In a ship, an engine room is where the main engine(s), generators, compressors, pumps, fuel/lubrication oil purifiers and other major machinery are located. It is sometimes referred to as the "machinery space". Engine Rooms are typically towards the stern, or rear, of the boat from the crews living accommodations. On modern ships, a sound-proofed, air-conditioned engine control room (ECR) is situated next to the engine room (ER), for the ship's machinery control systems.
The engine compartment of a locomotive may be described as an engine room.
An engine room will usually contain multiple engines, either diesel or heavy fuel. The engines are used to provide mechanical power to generators (which generate power) and the main propulsion propeller (the "screw"). Several different layouts exist, some involving gear boxes. As well as the main engine (or 'prime mover'), an engine room will often contain numerous other engines. For example, a typical steamship's engine room will also contain smaller steam engines driving ballast-trim pumps, water circulating pumps, boiler feed pumps, fuel oil pumps etc. On modern ships these functions are usually performed by smaller diesel engines or electric motors.
The electricity generating plant powers the ships electrics and pumps. This often runs on separate engines, with an array of smaller generators contributing towards the ships required power levels. A margin of error will be allowed, e.g. a ship requiring 3000 kW of power might employ four 1000 kW generators.
Thrusters, like main propellers, are reversible by hydraulic operation. Small embedded hydraulic motors rotate the blades up to 180 degrees to reverse the direction of the thrust.
If equipped with internal combustion or turbine engines, engine rooms employ some means of providing air for the operation of the engines and associated ventilation. If individuals are normally present in these rooms, additional ventilation should be available to keep engine room temperatures to acceptable limits. If personnel are not normally in the engine space, as in many pleasure boats, the ventilation need only be sufficient to supply the engines with intake air. This would require an unrestricted hull opening of the same size as the intake area of the engine itself assuming the hull opening is in the engine room itself. Commonly screens are placed over such openings and if this is done, airflow is reduced by approximately 50% so the opening area is increased appropriately. The requirement for general ventilation and the requirement for sufficient combustion air are quite different. A typical arrangement might be to make the opening large enough to provide intake air plus 1000 Cubic Feet per Minute (CFM) for additional ventilation. The engines will pull sufficient air into the engine room for their use. However, to achieve the additional airflow desired, intake/exhaust blowers will probably be required because the engines will only generate airflow sufficient for their demand at the time.