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.