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 TM 55-1925-273-10-1
OPERATOR'S MANUAL
INLAND AND COASTAL LARGE TUG (LT)
THEORY OF OPERATION
BOW THRUSTER SYSTEM
GENERAL
The bow thruster system is comprised of a bow thruster set, bow thruster engine, and reduction gear.
BOW THRUSTER SET
The bow thruster is used in combination with the vessel's main propulsion system to give the Large Tug (LT) added maneu-
verability. A fixed propeller (figure 1, item 1) is driven through a right angle reduction gearbox (figure 1, item 2) by the bow-
thruster engine (figure 1, item 3). The propeller is designed to operate in either a clockwise or counterclockwise direction,
as selected by the operator on the control panel. Engine speed controls the thrust force. Displacement of raw water in a
given direction generates an equal recoil force in the opposite direction, moving the bow of the LT as needed. Control of the
bow thruster can be local or remote from the bow thruster control panel on the pilothouse console and auxiliary control
stations.
BOW THRUSTER ENGINE
The bow thruster engine (figure 1, item 3) is a turbocharged, 4-cycle, inline 6-cylinder marine diesel engine. The engine is
air started. It has its own lubricating oil, cooling, and fuel oil systems. A jacket water heater is provided to ease cold weather
starting.
The raw water cooling system consists of a horizontal centrifugal pump driven off the bow thruster engine, a duplex strainer,
and a piping system. When the bow thruster engine is operating, the centrifugal pump draws raw water from the sea chest
through a duplex strainer. This raw water is routed to the heat exchanger, where the heat from engine coolant is transferred
to the raw water. The heated raw water is then pumped overboard (refer to WP 0018 00).
REDUCTION GEAR
A reverse reduction gear (figure 1, item 4) reduces the engine output revolutions per minute (r/min) and reverses rotational
direction to the drive shaft (figure 1, item 5). Direction of rotation and hydraulic clutch operation is controlled by a throttle
control on the pilothouse console or auxiliary control stations. The reduction gear is equipped with a shaft brake. The shaft
brake is designed to lock the drive shaft when the reduction gear is in neutral.
0021 00-1
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