Aluminium encyclopaedia

Shipbuilding

The first ships and boats were made from aluminium in the 1890s in Europe and the USA. Materials suitable for shipbuilding first appeared in the 1920s with the development of seawater-resistant alloys containing magnesium but the price of aluminium was still too high for widespread use. Numerous all-aluminium ships were built for the military (see military technology) in the Second World War, as well as some for civilian purposes. It was only in the 1950s that aluminium first became an important material in shipbuilding because by then the shipyards had gained experience in processing and construction with aluminium. The reason for the use of an aluminium construction instead of a conventional one is weight saving, which can be up to 50 per cent for a construction of comparable strength. This increases the pay load, saves operating power, improves stability because of the lower centre of gravity and reduces the draught of coastal vessels.

Applications

Aluminium-based materials, especially alloys containing magnesium and manganese, are now used in all types of vessel. Aluminium hulls are all made with a stiffened (using open profiles) and welded fabricated sheet structure. To join steel and aluminium, one uses composite profiles or explosion-welded plate, from which strips are cut and then used for joining to the same metal. The most important applications:


  • Aluminium is used in passenger liners, merchant ships and naval vessels, especially aircraft carriers, for superstructures and for the pistons of large diesel engines.
  • On liquefied gas tankers, the spherical tanks (up to 38 metres diameter, 25,000 cubic metres volume and 800 tonnes unladen weight) are made from aluminium.
  • The hulls of an increasing number of coastal and inland waterway vessels and ferries are also aluminium. In Germany, several all-aluminium sea-rescue cruisers have gone into service since 1975, in Japan lots of fishing cutters; aluminium is used in coastal patrol boats and police vessels all over the world, and in numerous passenger ferries in seaports like Hong Kong, San Francisco and Tokyo.
  • A lightweight construction made completely from aluminium is a prerequisite hydrofoils and hovercraft.
  • Although aluminium has proven itself in working boats, motor boats, sailing boats and rowing boats, as well as racing yachts, it has not established itself for small and medium-sized hulls up to about 13 metres long. For large and luxury yachts whose hulls are made almost exclusively from metal, aluminium has established a firm market share. Aluminium has almost completely superseded wood for boat masts.

 

Corrosion protection

For decades, new alloys have been tested for resistance to seawater. In Germany, the aluminium industry and researchers have conducted long-term exposure tests on aluminium alloys containing magnesium and manganese off the coast of Heligoland and in the laboratory since the 1980s. Together with earlier experience, it has been shown that with boats the natural oxide layer affords sufficient corrosion protection provided it remains undamaged and the outside is regularly cleaned. For larger ships, it is necessary to use either a protective lacquer, coating with zinc or cathodic protection for corrosion protection.