Ship Propulsion System

Ships come in many shapes and sizes according to what their purpose is and how they are propelled or which engine design they use. Someone might wonder what the difference between a boat and a ship is. Well, the distinction is based on size, shape, load capacity, and tradition— but, there is no universally accepted distinction.

There are freshwater, merchant ships, special purpose vessels, and naval vessels.  They can be used to carry passengers, for defense, research, or fishing. A ship can be powered by reciprocating steam engines, steam turbines, reciprocating diesel engines, LNG engines, gas turbines, sterling engines, and electric propulsion systems. However, the most common engine used on modern marine vessels are reciprocating diesel engines.

Reciprocating diesel engines offer operating simplicity, robustness, and better fuel economy compared to other power sources. They can be categorized into a four-stroke engines or two-stroke engines. Four-stroke engines are generally used in smaller vessels and are used to produce electrical power and propulsion. Two-stroke engines are used for propulsion and are larger.

Four-stroke engines operate by repeating a cycle of four strokes where the piston moves up and down twice. During intake, air is drawn into the cylinder through an air inlet valve as the piston moves down; when the inlet valve closes, the piston moves up and compresses the air mixture which heats it up. Fuel is injected into the hot gas and ignites. Once ignited, the piston is pushed down, and this drives the crankshaft that sends power to the wheels. The returning piston pushes a valve open and lets the exhaust gases out.

Two-stroke engines operate by repeating a cycle of two strokes where the piston moves up and down once. There are three stages. Fresh air is blown into the side of the cylinder and old exhaust is pushed out through valves located at the top. The piston will then move up, compress the air, and heat it up. Fuel is injected and ignites once the piston reaches the top of the cylinder. Once ignited, the piston moves down and drives the crankshaft which then sends power to the wheels. Two-stroke engines are smaller and lighter, but they tend to suffer higher wear and tear.

At Aviation Purchasing Platform, owned and operated by ASAP Semiconductor, we can help you find all the ship and boat propulsion components you need. As a premier supplier of parts for the aerospace, civil aviation, and marine industries, we’re always available and ready to help you find all the parts and equipment you need, 24/7x365. For a quick and competitive quote, email us at or call us at +1-714-705-4780.


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