Many copper alloys were introduced largely because of their excellent resistance to corrosion by salt-water and salt-laden atmospheres; they have found also applications where a wear resistance greater than that posessed by pure copper is required. Thus aluminum bronze, manganese bronze, aluminium brass, gunmetal, cupro-nickel and 'Monel' are copper alloys which have long been standard materials for shipbuilding.
In the evolution of warship construction the battleship has been replaced by the aircraft carrier and vessels such as the Vanguard, the King George V and the American Missouri have gone for ever. Recently several new classes of warship have been introduced. These include small commando carriers and guided missile destroyers which are virtually small cruisers. Since the Second World War the optimum size of ocean-going liners on the North Atlantic route has declined slightly and vessels like the Queen Elizabeth and Queen Mary are no longer built. Nevertheless in all new construction, both naval and merchant marine, from 2 to 3 percent of the deadweight is in copper and copper alloys.
Ships' propellers in small coastal vessels may be cast iron, but for warships and the vast majority of merchant vessels, copper alloys, such as high tensile brass or aluminium bronze, are invariably used. The propellers of a large ship may weigh up to 20 to 25 tons apiece (35 tons in the two Queens); and as spare propellers must be carried on board, this is in more than on sense a heavy item! The very heavy tailshafts of big ships are usually Admiralty gunmetal (a copper-tin-zinc alloy in proportions of 88/10/2), and the rudder stocks and massive propeller cone-nuts are often in the same material.
It is the engine and boiler rooms of a ship where copper and copper alloys are used to the greatest extent. Marine condenser tubes are invariably 70/30 cupro-nickel or arsenical aluminium brass, two alloys which are particularly resistant to the severe corrosive and erosive effects of rapidly flowing sea-water. The world's first nuclear-powered merchant ship, Savannah, has more than 30 tons of cupro-nickel condenser tubes; while the main condensers of the modern liner Empress of Britain each comprise 5,949 cupro-nickel tubes, with tube-plates and baffles of naval brass, a copper-zinc-tin alloy (62/37/1). Undoubtedly the great new Cunarder, now on the drawing board, will follow this practice. Copper and copper alloys are used for the feed-water, fresh-water and salt-water cooling systems, for ships' evaporators, low temperature steam lines and for numerous items of auxiliary equipment such as pumps, feed heaters, valves and miscellaneous coolers. Among the specific uses of which have arisen in recent years is the use of aluminium brass pipes for the large heating coils of oil tankers. Some of these vessels are giants of up to 100,000 tons with dozens of oil-storage tanks, and the heating systems are on a corresponding scale.
The electrical equipment in a ship has grown extraordinarily complex and, as on land, the generators, electric motors, lighting and communications systems depend almost entirely upon copper and copper alloys for their operation. With the advent of wireless telegraphy before the first world war and radar during the second, a considerable amount of space is now given over to communications equipment, particularly in warships, where it is standard practice to duplicate vital equipment. This precaution is not only confined to naval ships; for example, the Empress of Britain has an emergency system of thirty-five strategic points, each of which can communicate back to the control room.
Naval ordnance has changed out of all recognition since the brass cannon of the 16th and 17th Centuries, but if the gun-barrels no longer contain copper they are fired electrically and considerable use of copper piping is made for the turret hydraulic systems.
The value of sheathing a ship's bottom in warm waters or polluted harbours has already been mentioned; but another trouble, to which all ships both steel and wood are liable, is the perpetual growth of fouling organisms, such as barnacles, ascidians, small tube-forming worms and weeds. This can be largely inhibited by covering the underwater parts with a composition that will poison the layers of sea-water immediately adjacent. Very many such anti-fouling paints have been tried, but only two have been found of much value, one including mercury and the other copper salts.
Small boat design and construction has made spectacular progress during the past twenty years. Rising standards of living have made it possible for many people to possess a boat of their own - in USA alone there are now nearly a million private motor-boats, yachts and other small craft. Copper alloys such as manganese bronze are used for centre-boards, rudders and propellers, and naval brass is used for propeller shafts and miscellaneous deck fittings. Wood is still strongly favoured for small boats and copper alloys wood screws and nails, generally silicon bronze, have long been recognized as the most suitable fasteners for all-wood construction. Many of the screws are now thread-rolled, a more economical process than screw-cutting since no swarf is formed.
Most of the uses of copper mentioned hitherto in this section have resulted from careful research and development based on experience over the centuries, but probably few specific items of equipment have been so effective or vitally significant as the de-gaussing apparatus which was hastily improvised during the early part of the last war. German magnetic mines were then sinking Allied and neutral shipping indiscriminately at alarming rate. The mines were laid in shallow waters, even in the Thames Estuary, and detonated magnetically as soon as the ship's steel hall passed overhead. The resulting uprush of water usually broke the ship's back. Many ships were sunk and others, including the battleship Nelson, were damaged by this form of attack. Fortunately, the counter-measures devised were simple and completely effective. It was found that by attaching a copper strip around the hull and passing a current through it the ship's magnetic field was neutralized and the mines therefore failed to explode. All ships were subsequently provided with a de-gaussing system and by D-Day 1944 no fewer than 18,000 vessels had been protected in this way. On the large capital ships a considerable tonnage of copper was required - the Vanguard, which was completed immediately after the war, required twenty-eight miles of copper wire weighing 30 tons for the purpose.