Block and tackle has been used for centuries for lifting heavy objects. The increased mechanical advantage (IMA) of using a pulley system can aid in lifting heavy objects with the ease of one person. The IMA of a block and tackle can be determined by the number of times a rope passes through the lifting pulley wheels system. One pulley equals one advantage, two pulleys equal two, and so on. In other words, if you want to lift a 100-pound weight, a one-pulley system would still equal 100 pounds. A double pulley system would be half or fifty pounds and a three pulley would equal a 33-pound lift on the pull rope. By following a basic rigging you can use a block and tackle to increase your mechanical advantage in lifting a heavy weight.
Roping the Lifting Pulley Wheels
Hang the top pulley on a bar that is a comfortable height for you to reach. Once the double tackle is rigged you can move the rope and tackle and hang it from any overhead support you wish.
Pass the end of the rope through the left pulley of the hanging block. Bring the rope down and through the left pulley of the lower block. Allow the lower block to rest on the ground for now. Pass the rope through the right pulley of the hanging block. The two pulleys of the top block should now be filled with rope.
Finish Rigging Blocks and Pulleys
Bring the rope down and through the bottom side of the right pulley on the lower tackle. Pull on the rope to make the tackle blocks come together.
Tie the end of the rope to the bottom eye of the upper hanging pulley. All block and tackle pulleys will have a tie-off eye below the hanging hook on the bottom side of the tackle. This will complete the rigging of a double-pulley block and tackle. The coil of rope left on the ground is the pull side of the block and tackle.
Adding More Pulleys
Rigging a block and tackle with more pulleys is done in the same manner as described above. Always begin passing the rope through the upper block on the left pulley and then down to the lower block on the left pulley. All blocks are rigged from left to right and downward.
Estimating the IMA
Calculate the IMA of a block and tackle set by reducing the total number of pulleys filled with rope by one. The double-pulley block and tackle rigged in the above steps will have an IMA of three.
G.K. Bayne is a freelance writer for various websites, specializing in back-to-basics instructional articles on computers and electrical equipment. Bayne began her writing career in 1975 and studied history at the University of Tennessee.