![]() The hauling part is pulled from the fixed block. "Rove to disadvantage" – where the pull on the rope is in the opposite direction to that in which the load is to be moved.The hauling part is pulled from the moving block. "Rove to advantage" – where the pull on the rope is in the same direction as that in which the load is to be moved.In this case the block and tackle is said to be "rove to advantage." The mechanical advantage of any tackle can be increased by interchanging the fixed and moving blocks so the rope is attached to the moving block and the rope is pulled in the direction of the lifted load. Therefore, the mechanical advantage of a double tackle is 4. In other words, to raise a load at 1 metre per second, the hauling part of the rope must be pulled at 4 metres per second. A line with a mechanical advantage of 4 has a velocity ratio of 4:1. The velocity ratio of a tackle is the ratio between the velocity of the hauling line to that of the hauled load. Ideal mechanical advantage correlates directly with velocity ratio. Separation of the pulleys in the double tackle show the force balance that results in a rope tension of W/4. Note that the gun tackle, double tackle and threefold purchase all have the same number of pulleys in both blocks (one, two and three, respectively) whereas the Luff tackle and Gyn tackle have mis-matched blocks with differing numbers of pulleys. In the diagram shown here, the number of rope sections of the tackles shown is as follows: They are common on boats and sailing ships, where tasks are often performed manually, as well as on cranes and drilling rigs, where once rove, the tasks are performed by heavy equipment. A block and tackle system amplifies the tension force in the rope to lift heavy loads. The process of threading ropes or cables through blocks is called " reeving", and a threaded block and tackle is said to have been "rove". ![]() An assembly of blocks with a rope threaded through the pulleys is called tackle. All these are "rove to disadvantage" (see below).Ī block is a set of pulleys or sheaves mounted on a single frame.
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