Figure 4-24.Single-whip and runner tackle.
TYPES OF TACKLE
Tackles are designated in two ways: first,
according to the number of sheaves in the blocks that
are used to make the tackle, such as single whip or
twofold purchase; and second, by the purpose for
which the tackle is used, such as yard tackles or stay
Figure 4-25.Gun tackle.
tackles. In this section, well discuss some of the
different types of tackle in common use: namely,
single whip, runner, gun tackle, single luff, twofold
purchase, double luff, and threefold purchase. Before
proceeding, we should point out that the purpose of
the letters and arrows in figures 4-24 through 4-30 is
to indicate the sequence and direction in which the
standing part of the fall is led in reeving. You may
want to refer to these illustrations when we discuss
reeving of blocks in the next sections.
A single-whip tackle consists of one single-
sheave block (tail block) fixed to a support with a rope
passing over the sheave (figure 4-24.) It has a
mechanical advantage of 1. If a 100-pound load is
lifted, a pull of 100 pounds, plus an allowance for
friction, is required.
A runner (figure 4-24) is a single-sheave movable
block that is free to move along the line on which it is
reeved. It has a mechanical advantage of 2.
A gun tackle is made up of two single-sheave
blocks (figure 4-25). This tackle got its name in the
old days because it was used to haul muzzle-loading
guns back into the battery after the guns had been
fired and reloaded. A gun tackle has a mechanical
advantage of 2. To lift a 200-pound load with a gun
tackle requires 100 pounds of power, disregarding
Figure 4-26.Inverted gun tackle.