A turbocharged diesel engine directly drives the propeller, and in order to achieve high propulsion efficiency, a lower rotational speed is required. Medium and high-speed diesel engines drive propellers through gear reducers, which are generally equipped with reverse mechanisms to achieve propeller reversal. However, low-speed diesel engines and some medium speed diesel engines can reverse themselves. Medium and high-speed diesel engines also achieve electric transmission through generators, motors, and propellers. When high power is required, multiple engines can also be used in parallel. When sailing at low speeds, only one main engine can work, thereby improving operational efficiency and reliability. When installing two main engines on the same ship, they are divided into left engine and right engine based on the installation position and propeller rotation.