Copper 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.
It was common practice to coat the hull with the selected substance, then cover that with a thin outer layer of wooden planking.
[3] The use of copper sheathing was first suggested by Charles Perry in 1708, though it was rejected by the Navy Board on grounds of high cost and perceived maintenance difficulties.
[4] 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 had returned from service in the West Indies.
[5] Before the copper plates were applied, the hull was covered with "soft stuff", which was simply hair, yarn and brown paper.
[6] After this experiment, and deterred by the unanticipated and not understood galvanic 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, HMS Dolphin, had been sheathed in copper, specifically to prepare her for a voyage of discovery in tropical waters.
The onset and intensification from 1773 of the war with America took the focus off the bolting issue necessary to allow a full-scale coppering programme.
The ruler of Mysore, Tipu Sultan, ordered that all his navy vessels receive copper sheathing after observing the benefits in French and East India Company ships.
[11] In it he recommended "copper sheathing" as a solution to the problems of ship worm in warm tropical waters, and the effect on speed of tendrils of seaweed latching onto hulls.
The letter itself does not survive and is obliquely referred to in other official correspondence held by the National Maritime Museum; it may have contained or been coincidental with a critical new technical breakthrough of protecting the iron bolting by applying thick paper between the copper plates and the hull.
He understood that coppering allowed the navy to stay at sea for much longer without the need for cleaning and repairs to the underwater hull, making it a very attractive, if expensive, proposition.
The Royal Navy's newly coppered ships, as yet untested, were used successfully by Rodney in defeating the French at the Battle of the Saintes off Dominica in 1782.
At great cost the Admiralty decided in 1786 to go ahead with the re-bolting of every ship in the navy, thus finally eliminating the bolt corrosion problem.
This process lasted several years, after which no significant changes to the coppering system were required and metal plating remained a standard method of protecting a ship's underwater hull until the advent of modern anti-fouling paint.
A single coppered vessel was recorded on the register of Lloyd's of London in 1777, a slaver sloop Hawke, 140 tons.
Wood-boring organisms were less of a problem for these vessels and they were often routinely careened – an operation that could cause considerable damage to expensive coppering.
In the late 18th to early 19th century, Sir Humphry Davy performed many experiments to determine how to lessen the corrosion that the seawater caused on unprotected copper sheathing.
