Why Were Wooden Ships Copper Plated?

Copper plating 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.

The copper was found to perform very well, both in protecting the hull from worm invasion and in preventing weed growth for, when in contact with water, the copper produced a poisonous film, composed mainly of copper oxychloride, that deterred these marine organisms. Also, 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.

When the American Revolutionary War broke out, France (1778), Spain (1779) and the Netherlands (1780) declarared war on Britain, who had to face its three greatest rivals, and the loss of the Colony. The retreat to Canada resulted in the French blockading the British fleet.

Sir Charles Middleton (Controller of the Navy) and Lord Sandwich (Firts Lord of the Admiralty) attended on King George III with a model of HMS Bellona to explain to the King the process and benefits of copper plating.

Persuaded by the advantages of this technology the King authorised the Navy Board in 1779 to copper plate the fleet which 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.

Fortunately, mines in Wales at about that time begun large-scale production that had glutted the British market with cheap copper; however, the 14 tons of metal required to copper a 74- gun third-rate ship of the line still cost £1500, compared to £262 for wood cladding (which was largely ineffective after a short time at sea). The benefits of increased speed and time at sea were deemed by the Admiralty to justify the costs involved, and in May 1779 all ships up to and including 32 guns were ordered to be coppered when next they entered dry dock. In July, this order was expanded to include ships of 44 guns and fewer.

It was then decided that the entire fleet should be coppered, due to the difficulties in maintaining a mixed fleet of coppered and non-coppered ships. By 1781, 82 ships of the line had been coppered, along with fourteen 50-gun ships, 115 frigates, and 182 unrated vessels. By the time the American War ended in 1783, problems with the hull bolts were once more becoming an important issue.

Finally, a suitable alloy for the hull bolts was found, that of copper and zinc. 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.