and semi-gantry cranes may also use the facility power, but many use on-board
diesel engine-generator sets as their primary power source.
Older Navy facilities may have 240 VDC or 500 VDC as their primary power
source. New cranes installed in such facilities should be equipped with drives
designed for that power source.
Shore Power Operation. Waterside facilities normally have electrical
outlets for several varieties of power. Portal, floating, and container cranes
are normally designed with back-up capability to operate off shore power in case
of loss of their on-board diesel engine-generator power source. Crane electrical
systems of these cranes are configured to permit a quick transfer to shore power.
Additionally, shore power is required to energize cranes' ancillary systems, such
as lights and heaters, during prolonged periods of inactivity; for AC systems,
this power may have to be provided at a voltage lower than 480 volts, depending
upon the design of the crane.
Shore power connections are made near ground level by means of standard
commercial hardware. When on shore power, crane travel capability is severely
Main Diesel Engine-Generator Sets. The primary power for Navy portal,
floating, and container cranes is provided by on-board diesel
engine-generator sets. These sets are normally standard commercial combinations
of components, all mounted on a common base. A critical component of these sets
is the coupling between the diesel engine and the generator. The coupling
determines the natural torsional frequency of the set, and must perform equally
well for long periods under both full load and no load. It is important that the
assembler of the set consider the long period of idling at no load, which is
uncommon in commercial practice but is a normal condition in Navy operations.
Diesel Engines. Diesel engines are standard products of established
manufacturers. They are available in two-stroke-cycle and
four-stroke-cycle designs. The two designs are comparable in all respects and are
equally acceptable for use on Navy cranes. They may be either naturally aspirated
or supercharged. Although the naturally aspirated engines produce somewhat less
power per pound of engine weight than the supercharged models, they are
recommended in order to avoid the added complexity and maintenance requirements of
The starting systems are either electric (with on-board batteries) or
pneumatic. Pneumatic systems require a diesel engine or electric motor driven
compressor and an accumulator of sufficient volume to provide several engine
starting sequences. Both systems are satisfactory; however, the electric systems
are preferred where ambient temperature and humidity conditions may cause
condensation and freezing of water in the pneumatic system.
The standard operating speed of modern diesel engine-generator sets is
1800 revolutions per minute (RPM). Maintenance of relatively constant speed (for
the 60 Hertz electrical frequency) at fluctuating loads is important. Although
diesel engines are inherently constant-speed machines, speed loss (droop) occurs
with the sudden application of load. A speed governor, which senses the droop and
responds by increasing the rate of fuel injection is required to maintain the