Unit
- Diesel propulsion: The most common marine prime mover, using two-stroke or four-stroke engines. Two-stroke engines are preferred for large vessels due to their high power-to-weight ratio and ability to burn heavy fuel oil. Four-stroke engines serve smaller ships and auxiliary generators.
- Gas turbine propulsion: Used in naval vessels and high-speed ferries for their high power density and rapid start capability. They require reduction gearing because of high rotational speeds. Exhaust heat recovery can improve overall thermal efficiency.
- Steam turbine propulsion: Historically dominant in large tankers and LNG carriers. Modern steam plants use reheat cycles and waste heat recovery. They offer smooth operation and fuel flexibility but lower thermal efficiency than diesel engines.
- Electric propulsion: Podded azimuth thrusters powered by electric motors, common in cruise ships and icebreakers. This setup improves manoeuvrability, reduces noise, and allows flexible engine room layout. Diesel-electric configurations decouple engine speed from propeller speed.
- Nuclear propulsion: Limited to naval submarines and icebreakers due to regulatory and cost barriers. Nuclear reactors provide long endurance without refueling. Pressurized water reactors are the standard design, with secondary steam loops driving turbines.
- Hybrid propulsion: Combines diesel generators, battery banks, and electric motors for peak shaving and zero-emission operation in ports. Energy management systems optimize load sharing. This technology reduces fuel consumption and emissions during low-speed maneuvering.
- LNG propulsion: Dual-fuel engines capable of burning liquefied natural gas and conventional fuel. LNG reduces sulfur oxide and particulate emissions. Storage and handling systems require cryogenic tanks and vaporization equipment.
- Methanol and ammonia propulsion: Emerging alternative fuels for decarbonization. Methanol can be used in modified diesel engines; ammonia requires careful handling due to toxicity. Both require new fuel supply systems and safety protocols.
System Architecture
Pattern: Propulsion System Topology
Components:
- Prime mover: Diesel engine, gas turbine, or steam turbine producing mechanical power.
- Transmission: Reduction gearbox, shaft line, and bearings transmitting torque to the propeller.
- Propeller: Fixed-pitch or controllable-pitch propeller converting rotational power into thrust.
- Control system: Electronic governor and remote control station managing speed and pitch settings.
Quick Revision
- Diesel engines dominate merchant shipping; two-stroke for large vessels, four-stroke for smaller.
- Gas turbines offer high power density for naval and high-speed applications.
- Electric propulsion with podded drives improves manoeuvrability and layout flexibility.
- Alternative fuels like LNG, methanol, and ammonia are emerging for emission reduction.