Using a pulley on a toprope

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... :/

Drilling down into this a little.... According to Petzl, in a carabiner toprope setup, the force loss due to friction through the anchor biner is 34%. That is, 34% of the climber-generated force is lost through the anchor biner leaving 66% to be absorbed at the belay. Conversely, assuming a 0% force loss through a bearing'ed type pulley toprope setup, 100% of the fall force is left to be absorbed at the belay. Now i'm no physicist so please correct me if i'm wrong here but the force on the anchor should be the sum of the force on either side of the a frictionless pulley. This means the climber fall force x2 is exerted on the anchor. So not only would the pulley (vice biner) at the anchor increase load on the belayer but also on the anchor as well (right?).

So to put this to practical example: If a 600lb fall force is generated on both a biner-anchor toprope and a pulley-anchor toprope the following values are derived (rounded for simplicity):

Biner-anchor:
Fall force at climber: 600 lb
Force at belay: 400 lb
Force at anchor: 1000 lb

Pulley anchor:
Fall force at climber: 600 lb
Force at belay: 600 lb
Force at anchor: 1200 lb

You save a little wear on your sheath, sure but is it worth 200lb difference on both belayer and anchor?? The rope, anchors, belayer... the whole system suffers. The only component that doesn't seem affected is anything between the pulley/anchor and the climber. Someone please correct me if I'm dorking this up (it's been a long day, I've had a couple Coronas...)

CMI actually markets some of their pulleys with toproping verbiage mentioned in the description. ...unless i'm reading that wrong.

For the visual folks such as myself:

Toprope pulley effects
And for the record, i am, by no means, stating this as fact. I'm posting this as a question more than anything - looking for inputs and opinions.

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.

On the other hand, some kinetic energy is turned into heat at the top anchor because of friction.

Petzl's Fall Simulator. The simulator is for leader fall, but it allows one to play with various parameters and get a feel for the effect of friction in the system.

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.

I won't use a pulley any more, the added friction that a biner puts into the system helps soften the fall of the climber, besides replacing rope needs to happen more often than most of us want to believe anyway, so sheath wear is minimal to rope life...unless you fall continually, in which case the rope still needs to be replaced.

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.

Edit: they were using like a 3inch pulley

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.

In gyms and ropes courses, I have seen the use of Shear Reduction Devices, which look like a pulley, but the castor doesn't roll. Basically, its just a nice large diameter rounded edge for the rope to run over. I have scene these significantly increase rope life, but there is more force on the belayer.

IMHO(which might not be worth much) a SRD or pulley might offer an advantage in terms of rope life in an institutionalized setting with day after day use and a good floor anchor. Otherwise, it's not worth it.

From personal experience I highly do NOT recommend using a pulley on a toprope.

Very early in my climbing days, before I knew any better, I got on a top rope rigged with a regular crevase rescue style pulley (i.e., small diameter). I'm 200+, belayer was a skinny guy, maybe 150 (?). Just taking gently at the top I yanked him clean and fast to the top of the climb. Funny now, but we were very lucky not to get someone seriously hurt, and as it was I hit the ground pretty hard and got a bit of rope burn.

That rationale, saving rope wear, seems screwy to me. Aren't you just transferring the wear from the top biners to the belay device? The rope has to build up friction somewhere to hold the weight. And safety-wise you need a belayer really on the ball.

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!

Jeff Fiedler wrote:as it was I hit the ground pretty hard

Indeed! 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.

I don't hold a degree in physics, so I could be wrong about this, but...

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.

I think a pulley on a top rope is a solution looking for a problem.

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.

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.

Redundancy?

JF

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.

Something to consider with these pulleys, they are meant for for reducing rope drag on lead -- how bout catching a whipper with pulley-ed placements & also incorporating 1/2 ropes, I'd like to see the belayer's hands after this one.