Friction in Climber Rescue

Mechanical advantage systems are a cornerstone of climbing and rescue rigging, providing the means to move loads with less effort—or so we’ve traditionally thought. Richard Delaney of Rope Lab, in collaboration with the Rigging Lab Academy, explores how friction can undermine the effectiveness of a well-known mechanical advantage system, revealing hard truths about what we’ve been teaching for decades.

1. The Scenario: Top Rope Top Belay with a V Anchor

In this setup:

• A top rope top belay system is employed, using a V anchor for stability and redundancy.
• A climber reaches the crux of the climb but can’t progress without assistance.
• Traditionally, we manage this with a mechanical advantage system to help the climber complete the move.

2. Setting Up the Mechanical Advantage System

• System Components:
  • A GriGri 2 as an auto-locking belay device.
  • A 7mm Prusik loop with a Klemheist hitch for friction control.
  • A pulley for redirection and reducing effort.
• Setup Process:
  • Wrap the Prusik loop around the host rope with three full turns.
  • Add an overhand knot to shorten the throw.
  • Attach the carabiner and pulley to complete the Z-drag system.

Traditionally, this system is taught as providing a 3:1 mechanical advantage, meaning for every unit of force applied, three units of force are exerted on the load.

3. The Reality: The Hidden Impact of Friction

Richard reveals a key oversight in the system: friction dramatically reduces mechanical advantage.

• Friction Points in the System:
  1. The Edge:
     • The rope passes over a 90-degree rock or concrete edge, introducing a 1:2 friction disadvantage (halving the force transmitted).
  2. The Pulley or GriGri:
     • The rope bends 180 degrees around a metallic object, such as the GriGri or pulley.
     • This introduces another 1:2 friction disadvantage.
• The Combined Effect:
  • Each friction point reduces efficiency, compounding the disadvantage.
  • Instead of achieving the ideal 3:1 mechanical advantage, the system effectively operates at a 1:1 mechanical advantage.
  • In practical terms, the belayer must exert the same force as the climber’s weight to assist their movement.

4. Lessons Learned

Richard emphasizes the need to rethink and adjust our teachings:

• Friction’s Impact:
  • Friction over edges and through devices dramatically reduces system efficiency.
  • It’s critical to consider these factors when designing or teaching mechanical advantage systems.
• Testing and Validation:
  • Rigging systems must be tested under real-world conditions to validate their effectiveness.
  • Theoretical mechanical advantage does not always translate to practical performance.
• Future Considerations:
  • Explore alternative setups or tools, such as high-efficiency pulleys or edge protection, to mitigate friction.
  • Teach climbers and rescuers to evaluate their systems critically.

Conclusion

For decades, the Z-drag mechanical advantage system has been taught as a simple and effective solution for assisting climbers. However, as Richard Delaney demonstrates, friction significantly reduces its efficiency, turning a theoretical 3:1 advantage into an actual 1:1. This revelation underscores the importance of challenging assumptions and evolving our practices to ensure safety and effectiveness in climbing and rescue.

Reference for Friction in Climber Rescue

• Climber Rescue: Passing Knot Cordallete
• Mechanical Ascenders for Rope Rescue Systems
• Rope Rescue Training for New Recruits

Peace on your Days

Lance