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An ideal block and tackle with a moving block supported by n rope sections has the mechanical advantage (MA), = =, where F A is the hauling (or input) force and F B is the load. Consider the set of pulleys that form the moving block and the parts of the rope that support this block.
In order to determine the mechanical advantage of a block and tackle system consider the simple case of a gun tackle, which has a single mounted, or fixed, pulley and a single movable pulley. The rope is threaded around the fixed block and falls down to the moving block where it is threaded around the pulley and brought back up to be knotted to ...
In use, a block is fixed to the end of a line, to a spar, or to a surface. A line (rope) is reeved through the sheaves, and maybe through one or more matching blocks at some far end, to make up a tackle. The purchase of a tackle refers to its mechanical advantage. In general the more sheaves in the blocks that make up a tackle, the higher its ...
The ideal mechanical advantage of the block and tackle is equal to the number of sections of the rope that support the moving block. In the diagram on the right, the ideal mechanical advantage of each of the block and tackle assemblies [7] shown is as follows: Gun tackle: 2; Luff tackle: 3; Double tackle: 4; Gyn tackle: 5; Threefold purchase: 6
By looping more ropes around more pulleys we can construct a block and tackle to continue to increase the mechanical advantage. For example, if we have two pulleys attached to the rafter, two pulleys attached to the weight, one end attached to the rafter, and someone standing on the rafter pulling the rope, we have a mechanical advantage of four.
If one block has one more pulley than the other, then the maximum mechanical advantage is obtained when this larger block is used as the moving block and the smaller block which has the start of rope attached is mounted as the fixed block; this means that again the hauling rope is in the direction of the moving load.
Triple deadeyes are used in pairs; a line called a lanyard is run back and forth between them, through the holes, so that they function again much as a block and tackle would. [2] This provides a mechanical advantage , pulling harder on whatever the deadeyes are attached to.
Crown block (#13) is the stationary end of the block and tackle. Degasser (not pictured) is a device that separates air and/or gas from the drilling fluid. It is typically mounted on top of the mud tanks. Derrick (#14) is the support structure for the equipment used to lower and raise the drill string into and out of the wellbore. This consists ...