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 TM 55-1925-273-10-1
OPERATOR'S MANUAL
INLAND AND COASTAL LARGE TUG (LT)
THEORY OF OPERATION
REVERSE REDUCTION GEAR SYSTEM
GENERAL
There are two main propulsion plants on the vessel. Each propulsion plant consists of a main engine coupled to a two-speed
reversing reduction gear. The output shaft of the reduction gear is coupled to the propeller shaft.
The reverse reduction gear reduces the engine output revolutions per minute (r/min) and reverses rotational direction (when
required) to the propeller shaft. Gear ratios are: Ahead 1 4.677:1, Ahead 2 and Astern 5.444:1. Direction of rotation and
hydraulic clutch operation of each engine are controlled by a throttle control on the EOS console, pilothouse console, or
auxiliary control stations. A shaft brake is designed to lock the shaft when the reduction gear is in neutral.
LUBRICATION SYSTEM
A high-pressure gear pump (figure 1, item 1) is driven at engine speed to provide oil for clutch actuation and lubrication of the
reduction gear. A pressure-increasing valve (figure 1, item 2) maintains high oil pressure for clutch lockup. The excess oil that
bypasses the pressure-increasing valve is used for lubricating the gears, bearings, and clutch plates. The oil is cooled by a cooler
(heat exchanger) (figure 1, item 3). If the oil flow ceases, the flow indicator (flow alarm) (figure 1, item 4) switch will sound an
alarm and bring the reduction gear to neutral.
COOLING SYSTEM
A fresh water cooling system (figure 2) transfers heat from the reduction gear lubricating oil through the cooler (heat
exchanger) (figure 1, item 3). Water from the cooling system is cooled in turn through keel coolers (figure 2, item 1). Water
is circulated by an electric motor-driven coolant pump (figure 2, item 6).
HAND PUMP
A hand pump is provided to drain the PORT and STARBOARD reduction gear sumps.
REDUCTION GEAR RATIO SELECTION
A selector valve in the EOS console allows selection of the desired forward reduction gear ratio. The reduction gear selector
will be disabled whenever the throttle control is not in the center (NEUTRAL) position, or command is at a station other than
the EOS.
0019 00-1
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