(See figs. 6-20 and 6-21.) The first stage of the waterjet
A duplex filter mounted beneath the engine on the
pump operates at a lower speed for good suction
starboard side provides filtration for the supply oil. A
performance. The second stage runs at a higher speed to
duplex filter mounted beneath the engine on the port side
increase pressure and velocity. The propulsor assembly
provides filtration for the scavenge oil. The scavenge oil
housing assembly contains a magnetic chip detector.
is driven by the GTE through the gearbox assembly or
The scavenge oil is filtered, cooled, and returned to the
power train, which we will discuss next.
storage tank.
POWER TRAIN ASSEMBLY
Fuel Oil System
The power train assembly consists of the gearbox,
The GTE fuel system on the PHM is essentially the
flexible coupling, and shaft assemblies.The GTE drives
same as the fuel systems on other gas turbine-powered
the gearbox through a high-speed flexible coupling
ships. The PHM fuel system regulates and distributes
shaft. This shaft is designed to accommodate any axial
fuel to the combustion section of the gas generator,
or radial movement between the GTE and gearbox that
providing a control over gas generator speed. Although
results from dynamic loads and thermal expansion.
the power turbine speed is not directly controlled by the
Because the GTE is directly coupled to the propulsor
GTE fuel system, it is established by the gas stream
through the gearbox, there is no disengagement
energy level produced by the gas generator.
capability. This means that whenever the GTE is
operating, the propulsor is being driven.
Operation
Gearbox Assembly
The GTE is started by the operator in the engineer's
operating station (EOS). Throttle control then is
transferred to the helm (pilothouse) for foilborne
The gearbox assembly is a Western Gear
operation. During foilborne operation, the monitoring
lightweight, reduction transmission unit that sends
of operating parameters continues to take place in the
power from the GTE to the foilborne propulsor through
EOS. Before the GTE is shut down, control is
the bearing and seal assembly. The gearbox is split
transferred back to the EOS where the GTE is shut down
vertically into a high-speed assembly and a low-speed
by automatically controlled logic. Auxiliary functions,
assembly and consists of main drive pinions that drive
such as the GTE machinery room cooling, compressor
two coaxial output shafts through two sets of
washing, and engine waste drain pumping, are
double-helical reduction gears. This design allows it to
controlled by the operator in the EOS.
provide speed reduction and power split to the two
propulsor impellers. It does this by reducing the input
There is no local control at the GTE. The EOS
speed from the GTE and providing separate output
operator normal] y starts and stops the GTE by using the
shafts to the propulsor first-stage inducer and the
automatically controlled sequencer. In case of system
second-stage impeller, allowing these two sections to
malfunction or damage to the GTE, however, manual
operate at different speeds. An access hole in the
starting and stopping of the engine can be accomplished
high-speed assembly and one in the low-speed assembly
at the EOS control console.
provide a means for inspection. The gearbox assembly
The GTE drives the propulsor assembly by means
also provides four hydraulic pump accessory drive pads
of the power train assembly. We have already talked
as well as the drive pads for the lube oil supply and
about the LM2500 GTE that provides the power for the
scavenge pumps. Eight thermocouples, one in each
foilborne propulsion system. Now, let's take a look at
main bearing, monitor bearing temperatures.
the propulsor assembly for this system.
Flexible Coupling and Shaft Assemblies
PROPULSOR ASSEMBLY
The foilborne propulsor consists of a 2-stage
A double-diaphragm flexible coupling connects the
Aerojet Liquid Rocket waterjet pump, a bearing, and a
low-speed and high-speed pinion shafts. Each coaxial
seal assembly. The Aerojet pump forces seawater up
output shaft consists of an inner high-speed quill shaft
and an outer low-speed quill shaft. Splines in the
through the two ducts in the two aft foil struts into a
high-speed and low-speed output gears drive the output
single foilborne water jet nozzle that exhausts the
seawater through a transom at the hullborne waterline.
shafts.
