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patmay81
Apr 9, 2009, 4:05 PM
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jfitzpat wrote: Well, you can yell out that giant mutant sea monkeys live in your ass and control your brain by jabbing it with pixie sticks and I'll take your word for it. But in this case, verifiable reality is on my side.
I have never climbed at a gym that used static lines... for anything.
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acorneau
Apr 9, 2009, 4:22 PM
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jfitzpat wrote: kachoong wrote: More and more you see gyms using "gym ropes", which fall between dynamic and static ropes in terms of their elongation. Technically, they are "semi-static", with only very modest elongation.
Texas Rock Gym uses the Blue Water Dynagym 10.6 ropes:
Impact Force: 8.5kN
UIAA Falls Held: 9
Static Elongation: 5.6%
Dynamic Elongation: 32.8%
Yes, it's more "static" than a standard dynamic rope, but much more "dynamic" than a true static rope.
While it's not my cup of tea, I see guides using static ropes for top-roping all the time. No one is dying or breaking their backs by the hundreds, so I think it's a non-issue.
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westbend
Apr 9, 2009, 4:23 PM
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In reply to: Don't forget the hour long funeral after your 250 pound friend cross loads his carabiner.
A TR fall on a dynamic line is not going to generate enough force to exceed the cross loading strength of any decent carabiner.
I don't attach this way and don't advocate it. I was just pointing out that the 4-10 seconds patmay81 suggests is the difference in time does not represent the whole picture
Could have said that earlier but it is more fun this way.
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cracklover
Apr 9, 2009, 4:30 PM
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Four pages of this nonsense? Damn, I'm impressed.
GO
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bill413
Apr 9, 2009, 4:31 PM
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cracklover wrote: Four pages of this nonsense? Damn, I'm impressed.
That we've kept it so short?
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Alpine07
Apr 9, 2009, 4:34 PM
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westbend wrote: In reply to: Don't forget the hour long funeral after your 250 pound friend cross loads his carabiner. A TR fall on a dynamic line is not going to generate enough force to exceed the cross loading strength of any decent carabiner. I don't attach this way and don't advocate it. I was just pointing out that the 4-10 seconds patmay81 suggests is the difference in time does not represent the whole picture Could have said that earlier but it is more fun this way.
Maybe not, you never know, but the biner breaking is not your only worry in that situation, the gate can come unscrewed for example. This is climbing, crazy stuff happens, there is absolutely NO reason to clip in to the rope (in your normal climbing situation) rather than tying in. This subject has been beaten to death.
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antiqued
Apr 9, 2009, 4:34 PM
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jfitzpat wrote: Remember, on an industrial fall arrest system, the biner is connected directly to a shock absorbing lanyard, essentially a 'screamer', which reduces impact force on both the fallee and the biner. If you are using static line for top roping and the climber ends up with half a body length of slack, the biner is going to be subjected to more impact force than in it's designed application.
At Yates' site, industrial load limiters are described as having an activation strength of ">600lb" in one place, and "<800lb" in another (different products).
Dynamic ropes for climbing typically have 6% to 9% stretch at 80kg. Static ropes come in many types - nylon, nylon core with polyester mantle, polyester, and UHMPE cores. The ones we should be using for climbing and caving purposes are usually all nylon, and have elongations of 2 1/2 to 3% at 100kg. See the Beal site for standards, http://www.bealplanet.com/...s_static&lang=us.
These ropes are about 3x stiffer than lead ropes. If you are taking a half body length fall (0.5) on 10 m of rope, this is a fall factor of 0.05. The Petzl fall simulator seems to have disappeared, so a spring constant calculation for a 2.8% stretch (80kg) gives an impact force of 551lb in Bessems' fall calculator. That means that a biner designed to be used with 'fall arresters' should be safe for toproping on 'semi-static' lines.
All fall calculation stuff aside, if the falling climber is getting jerked with >6 kN of force, the belayer should be rising rapidly, or there is considerable friction between the belayer and climber. Is that what you expect?
PS Bessems seems to have disappeared from Google as well - I used a copy on my hard drive.
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jfitzpat
Apr 9, 2009, 4:35 PM
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stanhampton wrote: Common sense goes a long way......
I was mildly bemused by the arm waving, but this particular forum is for beginners, so a slightly more detailed answer is probably warrented.
When we say 'dynamic', we are talking about rope that is 'stretchy'. We would say that it's modulus (springyness) is about 6000 lb/ft/ft.
When we say 'static', we are talking about rope that is significantly less 'stretchy', it still has some stretch, just a lot less. I use the PMI line for static stuff, and it has a modulus of about 20000.
If we round up, we would say that the difference in stretch is a factor of 4.
Now, in falling we talk about something called a fall factor, basically a ratio of rope and distance. The worst case we look at is a fall factor of 2, you climb 5' above the belay, fall, and end up falling past the belay - you fall 10' on 5' feet of rope.
In this type of fall, the difference in impact force becomes proportional to the square root of the modulus, so the difference between the static and dynamic ropes is the square root of the factor. Sqrt(4) is 2. So falling on a static line would *double* the impact forces of a bad fall.
The puts horrible strain on the leader, and the anchor(s). So we NEVER, never, never lead on static line.
But what about top roping? Impact force is highly proportional to fall factor. In top roping, we generally have 1 to 2 times the height of the climb played out in rope, and falls are limited to slack. So the fall factor is generally very small. Even if we double it, it just isn't very big.
That is why so much TR has been done in gyms on static line and we don't hear about gobs of accidents or back wrenching falls.
Now, what about outdoors? There have been a fair amount of climbers toproping on 10-11mm static line for many, many years, and we don't see gobs of accidents suggesting that the practice is especially dangerous. Nor do we see much evidence that it is any safer.
It is true that on a tall route you can fall 3-4m and touch the ground on a dynamic line, but it is still a cushioned fall. Similarly, anchors do take more stress with static line, but at these fall factors, failure is more suggestive of a dodgy, inadaquate anchor than the choice of line.
The big differences are cost and durability. The later is why I use static line for anchoring TR, and extending anchor over the edge. I use dynamic rope for the actual climbing because it handles easier (it is less stiff and runs through the belay device better), TR is the exception for me, and I don't care about the cost of replacing dynamic lines.
Opinions are welcome to differ, but I find tying in on a biner to save 10 seconds, a pointless compromise in safety. But considering how much TR'ing actually occurs on static and near static lines in gyms, as well as years of use in the field, I find folks like Stan's intensity and insistance a little disproportionate to the measurable reality.
I hope that is clearer.
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jfitzpat
Apr 9, 2009, 4:42 PM
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acorneau wrote: \Yes, it's more "static" than a standard dynamic rope, but much more "dynamic" than a true static rope.
It is actually closer to the BW static line (modulus of about 14000) than my 10.5 mm Mammut dry line.
acorneau wrote: While it's not my cup of tea, I see guides using static ropes for top-roping all the time. No one is dying or breaking their backs by the hundreds, so I think it's a non-issue.
A point I made awhile back, but seems to be falling on deaf ears. As I just noted above, doubling the forces in a high fall factor is deadly business. Top roping? Not so much, unless the anchor is crap - in which case you shouldn't be climbing on it.
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bill413
Apr 9, 2009, 4:42 PM
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jfitzpat - nicely written.
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majid_sabet
Apr 9, 2009, 4:58 PM
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Eastern Iran, October of 2007
As I was getting ready to teach a class, I got informed that a climber fell to his death during TR so I called up the local climbing group to find out what had happened. It appeared that a very experienced sport climber was climbing under an over hanging wall (5.10+ on TR via biner) and somehow he falls near the end of the route. During his fall, his body rotates the rope and opens the gate (had a petzl locking biner which came unlock somewhere in the TR maneuver) and fell 12 meter to the ground.
Subject did not wear a helmet (almost all sport climbers do not wear helmet) and died from sever head injury 15 minutes later at the scene.
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jfitzpat
Apr 10, 2009, 4:56 PM
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antiqued wrote: That means that a biner designed to be used with 'fall arresters' should be safe for toproping on 'semi-static' lines. All fall calculation stuff aside, if the falling climber is getting jerked with >6 kN of force, the belayer should be rising rapidly, or there is considerable friction between the belayer and climber. Is that what you expect?
Sorry, I missed this before. Yes, that is about what I expect. The semi-static is about 3 times stiffer, static line is about 3.5 times stiffer (I rounded up to 4 above).
Properly rigged, the steel stuff is plenty strong. For that matter, properly rigged, a good alum. biner is plenty strong. But when anything goes amiss, strength plummets with the alum. I don't have one in front of me, but the Black Diamond biners I use a lot are something like 25 kN closed, 9 kN open, and 7 kN cross loaded.
As we can see from the accident right above, once a gate is open, bad things can happen without anything breaking at all.
I'm not saying that the practice is spectacularly dangerous, I just don't see that benefit for the extra complexity and additional failure point. I've been out to, say, Planet of the Apes wall, and I just don't get it. If you are going to spending all that time hanging on line and stuffing your hands in your backside rooting around for chalk, what's half a minute more changing climbers?
On the other hand, compared to the American Triangles rigged on manky bolts in soft rock, a locking biner clip in seems relatively safe...
I really can't be too nasty to Stan because I used to be a 'Crag Safety Douche' myself. My face would pucker up, like a toddler getting ready to make a poo, and I would lecture. Like alcoholism, you're never really over it. I still say the stuff in my head, but limit myself only to offering extra gear as politely and non judgementally as I can when something sets of the alarm bells in my head.
(This post was edited by jfitzpat on Apr 10, 2009, 4:57 PM)
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antiqued
Apr 10, 2009, 6:50 PM
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jfitzpat wrote: antiqued wrote: That means that a biner designed to be used with 'fall arresters' should be safe for toproping on 'semi-static' lines. All fall calculation stuff aside, if the falling climber is getting jerked with >6 kN of force, the belayer should be rising rapidly, or there is considerable friction between the belayer and climber. Is that what you expect? . Yes, that is about what I expect. I'm not saying that the practice is spectacularly dangerous, I just don't see that benefit for the extra complexity and additional failure point. .
The whole practice of climbers clipping in instead of tying in is bogus. A practiced one can tie in pretty quickly, and a really experienced one can make his own judgment of risks.
So the only people clipping in are ones who don't know how (or can't be trusted) to tie in. If they might become climbers, then they should learn. If they are just tourists, and you can't spare someone to supervise them, then the double biner clip in may be safest.
But I was writing about static ropes - you may expect that belayers get jerked up by 3 foot falls, but I was hoping you would report such actual experiences. I think that in a real 3 foot fall, much of the energy will go into knot tightening, buttock bouncing, etc, and a doubly or triply stiff rope will hardly be noticed. And a fall calculator says so without including any of those effects. But I dont' have a static to experiment with.
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jfitzpat
Apr 10, 2009, 7:37 PM
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antiqued wrote: But I was writing about static ropes - you may expect that belayers get jerked up by 3 foot falls, but I was hoping you would report such actual experiences. I think that in a real 3 foot fall, much of the energy will go into knot tightening, buttock bouncing, etc, and a doubly or triply stiff rope will hardly be noticed. And a fall calculator says so without including any of those effects. But I dont' have a static to experiment with.
I've climbed on static line at a gym, but don't generally take a 3' fall. If the belayer is that screwed up, I'm tripping on the line.
Practically speaking, the belayer is going to get jerked twice as hard with the static line as with the dynamic line. But how hard that is depends on a bunch of factors. Remember, climber, anchor, and belayer form a load triangle. How much is divided between the belayer and the anchor will depend on the friction and the angles.
The tie in point and anchor generally receive a higher peak 'shock' force, because the system often momentarily acts like a shorter rope (climber to anchor). You can measure this in experiments, but it is hard to precisely predict (like the sometimes herculean force it seems to require to pull down a rap line looped over webbing).
I'm sorry if I'm not understanding your question.
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