The sheer size of Titanic and her sister ships posed a major engineering challenge for Harland and Wolff; no shipbuilder had ever before attempted to construct vessels this size. The ships were constructed on Queen's Island, now known as the Titanic Quarter, in Belfast Harbour. Harland and Wolff had to demolish three existing slipways and build two new ones, the largest ever constructed up to that time, to accommodate both ships. Their construction was facilitated by an enormous gantry built by Sir William Arrol & Co., a Scottish firm responsible for the building of the Forth Bridge and London's Tower Bridge. The Arrol Gantry stood 228 feet (69 m) high, was 270 feet (82 m) wide and 840 feet (260 m) long, and weighed more than 6,000 tons. It accommodated a number of mobile cranes. A separate floating crane, capable of lifting 200 tons, was brought in from Germany.
The construction of Olympic and Titanic took place virtually in parallel, with Olympic's keel laid down first on 16 December 1908 and Titanic's on 31 March 1909. Both ships took about 26 months to build and followed much the same construction process. They were designed essentially as an enormous floating box girder, with the keel acting as a backbone and the frames of the hull forming the ribs. At the base of the ships, a double bottom 5 feet 3 inches (1.60 m) deep supported 300 frames, each between 24 inches (61 cm) and 36 inches (91 cm) apart and measuring up to about 66 feet (20 m) long. They terminated at the bridge deck (B Deck) and were covered with steel plates which formed the outer skin of the ships.
The 2,000 hull plates were single pieces of rolled steel plate, mostly up to 6 feet (1.8 m) wide and 30 feet (9.1 m) long and weighing between 2.5 and 3 tons. Their thickness varied from 1 inch (2.5 cm) to 1.5 inches (3.8 cm). The plates were laid in a clinkered (overlapping) fashion from the keel to the bilge. Above that point they were laid in the "in and out" fashion, where strake plating was applied in bands (the "in strakes") with the gaps covered by the "out strakes", overlapping on the edges. Commercial oxy-fuel and electric arc welding methods, ubiquitous in fabrication today, were still in their infancy; like most other iron and steel structures of the era, the hull was held together with over three million iron and steel rivets, which by themselves weighed over 1,200 tons. They were fitted using hydraulic machines or were hammered in by hand. In the 1990s some material scientists concluded that the steel plate used for the ship was subject to being especially brittle when cold, and that this brittleness exacerbated the impact damage and hastened the sinking. It is believed that, by the standards of the time, the steel plate's quality was good, not faulty, but that it was inferior to what would be used for shipbuilding purposes in later decades, owing to advances in the metallurgy of steelmaking.As for the rivets, considerable emphasis has also been placed on their quality and strength.
Among the last items to be fitted on Titanic before the ship's launch were her two side anchors and one centre anchor. The anchors themselves were a challenge to make, with the centre anchor being the largest ever forged by hand and weighing nearly 16 tons. Twenty Clydesdale draught horses were needed to haul the centre anchor by wagon from the Noah Hingley & Sons Ltd forge shop in Netherton, near Dudley, United Kingdom to the Dudley railway station two miles away. From there it was shipped by rail to Fleetwood in Lancashire before being loaded aboard a ship and sent to Belfast.
The work of constructing the ships was difficult and dangerous. For the 15,000 men who worked at Harland and Wolff at the time,safety precautions were rudimentary at best; a lot of the work was carried out without equipment like hard hats or hand guards on machinery. As a result, during Titanic's construction, 246 injuries were recorded, 28 of them "severe", such as arms severed by machines or legs crushed under falling pieces of steel. Six people died on the ship herself while she was being constructed and fitted out, and another two died in the shipyard workshops and sheds. Just before the launch a worker was killed when a piece of wood fell on him.
Titanic was launched at 12:15 p.m. on 31 May 1911 in the presence of Lord Pirrie, J. Pierpont Morgan, J. Bruce Ismay and 100,000 onlookers.Twenty-two tons of soap and tallow were spread on the slipway to lubricate the ship's passage into the River Lagan. In keeping with the White Star Line's traditional policy, the ship was not formally named or christened with champagne.The ship was towed to a fitting-out berth where, over the course of the next year, her engines, funnels and superstructure were installed and her interior was fitted out.
Although Titanic was virtually identical to the class's lead ship Olympic, a few changes were made to distinguish both ships. The most noticeable exterior difference was that Titanic (and the third vessel in class, Britannic) had a steel screen with sliding windows installed along the forward half of the A Deck promenade. This was installed as a last minute change at the personal request of Bruce Ismay, and was intended to provide additional shelter to First Class passengers.Extensive changes were made to B Deck on Titanic as the promenade space in this deck, which had proven unpopular on Olympic, was converted into additional First Class cabins, including two opulent parlour suites with their own private promenade spaces. The À la Carte restaurant was also enlarged and the Café Parisien, an entirely new feature which did not exist on Olympic, was added. These changes made Titanic slightly heavier than her sister, and thus she could claim to be the largest ship afloat. The work took longer than expected due to design changes requested by Ismay and a temporary pause in work occasioned by the need to repair Olympic, which had been in a collision in September 1911. Had Titanic been finished earlier, she might well have missed her collision with an iceberg.
Titanic's sea trials began at 6 a.m. on Tuesday, 2 April 1912, just two days after her fitting out was finished and eight days before she was due to leave Southampton on her maiden voyage. The trials were delayed for a day due to bad weather, but by Monday morning it was clear and fair. Aboard were 78 stokers, greasers and firemen, and 41 members of crew. No domestic staff appear to have been aboard. Representatives of various companies travelled on Titanic's sea trials, Thomas Andrews and Edward Wilding of Harland and Wolff and Harold A. Sanderson of IMM. Bruce Ismay and Lord Pirrie were too ill to attend. Jack Phillips and Harold Bride served as radio operators and performed fine-tuning of the Marconi equipment. Francis Carruthers, a surveyor from the Board of Trade, was also present to see that everything worked and that the ship was fit to carry passengers.
The sea trials consisted of a number of tests of her handling characteristics, carried out first in Belfast Lough and then in the open waters of the Irish Sea. Over the course of about 12 hours, Titanic was driven at different speeds, her turning ability was tested and a "crash stop" was performed in which the engines were reversed full ahead to full astern, bringing her to a stop in 850 yd (777 m) or 3 minutes and 15 seconds. The ship covered a distance of about 80 nautical miles (92 mi; 150 km), averaging 18 knots (21 mph; 33 km/h) and reaching a maximum speed of just under 21 knots (24 mph; 39 km/h).
On returning to Belfast at about 7 pm, the surveyor signed an "Agreement and Account of Voyages and Crew", valid for 12 months, which declared the ship seaworthy. An hour later, Titanic departed Belfast to head to Southampton, a voyage of about 570 nautical miles (660 mi; 1,060 km). After a journey lasting about 28 hours, she arrived about midnight on 4 April and was towed to the port's Berth 44, ready for the arrival of her passengers and the remainder of her crew.
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