The Z-Drag technique is thoroughly explained in AboveTopSecret.com's post by DaddyBare, all images from the post.
When traveling in remote areas, emergency can happen where a whole team of people is needed for rescue. Unfortunately, you only have the people you are with and that may not be enough. Fortunately, there are techniques that use a simple system of ropes and pulleys such as the Z-Drag that multiply your collective power and make rescue efforts much more effective.
One such situation is where a kayak gets pinned against a rock in a river. Watch the video below to see how easily this can happen in water that doesn't even look that dangerous:
As you can see, the current in the water is much much stronger than you would expect and a lot of power is needed to pull the boat and the paddler off.
THE Z-DRAG TECHNIQUE:
The Z-Drag technique is named for the shape of the rope between two pulleys and TRIPLES the power of a person pulling on the rope. Basically, the rope is attached to the overturned boat and passes through a pulley that is attached to a stable object like a tree. The rope from this first pulley then passes through a second pulley that is secured to the length of rope between the boat and the first pulley with a set length of rope. The rope that comes out of this second pulley is the bit that you tug on.
Though simple, this takes a LOT of practice because you only have so much time. Please read the article at AboveTopSecret.com for a full explanation and get some practice on dry land before trying it in the water.