Is a pulley system progression worth it in practice?
The practical question in any rope rescue haul is this: when the load gets heavy, do you step up to a higher mechanical advantage? And if you do, is the gain worth the time and complexity of reconfiguring the system? This article tests a series of pulley system progressions from a 3:1 simple through to an 11:1 complex, using load cells to compare predicted efficiency at 90% pulley efficiency against what the hauler actually felt. Two specific questions drove the testing.
What is a pulley system progression
A progression means stepping from a smaller mechanical advantage to a larger one — say from a 3:1 simple (3:1s) up through a 3:1 with change of direction (3:1sCD), to a 5:1 simple, and eventually to a 9:1 compound (9:1c) — as the haul gets harder.
You start with the smallest MA that makes hauling efficient for your load, team size, distance, and expected friction. A team of two with efficient pulleys can typically haul a 100kg load on a 3:1s without difficulty. When conditions change — load increases, haulers fatigue, friction rises — the question is which system to progress to, and whether the step up is worth making.
You have a progression planned and can go from one pulley system to the next to increase (or decrease) MA. Below is a complex pulley-system progression that integrates with the simple-to-compound progression above as needed.
For more detailed information:
Rope Rescue & Rigging Field Guide
for Cave, Canyon, Alpine and Rock
A waterproof, A6 field guide covering knots, anchors, lowering, pulleys, changeovers, and stretcher rigging for backcountry rope rescue — built for teams who carry their gear on foot.
Questions
These are the two questions I had regarding Pulley System Progressions:
- When you step up to the next pulley system in a progression, does it actually reduce the force on the haulers in practice?
- Are there any pulley systems in the progression that stand out as noticeably more or less efficient than the others?
Theory
We used the T (tension) method to calculate MA, first assuming 100% efficient pulleys, then at 90% — close to the 91% Petzl records for the Partner and Mini pulleys used in testing.
At 90% efficiency, the 3:1s becomes a 2.71:1. Friction compounds as the system grows, so the gap between theoretical and real-world MA widens with each additional pulley.
Equipment, Setup and Method
Equipment
- Load cells: ×2 Rock Exotica/CMC Enforcers, ±2% accuracy, 0.02kN increments
- Rope: 9.5mm Kordas Fina semi-static Type A (EN1891), 4.1% elongation, breaking strength 26.3kN
- Pulleys: Petzl Mini and Partner (91% efficiency)
- Redirect: Rock Exotica Large Omni Block
- Rope grabs: Petzl Tibloc, Petzl Basic
- Load: rocks in an Aspiring 75L PVC bag
- Hauler: one person via cowstail on harness
Setup
Method
- Load cells were zeroed before each test.
- The premade 5:1 was tested first to establish baseline force at the end of the system after the redirect pulley (0.92kN).
- For all subsequent tests, I walked back, monitoring the load cell, checking that max and actual readings were consistent, and hauling the load approximately 1m off the ground before stopping.
Results
Mechanical Advantage (MA) calculations were performed in a spreadsheet and rounded to two decimal places only at the final step.
- MA 100% — theoretical MA with no pulley friction
- MA 90% — theoretical MA at 10% friction loss per pulley
- Haulers 100% — force required with no friction
- Haulers 90% — force required at 10% friction loss per pulley
- Actual — measured force at the haul end. As baseline force was 0.92kN, all values were multiplied by 1.087 to normalise to 1kN
- Difference — gap between Haulers 90% and Actual
Conclusions
1. Is progressing to a higher MA worth it in practice?
- Yes. With efficient pulleys, the measured results tracked closely with the predicted 90% efficiency values, and each step up in the progression produced a genuine reduction in hauling force.
- As the hauler in the test, the difference was tangible — not just a change in the numbers.
2. Are there any pulley systems in the progression that stand out as more or less efficient than the others?
Two findings are worth noting.
- The 5:1cx and 5:1s perform almost identically, despite the 5:1s using four pulleys and the 5:1cx using only three. The reason comes down to how the travelling pulleys act on the load: in the 5:1s, both attach to the same rope grab and act directly; in the 5:1cx, one goes around a fixed pulley first, introducing a slight inefficiency that offsets the advantage of having fewer components.
- The 3:1sCD performs poorly when pulling in the opposite direction. Test results showed the hauliers apply 48% of the load — roughly half — making it a poor choice for pulling downhill or away from an anchor. For those situations, use the 5:1cx instead.
Want to learn more about:
Rope Rescue Training
for Cave, Canyon, Alpine and Rock
If you’re working through this with a team, Over the Edge Rescue training courses can be delivered in your environment using your own equipment — which makes the progression from theory to fieldwork considerably faster.
