air ejector condenser removes the air and
noncondensable gases from the condensate before
they enter the deaerating feed tank (DFT).
The feed phase starts in the DFT. The DFT
preheats the feedwater and removes dissolved
gases. The dissolved gases, if not removed, will
cause erosion and deterioration of the boiler
The main feed booster pump and main feed
pump increase the feedwater pressure to a pressure
greater than the operating pressure of the boiler.
The increased pressure ensures a flow of feedwater
through the boiler. That brings us back to the
point where we started. Thus, the system is a
Diesel engines are the favored means of power
for medium and light vessels. They are relatively
low-cost power plants to produce, are reliable, and
have a high fuel-efficiency rate. They can also be
started from a cold-plant condition and rapidly
brought on line.
The cycle of operation for diesel engines starts
with the intake of air. Next the air is compressed.
Following compression, combustion occurs. The
combustion produces a rapid expansion of gases
in the cylinder. This downward expansion is the
power stroke of the cylinder. As the waste gases
exhaust, new air intake occurs to start the cycle
Each cycle causes the pistons within the
cylinders to reciprocate. The rotary motion of the
pistons, connected to the crankshaft, drives the
Among the disadvantages are the frequent
overhaul and periodic maintenance requirements
and the power limitations of the engines. Diesels
cannot develop enough power to meet the high-
speed requirement of combatant ships.
In gas turbines, as in diesel engines, the
working substance is air. They are open systems;
that means the air passes through the engine once
and is discharged back to the atmosphere.
Air is drawn into the compressor from the
atmosphere. The compressor raises the pressure
of the air and discharges it to the combustion
chamber, where fuel is admitted. Here, as the
fuel-air mixture ignites, combustion occurs. The
hot combustion gases then expand and enter the
turbine. This turbine is similar in design and
theory to that of the conventional steam turbine.
Approximately 75 percent of the power developed
by the turbine is used to drive the compressor and
accessory systems. The remaining power is used
as engine output.
The shaft of a gas turbine ship rotates in one
direction only. An external method of reversing
the direction of travel of the ship is required to
propel the ship forward or backward. This
problem is overcome by the reversible pitch
propeller. As the shaft turns in one direction, the
ship is propelled forward or backward by a change
in the propeller pitch.
Because of the high rotational speed and high
temperatures of the gas turbine, operational
parameters must be closely monitored. Auto-
mated central operating systems have been
developed to monitor those parameters, thus
keeping the manning level low.
Two disadvantages of gas turbines are that the
engine must be removed for overhaul and that it
needs a high volume of air for operation.
However, these two disadvantages complement
each other because the engine can be removed
through the large ducts needed to accommodate
the high volume of air.
Gas turbines are becoming the preferred
propulsion plant for several ship types. They are
very light and compact and offer a high-power
plant that is relatively inexpensive to build. They
are as fuel efficient as a conventional steam plant.
NUCLEAR POWER PLANTS
Nuclear power plants are very similar to
conventional steam turbine plants. The major
difference is that a nuclear reactor replaces the
boiler as the device that generates steam.
Submarines are ideally suited for a nuclear
power plant because their reactor does not need
a supply of air from the atmosphere. Before the
advent of nuclear power, submarines ran on
motors charged by d.c. batteries when submerged.
When surfaced, diesel engines supplied power for
the submarine and recharged the batteries. The
charge of the batteries limited the endurance of
the submerged submarine. Nuclear power plants
enable submarines to remain submerged for
Nuclear reactors transfer the energy emitted
by the fission of radioactive material into thermal
energy. A primary and a secondary system (or