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The typical boat davit system is made up of five
major subsystem. These subsystems are the electrical
system, the winch system, the boat davit arms and
sheaves system, the boat falls system, and the stowage
system. The primary function of the davit arm, (or arms,
as applicable) is to swing out the boat from the inboard
position to a point outboard of the ship's side from which
the boat may be lowered. The reverse of this process
occurs when the boat is hoisted. Hoisting operations are
controlled by the winch and boat falls from which a
hoisting hook (or hooks) is (are) suspended. The number
of hoisting hooks is dependant on whether the boat davit
is the single arm or double arm configuration. The falls
lead from the boat davit winch (the source of power),
through the boat davit arms and sheaves to the hoisting
hooks. A drum type winch is used with all boat davits
having a wire rope fall or falls. A gypsy type winch is
used with some boat davits when the falls are synthetic
fiber rope. Boat davits are either of gravity or
mechanical type.
A gravity boat davit requires only the force of
gravity to move a boat suspended from the hooks at the
inboard position to the outboard position and down to
the water. The lowering evolution from the inboard
position to the water is controlled at the winch through
the boat falls. The winch's manual brake controls the
boat's descent speed and prevents the davit arms from
slamming into the outboard stops. The manual brake is
also used to stop the boat before it reaches the water to
allow the coxswain to start the boat's engines. The
power to hoist the boat from the water is provided by
the winch. Handcranks can be attached to the winch for
hoisting the boat by hand if a loss of electrical power
should make it necessary. Gravity boat davits are either
of the overhead suspended, trackway, pivoted, or
pivoted link type, and may be of the single or double
arm configurations. Figure 4-13 depicts the typical
operation of a trackway gravity boat davit.
The mechanical boat davit requires the application
of an external force to move the boat and davit arms from
the inboard to the outboard position in preparation for
lowering the boat to the water. Movement of the boat
outboard with mechanical boat davits is not under
control of the boat falls. Mechanical boat davits of the
pivot sheath screw (occasionally called crescent) and
radial designs are no longer being built for Navy ships.
However, these older design mechanical boat davits are
still used on some Navy and merchant vessels. The
newest type of a mechanical boat davit being used by
the Navy is the slewing arm boat davit. This boat davit
is often called the SLAD and it handles the rescue boat
called a rigid inflatable boat (RIB).
The double-link davit generally handles two boats.
The double-link configuration can handle both the
larger and heavier types of boats (officer/personnel,
utility cargo) as well as the lighter weight rescue boat.
A double-link pivoted gravity davit is shown in fig-
ure 4-14.
Figure 4-14.–Double-link pivoted gravity davit.
4-13
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