The Belfast Harbour Commissioners operate and maintain the port of Belfast. In the middle of the nineteenth century the geography of the port was restrictive to the city's ambitions to develop itself as a centre of shipbuilding. A scheme was implemented to remodel the port, which including taking Victoria Channel in a straight cut from the city to Belfast Lough. The excess spoil generated was deposited in the harbour forming an area of reclaimed subsequently called Queen's Island.
The Thompson Graving Dock is located on the west-side of Queen's Island in Belfast, within sight of the Harland and Wolff shipyard. The dock was constructed by the Belfast Harbour Commissioners and opened in 1911. It was designed to accommodate the new mammoth White Star liners Olympic and Titanic.
The hulls of each ship were built on slipways at the Harland & Wolff shipyard. Following the launch of the hull of the Olympic on 20 October 2010 Titanic on 31 May 1911 each empty hull was fitted out, and moved to the dry-dock for painting of the hull and fitting of the propellers. The dock would be used during the ship's lives when they returned to Belfast for refitting.
The adjacent building is the dock pump house and was used to pump out water from the dock. The pump house originally served the Alexandra Graving Dock, located on the other side of the pump house from the Thompson Graving Dock, and was extended to provide additional pumping capacity for the new Thompson Graving Dock.
Today, the dock is the only location where it is possible to properly gauge the scale of the Titanic, as the whole footprint of the graving dock would have been occupied by the hull of the ship. The pump house serves as a heritage attraction telling the story of the dock and the Titanic.
The dock is 850 feet (259 metres) in length, exactly the length of the Olympic-class liners between perpendiculars; their waterline length. The sides of the dock are flush for half their height, while above the sides are stepped outwards. The landward end of the dock is curved, while the harbour-end is flat, with a large, movable caisson gate.
The width of the dock floor measures 100 feet (30.48 metres), while at the caisson gate the width is 96 feet (29.26 metres), giving a margin of just 1 foot 9 inches (0.53 metres) either side of the dock gate for the transit of the Olympic and Titanic; the margin was even smaller for the 94 feet (28.7 metre) wide Britannic.
The graving dock was a dry dock; the dock would be flooded to allow a ship to enter the dock. The caisson gate to the dock would be closed and the dock pumped dry. The ship had to be positioned exactly, so that she would come to rest on the keel blocks. With the dock dry, shipyard workers from Harland and Wolff could descend on the ship to work on her, fitting the ship out and working on her hull, propellers and rudder; parts of the ship that would normally be underwater.
Today, Queen's Island is being remodelled as Belfast's Titanic Quarter, which includes the landmark Titanic Belfast attraction, the restored White Star Line tender Nomadic and the former Harland & Wolff building and drawing offices.