Pulley Ridge Pulley Ridge Pulley Ridge is a mesophotic coral reef system off the shores of the continental United States. The reef rests on sunken barrier islands and lies 100 miles west of the Tortugas Ecological Reserve and stretches north about 60 miles at depths ranging from 60–80 meters. Pulley Ridge was originally discovered in 1950 during a dredging operation conducted by an academic group from Texas. While well known to fishermen, this remarkable habitat remained undiscovered by scientists until 1999 when the U.S. Geological Survey (USGS) and graduate students from the University of South Florida happened upon it. This reef system,
Block and tackle more precise estimate of efficiency is possible by use of the sheave friction factor, formula_12 (which may be obtainable from the manufacturer or published tables). The relevant equation is: Typical formula_12 values are 1.04 for roller bearing sheaves and 1.09 for plain bearing sheaves (with wire rope). The increased force produced by a tackle is offset by both the increased length of rope needed and the friction in the system. In order to raise a block and tackle with a mechanical advantage of 6 a distance of 1 metre, it is necessary to pull 6 metres of rope through the