For a given weight, panel plates of aluminum alloy are thicker and stiffer than those of steel. For the last-named purpose, the increased deformation or stretch of these alloys is an advantage. They are also used for the superstructures and upper works of many cargo and passenger vessels they form the upper parts of steel hull girders which bend elastically in service. Specifications for shipbuilding steels of later decades required certain minimum limits on notch toughness and on adaptability to welding.Īluminum alloys are used for the hulls of patrol boats, small cargo ships, and for large shipboard elevator platforms and similar structures. Many ship structures have several riveted seams to permit adjustment of the strains due to butt welding and to localize progressive cracking. This quality is particularly important where all the plating seams around the girth are welded. This term refers to the steel’s ability to absorb energy by stretching in the vicinity of sharp corners, notches, and cracks, particularly at low temperatures or at high stretching rates. Investigations in the latter 1940s revealed that many of the fracture casualties of that period were due to the use of steel lacking in notch toughness. Cargo ships have been built entirely of high-tensile steel, with a considerable saving in steel weight. They are used for parts subjected to high strains in order to save hull weight. Both high-tensile and special-treatment steels have higher yield points the latter has ballistic and shock-resisting properties as well. By far the greatest proportion of parts are of medium steel, where the working strains are small or moderate compared with the yield strain.

The steels most widely used for hull structures are of the medium, high-tensile, and special-treatment types.

Molded plywood yacht hulls made of five thin layers glued together, with the grain running in different directions, are stiff enough to hold their shape without an internal framework. Checking, splitting, knots, and other imperfections are largely eliminated, and many short pieces can be used.

The development of strong waterproof glues and techniques for building up large curved members from thin laminations has greatly improved the strength and stiffness of wooden ship structures.

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Wooden ship construction