Mechanical Advantage Systems

TOPIC: MECHANICAL ADVANTAGE SYSTEMS TIME REQUIRED: THREE HOURS MATERIALS: ROPE, WEBBING, HARNESSES, CARABINERS, FIGURE EIGHTS, ASCENDERS, PULLEYS, PRUSSIC CORDS, SLINGS, PICKETS, SLEDGE HAMMER REFERENCES: RESCUE TECHNICIAN, MARYLAND FIRE...


      0. Attach an ascender or prussic cord between the first ascender or prussic cord and the first

          pulley but close to the pulley (this ascender or prussic cord serves as the brake for the system)

NOTE: If ascenders are being used, make sure they facing the load as denoted by the arrow on the side

       0. Connect the ascender or prussic cord to the sling or prussic cord at the anchor point using a

           carabiner (may require a longer prussic cord or a piece of webbing)

       0. Stretch out the rope to make sure that nothing is twisted and the system is laid out properly

       0. Make sure all carabiners are locked before applying any load

       0. Additional pulleys and ascenders or prussic cords can be added to increase mechanical

           advantage (the system as outlined above produces a 3:1 mechanical advantage based on two

           pulleys and pulling (hauling) in the direction that the load is moving)

       0. As the load is moved inward, the pulleys will be drawn closer together which requires setting

           the brake and moving the pulleys outward so that additional space is available on the rope to

           move the load

       0. Load being moved outward should have the pulleys placed as close together as possible since

           they will be moved outward as the load moved; the brake may need to be set to move the

           pulleys closer

B. Constructing a Piggy-Back Z-rig

NOTE: A piggy-back system is used to apply mechanical advantage to a rope that is being used for hauling or lifting

  1. Place a sling or piece of webbing around a secondary anchor point

  2. Attach an ascender or prussic cord to the original hauling/lifting rope

  3. Connect the ascender or prussic cord to the sling or piece of webbing using a carabiner (this will

      hold the original hauling/lifting line in place as well as a brake when the system needs to be

      adjusted)

  4. Lay the rope out in the shape of a “Z”

  5. Determine which end of the rope will be attached to the load and which end will be used for hauling

      (pulling)

  6. Place a pulley at each of the two bights in the rope

  7. Attach an ascender or prussic cord to the rope near where it is to be attached to the hauling/lifting

      rope

  8. Pull the pulley in the second bight to the ascender or prussic cord and connect the pulley using a

      carabiner

  9. Secure the pulley at the first bight to the sling or piece of webbing used at the anchor point using a

      carabiner

  10. Attach an ascender or prussic cord between the first ascender or prussic cord and the first pulley

        but close to the pulley (this ascender or prussic cord serves as the brake for the system)

NOTE: If ascenders are being used, make sure they facing the load as denoted by the arrow on the side

  11. Connect the ascender or prussic cord to the sling or piece of webbing at the anchor point using a

        carabiner (may require a longer prussic cord or a piece of webbing)

  12. Form a figure eight on a bight on the rope that is to be attached to the original rope

  13. Attach the ascender or prussic cord to the original hauling/lifting rope

  14. Connect the figure eight on a bight to the ascender or prussic cord on the original rope using a

        carabiner

  15. Stretch out the rope to make sure that nothing is twisted and the system is laid out properly

  16. Make sure that all carabiners are locked before applying any load

  17. Additional pulleys and ascenders or prussic cords can be added to increase mechanical

        advantage (the system as outlined above produces a 3:1 mechanical advantage based on two

        pulleys and pulling (hauling) in the direction that the load is moving)

  18. As the load is moved inward, the pulleys will be drawn closer together which requires setting the

        brake and moving the pulleys outward so that additional space is available on the rope to move