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Aviation Boatswains Mate F - Aviation theories and other practices | Next
PIPE PATCHES |
Types Of Tackle
Various types of tackle are in common use. Three
are shown in figure 2-20.
In studying each type illustrated, note the direction
in which the arrows are pointing for that particular
tackle. The purpose of the arrows is to indicate the
sequence and direction in which the standing part of the
fall is led in reeving.
A gun tackle is made up of two single sheave
blocks. This tackle got its name in the old days by
being used to haul muzzle-loading guns back into
battery after the guns had been fired and reloaded. As
stated, a gun tackle has a mechanical advantage of 2.
A single luff tackle consists of a double and a single
block. This type has a mechanical advantage of 3. A
twofold purchase consists of two double blocks, as
illustrated. It has a mechanical advantage of 4.
Chain Hoists
Chain hoists are portable lifting devices sus-
pended from a hook and operated by a hand chain.
Figure 2-19.—Inverted gun tackle.
Figure 2-20.—Three common types of tackle.
The one most commonly used by the ABF is the
spur-geared hoist. The spur-geared hoist gains its me-
chanical advantage from the difference in diameter of
the spur gears (reduction gear ratio) (fig. 2-21 ).
Figure 2-21.—Spur gear head chain hoist.
2-13
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