Puretic power block Puretic power 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 powered aluminium pulley 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. The Puretic power block revolutionized the technology of hauling fishing nets, particularly purse seine nets. According to the Food and Agriculture Organization of the United Nations (FAO), "no single invention has contributed more to the success of
Block and tackle each of the parts of the rope must be "F/n." This means the input force on the rope is "F"="F/n." Thus, the block and tackle reduces the input force by the factor "n." Ideal mechanical advantage correlates directly with velocity ratio. The velocity ratio of a tackle is the ratio between the velocity of the hauling line to that of the hauled load. A line with a mechanical advantage of 4 has a velocity ratio of 4:1. In other words, to raise a load at 1 metre per second, the hauling part of the rope must be pulled at 4