Royce Olympus, a 28,000-hp engine, for high-
speed situations.
The U.S. Navy entered the marine gas turbine
field with the Asheville class patrol gunboats.
These ships have the CODOG configuration with
two diesel engines for cruising and a General
Electric LM1500 GTE for high-speed operations.
The Navy has now designed and is building
destroyers, frigates, cruisers, hovercraft, and
patrol hydrofoils that are entirely propelled by
GTEs. This is a result of the reliability and
efficiency of the new GTE designs.
Figure 1-5.--Free piston engine.
ADVANTAGES AND
DISADVANTAGES
At that time applications of the use of a rotary
gasifier to drive a main propulsion turbine were
The GTE, when compared to other types of
used. The gasifier (used as a compressor) was
engines, offers many advantages. Its greatest asset
usually an aircraft jet engine or turboprop front
is its high power-to-weight ratio. This has made
end. In 1947 the Motor Gun Boat 2009 of the
it, in the forms of turboprop or turbojet engines,
British navy used a 2500-hp GTE. In 1951 the
the preferred engine for aircraft. Compared to the
tanker Auris, in an experimental application,
gasoline piston engine, the GTE operates on
replaced one of four diesel engines with a
cheaper and safer fuels. The relatively vibration-
1200-hp GTE. In 1956 the gas turbine ship John
free operation of the GTE, compared with
Sergeant had a very efficient installation. It gave
reciprocating engines, has made it even more
a fuel consumption rate of 0.523 pounds per
desirable in aircraft. Less vibration reduces strain
hp/hr. The efficiency was largely due to use of
on the airframe. In a warship, the lack of low-
a regenerator, which recovered heat from the
frequency vibration of GTEs makes them
exhaust gases.
preferable to diesel engines because there is less
By the late 1950s the marine GTE was
noise for a submarine to pick up at long range.
becoming widely used, mostly by European
Modern production techniques have made GTEs
navies. All the applications used a dual main
more economical in terms of horsepower-per-
propulsion system, combining the gas turbine
dollar on initial installation. Their increasing
plant with another conventional form of
reliability makes them a cost-effective alternative
propulsion machinery. The GTE was used for
to steam turbine or diesel engine installation. In
high-speed operation. The conventional plant was
terms of fuel economy, modern marine GTEs can
used for cruising. The most common arrange-
compete with diesel engines and they may even
ments were the combined diesel and gas
be superior to boiler/steam turbine plants that are
(CODAG) or the combined diesel or gas
operating on distillate fuel.
(CODOG) systems. Diesel engines give good
The GTEs do have a few disadvantages. Since
they are high-performance engines, many parts
cruising range and reliability, but they have a
disadvantage when used in antisubmarine warfare.
are under high stress. Improper maintenance and
Their low-frequency sounds travel great distances
lack of attention to details of the maintenance
through water. This makes them easily detected
procedures will impair engine performance and
by passive sonar. Steam turbines have been
may lead to engine failure. A pencil mark on a
combined to reduce low-frequency sound in the
compressor turbine blade can cause failure of the
combined steam and gas (COSAG) configuration
part. Most GTE propulsion control systems are
like those used on the British County class
very complex and require the monitoring of
destroyers. The COSAG configuration requires
numerous operating conditions and parameters.
more personnel to operate. Also they do not have
The control systems must react quickly to turbine
the long range of the diesel combinations.
operating conditions to avoid casualties to the
Another configuration that has been successful
equipment. In shipboard installations special
is the combined gas or gas (COGOG), such as
soundproofing is necessary because GTEs produce
high-pitched noises that can damage the human
used on the British 42. These ships use the
ear. The turbine takes in large quantities of air
4,500-hp Tyne GTE for cruising and the Rolls
1-3
