Tragic Titanic raised steam power profile

The White Star Line’s first move towards becoming proud owners of the world’s largest passenger liners, Olympic and Titanic, was made by managing director Bruce Ismay in 1907 at a private dinner with Lord Pirrie, chairman of the Harland and Wolff shipyard in Belfast. That evening he casually drew up plans for three vessels that would be far larger than any hitherto built.

An order for the third ship was soon postponed but construction of the others was swiftly started. Olympic was delivered first and was followed by Titanic, launched at end-May 1911 and fitted out over the next 10 months. The sea trials of Titanic started on 2nd April 1912 and a week later the ship set sail from Southampton for New York. The rest is tragic history.

Three days into the maiden voyage the liner was lying at the bottom of the North Atlantic. Some 1,517 passengers and crew had perished after the ‘unsinkable’ Titanic had struck an iceberg just before midnight on 14 April and sank two-and-a-half hours later.

Olympic and Titanic were launched at a time of aggressive competition by the great transatlantic steamship companies for supremacy in liner size, luxury and speed. White Star Line’s new pair may not have been the fastest but were certainly the largest and most luxurious. Design modifications made Titanic slightly larger than its sistership on completion and at 46,328gt the ill-fated vessel was, early in 1912, the largest ship ever built.

To propel such a structure at 24-25 knots dictated a power of at least 50,000 shp but, as it was designed at a time when the steam turbine was still not fully perfected, the main propulsive power had to come from reciprocating steam engines.

Although still in comparative infancy, however, the turbine was adopted for driving the centre propeller of the triple-screw liner. The port and starboard screws were each driven by a massive reciprocating steam engine, while the centre screw was driven by a low pressure direct-coupled turbine.

The machinery spaces were necessarily vast and extensive sub-division of the hull meant that the power plant was spread over most of the vessel’s 882.5ft (269m) length. Six watertight compartments were taken up by boiler rooms accommodating 24 double-ended and five single-ended Scotch boilers; further aft came the three enginerooms.

A forward engineroom housed the two steam reciprocating engines while – owing to its great size – the exhaust steam turbine coupled to the centre propeller had to be mounted in its own room immediately abaft the reciprocating engines.

Located with the turbine in the aft engineroom were the main condensers and auxiliaries for the turbine, while a considerable amount of ancillary machinery was arranged in the wings of the forward engineroom. The third and aftermost machinery space was allocated to the auxiliary generating sets.

The combination of reciprocating engines with a Parsons low pressure steam turbine was hailed at the time as an example of great progress in marine engineering. Olympic, however, was not the first ship to feature such an arrangement. Harland and Wolff had already put the concept to the test a couple of years earlier in the White Star liner Laurentic, whose power plant reportedly yielded remarkable results.

Titanic’s two sets of reciprocating engines were four-cylinder triple-expansion designs balanced by the Yarrow, Schlick and Tweedy system. The cylinder diameters were 54 inches (137.2cm) and 84 inches (213.4cm) for the high pressure (HP) and intermediate pressure (IP) units respectively, and 97 inches (246.4cm) for each of the low pressure (LP) cylinder pair; all shared a stroke of 75 inches (190.5cm).

It is interesting that each engine featured two LP cylinders according to the balancing system, rather than two IP units, as was more common for four-legged triple-expansion engines. An LP cylinder was arranged at each end of the engines. The typical steam conditions at the various stages were: HP cylinder inlet (215 lb/in²/394^oF); IP cylinder inlet (78 lb/in²/322^oF); and LP cylinder inlet (24 lb/in²/266^oF).

Each engine developed 16,000 ihp at 75 rpm, with steam supplied at a pressure of 215 lb/in² exhausting from the (four) LP cylinders of both engines to the single turbine at 9 lb/in² abs/188^oF. A key element of the machinery was a huge changeover valve to direct the exhaust steam from the LP cylinders to either the main condensers or the turbine.

The exhaust steam turbine was non-reversible, so manoeuvring the ship was executed using the wing propellers alone; once the ship was full away the turbine was brought into action.

The reciprocating main engines with an LP cylinder at each end were equipped with the traditional Stephenson’s Link motion valve gear but their size called for two D-type slide valves for each LP cylinder. The two valves worked side-by-side and were connected to a common crosshead operated by the usual double-bar links and eccentrics. For the other two cylinders of each engine, a single piston valve served the HP cylinder while two piston valves were fitted to the IP cylinder.

Each engine drove its associated 28-inch (71.1cm) diameter propeller shaft through a thrust block of the old multi-collar type, incorporating no less than 14 collars to each thrust unit.

Aspinall-type governors fitted to the engines relieved the watchkeeper from the tiresome task of manipulating the throttle in rough weather, while a ball governor coupled to the turbine acted directly on the control gear for the changeover valves between steam engines and turbine. In the event of the turbine running away, the engine exhaust steam could be automatically directed to the condensers, thus shutting off the steam supply to the turbine.

The Parsons multi-stage reaction design LP exhaust turbine developed around 16,000 shp when running at 165 rpm, an idea of its overall size given by a rotor that was 12ft (3.7m) in diameter and almost 14ft (4.3m) long over the blade section. The complete turbine weighed 420 tons, of which the rotor accounted for 130 tons; its Parsons laced-type blades ranged in length from 18 inches (45.7cm) to 25½ inches (64.8cm).

The 16½ft-diameter/22-ton central propeller driven by the turbine had four blades, while each wing shaft drove three-bladed 23½ft-diameter (7.2m)/38-ton propellers. The blades were bolted on to a cast steel hub, each secured by eight nuts and studs.

Providing a steam supply to match the massive reciprocating engines was a challenge for the machinery designers, resulting in the provision of 29 boilers, each 15ft 9-inches (4.8m) in diameter and 20ft (6m) long. Six furnaces were incorporated in the 24 double-ended units and three furnaces in the five single-ended types. A total of 159 coal-fired furnaces were thus deployed, consuming around 850 tons of fuel a day.

No.1 boiler room, closest to the engines, housed the five single-ended boilers abreast; Nos. 2, 3, 4 and 5 boiler rooms each contained five double-ended boilers abreast; and right forward only four boilers would fit into the narrowed space available.

Firing all these hungry furnaces was a challenge and the designers did their best to ease fuel handling and avoid coal heaps on the boiler room plates. The main coal bunkers were in a tweendeck space on each side of the ship between the lower and middle decks of the machinery space, from where the coal was hand trimmed to cross bunkers extending right across the full width of each boiler room.

Stokers took their coal from doors in the cross bunkers immediately opposite the furnaces. Watertight doors between each boiler room were placed at the centre of the cross bunkers.

The 24 double-ended boilers called for 48 firemen, 20 trimmers and five leading firemen to be on duty for each four-hour watch; and each boiler room required four trimmers to cart the coal and carry ash to the ejectors. One fireman was responsible for working one end of a double-ended boiler, while leading firemen supervised the boiler room crew.

Firing the boilers was to a schedule regulated by a Kilroy’s Stoking Regulator in conjunction with Kilroy’s Stoking Indicator for each boiler. These devices, via indicators and gongs, gave the signal for the firemen of the exact moment that each furnace was to be fired; the regulator could be set for firing the furnaces every eight, nine, 10, 12, 15, 20, 25 or 30 minutes, depending on how much steam was needed and the number of boilers on line at any time.

The instruments were so configured that the minimum number of furnace doors were open at the same time, and no two opposite doors in a double-ended furnace would be open at the same time. The intervals between firing could be set by the duty engineer.

Handling the ashes might seem to be a major problem but the arrangements on Olympic and Titanic were quite simple and effective. The firemen shovelled the ashes into a hopper placed on the stokehold floor, from where they were sucked to a water jet which carried the ashes well clear of the ship’s side. As well as the 10 See’s ash ejector pumps fitted, four hoists were provided for port use, by which bagged ashes were lifted to upper deck discharge points.

Firemen who served on Olympic described the work as good and not at all like earlier coal-burners, where coal was everywhere in the stokeholds and intense heat contributed to the traditional ‘hell-hole’ image. Their key task was to keep the furnaces full at regular intervals, and there was not too much slicing and raking of furnaces.

Conditions were further improved by the White Star Line policy of forced ventilation of the stokeholds and no forced draught of the boilers. With the average height of the four 24½-ft (7.5m) major axis diameter funnels some 150ft (45.7m) above the firebars, however, natural draught was hardly a problem.

The superlative dimensions of the main engines and boilers were mirrored by some of the auxiliary plant. Many ship designers of the period did not devote much importance and hence space to electricity generating machinery but the two superliners were in a league of their own in lighting demands alone.

A separate machinery space – described as palatial – housed the four large steam-powered generator engines, which were of the W H Allen totally-enclosed compound type. Each engine, comprising an HP cylinder (17-inch/43.2cm bore) and two LP cylinders (20-inch/50.8cm bores) with 13-inch (33cm) strokes, was directly coupled to a compound-wound 400kW DC dynamo also manufactured by W H Allen. Steam was supplied at 185 lb/in² and at a maximum speed of 325 rpm the auxiliary engines could each develop 580 ihp.

Large steam reciprocating engines were chosen for electrical power generation rather than turbines because of the exhaust steam being used for boiler feed water heating (turbines would have needed to exhaust into a condenser if their economy of operation was not to be seriously undermined). Power was generated at 100V with a full load plant capacity of around 20,000A.

In addition, two 30kW steam-driven gensets were mounted on the saloon deck level way above the waterline: these were running until Titanic sank, the doomed liner reportedly going under with ‘all lights blazing’.

Steam engines of a similar size to the main genset machines were also used to drive the main circulating pumps. Two separate centrifugal pumpsets, each driven by a 13-inch (33cm) and 22½-inch (57.4cm) bore/15-inch (38.1cm) stroke two-cylinder compound engine, were installed on each side of the turbine engineroom. These delivered huge quantities of sea water to the two main pear-shaped condensers in the same room which were designed to operate at 28½-inches (72.6cm) of vacuum.

Also arranged in the turbine room were the Weir Duplex-type main air pumps, four in all, incorporating air and water cylinders of 36-inch (91.4cm) diameter and 21-inch (53.3cm) stroke. MP