speed within predetermined limits. Mechanical, hydraulic, and electronic types of
governors are available, and all are found on cranes in the Navy inventory.
Modern diesel engines are normally equipped with electronic speed governors and
while maintaining constant speed. NCC policy is to specify electronic speed and
fuel controls for all new crane procurements. When such electronic controls are
not provided, diesel engine-electric generator sets usually require a resistor
load bank to provide an artificial load on the diesel engine to ensure complete
combustion and clean exhaust.
Generators. Generators of the main diesel engine-generator sets on
portal, floating, and container cranes serve to provide DC or AC power to the
drive control systems and DC power to the drive motors.
For crane applications, the DC generators are limited to two types flat
compound-wound for constant potential control systems, and separately excited
shunt-wound for adjustable voltage control systems. Flat compound-wound
generators have the same terminal voltage with no load and with full load on the
generator (which is defined as the rated voltage); and slightly higher than the
rated voltage at intermediate loads. Shunt-wound generators produce their rated
voltage only at full field strength and with no load. The terminal voltage drops
slightly with increasing load on the generator; but, for a given load, the
terminal voltage decreases significantly when the field is weakened.
AC generators (alternators) are used in combination with straight
rectifiers or with controlled rectifiers (thyristors) to produce DC power. The
straight rectifiers are employed for constant potential drives, and thyristors for
adjustable voltage systems. AC generator designs are selected to deliver the
rated voltage at 60 Hertz when driven at the rated speed of the diesel engine.
Auxiliary Generators. The auxiliary generators are driven directly by
the diesel engines, usually by means of multiple V-belts. Their function is to
provide AC power on cranes powered by DC main generators. The auxiliary
generators are sized for the total electrical load of the ancillary equipment
while the main diesel engine-generator is running. They are normally mounted in
"piggy-back" fashion on or beside the main generator.
Mounting and Installation. The base of the diesel engine-generator set
is a rigid structure, mounted to the crane structure through intervening vibration
isolators. The set location must ensure an adequate flow of cooling air and a
slight negative pressure with respect to the adjoining spaces. The exhaust system
should be entirely of stainless steel and must include a spark arresting muffler
and a bellows type duct section to compensate for expansion/contraction of the
exhaust duct between its anchor points. On newer portal cranes, the fuel system
is arranged to facilitate refueling from ground level. On floating cranes, the
diesel engine is fueled from a "day tank" on the crane; and the main tank is
installed in the barge.
Instrumentation. The mandatory instrumentation includes the engine speed
gauge. The tachometer and gauges must be installed in the operator's cab and on
the base of the diesel engine-generator set. Various additional items of the
instrumentation are available from the diesel engine and the generator
manufacturers, and they may be provided as required by the operational