TM 5-1940-322-24
GENERAL INFORMATION,
EQUIPMENT DESCRIPTION, AND THEORY OF OPERATION
BRIDGE ERECTION BOAT (BEB)
MK II-S
NSN 1940-01-526-0770
P/N 12492423
THEORY OF OPERATION
GENERAL
This section explains how components of the BEB work. Functional descriptions of components and their
operation are covered in the following paragraphs.
FUNCTION OF THE PROPULSION SYSTEM
The propulsion system creates thrust by drawing in water through inlet grills on the underside of the hull
and expelling it through nozzles aft of the boat. Thrust is generated by two hydrojet units mounted side-by-
side on the transom. The hydrojet contains a large impeller that functions as a high velocity water pump,
and the force with which the water is expelled depends on engine speed. Each hydrojet is powered by a
diesel engine in conjunction with a transmission. The transmission has a neutral position, one forward and
one reverse gear, and transmits power from the engine to the hydrojet through a driveshaft. Thrust from
both hydrojets is directed by moving the position of the steering deflectors and reverse deflector scoops.
FUNCTION OF THE STEERING SYSTEM
The scoop is a moveable metal shield that deflects the flow of water from the nozzles. Each scoop is
controlled independently by a separate control lever. In the neutral position, the scoops direct the thrust
straight down. To propel the boat forward the scoops are raised to allow thrust aft. To reverse the boat, the
scoops are lowered to deflect thrust toward the bow. At forward speeds, steering is accomplished by
controlling the position of the steering deflectors on each hydrojet by way of the boat's steering wheel, or by
use of both scoop controls. When stopped, or at low speeds, steering is made possible by placing one scoop in
the reverse position, the other in the forward position, and by using the steering wheel. In addition,
steering is affected by the amount of thrust generated at a given engine speed.
FUNCTION OF ENGINE COOLING SYSTEM
The engine cooling system is identical on both port and starboard engines. Coolant is pumped through the
primary cooling system using a water pump. The water pump draws coolant from three locations: water
pump supply hose attached to keel cooler, exhaust manifold cooler return hose, and reservoir tank draw
hose.
Coolant is pumped through the engine block and routed to the following locations:
a. Through thermostat housing, keel cooler supply hose, and back to keel cooler.
b. Through exhaust manifold, exhaust manifold cooler return hose, and back to water pump.
c. Through engine block air bleed return line and back to coolant reservoir tank.
d. Through exhaust manifold air bleed return line and back to coolant reservoir tank.
e. Through turbocharger supply line, turbocharger, turbocharger air bleed return hose, and back to
coolant reservoir tank.
f. Through keel cooler supply hose, thermostat air bleed return hose, and back to coolant reservoir
tank.
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