CHAPTER 3
POWER TRAIN AND PROPULSION SYSTEMS
As a GS supervisor, you will primarily supervise the
operation and maintenance of the power train equipment
and controllable pitch propeller systems. This chapter
will focus on the maintenance and repair of the main
propulsion systems needed to support the operations of
the main propulsion gas turbine engines.
After studying the information in this chapter, you
should have a well-rounded understanding of the drive
train equipment and propulsion plant systems in gas
turbine-powered ships. You should better understand
t e r m s o f n o r m a l o p e r a t i o n s , s o m e c o m m o n
malfunctions, and your role as the GS supervisor.
POWER TRAIN
In Gas Turbine Systems Technician (Electrical)
3/Gas Turbine Systems Technician (Mechanical) 3,
volume 1, NAVEDTRA 10563, there is a fairly detailed
description of the various power train arrangements
used by gas turbine-powered ships. You may wish to
review those chapters on such items as construction,
principles of operation, nomenclature, and operating
parameters. In this section, we will cover some of the
power train system tests, inspections, adjustments, and
repairs that you will be responsible for as a supervisor.
MAIN REDUCTION GEAR
The inspection procedures and problems that occur
in main reduction gears (MRGs) are basically the same
for any system. It will not be necessary to differentiate
between classes of ships in this section, except where
specific differences exist. Additional information on the
inspection and adjustment of gear trains can be found in
Naval Ships’ Technical Manual (NSTM), chapter 9420,
“Propulsion Reduction Gears, Couplings, and
Associated Components,” NAVSEA 0901-LP-420-
0002, or in the manufacturer’s technical manual for your
specific installation.
Inspection and Repair
Before reading descriptions and details on MRG
inspections, you need to be familiar with the
terminology used throughout this section. The majority
of the following gear nomenclature also applies to
helical gears. Figure 3-1 may be of help on some of
these definitions.
RATIO. The number of gear teeth divided by the
number of teeth in the pinion.
LINE OF ACTION. The locus of the points of
contact as the profiles go through mesh. This line
passes through the pitch point and is tangent to the
base circle.
HELIX ANGLE (fig. 3-l). The angle formed by a
tooth and a plane passing through the axis of the
gear.
PRESSURE ANGLE (fig. 3-1). The angle between
the line of action and the line tangent to the pitch
circles.
TRANSVERSE DIAMETRAL PITCH. The ratio
of the number of teeth to the number of inches of
the pitch diameter.
NORMAL DIAMETRAL PITCH. The transverse
diametral pitch divided by the cosine of the helix
angle.
CHORDAL TOOTH THICKNESS (normal) (fig.
3-1). The thickness of the tooth measured on the
chord of the pitch diameter in the normal plane.
CIRCULAR PITCH (axial) (fig. 3-l). The length
of the arc on the pitch circle between similar points
of adjacent teeth in the plane of rotation.
CIRCULAR PITCH (normal) (fig. 3-l). The length
of the arc on the pitch circle between similar points
of adjacent teeth in the normal plane.
OUTSIDE DIAMETER (fig. 3-l). The diameter
measured over the tops of the teeth.
PITCH DIAMETER (fig. 3-l). The diameter of the
pitch circle.
BASE DIAMETER (fig. 3-l). The circle from
which a line is unwound to generate the involute
curve.
ROOT DIAMETER (fig. 3-1). The diameter of the
root circle.
ADDENDUM (fig. 3-1). The distance from the
pitch circle to the top of the tooth.
3-1
