Steam generated in the boiler rooms was used to drive the two engines in this compartment, each directly coupled (no gearbox) to one of the propellers. The propellers rotated in opposite directions, the starboard engine being right hand and the port engine being left hand.
The main engines are 4 cylinder triple expansion reciprocating engines each of 2 750 indicated horse power. Triple expansion steam engines have 3 different sized cylinders, the small one is the high pressure (HP) cylinder, the medium one the Intermediate Pressure (IP) cylinder and the largest (at each end) the Low Pressure (LP) cylinder. Steam at high pressure is admitted into the HP cylinder and operates on the relatively small area of the piston. At the end of the stroke, the steam is exhausted at a lower pressure due to expansion and enters the IP cylinder where, although at reduced pressure, it works on a larger piston area. From the IP cylinder, the steam is exhausted at a further reduced pressure into the LP cylinders. Here the piston area is very large and although the pressure acting on the piston is low, the resulting effort is equal to that in either of the other 2 cylinders.
The steam then passes through a condenser, which cools it back to water for return to the boiler. This is located outboard behind each engine.
Engine speed instructions were transmitted from the wheelhouse to the engine room by engine telegraphs. The telegraph dials can be seen in the middle of the lower level. The engine room stokers would adjust the amount of steam fed to each engine by turning the large silver wheels which opened or closed valves in the steam lines.
The dial above and between the telegraph dials is the revolution telegraph.
In both aft corners and behind the upper grating are two steam driven electric generators, which supplied electrical power to the ship when at sea.
The green tank at the rear of the engine room is the fresh water distiller, capable of making 40 tons (about 40 600 litres) of fresh water a day from sea water. The pump beside the distiller is a 3 stage pump for pumping sea water, fresh water and brine.
When at sea, an Engine Room Artificer (ERA) was in charge of the engine room with one leading stoker watch-keeping the distiller and a stoker on each engine. Engine room and boiler room crew made up approximately one third of the ship’s company.
Steam pressure was 225 psi.. Maximum speed was 18/19 knots at 187 rpm. Fuel consumption was about 3 tons per hour at full speed.