1. Steam propulsion plants: This is the oldest type of naval propulsion and it is still used today by many ships. It comprises a series of boilers where coal (up to WWI) or fuel-oil (after WWI) is burned to heat the feed water and produce high pressure steam that is delivered to the turbines that turn the propellers. This derived of the force generated from the impact of the high pressure steam on the turbine blades.
2. Diesel propulsion plants: In these type of plants the fuel is injected and burned inside the cylinders of the diesel engines that move the propellers through a reduction gear. Since there are no boilers nor turbines, weight and space is saved. This system has higher efficiency, and because of its lower rate of fuel consumption provides ships with longer range than steam propulsion plants. However, diesel powered ships are generally slower than those powered by steam. Another disadvantage is that diesel engines are too noisy making them easily detected by passive sonar.
3. Gas propulsion plants: This system is similar to that used in jet aircraft and it became widely used in the 1950's. The fuel combustion generates gas that rotates the gas turbines and turn the propellers. It requires high fuel consumption and it is not efficient as diesels, but provides higher speed, quicker response time, faster acceleration/deceleration and weight reduction.
4. Combined propulsion plants: These plants are used to take advantage of both diesel and gas systems. Main arrangements for combined plants:
- a) CODAD (COmbined Diesel And Diesel). Usually comprised of 2 diesel engines for cruising speed, adding the power of 2 other diesel engines for high speed operation.
b) CODOG (COmbined Diesel Or Gas turbine). The cruising speed is attained with the diesel engines and the gas turbines are used for high speed operation.
c) COGOG (COmbined Gas turbine Or Gas turbine).
d) COGAG (COmbined Gas turbine And Gas turbine).