Z-drag

A Z-Drag or Z-Rig is an arrangement of lines and pulleys, effectively forming a block and tackle, that is commonly used in rescue situations.

[1] The basic arrangement results in pulling the hauling end 3 times the distance the load is moved, providing a theoretical mechanical advantage of three to one.

The typical configuration (see diagram) uses two single pulleys and two Prusik knot loops or other suitable friction hitches.

Because the tension on the line stores energy and could present a dangerous flying hazard if the rope were to break.

Borrowed from rock climbing, the Z-Drag is considered an important tool in whitewater rescue and is used primarily for the recovery of pinned boats.