Engines, boilers and generators

Titanic was equipped with three engines – two reciprocating four-cylinder, triple-expansion steam engines and one centrally placed low-pressure Parsons turbine – each driving a propeller. The two reciprocating engines had a combined output of 30,000hp and a further 16,000hp was contributed by the turbine.[13] The White Star Line had previously used the same combination of engines on an earlier liner, the SS Laurentic, where it had been a great success.[23] It provided a good combination of performance and speed; reciprocating engines by themselves were not powerful enough to propel an Olympic-class liner at the desired speeds, while turbines were sufficiently powerful but caused uncomfortable vibrations, a problem that affected the all-turbine Cunard liners Lusitania and Mauretania.[24] By combining reciprocating engines with a turbine, fuel usage could be reduced and motive power increased, while using the same amount of steam.[25]
The two reciprocating engines were giants, each 63 feet (19 m) long and weighing 720 tons. Their bedplates alone weighed a further 195 tons.[24] They were powered by steam produced in 29 boilers, 24 of which were double-ended and 5 single-ended, which contained a total of 159 furnaces.[26] The boilers were 15 feet 9 inches (4.80 m) in diameter and 20 feet (6.1 m) long, each weighing 91.5 tons and capable of holding 48.5 tons of water.[27]
They were heated by burning coal, 6,611 tons of which could be carried in Titanic's bunkers with a further 1,092 tons in Hold 3. The furnaces required over 600 tons of coal a day to be shovelled into them by hand, requiring the services of 176 firemen working around the clock.[28] 100 tons of ash a day had to be disposed of by ejecting it into the sea.[29] The work was relentless, dirty and dangerous, and although firemen were paid relatively generously[28] there was a high suicide rate among those who worked in that capacity.[30]
Exhaust steam leaving the reciprocating engines was fed into the turbine, which was situated aft. From there it passed into a condenser so that the steam could be condensed back into water and reused.[31] The engines were attached directly to long shafts which drove the propellers. There were three, one for each engine; the outer (or wing) propellers were the largest, each carrying three blades of manganese-bronze alloy with a total diameter of 23.5 feet (7.2 m).[27] The central propeller was somewhat smaller at 17 feet (5.2 m) in diameter,[32] and could be stopped but not reversed.
Titanic's electrical plant was capable of producing more power than a typical city power station of the time.[33] Immediately aft of the turbine engine were four 400kW steam-driven electric generators, used to provide electrical power to the ship, plus two 30 kW auxiliary generators for emergency use.[34] Their location at the rear of the ship meant that they remained operational until the last few minutes before the ship sank.