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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.
The Puretic power block is a special kind of mechanised winch used to haul nets on fishing vessels. The power block is a large pulley of aluminium with a hard rubber-coated sheave. While many men were needed for the back-breaking work of hauling a purse seine manually, the same work could be done by fewer men with a power block. [1]
The winch may be mounted to a vehicle, set into the ground by stakes, or tied to a tree. The cable may also be run through pulleys mounted offshore so that it pulls the person away from where the winch is located, and multiple pulleys may be used to multiply the force applied by a small but high revving motor instead of using a transmission.
A pulley is a wheel on an axle or shaft enabling a taut cable or belt passing over the wheel to move and change direction, or transfer power between itself and a shaft. A sheave or pulley wheel is a pulley using an axle supported by a frame or shell (block) to guide a cable or exert force.
It is accomplished with two lines (cables) and two winches (or cable drums). The mainline or yarding line extends out from one winch, while a second usually lighter line called the haulback line extends out from the other winch to a 'tail block' or pulley at the tail (back) end of the logging site, and passes through the tail block and connects ...
Vitruvius, a military engineer writing about 28 BC, defined a machine as "a combination of timber fastened together, chiefly efficacious in moving great weights".About a century later, Hero of Alexandria summarized the practice of his day by naming the "five simple machines" for "moving a given weight by a given force" as the lever, windlass, screw for power, wedge, and tackle block (pulley).