Unit 11
GT & Misc Propulsion
Gas Turbine Propulsion:
Notes:
Engine types:
Aircraft-derivative Gas
Turbines
(“marinized” jet engines)
 light weight (1 lb/SHP)
 reliable, familiar to (aircraft)
maintenance staff
 off-the-shelf design
 gas generator change-out for
maintenance
 quick starting (1-2 minute
warm-up)
 burns jet fuel (JP-4 or JP-5) or
DFM
Industrial (Heavy Duty) Gas
Turbines
 heavier (15 ibs/SHP)
 custom design with numerous
heat recovery devices
(intercoolers, regenerators,
reheaters, etc.)
 must be maintained in place
 slower starting (15-20 minute
warm-up)
 burns cheaper residual fuel
The LM2500 series engine was selected in the early 1970's as the
prime mover for propulsion on the Spruance (DD 963) Class ships.
Different configurations of this engine have since been used on
each new class of Surface Combatants including the Oliver Hazard
Perry (FFG 7) Class, the Ticonderoga (CG 47) Class, the Kidd
(DDG 993) Class, the Arleigh Burke (DDG 51)/Oscar Austin (DDG
79) Class as well as the AOE 6 Class supply ships.
PS 111. Professional Studies
Unit 11: GT & Misc Propulsion
GT Basic Components:
GAS
GENERATOR
POWER
(FREE)
TURBINE
ACCESSORIES
MANEUVERING
&
REVERSING
provides working fluid (combustion gas) at high
temperature and pressure to be expanded through
power turbine; consists of
 compressor (centrifugal or axial type)
 combustion chamber (can type, annular or canannular type)
 (compressor) turbine: alternate rows of nozzles (or
nozzle vanes) and blades (of impulse, reaction or
hybrid type cooled by air in internal air passages)
single-spool gas generator: compressor & turbine
mounted on single shaft
twin-spool gas generator: LP compressor & LP rotor on
inner, slower shaft; HP compressor & turbine on outer,
faster shaft for increased efficiency
mounted on a separate shaft from the gas generator
(i.e. “split shaft) the power turbine is connected to the
load (reduction gears and propeller). Coupled
aerodynamically, but not mechanically to the gas
generator, the power turbine is “free” to spin at varying
RPM while the gas generator rotates at constant
speed. On smaller units such as electric generator
applications, the power turbine may be mounted on the
same shaft as the gas generator (“single shaft”)
normally driven by a reduction gear connected to HP
compressor shaft and provided with engine:
 fuel oil boost pump: delivers fuel nozzles in
combustors
 lube oil pump: delivers LO to bearings and gears
 deaerator: removes entrained air
 starting motor: electric, hydraulic, or air driven to
bring engine up to self-sustaining speed during
engine start sequence (spark plugs fired in
combustion chamber for starting only)
 control equipment: hydraulic pumps, governors,
speed switches, tachometers, etc.
 The speed at which the power turbines operates is
determined by the quantity of hot gasses it
receives from the gas generator and the load
placed on the propeller. This is termed power
control rather than speed control of the free
turbine. Thus the control of the fuel and air to the
combustors determines, ultimately, ship speed
 Gas turbines are inherently irreversible.
Reversal of propeller thrust must be accomplished
by external means such as:
1. electric drive
2. controllable pitch (CP) propeller
3. reversing gears (with hydraulic,
electric or friction type clutches)
11 -- 2
Notes:
PS 111. Professional Studies
Unit 11: GT & Misc Propulsion
Advantages of Electric Drive: Ease of control, flexibility of
arrangement and adaptability to multiple use of prime mover
generator sets
Applications:
 Ferries, icebreakers, tugs oceanographic vessels, and cablelayers which require a high degree of maneuverability
 self-unloaders, fireboats, dredges, drill ships and tenders which
have extensive electric power requirements not coincident with
maximum propulsion power requirements
 Cruise ships with a large hotel loads
 Vessels using non-reversing, high-speed and/or multiple
prime movers (e.g. gas turbine powered vessels)
Basic Components:
Propulsion Cabling:
3-wire (AC)
2-wire (DC)
Prime Mover:
Steam turbine
Gas turbine
MS or HS diesel
switchgear:
fwd/stop/reverse
Propulsion Motor:
AC (synchronous)
AC (Induction)
DC
Propulsion Generator:
AC or DC
AC Electric Drive Arrangements:
 AC motors are usually used in applications above 10,000hp
 “classical” plant comprised of dedicated variable speed
propulsion generator to power propulsion motor (at sea) or
cargo pumps (in port)
Propulsion
Prime-mover
Bus
Reduction
Gear
Special Purpose
(variable frequency)
Non-propulsion Loads
Cargo Gear, etc.
F
R
F
R
Propulsion
Generator
F
R
Switchgear:
Fwd/Stop/Rev
11 -- 3
Propulsion
Motor
Notes:
PS 111. Professional Studies
Unit 11: GT & Misc Propulsion
 tendency in modern plants to utilize solid state controlled AC
drives and induction motors
60Hz
Bus
Propulsion Auxiliaries
and Hotel Loads
Converter
No.1
GenSets
Propulsion
Motors
Converter
No.2
Generator Bank:
60 Hz AC power produced
by various combinations of
generator sets. No. of
units determined by
demand
other arrangements:
Some GenSets dedicated
to propulsion and special
service, others to ship
service.
Propulsion Motors:
 Typically induction type AC motors
controlled by variable frequency
output of converters
 propeller reversal accomplished
electronically by converters
 occasionally combined with CP
propellers (maneuvering at min.
pitch via converter output then
increasing pitch at 60Hz to obtain
sea speed)
Other Propulsion Drive Trains applicable to Non-Reversing
Engines:
 Controllable-Reversible Pitch (CRP) Propeller
Contain mechanism within propeller hub that can be operated
remotely to change pitch (by rotating blades about their radial axis).
Advantageous in the following situations:
 where maximum thrust requirements at widely varying
operations (Tugs, Trawlers, etc.)
 where unidirectional rotation is beneficial/required (e.g. non
reversing engines, highly skewed propellers, operating in
ice covered water, etc.)
 where extensive low speed maneuvering and/or rapid
response to thrust reversal is required
 where constant shaft rpm is required (i.e. shaft-driven
generators)
11 -- 4
PS 111. Professional Studies
Unit 11: GT & Misc Propulsion
Notes:
CRP Propeller
Reversing Gears
Reversin
g Gear
Aster
n
Clutc
h
AST
AHD
ENGINE
Aster
n
Pinio
Ahea
n
d
Pinio
n
PROPELLER
SHAFT
Ahea
d
Clutc
hReduction
Gear



AHEAD and ASTERN clutches are interlocked to prevent
simultaneous engagement
Propeller Shaft often fitted with a shaft brake that is activated
when BOTH clutches are disengaged
Clutch mechanism may be
Mechanical
Hydraulic
Electro-magnetic, or
pneumatic
11 -- 5
PS 111. Professional Studies
Unit 11: GT & Misc Propulsion
Drive Train Components:
Notes:
REDUCTION GEARS
Problem: Turbines (steam or gas) are high speed, low torque devices (Re: HP =
torque x rpm), while propellers are high torque, low speed (relatively) devices for
the same HP. How can the two be connected?
Solution: Reduction Gears
Single Reduction:
rpm1
in equilibrium (constant speed)
F2
 F1 = F2
rpm2
 and pinion torque T1 = F1 x r1
 while rd. gear torque, T2 = F2 x r2
r1
then
HS
r2
PINION
T1/T2 = r1/r2
and since
rpm1/rpm2 = r2/r1
F1
then
1st
T1/T2 = rpm2/rpm1
REDUCTION
Finally
GEAR
P1 = T1 x rpm1 = T2 x rpm2 = P2
i.e. Pinion Power = Red. Gear Power
but speed is traded for torque !
rpm1
rpm2
HS
PINION
rpm2
1st
REDUCTION
GEAR
LS PINION
rpm3
2nd REDUCTION GEAR
(BULL GEAR)
rpm3
LINE SHAFT
Double reduction:
LS pinion radius = r3
2nd reduction gear radius = r4
but
LS Pinion mechanically joined to 1st
Reduction Gear
thus
rpm2/rpm3 = r4/r3
hence
T1/T3 = rpm3/rpm4 = [r1/r2]x[r3/r4]
Maximum limit for single reduction is
approx. 10:1
for double reduction, 100:1
For TSES at full power (17,500 HP)
HP turbine = 5600rpm
LP turbine = 3600rpm
HP 1st red. gear = 755 rpm
LP 1st red gear = 755 rpm
shaft = 104 rpm
Thus HP HS pinion:shaft =
[5600:755] x [755:104] =
[7.4:1] x [7:3:1] = 53.8:1
and LP HS pinion:shaft =
[3400:755] x [755:104] =
[4.5:1] x [7.3:1] = 32.7:1
11 -- 6
PS 111. Professional Studies
Unit 11: GT & Misc Propulsion
TSES VI Reduction Gears:
Double input (HP & LP turbines), Single Output, CrossCompounded, Articulated
LP Flex
Coupling
LP, HS Pinion
HP, 1st Reduction Gear
HP, LS Pinion
LP
Main
THRUST
Bearing
HP Flex
Coupling
Quill Shafts
HP
Line Shaft
(“SPRING”)
Bearing
HP, HS Pinion
2nd Reduction
(“BULL”)Gear
HP, LS Pinion
MAIN THRUST BEARING
11 -- 7
HP, 1st Reduction
Gear
Notes:
PS 111. Professional Studies
Unit 11: GT & Misc Propulsion
LINE SAFT BEARINGS
.
Notes:
STERN TUBE BEARINGS
Water Lubricated
 Lignum Vitae (wood!) – TSES VI
 Synthetic/composite
Oil Lubricated
11 -- 8
PS 111. Professional Studies
Combined Cycle Propulsion Plants
Diesel
And
Steam
COmbined Gas
Or
Nuclear
COGAG
COGOG
CODAG
CODOG
COGES
CONAG
Unit 11: GT & Misc Propulsion
Notes:
Gas
Steam
Small gas turbines used for cruising mode and large units for
maximum power (since GT’s are most efficient at near their full
power rating). A COGAG arrangement would utilize both the
large and small turbines together for maximum power situations.
In a COGOG arrangement, the larger GT(s) would replace the
smaller ones during high power operation.
Combine diesels (usually medium speed) for increased range at
low power while maintaining high speed capability with gas
turbines. A CODAG arrangement would utilize both Diesel and
GT’s at full power. In a CODOG arrangement the diesel engines
would be disconnected and secured when the GT is in operation
The LM2500 is also available as a Combined Gas Turbine Steam
and Electric System (COGES). High-pressure, superheated
steam is produced from exhaust gas, which is used to power the
steam turbine generator set. This arrangement increases system
thermal efficiency by 10 to 20 percent.
A thought experiment, combining the immense range properties
of nuclear propulsion with gas turbines for burst power. No such
plant exists today.
“Waste Heat”
Boiler
11 -- 9
PS 111. Professional Studies
Unit 11: GT & Misc Propulsion
The Engine Order Telegraph is the electrical/mechanical means by which Notes:
the bridge communicates to the propulsion control station the desired engine
speed. With a manually operated system, the engine orders are recorded in Bell
Book at the propulsion station and (a second copy is maintained on the bridge).
These records are extensions of the official log and should be treated as such.
The following standard shorthand is used for the corresponding maneuvering
speed:
STOP
STANDBY
DEAD SLOW
AHEAD
D
D
SLOW AHEAD
SLOW ASTERN
HALF AHEAD
HALF ASTERN
FULL AHEAD
E
EMERGENCY
FULL AHEAD
DEAD SLOW
ASTERN
FULL ASTERN
E
EMERGENCY
FULL ASTERN
When other than standard maneuvering speeds are required by the
bridge, the ordered RPM is recorded in lieu of the standard symbol
In automated plants, speed changes are recorded by a Bell Logger
interfaced with the control station console. The printout of the Bell
Logger supplants the Bell Book.
Maneuvering Modes:
Bridge Control: The bridge console engine order telegraph is
actually the throttle, ship speed and direction is initiated by bridge
personnel.
Engine Room (automated) Control: Engine console engine order
telegraph is actually the throttle, ship speed and direction as
indicated by bridge telegraph position is matched by engine
telegraph position. Control is transferred by bridge request
acknowledge by engine room. Engine room control may be
assumed at any time in an emergency.
Engine Room (manual) Control: Telegraph used to communicate
engine speed/direction order (as on TSES). Telegraph order
acknowledge by engine room personnel by matching pointer
position and engines maneuvered independently.
11 -- 10