 220 lb belayer hard enough to launch him 10+ feet into the air? That is some pretty hokey math you just did there.
Why don't you elaborate?
I think the assumptions could be questionable but I stand by the math unless you're prepared to be more specific.
In particular, I'll admit that I think the weakest link in that string of calculations was the assumption about the length of time for which the force is applied.
|
|
|
|
|
redlude97
Aug 23, 2011, 4:18 PM
Post #109 of 252
(7309 views)
Shortcut
Registered: Aug 27, 2008
Posts: 990
|
scrapedape wrote: redlude97 wrote: scrapedape wrote: How on Earth are you going to generate both a FF 1 fall AND a 1.67X load multiplication on the top anchor? If you are belaying in a slingshot TR system, the max fall factor would be 0.5. That would happen if the climber climbed all the way to the top and fell, without the belayer taking in any slack. If you are belaying from the top, you could generate a factor one fall if the climber climbed all the way to the top without the belayer taking in any slack. But in this case, why would you be running the slingshot to create the load multiplication on the anchor? ----- Let's step back for a minute and do a sanity check. Think about the credibility of these claims. And we'll do it with some math, bitches. What would a 9kN load at the belay mean for the belayer? Assume the belayer has a mass of 100 kg (fatty fatty fat fat...). The force of gravity on that belayer is 100*9.8 = 980 N. Therefore applying a 9kN upward force from the rope would create a net upward force of 9000-980 = 8020N on the belayer. Newton's second law tells us F = ma, so that 8000 N force on the 100 kg belayer would generate an upward acceleration of 80 m/s^2. How plausible is this number? * That's about 8 g's * It's the equivalent of accelerating from 0-60 mph in a third of a second. * If applied for one tenth of a second, this acceleration would create an upward velocity of 8 m/s (18 mph) * to a first approximation, this would launch the belayer up to a height of 3.3 m (11 feet) So I ask you this: how plausible do you find the idea of a belayer experiencing 8 g's of acceleration when catching a TR fall? The idea of a TR fall yanking a 220 lb belayer hard enough to launch him 10+ feet into the air? That is some pretty hokey math you just did there. Why don't you elaborate? I think the assumptions could be questionable but I stand by the math unless you're prepared to be more specific. In particular, I'll admit that I think the weakest link in that string of calculations was the assumption about the length of time for which the force is applied.
|
|
|
|
|
hugepedro
Aug 23, 2011, 4:43 PM
Post #110 of 252
(7300 views)
Shortcut
Registered: May 28, 2002
Posts: 2875
|
redlude97 wrote: scrapedape wrote: redlude97 wrote: scrapedape wrote: How on Earth are you going to generate both a FF 1 fall AND a 1.67X load multiplication on the top anchor? If you are belaying in a slingshot TR system, the max fall factor would be 0.5. That would happen if the climber climbed all the way to the top and fell, without the belayer taking in any slack. If you are belaying from the top, you could generate a factor one fall if the climber climbed all the way to the top without the belayer taking in any slack. But in this case, why would you be running the slingshot to create the load multiplication on the anchor? ----- Let's step back for a minute and do a sanity check. Think about the credibility of these claims. And we'll do it with some math, bitches. What would a 9kN load at the belay mean for the belayer? Assume the belayer has a mass of 100 kg (fatty fatty fat fat...). The force of gravity on that belayer is 100*9.8 = 980 N. Therefore applying a 9kN upward force from the rope would create a net upward force of 9000-980 = 8020N on the belayer. Newton's second law tells us F = ma, so that 8000 N force on the 100 kg belayer would generate an upward acceleration of 80 m/s^2. How plausible is this number? * That's about 8 g's * It's the equivalent of accelerating from 0-60 mph in a third of a second. * If applied for one tenth of a second, this acceleration would create an upward velocity of 8 m/s (18 mph) * to a first approximation, this would launch the belayer up to a height of 3.3 m (11 feet) So I ask you this: how plausible do you find the idea of a belayer experiencing 8 g's of acceleration when catching a TR fall? The idea of a TR fall yanking a 220 lb belayer hard enough to launch him 10+ feet into the air? That is some pretty hokey math you just did there. Why don't you elaborate? I think the assumptions could be questionable but I stand by the math unless you're prepared to be more specific. In particular, I'll admit that I think the weakest link in that string of calculations was the assumption about the length of time for which the force is applied. well for one thing using f=ma on the climber only calculates their static hanging weight on the rope and doesn't account for any fall whatsoever. I'm busy at work but i'll expand more later, but to be brief a 200lb climber can generate in the neighborhood of 5kn+ at the anchor in toprope falls relatively easily.
Bad math aside, none of this changes the fact that there ain't no way to generate 9kn at the belay in a top rope fall. Nor does it change the fact that there ain't no way the anchor biners, rigged as in the OP's picture, would be compromised. No. Effing. Way.
|
|
|
|
|
redlude97
Aug 23, 2011, 4:57 PM
Post #111 of 252
(7291 views)
Shortcut
Registered: Aug 27, 2008
Posts: 990
|
hugepedro wrote: redlude97 wrote: scrapedape wrote: redlude97 wrote: scrapedape wrote: How on Earth are you going to generate both a FF 1 fall AND a 1.67X load multiplication on the top anchor? If you are belaying in a slingshot TR system, the max fall factor would be 0.5. That would happen if the climber climbed all the way to the top and fell, without the belayer taking in any slack. If you are belaying from the top, you could generate a factor one fall if the climber climbed all the way to the top without the belayer taking in any slack. But in this case, why would you be running the slingshot to create the load multiplication on the anchor? ----- Let's step back for a minute and do a sanity check. Think about the credibility of these claims. And we'll do it with some math, bitches. What would a 9kN load at the belay mean for the belayer? Assume the belayer has a mass of 100 kg (fatty fatty fat fat...). The force of gravity on that belayer is 100*9.8 = 980 N. Therefore applying a 9kN upward force from the rope would create a net upward force of 9000-980 = 8020N on the belayer. Newton's second law tells us F = ma, so that 8000 N force on the 100 kg belayer would generate an upward acceleration of 80 m/s^2. How plausible is this number? * That's about 8 g's * It's the equivalent of accelerating from 0-60 mph in a third of a second. * If applied for one tenth of a second, this acceleration would create an upward velocity of 8 m/s (18 mph) * to a first approximation, this would launch the belayer up to a height of 3.3 m (11 feet) So I ask you this: how plausible do you find the idea of a belayer experiencing 8 g's of acceleration when catching a TR fall? The idea of a TR fall yanking a 220 lb belayer hard enough to launch him 10+ feet into the air? That is some pretty hokey math you just did there. Why don't you elaborate? I think the assumptions could be questionable but I stand by the math unless you're prepared to be more specific. In particular, I'll admit that I think the weakest link in that string of calculations was the assumption about the length of time for which the force is applied. well for one thing using f=ma on the climber only calculates their static hanging weight on the rope and doesn't account for any fall whatsoever. I'm busy at work but i'll expand more later, but to be brief a 200lb climber can generate in the neighborhood of 5kn+ at the anchor in toprope falls relatively easily. Bad math aside, none of this changes the fact that there ain't no way to generate 9kn at the belay in a top rope fall. Nor does it change the fact that there ain't no way the anchor biners, rigged as in the OP's picture, would be compromised. No. Effing. Way.
|
|
|
|
|
moose_droppings
Aug 23, 2011, 5:00 PM
Post #112 of 252
(7290 views)
Shortcut
Registered: Jun 7, 2005
Posts: 3371
|
Micro fractures, triaxial loading, g forces, oh my!!!
|
|
|
|
|
bearbreeder
Aug 23, 2011, 5:14 PM
Post #113 of 252
(7284 views)
Shortcut
Registered: Feb 2, 2009
Posts: 1960
|
the bottom line is that any triaxial loading is easily solved by clipping one biner to each bight opposed ... and with 2 biners even with triax whatever ya might call it loading ... they wont BOTH break
its not how i would set it up ... but if i saw it at the crag i wouldnt go crazy spewing "unsafe, unsafe, unsafe TR" like some rc rescue expert here 
if mr rescue expert REALLY wanted to make a positive contribution, he would ask the OP for which service taught him that setup, then contact said service about their safety ...
im totally absolutely 1000000% super duper sure that any reputable service would appreciate the feedback from a highly experienced intraweb rc rescue expert ... and review their policy accordingly
however the likely result is that said rescue "expert" keeps on spewing about deadly TR setups and 9 kn at TR belays ... without contacting said service
thats often the result of RC threads 
|
|
|
|
|
redlude97
Aug 23, 2011, 5:22 PM
Post #114 of 252
(7276 views)
Shortcut
Registered: Aug 27, 2008
Posts: 990
|
bearbreeder wrote: the bottom line is that any triaxial loading is easily solved by clipping one biner to each bight opposed ... and with 2 biners even with triax whatever ya might call it loading ... they wont BOTH break its not how i would set it up ... but if i saw it at the crag i wouldnt go crazy spewing "unsafe, unsafe, unsafe TR" like some rc rescue expert here if mr rescue expert REALLY wanted to make a positive contribution, he would ask the OP for which service taught him that setup, then contact said service about their safety ... im totally absolutely 1000000% super duper sure that any reputable service would appreciate the feedback from a highly experienced intraweb rc rescue expert ... and review their policy accordingly however the likely result is that said rescue "expert" keeps on spewing about deadly TR setups and 9 kn at TR belays ... without contacting said service thats often the result of RC threads
|
|
|
|
|
hugepedro
Aug 23, 2011, 5:23 PM
Post #115 of 252
(7273 views)
Shortcut
Registered: May 28, 2002
Posts: 2875
|
redlude97 wrote: hugepedro wrote: redlude97 wrote: scrapedape wrote: redlude97 wrote: scrapedape wrote: How on Earth are you going to generate both a FF 1 fall AND a 1.67X load multiplication on the top anchor? If you are belaying in a slingshot TR system, the max fall factor would be 0.5. That would happen if the climber climbed all the way to the top and fell, without the belayer taking in any slack. If you are belaying from the top, you could generate a factor one fall if the climber climbed all the way to the top without the belayer taking in any slack. But in this case, why would you be running the slingshot to create the load multiplication on the anchor? ----- Let's step back for a minute and do a sanity check. Think about the credibility of these claims. And we'll do it with some math, bitches. What would a 9kN load at the belay mean for the belayer? Assume the belayer has a mass of 100 kg (fatty fatty fat fat...). The force of gravity on that belayer is 100*9.8 = 980 N. Therefore applying a 9kN upward force from the rope would create a net upward force of 9000-980 = 8020N on the belayer. Newton's second law tells us F = ma, so that 8000 N force on the 100 kg belayer would generate an upward acceleration of 80 m/s^2. How plausible is this number? * That's about 8 g's * It's the equivalent of accelerating from 0-60 mph in a third of a second. * If applied for one tenth of a second, this acceleration would create an upward velocity of 8 m/s (18 mph) * to a first approximation, this would launch the belayer up to a height of 3.3 m (11 feet) So I ask you this: how plausible do you find the idea of a belayer experiencing 8 g's of acceleration when catching a TR fall? The idea of a TR fall yanking a 220 lb belayer hard enough to launch him 10+ feet into the air? That is some pretty hokey math you just did there. Why don't you elaborate? I think the assumptions could be questionable but I stand by the math unless you're prepared to be more specific. In particular, I'll admit that I think the weakest link in that string of calculations was the assumption about the length of time for which the force is applied. well for one thing using f=ma on the climber only calculates their static hanging weight on the rope and doesn't account for any fall whatsoever. I'm busy at work but i'll expand more later, but to be brief a 200lb climber can generate in the neighborhood of 5kn+ at the anchor in toprope falls relatively easily. Bad math aside, none of this changes the fact that there ain't no way to generate 9kn at the belay in a top rope fall. Nor does it change the fact that there ain't no way the anchor biners, rigged as in the OP's picture, would be compromised. No. Effing. Way. I'm pretty sure i never made such a claim, but once you consider the tri-axial loading on the biner the forces are closer to the breaking strength than you think. Does it mean you shouldn't use this configuration? Its probably okay as long as the angles stay well below 45 degrees
I know you didn't make that claim, I was just clarifying lest some folks that don't read too good get confused by the discussion.
I don't think you meant to say that this rig could approach the breaking strength of 2 biners, did you? Because that is the situation we are discussing. Nobody is talking about a single biner at the anchor.
|
|
|
|
|
redlude97
Aug 23, 2011, 5:27 PM
Post #116 of 252
(7269 views)
Shortcut
Registered: Aug 27, 2008
Posts: 990
|
hugepedro wrote: redlude97 wrote: hugepedro wrote: redlude97 wrote: scrapedape wrote: redlude97 wrote: scrapedape wrote: How on Earth are you going to generate both a FF 1 fall AND a 1.67X load multiplication on the top anchor? If you are belaying in a slingshot TR system, the max fall factor would be 0.5. That would happen if the climber climbed all the way to the top and fell, without the belayer taking in any slack. If you are belaying from the top, you could generate a factor one fall if the climber climbed all the way to the top without the belayer taking in any slack. But in this case, why would you be running the slingshot to create the load multiplication on the anchor? ----- Let's step back for a minute and do a sanity check. Think about the credibility of these claims. And we'll do it with some math, bitches. What would a 9kN load at the belay mean for the belayer? Assume the belayer has a mass of 100 kg (fatty fatty fat fat...). The force of gravity on that belayer is 100*9.8 = 980 N. Therefore applying a 9kN upward force from the rope would create a net upward force of 9000-980 = 8020N on the belayer. Newton's second law tells us F = ma, so that 8000 N force on the 100 kg belayer would generate an upward acceleration of 80 m/s^2. How plausible is this number? * That's about 8 g's * It's the equivalent of accelerating from 0-60 mph in a third of a second. * If applied for one tenth of a second, this acceleration would create an upward velocity of 8 m/s (18 mph) * to a first approximation, this would launch the belayer up to a height of 3.3 m (11 feet) So I ask you this: how plausible do you find the idea of a belayer experiencing 8 g's of acceleration when catching a TR fall? The idea of a TR fall yanking a 220 lb belayer hard enough to launch him 10+ feet into the air? That is some pretty hokey math you just did there. Why don't you elaborate? I think the assumptions could be questionable but I stand by the math unless you're prepared to be more specific. In particular, I'll admit that I think the weakest link in that string of calculations was the assumption about the length of time for which the force is applied. well for one thing using f=ma on the climber only calculates their static hanging weight on the rope and doesn't account for any fall whatsoever. I'm busy at work but i'll expand more later, but to be brief a 200lb climber can generate in the neighborhood of 5kn+ at the anchor in toprope falls relatively easily. Bad math aside, none of this changes the fact that there ain't no way to generate 9kn at the belay in a top rope fall. Nor does it change the fact that there ain't no way the anchor biners, rigged as in the OP's picture, would be compromised. No. Effing. Way. I'm pretty sure i never made such a claim, but once you consider the tri-axial loading on the biner the forces are closer to the breaking strength than you think. Does it mean you shouldn't use this configuration? Its probably okay as long as the angles stay well below 45 degrees I know you didn't make that claim, I was just clarifying lest some folks that don't read too good get confused by the discussion. I don't think you meant to say that this rig could approach the breaking strength of 2 biners, did you? Because that is the situation we are discussing. Nobody is talking about a single biner at the anchor.
|
|
|
|
|
hugepedro
Aug 23, 2011, 5:51 PM
Post #117 of 252
(7255 views)
Shortcut
Registered: May 28, 2002
Posts: 2875
|
redlude97 wrote: Well the OPs pic shows 1 biner, and it isn't too uncommon to see people use a single locker for a TR setup
Yeah and it was not a locker either. His pic was just to demonstrate the rigging of his cord. The use of a single locker was also discussed earlier in the thread as being dumb because they can become unlocked.
|
|
|
|
|
scrapedape
Aug 23, 2011, 6:54 PM
Post #118 of 252
(7231 views)
Shortcut
Registered: Jun 24, 2004
Posts: 2392
|
redlude97 wrote: scrapedape wrote: redlude97 wrote: scrapedape wrote: How on Earth are you going to generate both a FF 1 fall AND a 1.67X load multiplication on the top anchor? If you are belaying in a slingshot TR system, the max fall factor would be 0.5. That would happen if the climber climbed all the way to the top and fell, without the belayer taking in any slack. If you are belaying from the top, you could generate a factor one fall if the climber climbed all the way to the top without the belayer taking in any slack. But in this case, why would you be running the slingshot to create the load multiplication on the anchor? ----- Let's step back for a minute and do a sanity check. Think about the credibility of these claims. And we'll do it with some math, bitches. What would a 9kN load at the belay mean for the belayer? Assume the belayer has a mass of 100 kg (fatty fatty fat fat...). The force of gravity on that belayer is 100*9.8 = 980 N. Therefore applying a 9kN upward force from the rope would create a net upward force of 9000-980 = 8020N on the belayer. Newton's second law tells us F = ma, so that 8000 N force on the 100 kg belayer would generate an upward acceleration of 80 m/s^2. How plausible is this number? * That's about 8 g's * It's the equivalent of accelerating from 0-60 mph in a third of a second. * If applied for one tenth of a second, this acceleration would create an upward velocity of 8 m/s (18 mph) * to a first approximation, this would launch the belayer up to a height of 3.3 m (11 feet) So I ask you this: how plausible do you find the idea of a belayer experiencing 8 g's of acceleration when catching a TR fall? The idea of a TR fall yanking a 220 lb belayer hard enough to launch him 10+ feet into the air? That is some pretty hokey math you just did there. Why don't you elaborate? I think the assumptions could be questionable but I stand by the math unless you're prepared to be more specific. In particular, I'll admit that I think the weakest link in that string of calculations was the assumption about the length of time for which the force is applied. well for one thing using f=ma on the climber only calculates their static hanging weight on the rope and doesn't account for any fall whatsoever. I'm busy at work but i'll expand more later, but to be brief a 200lb climber can generate in the neighborhood of 5kn+ at the anchor in toprope falls relatively easily.
Thanks for confirming that you didn't actually read my post. I said nothing about the force on the climber or on the anchor. I was questioning the claim that a TR belayer could be subjected to a 9 kN force.
And if you don't believe that F=ma still applies in the case of a fall, I suggest you (a) head back for a high school physics refresher, and/or (b) stop pretending that you know what you're talking about.
|
|
|
|
|
rescueman
Aug 23, 2011, 7:05 PM
Post #119 of 252
(7228 views)
Shortcut
Registered: Mar 1, 2004
Posts: 439
|
redlude97 wrote: a 200lb climber can generate in the neighborhood of 5kn+ at the anchor in toprope falls relatively easily.
And that's what most climbers, even those with "28 years at the sharp end", don't realize. That's 1125 lbs force. And that's with a typical dynamic belay, such as a tube or plate device (2 kN maximum stopping power). A GriGri (9 kN stopping force) increases the effective force by a factor of up to 4.5, and even a belayer who's tied off to a ground anchor will increase the force somewhat.
Most think, as has been stated here, that the maximum fall factor in a sling-shot top-rope can be 0.5. But any friction of rope on rock, particularly between the sling-shot 'biner and the belayer, will reduce the effective rope length and increase the effective fall factor.
In lead climbing (yes that's a different subject), a lot of rope drag and zig-zag protection can multiply the effective fall factor by as much as 3 and increase the load on climber and topmost anchor anchor by 75%.
A top-roped climber losing his grip and falling on a completely taught rope (fall factor zero) puts double his weight on the rope, and at least 1.5 times that load on the anchor. Even a 0.2 fall factor fall on top rope with no rope drag and a 2 kN belay can put 5 kN of force on the anchor system.
I won't bother checking the math about the belayer's upwards acceleration, but I've been lifted and moved 10 feet horizontally toward the rock while belaying a top rope falling climber. The forces can be surprisingly large.
The whole point of this discussion should be that, in a top-rope situation, there's no reason to skimp on the strength and static quality of the anchor. (And there's no need to oppose locking biners, which creates all kinds of potential problems.)
(This post was edited by rescueman on Aug 23, 2011, 7:13 PM)
|
|
|
|
|
scrapedape
Aug 23, 2011, 8:11 PM
Post #120 of 252
(7211 views)
Shortcut
Registered: Jun 24, 2004
Posts: 2392
|
rescueman wrote: The whole point of this discussion should be that, in a top-rope situation, there's no reason to skimp on the strength and static quality of the anchor. (And there's no need to oppose locking biners, which creates all kinds of potential problems.)
And you can make that point without relying on absurd claims that a belayer could experience a 9kN load in a TR fall, which corresponds to a 15 kN load on the anchor, which is what you said here:
rescueman wrote: According to a test report by Stephen Attaway, PhD and J. Marc Beverly, "the maximum credible event for belay loads for new ropes…would be 9 kN for devices limited to fall factors of less than one (single pitch or top rope)." That's at the belay device. At the top rope change of direction, the force would be approximately 1.67 times that. http://www.caves.org/...ng_Em_High_Final.pdf
And for what it's worth, I believe the 1.67 factor is usually applied to the force on the climber's end of the rope. If you are starting from the force on the belayer's end of the rope, I think a multiplier of 2.5 would be more appropriate.
Nevertheless, the basic fact that you can't seem to understand is that just because a belay device can apply a certain force to the rope, doesn't mean it will apply that force to the rope.
|
|
|
|
|
hugepedro
Aug 23, 2011, 8:29 PM
Post #121 of 252
(7204 views)
Shortcut
Registered: May 28, 2002
Posts: 2875
|
rescueman wrote: redlude97 wrote: a 200lb climber can generate in the neighborhood of 5kn+ at the anchor in toprope falls relatively easily. And that's what most climbers, even those with "28 years at the sharp end", don't realize. That's 1125 lbs force. And that's with a typical dynamic belay, such as a tube or plate device (2 kN maximum stopping power). A GriGri (9 kN stopping force) increases the effective force by a factor of up to 4.5, and even a belayer who's tied off to a ground anchor will increase the force somewhat. Most think, as has been stated here, that the maximum fall factor in a sling-shot top-rope can be 0.5. But any friction of rope on rock, particularly between the sling-shot 'biner and the belayer, will reduce the effective rope length and increase the effective fall factor. In lead climbing (yes that's a different subject), a lot of rope drag and zig-zag protection can multiply the effective fall factor by as much as 3 and increase the load on climber and topmost anchor anchor by 75%. A top-roped climber losing his grip and falling on a completely taught rope (fall factor zero) puts double his weight on the rope, and at least 1.5 times that load on the anchor. Even a 0.2 fall factor fall on top rope with no rope drag and a 2 kN belay can put 5 kN of force on the anchor system. I won't bother checking the math about the belayer's upwards acceleration, but I've been lifted and moved 10 feet horizontally toward the rock while belaying a top rope falling climber. The forces can be surprisingly large. The whole point of this discussion should be that, in a top-rope situation, there's no reason to skimp on the strength and static quality of the anchor. (And there's no need to oppose locking biners, which creates all kinds of potential problems.)
None of the above will come anywhere close to compromising the anchor biners. Nor will 9kn ever occur at the belay in a top rop fall, as you have claimed. (You sill holding to that claim, or have you learned something here? Just curious.)
You've presented nothing in here that I wasn't already well aware of. It doesn't help your argument to make stupid assumptions about who you are talking to.
You, on the other hand, have presented incorrect information.
Have you re-read that report yet? Do you understand it this time?
|
|
|
|
|
hugepedro
Aug 23, 2011, 9:31 PM
Post #122 of 252
(7185 views)
Shortcut
Registered: May 28, 2002
Posts: 2875
|
scrapedape wrote: And you can make that point without relying on absurd claims that a belayer could experience a 9kN load in a TR fall, which corresponds to a 15 kN load on the anchor
Actually the 15kn load would be on the climber's end of the rope, 24kn at the anchor, which makes his claim obviously ridiculous to anyone that knows even just a little bit about this subject.
There's a reason the UIAA standards limit the force on the climber to <12kn, because the human body is not designed to survive higher loads. Anyone ever heard of a top rope climber dying or being seriously injured in a fall that didn't involve a collision with another object? Hahahaha, such silliness.
|
|
|
|
|
sherpa79
Aug 23, 2011, 11:59 PM
Post #123 of 252
(7165 views)
Shortcut
Registered: Dec 15, 2004
Posts: 108
|
This discussion has devolved into wankery.
Most people don't understand, or at least cannot accurately guess precisely what kinds of loads happen in climbing scenarios. Unless you clip a dynomometer onto every piece of protection on the outside chance that you'll fall on it and we'll all learn something...
However, rescueman, you are making some pretty outrageous claims that most folks just won't believe, me included. I give dynamic belays to items falling onto an anchor that exceed in weight what the standard "rescue load" is. And I do all of this at height and next to the anchor. If I didn't have a good working knowledge of what kinds of forces can be generated by falling masses based upon distance, elongation of the rope, characteristics of the belay, and weight, I'd quite simply be dead.
Can I do the math reliably? No. But I don't teach. I DO.
And back to the original post. There has been some bandying about of the idea that jacketing cord in webbing is a good idea. I've done this and it has merits in very specific circumstances. However, as one who has fed 20 or 30 feet of cord through webbing, you don't really want to waste that time.
What if the cord underneath has been abraided? How will you know, but if you take it out and look and waste even further time stuffing it back in there. Use a burly material (and here I agree with rescueman) and further use a rope pad if you are worried about it. The advantage of the rope pad is that it allows you to inspect your anchor material.
So, my advice would be not to jacket your 6 mil cord in webbing to make the top rope anchor. Just use the webbing and be done. Pad it if necessary.
|
|
|
|
|
sherpa79
Aug 24, 2011, 12:46 AM
Post #124 of 252
(7159 views)
Shortcut
Registered: Dec 15, 2004
Posts: 108
|
Also, if we were generating 9+ kilonewtons anywhere in the system on a top rope and assuming 2 opposite and opposed biners at 22 kn's apiece aren't we still way under a 10:1 safety margin? Shouldn't we be using O+O steel carabiners for that? Or is there some trail of dead bodies I can follow
|
|
|
|
|
SillyG
Aug 24, 2011, 12:49 AM
Post #125 of 252
(7158 views)
Shortcut
Registered: Oct 19, 2010
Posts: 12
|
Very lively discussion guys. Thanks for the input. So I just went ahead and bought some 11mm static rope to setup my anchors. My rigged setup is pictured below.
I know some folks don't like the clove hitch (it's adjustable!) and others don't like the two loops on a bite at the master point (it makes me happy), but all I really want is to prevent falling to my death! Hopefully this will do the job. :)
Thanks again for your insight. It's been a real help and might have contributed to my long life!
Opposite/opposed locking 'biners on two loops made from overhands on a bite. I know O and O doesn't matter for lockers, but it helps me remember to pay attention.
One leg is a figure eight. The master point is made to length and the second leg is adjusted on a clove hitch to equalize the anchor.
For those of you who don't like clove hitches, what knot would you suggest and why is it better?
*edit: I bought *static* rope, not dynamic. ;p
(This post was edited by SillyG on Aug 24, 2011, 12:55 AM)
|
|
|
|
|
|
|
|
|
