What is the most commonly used marine propulsion system?

The most commonly used marine propulsion system is the internal combustion engine. It typically operates on diesel fuel or heavy fuel oil and works by converting the energy released from the combustion of the fuel into mechanical energy that turns the boat's propeller.

There are two main types of marine internal combustion engines: two-stroke and four-stroke engines. Two-stroke engines are simpler and lighter, but less fuel-efficient and more polluting than four-stroke engines. Four-stroke engines are heavier but more efficient and cleaner, as they burn fuel more completely and have a separate system for removing the exhaust gases.

In addition to internal combustion engines, there are other types of marine propulsion systems, such as steam turbines, gas turbines, and electric motors. Steam turbines are less common today but have been historically used to power large ships like ocean liners. Gas turbines are efficient and powerful but are mostly used for military and high-speed vessels. Electric motors powered by batteries or generators are becoming more popular for smaller boats due to their low noise levels, low emissions, and low maintenance requirements.