Key takeaways
- A Z-pulley (Z-drag) is a 3:1 mechanical-advantage rope hauling system in a Z-shaped rigging.
- Pulling three feet of rope raises the load one foot — enough for one or two to haul a person out.
- It's a cornerstone of crevasse rescue, using an anchor, a progress-capture prusik, and a hauling prusik.
- It can be combined/compounded for greater mechanical advantage in harder hauls.
From the Z-shape of the rigged rope.
This is general educational information, not instruction. Crevasse rescue is life-critical — learn it hands-on with qualified instruction and practice it before you need it.
What a Z-pulley is
A Z-pulley (or Z-drag) is a rope hauling system that provides a 3:1 mechanical advantage, rigged in a Z-shaped configuration with pulleys and friction hitches so that pulling three feet of rope raises the load one foot — making it possible for one or two people to haul a fallen climber out of a crevasse.
How it works
It uses an anchor, a progress-capture prusik or pulley near the anchor (which grips the rope so the load doesn’t slide back when you rest), and a hauling prusik further down the loaded rope, with a pulley redirecting the haul. As you pull, the system multiplies your force threefold; the progress-capture device holds each gain as you reset and pull again — ratcheting the load upward.
After a teammate drops into a crevasse, the remaining climbers build an anchor, rig a Z-pulley off it, and haul — the 3:1 advantage letting two people steadily raise their partner’s full weight up over the lip, resetting the hauling prusik with each pull.
Where it’s used
Most famously in crevasse rescue, when a member of a roped team falls into a crevasse during glacier travel. The same principle appears in other rescue and hauling scenarios, and for very heavy or high-friction hauls the Z-pulley can be compounded with additional systems for even more advantage.
The bottom line
A Z-pulley (Z-drag) is a 3:1 mechanical-advantage hauling system rigged in a Z shape with pulleys and prusiks — pull three feet of rope, raise the load one foot — making it possible for a small team to haul a climber out of a crevasse. With an anchor, a progress-capture prusik, and a hauling prusik, it's the cornerstone of crevasse rescue, and can be compounded for harder hauls.
Frequently asked questions
What is a Z-pulley?
A Z-pulley (or Z-drag) is a rope hauling system that gives a 3:1 mechanical advantage, set up so the rope runs in a Z shape through pulleys and friction hitches. The mechanical advantage means that for every three feet of rope you pull, the load rises about one foot — making it feasible for a small team, or even one person, to haul a fallen climber up out of a crevasse.
How does the Z-pulley work?
It uses an anchor, a 'progress-capture' prusik or pulley near the anchor (which grips the rope so the load doesn't slide back when you rest), and a 'hauling' prusik further down the loaded rope, with a pulley redirecting the haul. As you pull, the system multiplies your force threefold; the progress-capture device holds the gain each time you reset and pull again. The result is a 3:1 advantage that ratchets the load upward.
Where is the Z-pulley used?
Most famously in crevasse rescue, where a member of a roped team falls into a crevasse and the others must haul them out — the 3:1 advantage makes this possible despite the friction and weight involved. The same mechanical-advantage principle is used in other rescue and hauling scenarios (and in swiftwater and rescue work). For very heavy or high-friction hauls, the Z-pulley can be compounded with additional systems for even more advantage.
Sources
- Crevasse rescue — American Alpine Club
- Mountaineering: The Freedom of the Hills — The Mountaineers