low-frequency vibration in gas turbines makes
them preferable to diesel engines because there is
less noise for a submarine to pick up at long
range. Modern production techniques have made
gas turbines economical in terms of horsepower-
per-dollar on initial installation, and their
increasing reliability makes them a cost-effective
alternative to steam turbine or diesel engine
installation. In terms of fuel economy, modern
marine gas turbines can compete with diesel
engines and may be superior to boiler/steam
turbine plants when these are operating on
distillate fuel.
However, there are some disadvantages to gas
turbines. Since they are high-performance engines,
many parts are under high stress. Improper
maintenance and lack of attention to details of
procedure will impair engine performance and
may ultimately lead to engine failure. A pencil
mark on a compressor turbine blade or a finger-
print in the wrong place can cause failure of the
part. The turbine takes in large quantities of air
that may contain substances or objects that can
harm the engine. Most gas turbine propulsion
control systems are complex because several
factors have to be controlled, and numerous
operating conditions and parameters must be
monitored. The control systems must react
quickly to turbine operating conditions to avoid
casualties to the equipment. Gas turbines produce
loud, high-pitched noises that can damage the
human ear. In shipboard installations, special
soundproofing is necessary. This adds to the
complexity of the installation and makes access
for maintenance more difficult.
From a tactical standpoint, there are two
major drawbacks to the gas turbine engine. The
first is the large amount of exhaust heat produced
by the engines. Most current antiship missiles are
heat-seekers, and the infrared signature of a gas
turbine engine makes it an easy target.
Countermeasures, such as exhaust gas cooling and
infrared decoys, have been developed to reduce
this problem.
The second tactical disadvantage is the require-
ment for depot maintenance and repair of major
casualties. The turbines cannot be repaired in
place on the ship and must be removed and
replaced by rebuilt engines if anything goes wrong.
Here too, design has reduced the problem; an
engine change can be accomplished wherever
crane service or a Navy tender is available, and
the replacement engine can be obtained.
SUMMARY
This chapter has given you some basic
information on gas turbine engines and gas
turbine control systems. For a more in-depth look
at gas turbines, refer to Gas Turbine Systems
Technician (Mechanical) 3 & 2, NAVEDTRA
10548-2.
6-20
