copper sheathing

copper sheathing, the process of protecting the hull of a wooden ship with thin sheets of copper. It prevents the teredo worm eating into the planks, and inhibits seaweed and barnacles from building up on the ship's bottom so as to improve the ship's performance at sea.

marine archaeology has unearthed evidence that copper and lead sheathing was used on some Roman and Greek vessels, and from the 15th century lead was used for sheathing by the Spanish and Portuguese navies. John Cabot's son Sebastian, who in 1514 saw a Spanish ship sheathed in lead, may have brought back the idea of using lead to England, and certainly a number of English ships were clad underwater with lead in the 1670s. Other methods of protecting the hull were also tried in England and elsewhere, including an extra, sacrificial, layer of planks beyond which the teredo was unlikely to penetrate.

The Dutch admiral Piet Heyn may well have experimented with copper sheathing early in the 17th century, and the British dallied with the idea of using both copper and brass during the first half of the 18th century. However, the earliest evidence of it being used in the Royal Navy came when an examination of the wreck of the 74-gun Invincible, which sank in 1758, revealed that she was partly copper sheathed. The first documentary evidence that copper sheathing was ordered for the keels of two British naval ships is dated October 1759, and in December of that year the keels of two more ships were sheathed in this way.

Though experiments on other methods to prevent fouling continued at the same time, the first trial of a ship with a fully coppered hull began in October 1761 when the 32-gun frigate Alarm was sheathed in copper. This proved successful but few other ships were similarly treated. This was partly expense and partly because galvanic action had occurred between the copper sheets and the iron bolts by which the planks of the Alarm's hull was secured to her timbers. Though a sloop called the Swallow was built in 1770 with copper bolts, thus becoming the first ship whose underwater hull was totally copper fastened, it was some years before the copper sheathing of smaller vessels began. Then in 1779 orders went out to copper the entire fleet, and in 1783 orders were issued that copper bolts should replace iron ones in naval shipbuilding. Copper sheathing then became general, and other navies soon followed suit.

Copper-bottomed, a slang term for secure, to be trusted, cannot fail, was derived from the coppering of ships. Cock, R. , ‘ “The Finest Invention in the World”: The Royal Navy's Early Trials of Copper Sheathing, 1708–1770’, Mariners' Mirror, 87 (2001), 44.