A Z-Drag or Z-Rig is an arrangement of lines and pulleys, effectively forming a

block and tackle A block and tackle or only tackle is a system of two or more pulleys with a rope or cable threaded between them, used to provide tension and lift heavy loads. The pulleys are assembled to form blocks and then blocks are paired so that one is ...

, that is commonly used in rescue situations. 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''. In actual practice the advantage will be reduced by friction in the pulleys or carabiners. The advantage will also be reduced if the pull on the hauling end is not parallel to the direction the load moves in. The name comes from the fact that the arrangement of lines is roughly Z-shaped. Besides the mechanical advantage to pulling, it also uses only part of the total length of the rope for the

arrangement. The typical configuration (see diagram) uses two single

pulley Sheave without a rope A pulley is a wheel on an axle or shaft enabling a taut cable or belt passing over the wheel to move and change direction, or transfer power between itself and a shaft. A pulley may have a groove or grooves between flan ...

s and two Prusik knot loops or other suitable

friction hitch Friction is the force resisting the relative motion of solid surfaces, fluid layers, and material elements sliding against each other. Types of friction include dry, fluid, lubricated, skin, and internal -- an incomplete list. The study of t ...

es. These Prusiks provide fixed attachment points on the rope that can be moved when slightly loosened. The first Prusik knot is attached to the "traveling pulley," allowing it to pull on the load. The second Prusik knot is used to hold the position of the rope and is referred to as a 'progress capture device' or ratchet. Because the tension on the line stores energy and could present a dangerous flying hazard if the rope were to break. It is also advisable to attach a towel or soft object (such as a life vest) to the end of the line near the connection to the object being pulled, to act as padding, and/or a damping device. Borrowed from

rock climbing Rock climbing is a climbing sports discipline that involves ascending climbing routes, routes consisting of natural rock in an outdoor environment, or on artificial resin climbing walls in a mostly indoor environment. Routes are documented in c ...

, the Z-Drag is considered an important tool in

whitewater Whitewater forms in the context of rapids, in particular, when a river's Stream gradient, gradient changes enough to generate so much turbulence that air is trapped within the water. This forms an unstable current that foam, froths, making t ...

rescue and is used primarily for the recovery of pinned boats. It is also considered a useful tool in many types of

rope rescue Rope rescue is a subset of technical rescue that involves the use of rope, be it steel or cable rope, or more commonly used nylon, polyester, or other type of rope. Principles The key to any type of rescue is understanding and identifying th ...

, such as

crevasse rescue Crevasse rescue (or crevasse-extraction) is a set of techniques in mountaineering where climbers use their equipment to pull a climber, who has just fallen into a crevasse, to safety. Crevasse rescue is considered a core skill set in alpine cli ...

, because of its simplicity, and is commonly used for lifting systems that don't require much more mechanical advantage. It also serves as a method for tightening the rope in a Tyrolean traverse, where the other end is fixed to a stable object.

References

General references

* Swiftwater Rescue: A Manual for the Rescue Professional * Whitewater Rescue Manual: New Techniques for Canoeists, Kayakers, and Rafters * River Rescue: A Manual for Whitewater Safety * Swiftwater Rescue Safety equipment Ropework Swiftwater rescue {{tool-stub

See also

References

General references