SRT Mechanical Advantage & Z-Drag 2

Question 1

In a 3:1 Z-drag system, if the load weighs 300 lbs, approximately how much force must the hauling team apply (ignoring friction)?

Accepted Answer

100 lbs

Answer

A 3:1 mechanical advantage divides the load force by 3, so 300 lbs ÷ 3 = 100 lbs of required input force.

Question 2

What is the primary function of the progress-capture device (PCD) in a Z-drag system?

Accepted Answer

Prevent the load from slipping back while haulers reposition

Answer

The PCD (typically a prussik or ratchet) holds the load in place so haulers can reset their grip without the load sliding back.

Question 3

When rigging a Z-drag, the rescue rope from the anchor traveling to the load and back creates what characteristic shape?

Accepted Answer

Z-shape

Answer

The rope path traces a Z (or N) shape from anchor to traveling pulley to load attachment, which gives the system its name.

Question 4

Which knot or hitch is most commonly used as a progress-capture device on the haul line in a Z-drag?

Accepted Answer

Prussik hitch

Answer

A prussik hitch grips the haul line under load and slides freely when unweighted, making it ideal as a PCD.

Question 5

A rescuer is building a Z-drag and only has one pulley. Where should the single pulley be placed for maximum efficiency?

Accepted Answer

On the traveling (moving) block position

Answer

Placing the pulley at the traveling (load-side) block reduces the most friction, since that sheave turns the most under a changing angle.

(SRT) Swiftwater Rescue Technician Certification Practice Test