Cargo ships are used for transporting cargo in large quantity from one seaport to another. They are large vessels usually from 40000 tons and above. They are constructed with compartments to hold cargo such as iron ore, coal, rice etc. Their propulsion system is diesel engines which are usually two- stroke engines.Two stroke engines consist of a piston enclosed in a cylinder in which fuel combustion takes place. The piston is connected to the crankshaft by a connecting rod. The crankshaft is connected to the propeller shaft which rotates in water and provides thrust that propels the ship forward. When the fuel is injected into the combustion chamber in the cylinder explosion takes places as the compressed fuel is mixed with hot air. The energy produced during this explosion pushes the piston downwards and this motion is transmitted by the connecting rod to the crankshaft. The crankshaft then rotates and transmits mechanical energy to the propeller shaft which provides thrust to propel the ship forward on water.