Figure 4-27. - Single-luff tackle.

Figure 4-29. - Twofold purchase.

By inverting any tackle, you always gain a mechanical advantage of 1 because the number of parts at the movable block is increased. By inverting a gun tackle, for example, you gain a mechanical advantage of 3 (figure 4-26). When a tackle is inverted, the direction of pull is difficult. This can easily be overcome by adding a snatch block, which changes the direction of the pull, but does not increase the mechanical advantage.

A single-luff tackle consists of a double and single block as indicated in figure 4-27, and the double-luff tackle has one triple and one double

Figure 4-28. - Double-luff tackle.

Figure 4-30. - Threefold purchase.