Z-drag
Encyclopedia
A Z-Drag is an arrangement of lines and pulleys commonly used in rescue situations. The basic arrangement provides a theoretical mechanical advantage of three. 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 block and tackle
arrangement.
The typical configuration (shown below) uses two single pulley
s and two Prusik knot loops or other suitable friction hitch
es. The first Prusik knot provides the mechanical advantage. The second Prusik knot can be used to hold the position of the rope and is sometimes referred to as a 'progress capture device' or ratchet. 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 since the line is under high tension and could break free and present a dangerous flying hazard.
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.
The Z-Drag is considered an important tool in mountain rescue
because of its simplicity and is used for nearly all lifting systems.
It also serves as an excellent method for tightening the rope to be crossed in a Tyrolean traverse
, where the other end is also fixed to a stable object.
Block and tackle
A block and tackle is a system of two or more pulleys with a rope or cable threaded between them, usually used to lift or pull heavy loads.The pulleys are assembled together to form blocks so that one is fixed and one moves with the load...
arrangement.
The typical configuration (shown below) uses two single pulley
Pulley
A pulley, also called a sheave or a drum, is a mechanism composed of a wheel on an axle or shaft that may have a groove between two flanges around its circumference. A rope, cable, belt, or chain usually runs over the wheel and inside the groove, if present...
s and two Prusik knot loops or other suitable friction hitch
Friction hitch
A friction hitch is a kind of knot used to attach one rope to another in a way that is easily adjusted. These knots are commonly used in Single Rope Technique while climbing to ascend a hanging rope by alternately hanging on one friction hitch and sliding the other up...
es. The first Prusik knot provides the mechanical advantage. The second Prusik knot can be used to hold the position of the rope and is sometimes referred to as a 'progress capture device' or ratchet. 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 since the line is under high tension and could break free and present a dangerous flying hazard.
Borrowed from rock climbing
Rock climbing
Rock climbing also lightly called 'The Gravity Game', is a sport in which participants climb up, down or across natural rock formations or artificial rock walls. The goal is to reach the summit of a formation or the endpoint of a pre-defined route without falling...
, the Z-Drag is considered an important tool in whitewater
Whitewater
Whitewater is formed in a rapid, when a river's gradient increases enough to disturb its laminar flow and create turbulence, i.e. form a bubbly, or aerated and unstable current; the frothy water appears white...
rescue and is used primarily for the recovery of pinned boats.
The Z-Drag is considered an important tool in mountain rescue
Mountain rescue
Mountain rescue refers to search and rescue activities that occur in a mountainous environment, although the term is sometimes also used to apply to search and rescue in other wilderness environments. The difficult and remote nature of the terrain in which mountain rescue often occurs has resulted...
because of its simplicity and is used for nearly all lifting systems.
It also serves as an excellent method for tightening the rope to be crossed in a Tyrolean traverse
Tyrolean traverse
A Tyrolean traverse is a method of crossing through free space between two high points on a rope without a hanging cart or cart equivalent. This is used in a range of mountaineering activities: rock climbing, technical tree climbing, caving and water crossings. A zip-line is in essence a Tyrolean...
, where the other end is also fixed to a stable object.
See also
- Truckers hitch - another 3-fold advantage system using single loops
- Mechanical advantageMechanical advantageMechanical advantage is a measure of the force amplification achieved by using a tool, mechanical device or machine system. Ideally, the device preserves the input power and simply trades off forces against movement to obtain a desired amplification in the output force...