7.13 Main Propulsion - 7.13 Main Propulsion

Question 1

Types of Propulsion Plants

Answer 1

Diesel
Gas Turbine
Hybrid
Steam

Question 2

Gas Turbine Advantages

Answer 2

High power to weight ratio
Lack of low-frequency vibrations (ASW)
Economical on power/dollar basis
Good fuel efficiency at high speeds (near rated power)

Question 3

Gas Turbine Disadvantages

Answer 3

High complexity, sensitive tolerances
More maintenance load
Depot level repairs
Large amount of exhaust heat (concern for IR seeker missiles)
Poor fuel efficiency at low and moderate speeds
Large intake air requirements – stack configuration

Question 4

Gas Turbine Theory

Answer 4

Brayton Cycle

LM2500 has two major sections:
Gas Generator (GG)
Power Turbine (PT)

Question 5

Diesel Engine Advantages

Answer 5

Highly efficient throughout load range
Low cost
Low RPM ? Smaller MRG
Reliable

Question 6

Diesel Engine Disadvantages

Answer 6

Lower power to weight than GT
Periodic engine overhauls
Large vessels require multiple units to drive each shaft

Question 7

Diesel Engine Cycle (Theory)

Answer 7

4-Stroke Operation

Question 8

Steam Plant Advantages

Answer 8

High efficiency and reliability
Adaptable to nuclear power (less logistics/ greater endurance)
Steam used for propulsion as well as auxiliaries (i.e. generators, distillers)
No air required (submarine advantage)

Question 9

Steam Plant Disadvantages

Answer 9

Many components and subsystems; large size/weight
High watchstander and maintenance requirements
Long light-off times (steam plant warmups)

Question 10

Basic Steam Cycle

Answer 10

Question 11

Steam-Nuclear Advantages

Answer 11

Nearly unlimited endurance (carriers refuel once every 25 years). No air required. Nuclear submarines can remain submerged much longer than diesel-electric submarines.

Question 12

Steam-Nuclear Disadvantages

Answer 12

Many components and subsystems; large size/weight
High watchstander and maintenance requirements
Long light-off times (steam plant warmups)

Question 13

Hybrid Plants

Answer 13

New ship classes such as LCS and LHA employ a hybrid propulsion plant to optimize performance over a range of conditions.

LCS class uses gas turbines at higher speeds, and diesels for transiting at lower speeds.

LHA class (and LHD 8) uses gas turbines at high speeds, and electric propulsion motors at lower speeds. The EPMs are powered by the ship’s diesel generators.