Figure 8-2.—Geared steam turbine drive.
may be either a geared turbine (steam
diesel engine.
STEAM TURBINE GEAR DRIVE
or gas) or
In the steam turbine gear drive, the individual
propulsion units consist of the main turbines and
the main reduction gear (fig. 8-2). These types of
turbine drives are used on most types of naval
ships. They provide a high power-to-weight ratio
and are ruggedly constructed. When repairs are
needed, they can usually be completed without
removing the turbines from the ship. Steam
turbine gear drives consist of one high-pressure
turbine and one low-pressure turbine. They
provide ahead propulsion. Smaller and simpler
turbine elements inside the low-pressure turbine
provide astern propulsion (fig. 8-2).
DIESEL GEAR DRIVE
In the diesel gear drive engine, the parts that
make up the unit consist of the diesel engine, the
reduction gear, and either the controllable-pitch
propeller unit or the dc motor/generator drive
unit. The diesel gear drive engine is used on
auxiliary ships, minesweepers, fleet tugs, patrol
crafts, and numerous other yard craft and small
boats. Standardization of fuels, cheaper fuel, and
reduction in fire hazards are the chief factors why
the Navy favors diesel engines.
Some diesel engines are directly reversible. The
propeller shaft is connected directly to the diesel
engine so that the speed of the propeller shaft is
controlled by the speed of the diesel engine. When
it becomes necessary to reverse the direction of
rotation of the propeller shaft, the diesel engine
is stopped, the cam shaft of the engine is shifted
for reverse rotation, and then the engine is
Figure 8-3.—Diesel engine and reduction gear.
8-2
