Copper sheathing
Copper sheathing was the practice of protecting the under-water hull of a ship or boat through the use of copper
Copper is a chemical element with the symbol Cu and atomic number 29. It is a ductile metal with very high thermal and electrical conductivity. Pure copper is soft and malleable; an exposed surface has a reddish-orange tarnish...

 plates affixed to the outside of the hull. It was pioneered and developed by the Royal Navy
Royal Navy
The Royal Navy is the naval warfare service branch of the British Armed Forces. Founded in the 16th century, it is the oldest service branch and is known as the Senior Service...

 during the 18th century.


Deterioration of the hull of a wooden ship was a significant problem during the Age of Sail
Age of Sail
The Age of Sail was the period in which international trade and naval warfare were dominated by sailing ships, lasting from the 16th to the mid 19th century...

. Several methods were developed for protecting it from attack by shipworm
Shipworms are not worms at all, but rather a group of unusual saltwater clams with very small shells, notorious for boring into wooden structures that are immersed in sea water, such as piers, docks and wooden ships...

 and the 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
Dry dock
A drydock is a narrow basin or vessel that can be flooded to allow a load to be floated in, then drained to allow that load to come to rest on a dry platform...

 at regular intervals. Weed, however, grew rapidly and slowed ships. Lead sheathing, while more effective than wood in mitigating these problems, reacted badly with the iron bolts of the ships causing sometimes severe damage.

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 train oil, rosin
.Rosin, also called colophony or Greek pitch , is a solid form of resin obtained from pines and some other plants, mostly conifers, produced by heating fresh liquid resin to vaporize the volatile liquid terpene components. It is semi-transparent and varies in color from yellow to black...

 and brimstone; Black stuff, a mixture of tar
Tar is modified pitch produced primarily from the wood and roots of pine by destructive distillation under pyrolysis. Production and trade in tar was a major contributor in the economies of Northern Europe and Colonial America. Its main use was in preserving wooden vessels against rot. The largest...

 and pitch
Pitch (resin)
Pitch is the name for any of a number of viscoelastic, solid polymers. Pitch can be made from petroleum products or plants. Petroleum-derived pitch is also called bitumen. Pitch produced from plants is also known as resin. Products made from plant resin are also known as rosin.Pitch was...

; and Brown stuff, which was simply brimstone
Brimstone is an alternative name for sulfur. It may also refer to:* Fire and brimstone, an idiomatic expression of signs of God's wrath in the Bible* Brimstone , a DC Comics character...

 added to Black stuff. It was common practise to first apply wood sheathing and then pay 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
Navy Board
The Navy Board is today the body responsible for the day-to-day running of the British Royal Navy. Its composition is identical to that of the Admiralty Board of the Defence Council of the United Kingdom, except that it does not include any of Her Majesty's Ministers.From 1546 to 1831, the Navy...

 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' keel
In boats and ships, keel can refer to either of two parts: a structural element, or a hydrodynamic element. These parts overlap. As the laying down of the keel is the initial step in construction of a ship, in British and American shipbuilding traditions the construction is dated from this event...

s and false keel
False keel
The false keel was a timber, forming part of the hull of a wooden sailing ship. Typically 6 inches thick for a 74-gun ship in the 19th century, the false keel was constructed in several pieces, which were scarphed together, and attached to the underside of the keel by iron staples...

s were sheathed with copper plates.

In 1761 the experiment was expanded, and the 32-gun frigate
A frigate is any of several types of warship, the term having been used for ships of various sizes and roles over the last few centuries.In the 17th century, the term was used for any warship built for speed and maneuverability, the description often used being "frigate-built"...

 HMS Alarm
HMS Alarm (1758)
HMS Alarm was a 32-gun fifth rate Niger-class frigate of the Royal Navy, and was the first Royal Navy ship to bear this name. Copper-sheathed in 1761, she was the first ship in the Royal Navy to have a fully copper-sheathed hull....

 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
The Admiralty was formerly the authority in the Kingdom of England, and later in the United Kingdom, responsible for the command of the Royal Navy...

 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, due to 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. In 1768 a ship named the Dolphin was sheathed in the same way and sailed for a few years around the world. It came back with corrosion on the iron components of the hull; they were basically irreparable and 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
American Revolution
The American Revolution was the political upheaval during the last half of the 18th century in which thirteen colonies in North America joined together to break free from the British Empire, combining to become the United States of America...

 prevented the re-bolting of the Royal Navy's ships necessary to allow a full-scale coppering programme.

Humphry Davy's experiments with copper sheathing

In the late 18th to early 19th century, Sir Humphry Davy performed many experiments where he had various thicknesses of copper submerged on the shore and then measured how much the sea water had degraded each one. Sheets of different metals remained in the seawater for four months and then were examined. Two harbour ships were also used in this test, one with a zinc and the other with an iron band. Both the zinc and iron became covered in a carbonate which allowed weeds, plant life and insects to attach themselves to the metal. The sheets that had cast iron or zinc were free of any attached life forms or discoloration. The main purpose of these experiments was to determine how to lessen the corrosion that the seawater caused on unprotected copper sheathing. Unprotected copper, such as that which was not covered in another metal such as iron, would quickly go from a reddish color to a greenish color of corrosion. When the other metal was mixed in copper in ratios from 1/40 to 1/150, there was no visible sign of corrosion and very minimal weight loss. When the ratio was changed to 1/200 and 1/400, there was significant corrosion and weight loss. Davy concluded that cast iron, which was the cheapest to manufacture, was the best for protection of the copper since malleable iron and zinc wore down faster.

Widespread implementation

With the American war in full swing, the Royal Navy set about coppering the bottoms of the entire fleet. This would not have happened but for the declarations of war from France
The French Republic , The French Republic , The French Republic , (commonly known as France , is a unitary semi-presidential republic in Western Europe with several overseas territories and islands located on other continents and in the Indian, Pacific, and Atlantic oceans. Metropolitan France...

 (1778), Spain
Spain , officially the Kingdom of Spain languages]] under the European Charter for Regional or Minority Languages. In each of these, Spain's official name is as follows:;;;;;;), is a country and member state of the European Union located in southwestern Europe on the Iberian Peninsula...

 (1779) and the Netherlands
The Netherlands is a constituent country of the Kingdom of the Netherlands, located mainly in North-West Europe and with several islands in the Caribbean. Mainland Netherlands borders the North Sea to the north and west, Belgium to the south, and Germany to the east, and shares maritime borders...

 (1780): Britain
Kingdom of Great Britain
The former Kingdom of Great Britain, sometimes described as the 'United Kingdom of Great Britain', That the Two Kingdoms of Scotland and England, shall upon the 1st May next ensuing the date hereof, and forever after, be United into One Kingdom by the Name of GREAT BRITAIN. was a sovereign...

 had to face her three greatest rivals, and 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.

Fortunately the Parys Mountain
Parys Mountain
Parys Mountain – in the Welsh language Mynydd Parys – is located south of the town of Amlwch in north east Anglesey, Wales. It is the site of a large copper mine that was extensively exploited in the late 18th century.-History:...

 copper mine on Anglesey
Anglesey , also known by its Welsh name Ynys Môn , is an island and, as Isle of Anglesey, a county off the north west coast of Wales...

, Wales had recently 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
In the British Royal Navy, a third rate was a ship of the line which from the 1720s mounted between 64 and 80 guns, typically built with two gun decks . Years of experience proved that the third rate ships embodied the best compromise between sailing ability , firepower, and cost...

 ship of the line
Ship of the line
A ship of the line was a type of naval warship constructed from the 17th through the mid-19th century to take part in the naval tactic known as the line of battle, in which two columns of opposing warships would manoeuvre to bring the greatest weight of broadside guns to bear...

 still cost £1500, compared to £262 for wood. 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. 82 ships of the line had been coppered by 1781, along with 14 50-gun ships, 115 frigates, and 182 unrated vessels. By the time the war ended in 1783 problems with the hull bolts were once more becoming apparent.

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 copper plating remained the standard method of protecting a ship's underwater hull until the advent of modern anti-fouling paint.

Civilian use

With its widespread adoption by the Royal Navy, many shipping owners employed the method on their merchant vessels. They were attracted by the savings made possible by copper sheathing, despite the initial outlay. As the coppering was expensive, only the better ship owners tended to invest in the method, and as a result the use of copper sheathing tended to indicate a well-found and maintained ship, which led to Lloyd's of London
Lloyd's of London
Lloyd's, also known as Lloyd's of London, is a British insurance and reinsurance market. It serves as a partially mutualised marketplace where multiple financial backers, underwriters, or members, whether individuals or corporations, come together to pool and spread risk...

 charging lower insurance premiums, as the vessels were better risks. The term copper–bottomed continues to be used to describe a venture, plan or investment that is safe and is certain to be successful.

See also

  • Careening
    Careening a sailing vessel is the practice of beaching it at high tide. This is usually done in order to expose one side or another of the ship's hull for maintenance and repairs below the water line when the tide goes out....

  • Bug shoe
    Bug shoe
    The bug shoe is a length of iron bark on the bottom of a ship that goes on the bottom of the skeg to protect it from shipworms....

  • Biofouling
    Biofouling or biological fouling is the undesirable accumulation of microorganisms, plants, algae, or animals on wetted structures.-Impact:...

  • Muntz metal
    Muntz metal
    Muntz metal is a form of alpha-beta brass with about 60% copper, 40% zinc and a trace of iron. It is named after George Fredrick Muntz, a metal-roller of Birmingham, England who commercialised the alloy following his patent of 1832....

  • Anti-fouling paint

External links

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