The glass plate will provide a dry, stable and protective environment to halt corrosion, keeping humidity constant at a level of 20%, approximately the same as in America's Arizona desert. From above, a layer of water will give the illusion that the ship is afloat.

Structural engineers Arup designed the waterline plate, which will consist of 170 laminated glass panels of different sizes to make a total glass area of some 1,000m 2. The largest panel is 4.34m by 1.88m and weighs 450kg. The glass plate is sealed to the dry dock and the hull of the ship using a watertight flexible membrane to allow for slight movements of the hull. A 50mm deep layer of water flows above the glass and insulates the space below.

Extensive impact testing was undertaken to validate the design of the glass panels, ensuring the safety of visitors viewing the ship's lower hull from the chamber beneath the glass.

The glass will withstand tools being dropped from the ship's rigging or a drunken visitor falling overboard.

Arup also led the repair and restoration of the original dry dock, a process that proved delicate because of the poor stability of the remaining dock structure.

Horizontal steel joists and glass beams support the laminated glass plate. Tubular steel columns rising from the dock floor and walls provide additional support. The glass plate must support the 50 tons of water flowing over it without any leakage.

The SS Great Britain Trust will spend £5 million on the glass and dehumidification plant. Major funding for the overall project comes from the Heritage Lottery Fund but £542,000 must still be raised before work is completed in July.

The Trust's development team has worked closely with experts from Cardiff University, iron conservators Eura Conservation Ltd, and project managers Capita Symonds. Arup and architects Alec French Partnership have worked with consulting engineers WSP, glass specialists Space Decks Ltd, and construction company Bluestone. Work on the SS Great Britain and its dry dock is expected to influence the way museums across the world conserve large, important metal artefacts.

MJ Information No: 20407