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Metal Hull

Shipbuilders used iron first as framing and then as a material for the entire ship. Iron was first used as framing to reinforce ships so that they could be used to ram their opponents as well as fire on them. It was several years before an economical way to process iron strong enough for the entire construction could be found. Wooden ships had the advantage of being cheaper to build than iron ships.

Construction of wooden sailing ships remained relatively uniform over several centuries. It was said that a sailor from the Spanish Armada of 1588 transported suddenly to the first half of the 19th Century, would be instantly familiar with the ship and could take up his duties with a minimum of delay. Wooden ship building was considered more of an art form than iron ship building, with years of apprenticeship needed to learn the necessary skills of working and shaping large timbers. With the introduction of iron into ship construction, the business of shipbuilding "industrialized."

The most prominent weakness in wooden hulls is the lack of longitudinal rigidity. The keel is timber, or a series of or timbers joined together, extending along the center of the bottom of a ship from stem to stern and often projecting below the bottom, to which the frames and hull plating are attached. When the hull is sagging, the keel goes into tension. Timber is good in tension and good in perpendicular shear, a rare loading failure.

Hog is the curvature of the ship's keel, which occurs when weight and buoyancy factors cause the ship's bow and stern to sag and forces the keel to rise in the middle. It is caused by having the vessel too light on her lines. Because the ends have a higher structural weight to buoyancy, they tend to sag. Conversely, midships has more buoyancy than structural weight, so the middle is pressed up. The hogging is a natural result of the keel material attempting to minimize internal stress. Hogging reduces the internal stress on the keel (by lowering the sectional modulus of the hull) at the point where the keel has the highest shear stress.

Diagonal riders are wooden support structures. They are cut into the overhead lower deck beams and follow the curve of the hull to the keelson, the area protecting the keel or spine of the ship. Diagonal riders prevent hogging.

Wooden hulls throughout history were constructed by numerous, relatively small individual planks, often overlapping or staggered to increase longitudinal strength. While these shipbuilding techniques were effective for centuries of large, wooden ship construction, ships intended for the 19th-century shipping industry required maximum hull volumes and increased rigidity. Ships that incorporated iron bracing still faced problems of optimizing cargo volume because wooden support structures still occupied internal volume.

Composite Hulls

Sailing, iron-hulled ship design began with a period of composite-hull construction. This type of ship utilized wooden hulls with iron frames and internal supports, but it was abandoned by the 1870's in favor of hulls completely built of iron. Composite ships had the internal strength of iron, and with wooden planking, copper sheathing could be added to protect the hulls.

Iron hull construction was similar to wooden construction as evident by the structural configuration of iron ships. Keels were laid first, then articulating frames attached transversely. In composite ships, these frames were wooden with iron supports, eventually evolving into complete iron frames. Centerline keelsons were built up from heavy timbers with iron plating on all sides. Iron shipbuilders removed the wooden component and replaced it with a large, T-shaped iron beam with a flat iron plate on top. Sister keelsons, bilge keelsons, and side keelsons in both composite and iron ships replaced stringers in wooden ships. They were located parallel to the centerline keelson and spaced evenly across the lower hull. By relying on strength of iron, more support structures found in wooden ships could be eliminated.

Metal-sheathed wooden ships were better protected than iron hulls because the copper sheathing resisted marine corrosion. Early iron ships corroded quite quickly, but the galvanic reaction between iron and copper made copper sheathing impractical. Wood vessels needed metal sheathing to protect them from degradation caused by marine organisms.

Composite ships' internal framing was nearly as strong as iron ships. They were less expensive to construct, and also lighter than entirely wooden ships, while needing fewer repairs. Because composite ships were built on wooden ship designs, many terms for wooden structures carried over to composite and iron ships. Metal framing also increased cargo capacity by reducing the size of internal components.

By the mid-19th century steam engines had been fitted in some wooden ships of the line. But the Royal Navy was shocked when, in 1858, the French started building La Gloire. This was the first armour-hulled ship. However, because French industry could not make an iron hull, the Gloire had to be built of wood protected by 11 cm (4.5 in) of iron. Iron cladding the wooden British fleet was the simplest way of responding to this French challenge. However, Sir John Pakingham, the First Lord of the Admiralty, supported the idea of a completely iron hull. So, the Warrior was ordered in June 1859.

Iron Hulls

Soon shipbuilders incorporated iron framing fully, and completely eliminate wooden supports. Iron shipbuilding benefits included a reduced amount of time needed for construction, added strength, and an increase in internal volume by eliminating unnecessary support structures. Even with these benefits, iron ships did not replace wooden ships immediately.

Iron ships built upon composite ship designs by replacing the remaining wooden components with iron. Wood outer hull planking was replaced with riveted iron plates bolted to frames. Side and bilge stringers connected frames on the inboard side. Butt plates, flat iron plates with multiple rows of rivets, secured the plates to each other and covered plate seams on the inner face. Iron bulwarks and caprails were fixed on bulwark plating supported by bulwark plates. These features developed from and replaced wooden waterways, bulwark stanchions, and bulwark planking in composite-built ships.

Iron ships possessed physical characteristics that slowed their acceptance initially. Three characteristics of iron ships led many naval engineers to oppose ships made entirely of iron. Magnetic deviation caused by the innate magnetic property of iron affected accuracy in compasses. Navigation on ships relied heavily on a compass that could accurately detect magnetic north. The construction process, which included repetitive hammering of iron, caused early iron ships to magnetize and disrupt the surrounding magnetic field. Another innate characteristic of iron ships is the susceptibility to corrosion from the marine environment. Iron oxidation, or rust, quickly damaged iron hulls, often weakening them beyond repair. Iron ships also attracted lightening during storms. The extension of iron plated masts only increased the chances of being struck by lightening at sea. Most problems with iron ships were rectified with the production of higher quality iron and proper electrical grounding.

Deck structures on iron ships, for the most part, remained relatively unchanged from wooden and composite ships. Iron ships were often built with wooden decks, and wooden superstructure, such as deck houses located on the main level. Similar deck machinery, including capstans and windlasses, was used on wooden and iron sailing vessels. Likewise, the same types of anchors, chains, and other ground tackle could be found on wooden, composite, and iron ships.

Rigging on iron ships differed greatly from wooden ship rigging. Iron wire rigging began in the early 19 th century when chain and linked iron rods were used for standing rigging. Reduction in weight, durability, and strength were benefits of iron rigging, and with the support of standing rigging, "less bulky" masts were used. This technological development gave iron ships a distinct advantage over wooden ships by decreasing maintenance over time and reducing the top-weight of vessels.

At the same time it was harnessing steam power for ship propulsion, the Navy was making advances in ship construction. The Navy began making its ships with iron instead of wooden hulls. The first iron ship was authorized by Congress in 1841. In 1843 the Navy launched it first iron-hulled warship [as well as first prefabricated ship] the Paddle sloop USS Michigan. The USS MICHIGAN, renamed the USS WOLVERINE, was the first iron warship in the US Navy and probably the first iron or steel warship of her size in the world. This side-wheeler was 163 feet long and displaced 685 tons. She was powered by a 170-horsepower, two-cylinder, steam engine. Without using its sails, the USS Michigan was capable of making 8 knots. She was originally designed as a "three-mast, topsail schooner" with auxiliary steam power. Michigan was designed by naval constructor Samuel Hart; fabricated in parts at Pittsburgh, Pa., during the last half of 1842; and carried overland to Erie, Pa., where assembled. When Hart attempted to launch this pioneer steam man-of-war 5 December 1843, she slipped down the ways some 50 feet but halted and stuck before reaching water. After strenuous but fruitless efforts to prod the ship into resuming her descent were ended by darkness, the shipwrights retired for the night. But upon returning to the shipyard before the next morning, Hart found the ways empty. Some distance offshore Michigan floated easily in Lake Erie, after launching herself in the night. She commissioned 29 September 1844.

Michigan's mission was to patrol the often volitile Great Lakes region, quelling port town civil disturbances, while at the same time rescuing both Canadian and American ships in distress. During the course of it's duty ship and crew engaged in battling lumber pirates, The Mormon tyrant (King) Jesse James Strang of Beaver Island as well as Miners and conflicts associated with the Civil War. The MICHIGAN was on duty on the Great Lakes during the Civil War but never engaged in battle. In March 1864 Secretary Welles ordered Commander John C. Carter to have USS Michigan "prepared for active service as soon as the ice will permit." Michigan, an iron side-wheel steamer, was at Erie, Pennsylvania, and it was rumored that the Confederates were planning a naval raid from Canada against a city on the Great Lakes. When fundraising efforts failed to acquire sufficient money for her restoration and preservation, she was cut up and sold for scrap in 1949. The next year her bow and cutwater were erected as a monument, near the shipyard where she had been built.

In response to the French Navy ordering six iron-hulled ships, the First Sea Lord, Sir John Pakington, developed plans for what would be the most powerful and heavily armoured ship afloat. Built by Thames Iron Works, Blackwall, England in 1861, on the basis of the heaviest guns alone, Warrior was classified as a 40-gun ship. Warrior's great innovation was in being the first ocean going warship to have an iron hull. As a result, she was also the largest warship of her day. Perhaps more distinctive was Warrior's grateful 6.5:1 length to breadth ratio. Warrior was not included as a line of battleship. Rather her superior speed enabled her to outdistance and outmanoeuvre any steam battleship that she might encounter. Although designed to fight under steam, she was alsorigged as a three-masted ship.

Development of iron ships after the 1850s resulted from technological advances and a demand for larger, stronger ships. During the era of imperialism, countries seeking new lands competed for markets of raw materials and foreign goods. Delivery speed and amount of cargo transported became measurable factors of business success, and led to demands for increases in hull size and sail area, and, eventually, for the mechanical propulsion of ships.

The City of Peking, the first iron-hulled, propeller-driven steamer built for the Pacific Mail Steamship Company was built in 1874 by John Roach & Son, New York, NY. Pacific Mail took delivery on the first of 11 iron-hulled, screw-propelled steamers, including the City of Peking. These ships soon took their place in the company's thriving trans-Pacific service. By 1880 steel hulls had replaced iron in new vessel construction.

USS Alert was an iron hulled screw steamer built in 1873-74 by John Roach & Sons, Chester PA. Armed with an 11-inch gun and two 9-inch guns for main battery, she saw active service in such configuration until 1903. The Alert was one of three vessels that were built of iron in 1874, the exceptional and spasmodic indication of an effort to change the material for construction, much induced by pressure from the iron interests of the country. This effort was made in a very mild and tentative manner, and was limited to this small class of diminutive vessels. The length of the Alert ws 175 feet; beam, 32 feet; draft of water, 12.9 feet. She had a displacement of 1020 tons, and attained a speed of 10 knots per hour with an indicated horsepower of 655. The capacity of her coal-bunkers was 133 tons. Her battery consisted of 1 xi-inch and 4 ix-inch smooth-bores, and 1 60-pounder. The shock attending the first step toward a change in the material for construction was so great as to cause a suspension of the effort, and in 1876 was launched the 3900-ton Trenton, built of wood.

With the exception of the vessels of the Alert class built of iron, the US had nothing but wooden hulls with which to celebrate the Centennial of 1876. The US Navy continued to build in perishable material, requiring large sums to be spent in repairs, and ignoring the manufactures of the country which could have been aided in their development by the contrary course. America permitted the age of steel to reach its zenith without indicating awareness of its presence.

Steel Hulls

Steel is iron that has most of the impurities removed. Steel also has a consistent concentration of carbon throughout (0.5 percent to 1.5 percent). Pig iron contains large amounts of carbon as well as other impurities (mainly sulphur and phosphorus). Impurities like silica, phosphorous and sulfur weaken steel tremendously, so they must be eliminated. The carbon content must be reduced, the impurities oxidized and removed, and the iron converted into a highly elastic metal which can be forged and fabricated -- steel. The advantage of steel over iron is greatly improved strength. Steel had many advantages over wood. It won't warp, splinter, or crack. Steel is also pest resistant and will not rot.

British inventor Henry Bessemer (1813-1898) announced a new steel making process in 1856. Bessemer patented a process for cheaply and rapidly converting pig iron into steel, thus further accelerating the Industrial Revolution. He correctly foresaw it would be a quick, high volume, fuel efficient approach and trod lightly on the fact that it hadn't actually worked yet. After some further innovations with others, it developed into a thriving business in the 1860s. It took longer to transplant the technology to the US, which took another wave of innovations. During the Civil War, an American, Alexander Lyman Holley (1832-1882), redesigned the Bessemer process, increasing its efficiency and laying the foundation for the swift growth of the American steel industry under the leadership of entrepreneurs like Andrew Carnegie.

Huge demand for steel rails for railroad construction sustained the industry through a depression that started in 1873. Production quantities rose dramatically. The technologies in use improved quickly, and the price of Bessemer steel fell from over $100 per gross ton of rails in 1870 to about $60 in 1880. Bessemer and acid open-hearth were new methods of steel production introduced in the late 1860s. Another method, called basic open hearth, was introduced in 1878.

From iron, coal and limestone, steel was milled and forged into the thousand-and-one shapes demanded as the Industrial Revolution matured in the late 19th century and transformed the nation.

The cranes of Cammell Laird shipyard cast long shadows over Birkenhead. Among the famous ships to go down the old yard's great slipways onto the Mersey was the world's first steel ship, the Ma Roberts, built in 1858 by John Laird for Dr David Livingstone's Zambezi expedition. The river that flows through Newcastle is called her the River Tyne. This river was part of a significant history told long long time ago. The first steel ship was constructed here. In March 1858 at age 46 he set out for Africa. On New Year's Day, 1859, the Scottish explorer turned the bow of his boat, the Ma-Roberts to the north. Steaming, out of the mighty Zambezi River, from what is now Mozambique and into the Shire River, he thus changed the course of history for a small mysterious part of Africa. There were myriad obstacles to the navigation of the Zambezi. His modern equipped boat, the Ma Roberts, was more of a hindrance than a help. She was so slow that a native canoe could easily outdistance her. She burned so much fuel that half of the time was given just to cut wood for her. At the beginning of 1861 a new boat, the Pioneer, came to replace its antiquated predecessor.

Banshee was the first steel ship from the keel up. Built as a blockade-runner for the Anglo-Confederate Trading Company, her design set the pattern for about a hundred further paddlewheel blockade-runners, including over thirty built of steel, that followed from British and Scottish shipyards. Banshee, a 533-ton (burden) side-wheel steamship, was built in Liverpool, England, in 1862 for employment running the Federal blockade of the Confederate coast. Her trans-Atlantic maiden voyage, in April 1863, was a "first" for a steel-hulled ship, though her innovative construction proved troublesome in service. The Banshee was built by Jones, Quiggin & Co., and engines by H.N. Lawrence & Co., both Liverpool firms. Jones, Quiggin & Co., was founded in 1855, and built composite and iron ships including sailing vessels, paddle and screw steamers. Much work was for customers abroad, and included commissions for the Confederate Government, arranged through Fraser, Trenholm & Co. Ships built at this time include five blockade runners, one of which, the Banshee, became the first steel ship to cross the Atlantic in 1863. The impact of Merseyside built ships like the "Alabama" and the "Banshee" was so significant that after the war an arbitration tribunal in Geneva awarded the United States $15,500,000 as compensation.

Designed especially for speed in order to run the Union blockade, Banshee [length 220', beam 20'4", draft 10', speed 15 knots] ferried cotton and other goods back and forth between Nassau, the Bahamas, and Confederate ports. Larger oceangoing vessels brought goods between Nassau and England. Banshee's captain, Jonathan W. Steele, was a daring Englishman who believed himself immune from arrest if caught by the U.S. Navy because he was a British citizen who had never lived in America. His ship had genuine British registration papers. Banshee made eight successful round trips from Nassau to Wilmington with incoming cargoes of guns, chemicals, metals, and clothing (gray, of course), and outgoing cargoes of cotton. On his ninth attempt to run the blockade, however, Captain Steele's luck ran out. Decommissioned after the fighting ended, she was sold in November 1865. Her new owners placed her in commercial service under the name T.L. Smallwood (or J.L. Smallwood). Sold to British interests in 1867, she was renamed Irene and remained in use at least until the 1890s.

Bat, a 750-ton (burden) Owl class side-wheel steamship, was built in Liverpool, England, in 1864 for the Confederate States Government. Bat and her sisters Owl, Stag, and Deer were side-wheelers with long, low, molded steel hulls, schooner-rigged fore and aft, with two funnels [length 230', beam 26', draft 7'6", speed 16 knots]. Though maintaining British commercial registry, she was manned by the Confederate Navy with the intent of running badly needed supplies and equipment through the Federal blockade of the Southern coast. On her first such voyage, Bat was captured by USS Montgomery as she attempted to enter the port of Wilmington, North Carolina, on 10 October 1864. About a month later, the Navy purchased the former blockade runner, converted her to a gunboat and, in mid-December 1864, placed her in commission as USS Bat. She served off the Atlantic coast and in the Potomac River area during the remaining months of the Civil War. Decommissioned in mid-May 1865, Bat was sold in October of that year to civilian owners. She was employed commercially under the name Teazer until 1872, when she reentered British registry as Miramichi. The steamer operated in Canadian waters for three more decades, and was finally scrapped in about 1902.

The full-rigged ship, Formby, was built in Liverpool by Jones, Quiggin & Co. in 1863. Although iron was replacing timber in the construction of larger ships, Formby was probably the first full-rigged ship to be built of steel. Although her hull form allowed a much greater cargo capacity than the fast tea clippers, she can be described as a medium clipper and at 1,271 tons she typifies the cargo ships of the 1860s.

As pioneer in shipbuilding industry of China, Jiangnan Shipyard has made significant contributions to the country. In 1868, China's first steel ship known as Hui Ji was successfully built.

The dispatch vessel Iris (later reclassified as a 2nd Class cruiser), the Royal Navy's first steel ship, was launched in 1877. The Royal Navy's last composite built ship, the sloop Blonde, was launched in 1889, and the following year saw the final end of the use of wood for ship construction when the training brig Mayflower was launched.

During the late 1870's the Cunard Board of Directors were required to consider yet another scientific discovery. Just as iron had superseded wood, so steel was about to supplant iron. The directors were convinced that steel possessed greater strength than iron, and it was lighter. This saved so much weight that the extra cost was well repaid in fuel saved. The first steel ship to be built for Cunard was the Servia, and she was the largest and most powerful ship at the time (except the Great Eastern). The Servia possessed compound engines of massive proportions generating a total of 10,000 horse-power. The passenger accommodation was also of a high standard and modern appliances such as electric lamps were introduced. The Servia made her maiden voyage from Liverpool to New York, via Queenstown, on 26 November 1881. The fastest passage of the ship was made in December 1884, when it steamed from New York to Queenstown in 7 days 1 hour 38 minutes.

In 1881, the People's Line of Columbus, Georgia contracted with James Rees and Sons in Pittsburg to build "the finest vessel ever to wet the Apalachicola-Chattahoochee." The Chattahoochee was the first steel hull steamboat built in the United States and also the first with longitudinal and transverse bulkheads. In 1881, the Orient Line commissioned a new 5 524 grt passenger ship for their Australian service. Austral was the first steel ship in the company's fleet. The SS Olympian was the first steel-hull vessel built by Harlan & Hollingsworth of Wilmington, DE, in 1883.

Rivets and Welding

By the early 1900's, ship plates were still riveted together. A rivet is a short round metal connection used to fasten two or moremembers together by clinching after being heated red hot. The ship is given its shape by a series of symmetrically curved ribs or frames that run transversely and that are fastened to the keel. The skin of the vessel is mounted outside the frame. In steel vessels the skin consists of a number of metal plates riveted or welded to the frame.

At the end of WWI a push for faster construction times drove shipbuilders toward using substantially welded ship plates, but as the war stopped, the money for development dried up.

Brocklebank is one of the oldest firms in the world of merchant shipping, dating back to 1801. The firm experimented with motor ships including, for a short time, the first all-welded vessel, the small merchant coaster Fullagar (150 ft. long) of 1920. Cammell Laird, one of the most famous names in British shipbuilding during the nineteenth and twentieth centuries, built the first all-welded ship, the Fullagar.

At the start of WWII, the push came on to rapidly produce ships for the merchant marine fleet to supply the war effort, and welding technology was again pushed. The rapid and massive scale-up required by the war meant that unskilled laborers and inadequate welding practice were used. This method of construction reduced the amount of steel weight by 200 tons per vessel. Modern steel ocean-going ships owe much of their strength to the welding methods which bind their parts firmly together.

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Page last modified: 22-07-2011 17:42:55 ZULU