Rope rescue rope grabs, and other tools, to raise, or haul, a load up a vertical section, or across a gully or canyon. Pulleys systems are used in conjunction with the rope, rope grabbing devices, i.e.: Prusiks, or mechanical grabs, to capture the progress made during the lift. Since pulley systems are generally short in length, they are used in conjunction with a progress (raise) capturing technique, and a long rope; and a backup safety or belay. This specialized equipment is used to reach the subject(s) and safely recover them. These techniques are subdivided, and are sometimes the techniques and equipment are
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