Using a pulley on a toprope
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Anyone ever do this? I've seen folks do it near the Ocoee, TN area but i've never tried it, personally. Just observing the operation it seemed like they had a great deal of upward pull on the belay (stitch plate if i recall correctly) but the belayer was backed up pretty good; slung to tree trunks and what not. I chatted with the group doing this and their contention was that it was less stress on the rope. I can see that argument but I'm just soliciting some feedback from folks who have done it. I'm not quite sold on it... :/ |
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For the visual folks such as myself: Toprope pulley effects |
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Friction in the top anchor changes the impact force by causing more energy to be absorbed by the load strand than by the brake strand. This imbalance increases the force on the falling climber and partially negates the reduction of force on the top anchor due to the decreased pulley effect. |
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I've used a pulley at the top before, it makes it easier for the belayer to take up rope, but the belayer MUST BE ANCHORED as there isn't friction in the system to offset the load of a falling climber. It also takes away from the time an inatentive belayer has to stop a fall if they can't close their hand fast enough. |
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I saw some noobs climbing once the belayer looked like a 110 pound female and climber a 180 pound male, he fell she got lifted off the ground... funny to watch. |
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I've never used pulleys in an outdoor TR setting. The most I'll do is triple stack oval biners at the masterpoint to create a more moderate shear edge for the rope to run through. I don't really notice any difference on the belayer with this method, but I don't know that it helps increase rope life either. |
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From personal experience I highly do NOT recommend using a pulley on a toprope. |
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Jeff Fiedler wrote:Aren't you just transferring the wear from the top biners to the belay device?Good point... Hit the deck and yanked the belayer up to the top? Wow! That's like something you'd see in a cartoon. I bet there were skid marks in that belayer's bloomers! |
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Jeff Fiedler wrote:as it was I hit the ground pretty hardIndeed! With those weights and without friction, the speed when you hit the ground is almost half the speed you'd reach in a free fall of the same length. |
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I don't hold a degree in physics, so I could be wrong about this, but... |
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RiggerMortis wrote: I think a pulley on a top rope is a solution looking for a problem.Yes, and maybe even an accident looking for a place to happen. |
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RiggerMortis wrote:I don't think that the friction through the 'biner changes the amount of force on the anchor. The combined mass of climber and belay remain the same regardless of the mechanical efficiency of the pulley or 'biner. Force = Mass x Acceleration.Actually, the force on the anchor depends on the pulley efficiency. If there's friction in the pulley, the belayer can hold the climber being lowered (or falling) with a smaller force than that applied by the climber. If the efficiency is k, and the load is F, then the minimum force on the anchor that results in equilibrium is (1+k)F, which is monotonic increasing in k. If the belayer hoists the climber, it's the other way around, with the minimum force on the anchor required to raise the load decreasing with the pulley's efficiency: (1+1/k)F. In summary, if you try to stop, friction helps you; if you try to start, friction works against you. |
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Redundancy? |
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some of the force is absorbed through the rope, knot, harnesses, body deformation, belayer stance resistance from the ground/earth, & anchor rigging if using nylon cords/ropes -- it doesn't all go directly to the belay device, but certainly more than the biner friction. So what? maybe you get body weight x2 to register; anchor the belayer or belay direct off an anchor -- oh it's not cool to use a lower anchor; if you can't hold the rope don't belay, or construct rigging to hold more of the load. |