The piggybacked 4:1 haul system is the most efficient simple haul system because the greatest mechanical advantage is created with the fewest pulleys, thus minimizing friction within the haul system.
Consequently, it is a valuable addition to the riggers and rescuers toolbox. However, it has two notable drawbacks; it is often difficult to remember, and it can be hard to build to maximize the throw.
This brief article walks though how to build a 4:1 haul system, optimizing it for throw as it is being built. At the end some additional tips and tricks are suggested for improved efficiency.
Rigging a Piggyback 4:1 for Maximum Throw
Gather supplies, usually a rope, two pulleys, three carabiners, a prusik or other rope grab, and anchor material (Figure 1).
Start by connecting a pulley to the end of the rope (Figure 2A). Take a bight of the rope and pass it through the pulley and clip it shut (Figure 2B).
Attach a pulley to the loop of rope formed by the previous step (Figure 2C), and attach this pulley to the rope the 4:1 is piggybacked onto with a prusik (not shown). Extend the haul system toward the lip as far as it will go.
At this point the rope will run out, or the haul system will reach the edge. One or the other will limit the throw. If the rope length limits the throw (Figure 2D), leave a tail of rope out at the pulley closest to the haulers.
Pull the rope between the two pulleys tight, forming a bight (Figure 2E), then tie a figure 8 knot (Figure 2F) and clip this knot to the anchor (Figure 2G). This makes the longest possible haul system with the available rope (Figure 2I).
If the haul system reaches the lip with rope to spare the final product will look like Figure 2H with extra rope on the haul side.
Further 4:1 Optimization
At times it may be necessary to build the haul system with less rope. This can be done by using more efficient knots. The figure 8 knot by the pulleys (Figure 3A) can be replaced with a slip barrel knot (Figure 3B, Figure 4E-H).
The figure 8 knot at the anchor can be replaced by a clove hitch (Figure 3C, Figure 4E-H). To further reduce mass and size, the haul system can be built with screw links (Figure 3D, Figure 4C, D, G, H) or the end of the rope can be tied directly to the pulley (not shown).
If need be the 4:1 can be built without pulleys, just running the rope through carabiners (Figure 4B, F) or screw links (Figure 4D, H) however this creates considerably more friction and makes hauling difficult.
Lastly, if you have a choice between where to put the most efficient pulleys, the most efficient pulley should be placed closer to the haulers (the first pulley installed).
Having the most efficient pulley closest to the haulers reduces the frictional loss propagated through the system, thus improving overall efficiency.