hey brenta....

silly mistake on my part. I didn't properly add the forces together :-/ I'm embarressed now. Although in my defense it was late and I was working on econ.

You are of course correct.

I suppose that's what I get for trying to find threads to look smart on...

it is really, really sad to see how many climbers have no idea how gear works, or what its limitations are. jerome, i really hope you don't kill yourself, or worse yet, somebody else some day.

ian, good job of looking at this, one thing that you are not addressing is the acceleration aspect of the situation. say for instance, your friend of equal weight is toproping the route and in the middle of a move, he comes off. let's also say that there is a small amount of slack in the rope. your body weight is not only going to be needed to counterweight his static weight, but also to decelerate his downward movement. the combo of these two things is known as the peak force. this will pull you off the ground if you are using a pulley. even if the climber is of LESS weight the peak force (sum of his static weight plus the force needed to decellerate his fall) could potentially pull a belayer off the ground. This gets a LOT worse if the climber outweighs the belayer.

similarly, when the belayer is lowering the climber, if he isn't lowering at a perfectly constant speed, the change in speed (ie acceleration) is going to cause force that will need to be counteracted. this, again, could result in the belayer being lifted. the thing with using a pulley, is that there is very little friction to help control this. jerome, if the only friction in the system is at the belay device, and the device is locked off, where is the friction going to come from to prohibit movement?

when a lead climber (or toproper for that matter) falls on gear it is ultimately the friction in the system that stops him. if there was no friction in the system, he would simply yank his belayer up to the top piece (actually the climber would probably hit the ground first). this is one of the reasons that you have to be very careful about when and if to use a revolver. if you have a ton of rope drag (ie friction) in your system, then the revolver can be of help. however, if you have very little friction in your system, i would avoid using a revolver.

one of the common things that climbers don't realize is the amount of force that can be involved in toproping. most climbers think that the total anchor force will be equal to the sum of the belayer and climber's weights in the event of a TR fall. this is fairly close to true if you are using a static rope and a snug belay. however, with a dynamic rope and a typical belay, when the climber falls there will be rope stretch. the rope stretch will cause the climber to move downwards, which will need to be declerated. either rock and ice or climbing magazine did a test on toprope forces several years ago. if i remember correctly, the total peak force on the anchor was typically 2 to 4 times the combined weight of the climbers.

I can see everyone's point on the use of a pulley.

Don't really see why talking about an idea means they're an idiot or need to be called an idiot. Jerome is not gonna go out and kill people. I'd say he has been quite the contrary.

On the same token, everybody fucks up. It doesn't matter what the experience, talent, education, proficiency, preparedness, etc. someone has. One of the best climbers in the world forgot to retrace her 8. No-one on this site is any better.

This got me thinking a little bit about friction on the 'biner in a lead climbing situation. For example, if there are many pieces between the leader and the belayer, all those pieces tend to absorb quite a lot of the force during a fall, as long as they're not in a perfect line straight to the belayer. But my own empirical experience suggests that a single point (normal carabiner) absorbs quite a lot more of the force than what some of these theoretical musings might lead one to believe. I weigh between 30 and 50 lbs more than most of my partners, but on the occasions where I've been above and then fallen on the first piece, they certainly haven't gotten yanked too far. Maybe rope stretch, friction on the single carabiner, etc. are absorbing much more of the force than the equations indicate...? Nonetheless, I'm not sure I'd use one of those "revolver" 'biners for ANY normal climbing situation.

Richard, I'd see it useful for managing drag when a leader needs no drag. Certainly getting into a lie-back/overhang and having rope drag when trying to pull the moves is scary. Therein is the choice, count on the belay or your climbing ability. I go for my ability & fire the section without the rope pulling me down. I think I'm safer as a lead climber here.

Another useful application I think would be a seconding change of direction/vector placement, this would enable the belayer to work the rope with much less friction when bringing up a second.

Of course if the belayer is anchored like he's supposed to be that is all academic.

This has all got me thinking about how my TR anchor's will only be as strong as the weakest point.

Is a single sling fashioned into a sliding x or even a cordelette ok for a TR, which is after all the whole ball of wax? I know rapping off of a single runner is commonplace.

I suppose using the big static line as a sling/cordelette would take care of everything since it is stronger than the climbing rope.

brent,

actually you are incorrect. you are looking at this purely static, which is rarely the case. if you were belaying with a dynamic rope, and had it mega tight, such that the climber didn't drop at all, then i would basically agree. also, if you were to say that belaying with a static rope and some slack would cause a higher force, i would agree. however...

here is a link to a good paper that explains what is going on.

http://www.amrg.org/Rope_system_analysis_Attaway.pdf

Look at Example 0 on page 5. In the example, the climber is being belayed from above, and note that when the toproping climber falls, there is an amplification in force that is caused by the extra rope force necessary to decelerate him when he drops a certain distance. so, the peak force ends up being the sum of the climber's static weight + the extra force needed to bring him to a stop. the auther calculates this total factor to be approximately 2.0.

note that in this example, the climber is being directly belayed from above. if he was being belayed through a redirect (ie texas slingshot style), this total force from the climber's side would have to be counter balanced on the belay side. so, the total factor would be 4 times the climber's static weight (given a frictionless redirect point). however, friction through the biners at the redirect point provide friction to help out (as long as you aren't using a revolver or some other pulley). the interesting thing about friction is that it acts in the opposite direction of the moving body, so it is handy for adding control to the system.

ah, once more into the fray (and once more against my better judgment):

my original point was that a pair of locking revolvers would be ideal for a toprope anchor system. Why? Reduced wear on biners and rope and reduced rope drag at the anchor (i.e. friction). What? Reduced friction at the anchor you say! Heavens no! We shall all be imperiled and perhaps even lifted off the ground! NEVER! Jerome is a know-nothing so-and-so.

Well, here in the real world, the only really important (i.e. worthy of concern) forces in a toprope system are belay friction and rope stretch. Period. No, exclamation point. If the climber is much heavier than the belayer, the belayer should be anchored. Always. Sure, there is some friction supplied by the anchor biners but if you're rigging your toprope system based on the friction supplied by the anchor biners then I'm sure not going climbing with you. There, I said it.

Jerome

Jerome, thanks for clarifying your stance. Kudos for deflecting the insults and condescending remarks with flair and composure. I see where you're coming from. I still think that the friction at the top anchor is far from inconsequential. If a pulley were used, the belayer would have to be anchored even if the climber were about the same weight. On the other hand, you are quite right that one cannot always rely on friction at the anchor to make toproping safe.

Real-world results:
I've got a couple of non-locking DMM Revolvers. This spring I tested this very idea. It seemed that it would be much kinder to the rope.
(*note: before you say it - I know, two lockers at the top are the only smart way to go. I was conducting a test and I'm not claiming to be smart.)
I weigh 165 and my partner weighs about 145. We used a 9.9mm rope and a Trango B-52 device, which runs slicker than most. Neither of us liked the results. Both of us fell attempting the climb (it was harder than we were willing to lead), but we didn't get jerked off the ground. The rope didn't contact the rock, but the angle wasn't straight vertical. It was difficult to control the speed while lowering the climber. If I were to try it again, I would put two identical biners at the belay device to increase the friction there.

Greg, thanks for reporting your test. I was wondering if you noticed either of these: (1) The rope is pinched between the spines of the two (opposed) Revolvers; (2) the two pulleys rub against each other reducing the overall efficiency.

These are just conjectures, since I have only one (wiregate) DMM Revolver, which I use from time to time to reduce rope drag. Hence, I cannot try your experiment.

As for the fact that neither of you was yanked off the ground when the other fell, it may have to do with energy dissipation in the rope itself. (Real ropes behave very differently from ideal springs during falls.)

You guys can sit here arguing mathmatics until the cows come home, but the best way to test the performance of these carabiners is to test drive them in the real world.

I can tell you that, at $25.95 plus tax, you are looking at $415.00 to equip the rope end of 15 quickdraws with these things. That equates to the price of two good 70m ropes.

Add up the cost, the cheesy wire gates, and a few seasons of dirt in the pully bearings and general bearing wear, and you've got a very expensive gimmick.

I'll take my Petzl Spirits, anyday.

I'd keep one around for rescue or hauling applications, maybe for a high-angle redirect, but certainly not for standard climbing usage.

I see. I'm sure you don't need to be warned against paying too much attention to ads. If one listened to Metolius, one would buy less than two meters of accessory cord for $19.95. It's like paying $700 for a 70 m rope...

As for the academic discussion, I hope we agree that both theory without experiment and experiment without theory don't go very far.

brenta -
I didn't notice if the pulleys rubbed together. They appeared to run fine when I was rigging it up and pulling down hard on each side by hand.
I don't plan on buying more of these, but having a couple on my rack is nice. They each live on the end of a 4' runner where they are most likely to do some good on lead. Mostly I use them to redirect the belay for the second and to haul the pig with a jumar.
-gg

brenta,

i apologize for nor reading your previous post more carefully, for some reason i had thought that you were saying the force on the anchor (as opposed to the tension in the rope) was doubled. i think we are more or less on the same page.

jerome,

first, i apologize for being so harsh. however, i still think that using the revolvers at the anchor is wrong though. the friction through anchor biners IS an important part of the system, not inconsequential. as far as anchoring a lighter belayer, that isn't ALWAYS practical, particularly if there isn't anything to anchor to, or if choss is raining down from above.

ken summed it up pretty well though. pretty expensive gimmick to avoid wearing out a couple normal biners.