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This shows the two common variations on a Z drag hauling system, both using a prussik minding pulley with two triple wrap prussik loops for progress capture. In the first variation the traveling pulley is connected to, and pulls on, the hauling line. Because the traveling pulley can be much closer to the anchor than to the load it can be set up with less rope. The disadvantage is that the system may need to be reset depending on how far the load has to be hauled. To facilitate resetting, the traveling pulley is typically connected to the haul line with a prussik loop. In the second variation the traveling pulley is connected to, and pulls directly on, the load. This requires a rope that is at least twice the distance between the load and the anchor, but can pull the load all the way to the anchor without resetting the system.
Like other mechanical advantage systems, the Z drag works by pulling the rope 3 times the distance the load is moved, to "collapse" the system. For example moving the load 5' requires pulling 15' of rope, which is 5' on each of the 3 legs of the Z. Ideally each leg is parallel so the entire system can collapse to a length of zero. As the angle between the two legs at the travelling pulley increases from 0º the advantage gained from the second pulley is reduced because it changes from a force multiplier to a simple directional change.
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