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...


  3. Apparatus (sturdy components) such as steamer connections, chassis, or tow hooks

  4. Picket systems

             . One-inch steel

             . Four-inch hardwood or five-inch softwood

             . Five feet long

             . Three pickets are driven into the ground in a straight line in line with load to be moved

             . Pickets should be spaced at least three feet apart

             . Pickets should be driven in approximately two-thirds of their length and at a 90-degree angle

               of the load

             . Holdfast is formed by wrapping rope approximately 50 feet long between the top of the first

               picket and the bottom of the second picket with four to six wraps (finish off each end of the

               rope with a clove hitch)

             . Wrapping is repeated between the second picket and third picket using a separate piece of

                rope

            . Short object such as a piece of wood is inserted in the middle of the rope between the first

              and second pickets, three or four twists are made to tighten the rope, and the object is

              secured in the ground

            . Picket tightening process is repeated between the second and third pickets

           . Bottom portion of the first picket should be used as the anchor point

           . Three-picket system will support about 4,000 pounds depending on the firmness of the soil

B. Anchoring to Objects

  1. Single point

      a. Tying a knot or placing a sling or piece of webbing around a single object

      b. One method is to wrap the sling or piece of webbing formed in a loop around the anchor and

          connecting the two bights using a carabiner

      c. Second method is to wrap the piece of webbing around the anchor three times, connect the two

         ends together using a water knot, and pull two of the wraps and connect a carabiner to them

         (wrap three, pull two)

      d. Tensionless consists of wrapping a rope around an anchor point several times, placing a figure

          eight on a bight in the working end, attaching a carabiner to the knot, and placing the other end

          of the carabiner over the standing part of the rope

  2. Multiple points

      a. Tying a sling or piece of webbing around multiple objects either in line or adjacent to one another

      b. Using three picket or trees in line with the second and third pickets or trees backing up the first

      c. Using pickets or trees adjacent to one another where a sling or piece of webbing formed in a

          loop can be placed around each object, a piece of webbing can be made into a loop and

          connected to the bights of the slings or webbing around the objects using carabiners, and a

          carabiner can be placed in the middle to the middle piece of webbing (this allows load sharing

          since the carabiner will slide in the direction of the load

NOTE: Instructor should review each method of anchoring using illustrations, demonstrations, or both.

 

III. CONSTRUCTING MECHANICAL ADVANTAGE SYSTEMS (1-3)

A. Constructing a Z-Rig

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

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

         hauling (pulling)

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

     0. Attach an ascender or prussic cord to the rope near the load

     0. Pull the pulley in the second bight to the ascender or prussic cord and connect the pulley to the

         ascender or prussic cord using a carabiner

      0. Secure the pulley at the first bight to the anchor point using a carabiner to attach to the sling or

          webbing used at the anchor point