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Copper sheathing is the practice of protecting the under-water hull of a ship or boat from the corrosive effects of salt water and biofouling through the use of copper plates affixed to the outside of the hull. It was pioneered and developed by the Royal Navy during the 18th century. ==Development== Deterioration of the hull of a wooden ship was a significant problem during the Age of Sail. Ships' hulls were under continuous attack by shipworm and various marine weeds, all of which had some adverse effect on the ship, be it structurally, in the case of the worm, or affecting speed and handling in the case of the weeds. The most common methods of dealing with these problems were through the use of wood, and sometimes lead, sheathing. Expendable wood sheathing effectively provided a non-structural skin to the hull for the worm to attack, and could be easily replaced in dry dock at regular intervals. Weed, however, grew rapidly and slowed ships. Lead sheathing, while more effective than wood in mitigating these problems, was too heavy and reacted badly with the iron bolts of the ships.〔McKee, A. in Bass (ed.) 1972, p.235〕 Even older than the sheathing methods were the various graving and paying techniques. There were three main substances used: White stuff, which was a mixture of whale oil, rosin and brimstone; Black stuff,〔 a mixture of tar and pitch; and Brown stuff,〔 which was simply brimstone added to Black stuff. It was common practice to first apply wood sheathing and then paint it with white stuff, although black stuff was occasionally used in this way. The use of copper sheathing was first suggested in 1708 by Charles Perry, though it was rejected by the Navy Board on grounds of high cost and perceived maintenance difficulties. The first experiments with copper sheathing were made in the late 1750s: the bottoms and sides of several ships' keels and false keels were sheathed with copper plates. In 1761 the experiment was expanded, and the 32-gun frigate HMS ''Alarm'' was ordered to have her entire bottom coppered, in response to the terrible condition in which she returned from service in the West Indies. HMS ''Alarm'' was chosen because in 1761 a letter had been sent regarding the ship's condition, saying that the worms from the waters had taken a significant toll on the ship’s wooden hull.〔 Before the copper plates were applied the hull was covered with Soft stuff, which was simply hair, yarn and brown paper. The copper performed very well both in protecting the hull from invasion by worm and in preventing the growth of weed for, when in contact with water, the copper produced a poisonous film, composed mainly of oxychloride, that deterred these marine organisms. Furthermore, as this film was slightly soluble it gradually washed away, leaving no way in which marine life could attach itself to the ship. However, it was soon discovered by the Admiralty that the copper bolts used to hold the plates to the hull had reacted with the iron bolts used in the construction of the ship, rendering many bolts nearly useless. In 1766, because of the poor condition of the iron bolts, ''Alarms copper was removed. After this experiment, and deterred by the unanticipated and not understood electrolytic reaction between the copper and iron, lead sheathing was tried again, though it was found to be unsuitable to the task, as the plates tended to fall from the hull alarmingly quickly. By 1764 a second vessel, had been sheathed in copper, specifically to prepare it for a voyage of discovery in tropical waters.〔Beaglehole 1966, p.195〕 ''Dolphin''s hull was inspected in 1768 after the ship had twice circumnavigated the world; there was significant corrosion of the iron components of the hull, and these had to be replaced. In 1769 another attempt was made at coppering a ship's hull, this time on a new ship that had been constructed using bolts made from a copper alloy. The results were far more favourable this time, but the onset and intensification of the war with America prevented the re-bolting of the Royal Navy's ships necessary to allow a full-scale coppering programme. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「copper sheathing」の詳細全文を読む スポンサード リンク
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