For centuries, sailing ships dominated global trade and warfare during the Age of Sail. While they faced the constant threat of enemy fire, they also battled a quieter opponent: shipworms. These mollusks were especially prevalent in warm waters. They bored into hulls and created tunnels that led to rot and structural failure. Early solutions included sheathing hulls with wood or lead. Expendable wood sheathing provided a nonstructural skin for shipworms to attack, but it needed to be replaced frequently. Lead was more resistant to organisms, but it corroded ships’ iron bolts.
The British clipper ship Cutty Sark pictured here at the Royal Museums Greenwich displays a more durable solution pioneered by the Royal Navy in the 18th century. Copper sheathing was first proposed by Charles Perry in 1708. The 32-gun frigate HMS Alarm was the first ship in the Royal Navy to have a fully copper-sheathed hull, which effectively protected the ship from weed growth and shipworm damage, but her iron bolts suffered galvanic corrosion. Her sheathing was removed in 1766.
Further trials followed. HMS Dolphin circumnavigated the globe twice with copper sheathing but suffered similar corrosion. In 1769, another attempt was made with a ship built from copper-alloy bolts, but corrosion persisted. The initiative was stalled until the onset of the Revolutionary War.
Royal Navy Comptroller Charles Middleton faced the challenge of keeping a large fleet ready for extended deployments. He decided to refurbish existing ships with copper sheathing, to reduce maintenance and keep ships at sea longer. The Royal Navy started coppering the entire fleet in 1778. To protect the ships’ iron bolts from corrosion, thick paper was placed between the copper plates and wooden hulls. After the war, in 1786, remaining corrosion was handled by rebolting every ship in the navy with a copper-zinc alloy.
In the 19th century, Muntz metal—a less expensive alloy of 60 percent copper and 40 percent zinc—started to supersede pure copper. When Cutty Sark launched in 1869, she was sheathed up to the 18-foot depth mark in Muntz metal. Today, her hull is sheathed in a modern alloy of similar composition and appearance.
October 2025
