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Copper Sheathing

One of the most important technical innovations implemented by the naval antagonists during the American Revolution was the sheathing of ship's hulls with copper. The British developed this technique, and held the initiative. Britain's ships had an important technical lead with copper-plated bottoms. British war vessels often had the advantage of speed over those of the French and Americans and could either escape from or overtake enemy ships almost at will.

Keel-hauling was a brutal punishment inflicted on seamen guilty of mutiny or some other high crime in the days of sail. It practically amounted to a death sentence, for the chances of recovery after the ordeal were slight. The culprit was fastened to a line which had been passed beneath the vessel's keel. He was then dragged under the water on the starboard side of the ship, hauled along the barnacle-encrusted bottom and hoisted up and onto the deck on the port side. If the barnacles didn't cut him to pieces, and if he hadn't been drowned in the process of the operations, he was considered to have paid for his crime and was free.

Prior to around 1800 hulls were made almost entirely of white oak, possibly with sacrificial planking on the outside of the hull. The sacrificial planking was used on ships that traveled in warm ocean waters, where wooden hulls are susceptible to damage by burrowing marine organisms such as teredo worms. Sacrificial planking was applied to hulls to decrease the risk of damage. This half-inch thick layer of wood, such as pine, was replaced regularly when infested with marine borers. By the late eighteenth century copper sheathing replaced sacrificial planking as the preferred method of hull protection.

As far back as the reign of Edward the III, in 1336, several compositions containing pitch, tar, sulphur and oil were employed for coating the hulls of ships to prevent the attack of sea worms and the adherance of barnacles and sea weeds. It was also a common practice to use a thin planking, secured by nails, over the main planking, in those olden times. In 1625, a patent was granted to one William Beale, in England, for a composition not described, but the object of which was to render the hull and rigging incombustible.

Lead sheathing was used underwater on ancient Roman ships to repel marine organisms. This was forgotten during the middle ages. From the 18th century, wooden ships were again sheathed with lead. The Spanish sheathed ships in lead beginning around 1508 until 1567. In 1605 lead sheathing was resumed on Spanish ships going to only Mexico. The only other country to use lead sheathing was England. By the middle of the seventeenth century lead sheathing was being tried, and in Charles II's reign there were favorable reports on the results of the lead sheathing of several battleships. But this method of preserving the hull and adding to the ships sailing abilities was not persevered in.

In 1670, a patent was granted to Sir Philip Howard and Francis Watson, for sheathing ships with milled lead. These inventors state that they had discovered they could draw out lead into thin sheets by passing it between rollers, which was a very valuable invention. Milling Sheet Lead was was tried first upon a few ships of the Royal Navy. It was found to possess so many advantages over the old wooden, weed, barnacle, muscle, and other rubbish-creating impediments to a ship's sailing, that twenty of His Majesty's ships were ordered to be sheathed with the said milled lead. Many of the English ships were sheathed with thin lead fastened by copper nails and it continued in moderate use for about a century. It was better than nothing, hut was too soft for the purpose. Soon it was discovered that the lead had corroded the rudder-irons in a shorter time than ever had been known with the wooden sheathing, or without any sheathing whatever. The Milled Lead sheathing was abandoned, and the wooden sheathing was re-adopted.

From 1620 to 1770 the Colonial and English shiphuilders used lead as a sheathing material, and they nailed it on the wooden bottoms of their ships with large copper nails. Later, a mixture of tar, pitch, and brimstone was applied to the bottoms to protect the ships from the barnacles and teredo. Lead sheathing of Spanish ship hulls continued through the end of the 18th Century.

Copper Sheathing

The use of copper for ship fasteners dates to classical antiquity, and they are found on wrecks dating to the 5th century BC in the form of clenched nails. By the Roman era, iron had replaced copperr in shipbuilding, due to its greater strength and lower cost. Fasteners of iron or wood remained the standard through the medieval and early modern periods, until the last quarter of the 18th century. The re-appearance of copper and copper-alloy fasteners resulted from the Royal Navy's experiments with copper sheathing to protect the bottoms of wooden ships.

In 1708 Charles Perry proposed copper sheathing, but the idea was rejected because of the costs. And in 1740, Nehemiah Champion again suggested using sheets of "brass lateen" as sheathing, and an experiment produced inconclusive results.

In 1727 Benjamin Robinson and Francis Hankshee obtained a patent for sheathing ships either with thin copper, brass, tin or iron plates. This was the first application of brass and copper to the purpose. In 1759 the Royal Navy conducted an experimental, coppering the false keel of the HMS Invincible, and useing copper plates in the sternpost and keels of other warships.

The first ship fully sheathed in copper was the 32-gun English frigate, HMS Alarm, in 1761. She soon afterwards made a voyage to the West Indies the very place to test the sheathing completely. Upon her return to England, the metal was found clean, and as good as when it was put on.

The green oxide formed on copper sheathing is a benefit rather than an injury, because, although it is a sign of slight decay in the metal, the oxide prevents the adhesion of barnacles because it is very poisonous. The copper of ships may be kept perfectly bright by connecting it with small plates of zinc; the latter are decomposed and the former remains perfect. This was a discovery of Sir humphrey Davy; and it was supposed that by it the copper of a vessel might be made to last forever, with only the expense of some zinc plates. Such hopes, however, proved falacious.

Copper sheathing proved remarkable success in improving sailing speed by keeping ship's bottoms free of marine growth, and prolonged hull life by repelling teredo worms. However copper was expensive, it wore out quickly, and most seriously, copper sheathing over iron-fastened hulls created a galvanic reaction that quickly destroyed iron.

In 1766 the Alarm was surveyed, and many flaws and problems were discovered. The major problem was the damage done by the coppering to the iron bolts due to the galvanic activity generated between the iron and the copper. The iron straps of the rudder were rusted almost entirely oil; and when some of the copper sheets were removed for examination, the naval authorities were surprised and alarmed to witness all the iron fastenings corroded to a dangerous extent.

The reason why the iron fastenings corroded so rapidly, in connection with the copper, was unknown in those days; but since the discovery of the galvanic battery, the cause has been obvious. A simple galvanic battery is composed of two plates of different metals (the one more oxydizable than the other), and when they come in contact with moisture such as sea-water, a galvanic action at once ensues, at the expense of the rapid destruction of the positive or most oxydizable metal. Iron-fustened and copper-sheathed ships generate galvanic action when the two metals are connected, and, as a consequence, the most oxydizable metal (the iron) corrodes rapidly.

To prevent this in other vessels which were afterwards coppered, the holes at the outer ends of the iron bolts were filled with pitch, and over these pieces of canvas were laid, then the copper on the top; and the rudder braces were covered with lead. These measures all failed to prevent considerable deterioration of the iron fastenings when copper sheathing was used.

It therefore became a question whether to use some other fastenings than iron, or else give up the use of copper sheathing. The former course was adopted, and brass and copper bolts were employed in 1783. In that year the Royal Navy learned to build its warships with copper spikes and bolts below the waterline. By December 1783 a new copper and zinc bolt, hardened by mechanical means and developed by William Forbes, entered in service. By August 1786, all British ships were changed to the new bolts.

Copper Sheathing and the American Revolution

In October 1776 The American Turtle was the first submarine used in combat, sent to blow up the flagship of the British fleet, the HMS Eagle, a fifty-gun frigate. Ezra Lee piloted the complicated craft, but he couuld not get the screw to attach the explosive charge to the hull. Some accounts say that the reason was because there was a copper sheeting covering the hull. Others say the British did not use sheeting at that time, claiming he must have hit a bolt. And others say the screw, designed to perforate the copper sheathing, unfortunately struck against an iron plate.

The Schuyler Copper Mine, on the Passaic River, near Newark, operated during the American Revolution. Nicholas Roosevelt, the steamboat pioneer, bought the mine, and built a foundry and machineshop there, patterned after the famous Boulton and Watts works in England. It was called the Soho works, after the English shops. Among other items, he manufactured copper sheathing for the hulls of ships.

The first Bonhomme Richard was placed at the disposal of John Paul Jones on 04 February 1779 by the French King. On 23 September 1779 Bonhomme Richard encountered a British convoy escorted by HMS Serapis (44) and Countess of Scarborough (22) near Flamborough Head. The Serapis not only had more and bigger guns, but she had copper sheathing on her hull, which made her much faster than the Richard. Bonhomme Richard engaged Serapis and a bitter engagement ensued during the next four hours before Serapis struck her colors.

After the American Revolution, new demand arose in the form of copper sheathing to protect wooden ships crossing the Atlantic Ocean. The only piece of hardware Paul Revere could not make for the USS Constitution, "Old Ironsides," and other frigates being constructed, was the copper sheathing for the base of the hull. Since France was recovering from revolution, and the British still mistrusted America, the availability of copper sheathing could not be depended upon. In 1800, at the age of 65, Paul Revere, no longer young, sank every penny he had into the old gunpowder factory land in Canton, and built a copper foundry. Revere opened the first copper rolling mill in North America in 1801. He provided copper sheeting for the dome of the new Massachusetts State House in 1802, and in 1803 the company was commissioned to provide copper sheathing for the hull of the USS Constitution. The nickname "Old Ironsides" comes from the ship's success in the War of 1812. During battle, the wooden hull was not penetrated by a single British cannonball, a fact unrelated to the copper sheathing. The Revere Copper Company even mad the copper used for the boilers of Fulton's first steamboat.

Brass Sheathing

The great expense and short life span of pure copper plates a problem that kept this type of sheathing from being widely adapted. Copper possesses the advantage that, no matter how old it may be, the sheets will sell for only a few cents less per pound than when new. On the other band, it is not very durable, while it is very dear. By experience, it has been found that the purest copper sheets decay most rapidly; some of the sheets will wear into holes in one year, while sheets of alloys endure much longer.

In 1800, M. Collins secured a patent in England for alloys to make sheathing more durable. These consisted, first, of 8 parts of copper and 1 of zinc, which could be rolled cold; the second consisted of 180 of copper and 80 of zinc, which required a low red heat to work; and a third was composed of 16 of tin, 16 of zinc and 1 of copper. In 1817, he obtained another patent for a bronze sheathing, composed of 80 of copper and 20 of tin.

In 1823, John Revere secured a patent for a brass sheathing composed of 95 of zinc and 5 of copper.

The problems were finally overcome in 1832 by the English businessman George F. Muntz, MP for Birmingham. Muntz metal is a brass that has more zinc and is stronger than alpha brass used for sheathing bottoms of ships [and later other purposes such as castings and hot-worked products]. Brass is the most yellow in color, while Muntz Metal is a little redder in tone, and Copper is the reddest of the metals. Muntz metal retains a yellow dull color, while copper sheating turns greenish or bluish. Muntz metal must be worked hot, and is flexible enough to adapt itself to a wooden hull. Muntz metal corroded at a slower rate than copper, and the high percentage of inexpensive zinc reduced the cost substantially below pure copper.

The Muntz metal is simply a brass sheathing composed of copper and zinc, and had been previously patented by Collins, hut, for all this, it made a fortune to Mr. Muntz. His proportions were about equal weights of copper and zinc; but he preferred an alloy of 60 of copper and 40 of zinc, which is like the second alloy of Mr. Collins, patented in 1800. A very small portion of zinc, tin or iron, mixed with copper, for sheathing, renders it far more durable.

By mid-nineteenth century many, perhaps most, US ships were sheathed with plates made from a composition called "Muntz Metal" which was 60% copper and 40% zinc. Beaten to the shape of the hull with wooden hammers, the sheets were designed to protect the vessel from the voracious Teredo worm, which is capable of doing sufficient damage to sink a wooden sailing vessel. The metal, which consists of three parts copper to two parts zinc, is also effective in preventing marine growth developing on the hull. Muntz Metal was slightly ablative, that is, its surface wore off, exposing fresh copper to the attached marine growth.

Around 80 clipperships were built for the lucrative China Tea trade between 1850 and 1872, with the trade for sailing ships being killed off by the opening of the Suez Canal in 1869, the year that Cutty Sark [the only surviving clipper] was built. The construction of the clippers varied between all wood, all iron and composite, and Cutty Sark is of composite construction. She has an iron frame consisting of an iron flat plate keel which is laid on top of the wooden keel and is swept up at the ends, being inboard of the wooden stem and stern posts. She has iron frames, reverse frames, floors, box keelson, side and bilge keelsons, longitudinal and diagonal tie plates, sheer and bilge strakes main and 'tween deck beams, deck stringers and mast partners. Over this iron framework is laid a wooden skin, with teak being used for the maindeck and topside planking and American rock elm for the bottom planking, keel and false keel. Muntz metal encased the wooden hull and keel.

By the late 1880s nearly all of yachts built of wood are sheathed with copper, and so were many of the sea-going tugs and wooden merchant vessels. The operation is an expensive one, but in the end it was unquestionable that the results justified the extra outlay.

By the early 1890s Great Britain possessed a great array of vessels-of-war of, from battleships to torpedo gunboats. Of seventy-nine armored vessels, eight were sheathed with copper and five with zinc; eighteen were built prior to 1890, and twenty-one more before 1880. Of unarmored cruisers there were sixty-two with iron or steel bottoms, forty-nine others were sheathed with copper and two with zinc. Twenty-one others were composite, of various sizes, all of them above 1,000 and some of them over 2,000 tons displacement. They had iron or steel frames, wooden bottoms, and copper sheathing. Of the total, twenty-four were built prior to 1880, twenty-four from 1880 to 1885 inclusive, and seventy-seven from that date to 1893, some of them not completed as of that date. Of the total a rough estimate gave 100 which may be supposed available cruisers for any part of the world as commerce destroyers.

Sheathing Metal Ships

England made the first attempt to sheath vessels of the modern iron and steel navies in 1868, when the iron cruiser Inconstant was prepared for service in warm seas. She had her bottom completely sheathed in copper, and she proved so successful that between that date and 1889 thirty-two other vessels of the English navy were copper-sheathed. The process adopted then was a little crude compared with later-day methods. The bottom was what is called flush-plated, with heavy seam straps on the outside. Since 1889 the British Admiralty made it a practice to copper-sheath every war vessel intended for foreign waters where docking facilities were poor, and the result is England has a large fleet of copper-sheathed cruisers that could stay in tropical waters for a long period without becoming badly fouled.

While copper sheathing was not a perfect anti-fouling material, it is so satisfactory that ships with their bottoms so treated can often remain in warm seas for two years without being docked. Ordinarily an unsheathed vessel could not remain in such waters more than six months without having its bottom so covered with barnacles that its speed would be seriously reduced. Copper sheathing not only gives a smooth surface which offers no friction to the water, but the barnacles are killed by the poison from the copper. The small marine animals attach themselves to this copper surface and absorb the poison, which kills them and makes them drop off. This poison is produced by the gradual dissolution of the copper by coming in contact with the salt water. The chemical process in time ruins the copper bottom, and if it does not dissolve fast enough the marine animals secure a good foothold on it.

The US Navy did not possess one sheathed vessel of war. In 1875, when the construction of half a dozen iron vessels was discussed at the so-called Board meetings of the chiefs of bureaus, presided over by the Secretary of the Navy, the Rear-Admirals Case, Reynolds, and C. R. P. Rodgers, insisted that some of the vessels should be sheathed. The Chief of Bureau of Construction craftily replied, That could be done afterward. He was an expert, and we were supposed to know nothing as to what should be done in turn in the progress of construction. To sheathe a vessel after her construction would require tearing her to pieces in a great measure.

In the US Navy in the 1880s, copper-sheathing of new vessels had its advocates, but little was initially done in a practical way in this direction. When the first members of the White Squadron, the Chicago, Boston, Atlanta, and Dolphin, were built, the Naval Advisory Board considered the question of copper-sheathing their bottoms, but it decided adversely. It was estimated then that it would cost $75,000 to sheath the Chicago and a little less for the others. The decision then reached established a precedent that was difficult to overcome.

After a few months in tropical waters the fastest cruiser would have been slow indeed. If twenty knots was obtained on the speed trial, with the same number of revolutions it would probably not exceed fourteen knots. This great falling off can be verified by an examination of logbooks. In 1883 the USS Ranger spent seven months, after a previous dockage, in voyages to and from the coast of Mexico and in making surveys. Barnacles more than an inch long covered the entire bottom, and a heavy marine vegetable growth sujplemented the barnacles. Her voyage to San Francisco was at less than half the speed, with the same number of revolutions per hour as when she left with a clean bottom.

There were two other important objections to performing the work besides that of expense, and the Naval Advisory Board at that time justified their decision, which had a far reaching effect ever since. One was that the copper-sheathing would add enormously to the weight of the cruisers, and thus reduce their speed. In the case of the Chicago it was estimated that the additional weight would be about 255 tons, and 160 tons each for the Boston and Atlanta. The second consideration was that the process of copper-sheathing was far from perfection, and that it was barely beyond the experimental stages. A slight derangement or scratch of the copper plates might at any time expose the steel hull to great danger. Galvanic action might begin instantly, and do considerable damage before the ship could be docked. As an instance of what damage can be created in this way on short notice mention should be made of the cruiser Cincinnati. She anchored alongside of a copper-sheathed vessel at her moorings, and as a result her bottom was seriously injured. It was a strict order in the navy that an unsheathed vessel was never to anchor alongside of a sheathed steamer of any kind.

Copper sheathing was not a perfect anti-fouler, and consequently experiments were made continually with paints and compositions to preserve the hulls of warships. Some curious substances were tried for this work, and the results are of historical interest if not of exact scientific value. The Japanese, for instance, startled the navies of the world by announcing a number of years ago that they had discovered the great sheathing material for the future. This was nothing more than Japanese lacquer prepared in a certain way. A lacquer manufacturer of Tokyo made experiments in covering steel plates with his lacquer, and these were submerged in salt water for many months. The condition of the plates after they were recovered seemed to justify further experiments, and the steamer Fuso-kan was docked, and part of her bottom sheathed with the lacquer. Immediately after an examination of her hull a year later, the Japanese Admiralty ordered a cruiser to be treated by this process, and the European nations, not to be left behind in the game, followed suit.

The Russian Government had the warships Dmitri Douskol and Admiral Nachimoff lacquered in 1890, and the United States naval authorities took cognizance of the new invention in 1891. In that year the Japanese lacquering company sent over steel plates treated with the new preservative, which were submerged at the Norfolk Navy Yard and taken up three months inter. Nothing, however, was done by the US Government to adopt this method of preserving our warships from fouling, and for various reasons the Japanese process of lacquering warships bottoms did not make much advance in the European navies. All of the governments fell back upon copper, or compositions in which copper was the predominant metal, for sheathing their warships.

Electroplating the bottoms of ships with copper was experimented extensively with, and this did away with many of the old objections to copper sheathing. Where the copper plates were nailed onthe ships, pitting nearly always started at the nail holes. If the salt water was allowed to enter here even in the smallest quantity, corrosion would begin at once, and in a short time do great damage to the steel hull. In electroplating, however, the copper sheathing is put on in one unbroken mass, and there is no danger from pitting. When the whole surface has been electroplated with copper a smooth and unbroken surface is presented, and it fits so closely that the sheathing cannot be removed without sometimes chipping off the iron. Moreover, this sheathing is merely a light film of copper, and its weight is so small that it averaged only 2.85 pounds to the square foot.

Several plans for the electrolytic deposition of copper on ships plates were proposed, but they were never been applied in practice to a large vessel, such as a warship, for which they were specially recommended. There was no apparent difficulty in carrying these plans into effect, but they did not materialize. The reason was probably to be found in the well-grounded fear that the application of the copper directly upon the iron or steel would have the effect of causing the rapid pitting and corrosion of the latter by galvanic action. No matter how carefully the plates were cleansed before coppering, there would be numerous places over the extended surfacesas, for example, about the joints, rivets, etc. where the coating would be imperfect, and every place of this kind would become the seat of galvanic action, by which the electro-positive iron would suffer active corrosion. Promising as the process appeared to be on paper, this difficulty, which is a serious one, and apparently insuperable, prevented its adoption.

Sheathing the metal plates with wood, and fastening the copper sheet to this, appeared to be the only alternative where the coppering of the immersed section of iron or steel hulls was found necessary.

Of all metals in common use, zinc is the most subject to destruction, the other metals remaining unaffected by galvanic action in connection with it, and zinc taking the bite. Some suggested the possible advantage of sheathed vessels having a strip of zinc of two feet in width put round the vessel, extending from a few inches below the water line to more than one foot above it. If fastened to the hull above and below with suitable metallic battens, the zinc could be renewed readily as might be required.

The End of Sheathing

All of the anti-fouling paints and compositions imitated the action of copper. Most of them were composed of copper, mercury, zinc, or arsenic. The British company Peacock & Buchanan's catalog of 1874 offered an "Anti-Fouling (Salmon Colour) - for Iron Ships' Bottoms..." Next to copper, zinc was used more commonly in European navies than any other metal, but this did not act as well in salt water as copper, and its use was gradually dying out by 1900. By the time thhe "Cressy" class of British armored cruiser was laid down 1898-1899, none were sheathed and coppered as successful Antifouling paints were by then available.

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Page last modified: 22-07-2011 17:37:28 ZULU