HMS Alliance -The Engine Room

The main engines are 8-cylinder 4-stroke supercharged Vickers diesels rated at 2,150 hp at 450rpm. The cylinder bore is 17.4 inches and the stroke 18.5inches. 215 tons of diesel fuel and 18 tons of lubricating oil were normally carried.

Unlike modern submarines, which have generators supplying the main battery, which in turn feeds the motors, Alliance had a common shaft running from each engine through the main motor to the propeller. A tail clutch and an engine clutch enabled either the engine or the motor to drive the propeller; or, alternatively, the motor could be used as a generator to recharge the main battery, with or without turning the propeller, or to float the load. These arrangements were similar on both sides.

The snort mast is simply a long tube with a head valve at the top to prevent the entry of seawater when raised and a hull valve where the induction system enters the Engine Room. Exhaust gases from the engines on the surface were passed outboard through muffler tanks at water level; but when snorting the gases had to be taken up through an exhaust mast whose open end was a few feet below the surface. There was therefore a backpressure on the engines and it was very important to open up the exhaust valves at exactly the right moment on starting to snort.

Starboard engine facing aft

Port engine facing forward

There was always a partial vacuum throughout the submarine when snorting because the engines inevitably drew air from inside the boat as well as down through the snort mast; there were strict limitations on the amount of vacuum permitted as well as on other conditions involving crew and engine safety.