Marine engineering is a close cousin of mechanical engineering and covers a wide spectrum of subjects within itself. Basically it relates to the machinery and other equipment on board ships which include, but is not limited to the following.
2-Stroke engines: a normal sized ship contains at least one main propulsion plant that is concerned with the rotation of the propeller. The engine normally starts off on diesel later changed over to heavy fuel oil to save costs.
4-Stroke engines: normally there could be 3 auxiliary engines on a ship which are four stroke engines running on diesel/heavy fuel oil which are used to supply the power needs of the vessel including other machineries, accommodation power, cranes, hatches etc.
Oil purifiers: a ship contains several types of oil such as heavy fuel oil, diesel oil, lubricating oil etc in tanks and appropriate storage spaces. This oil needs to be purified prior to consumption which is done with the help of centrifuges or purifiers which separate the oil and impurities based on their density difference
RAC equipment: a ship has to move literally all over the globe and hence is subject to extremes of temperature and climate in different regions of the world and also there needs to be sub-zero storage facilities for foodstuff to make it last longer. Hence refrigeration and air conditioning equipment form an important part of the ships accessories.
Boilers: steam is used on board ships for various purposes such as heating heavy oil, lubricating oil etc and in cargo tanks for maintaining temperature of the cargo. This steam is generated with the help of boilers which are driven by oil.
Inert Gas generators: IG generators are used mostly on board tankers and OBOs which is used to making the atmosphere of cargo tanks as inert so that the risk of flame and explosion is minimized during transportation of the same.
Pumps: pumps form the lifeline of a ship since various fluids are transported all over the vessel including water, oil, cargo etc. There is a huge network of pipelines all over the vessel for the same purpose and usually color coding is used to distinguish one type of pipeline from the other. Valves are fitted at appropriate places to control and navigate the direction and quantity of flow of the fluids.
Electronics: a modern ship is fitted with most modern gadgets necessary for operation and safety of the vessel such as Radar, Transponder, Satellite transmitter/receiver, automation circuitry and so forth.
The main tasks of a marine engineer are related to the routine as well as breakdown maintenance of the above machinery. There is a hierarchy of engineers topped by the Chief Engineer and other engineers who work as a team to take care of the machinery. The engineers have to pass rigorous exams conducted by maritime authorities of the individual nations.