A ship IPA|/ʃɪp/ audio|en-us-ship.ogg|Audio (US) is a large vessel that floats on water. Ships are generally distinguished from
boatsbased on size. Ships may be found on lakes, seas, and rivers and they allow for a variety of activities, such as the transport of persons or goods, fishing, entertainment, public safety, and warfare.
Ships and boats have developed alongside mankind. In major wars, and in day to day life, they have become an integral part of modern commercial and military systems. Fishing boats are used by millions of fishermen throughout the world. Military forces operate highly sophisticated vessels to transport and support forces ashore. Commercial vessels, nearly 35,000 in number, carried 7.4 billion tons of cargo in 2007.UNCTAD 2007, p. "x" and p. 32.]
These vessels were also key in history's great explorations and scientific and technological development. Navigators such as
Zheng Hespread such inventions as the compassand gunpowder. On one hand, ships have been used for colonizationand the slave trade. On the other, they also have served scientific, cultural, and humanitarian needs.
Thor Heyerdahldemonstrated with his tiny boat the " Kon-Tiki", it is possible to achieve great things with a simple log raft. From Mesolithic canoes to today's powerful nuclear-powered aircraft carriers, ships tell the history of man.
Ships can usually be distinguished from
boatsbased on size and the ship's ability to operate independently for extended periods.Cutler 1999, p. 620.] A commonly used rule of thumbis that if one vessel can carry another, the larger of the two is a ship.Cutler 1999, p. 611.] As dinghies are common on sailing yachts as small as convert|35|ft|m, this rule of thumb is not foolproof.
A number of large vessels are traditionally referred to as boats.
Submarines are a prime example.cite web |url=http://www.navy.mil/navydata/cno/n87/history/subsaga5.html |title=The Saga of the Submarine: Early Years to the Beginning of Nuclear Power |accessdate=2008-10-03 |author=Chief of Naval Operations |authorlink= Chief of Naval Operations |coauthors= |date= |year=2001 |month=March |format= |work= |publisher=United States Navy |location= |pages= |language= |doi= |archiveurl= |archivedate= |quote= ] Other types of large vessels which are traditionally called boats are the Great Lakes freighter, the riverboat, and the ferryboat.cn|date=October 2008 Though large enough to carry their own boats and heavy cargoes, these vessels are designed for operation on inland or protected coastal waters.
Prehistory and antiquity
The history of boats parallels the human adventure. The first known boats date back to the
Neolithic Period, about 10,000 years ago. These early vessels had limited function: they could move on water, but that was it. They were used mainly for huntingand fishing. The oldest dugout canoes found by archaeologists were often cut from coniferous treelogs, using simple stone tools
Roughly 5,000 years ago,
Ancient Egyptians already knew how to assemble planks of woodinto a ship hull.Ward, Cheryl. "World's Oldest Planked Boats," in "Archaeology" (Volume 54, Number 3, May/June 2001). Archaeological Institute of America, [http://www.archaeology.org/0105/abstracts/abydos3.html] .] Woven straps were used to lash the planks together, and reeds or grassstuffed between the planks helped to seal the seams.
At about the same time, people living near
Kongens Lyngbyin Denmark invented the segregated hull, which allowed the size of boats to gradually be increased. Boats soon developed into keel boats similar to today's wooden pleasure craft.
The first navigators began to use animal skins or woven fabrics as
sails. Affixed to the top of a pole set vertically in a boat, these sails gave early ships great range. This allowed man to explore widely, allowing, for example the settlement of Oceaniaabout 3,000 years ago.
ancient Egyptians were perfectly at ease building sailboats. A remarkable example of their shipbuildingskills was the Khufu ship, a vessel convert|143|ft|m in length entombed at the foot of the Great Pyramid of Gizaaround 2,500 BC and found intact in 1954. According to Herodotus, the Egyptians made the first circumnavigation of Africa around 600 BC.
Phoenicians and Greeks gradually mastered navigation at sea aboard triremes, exploring and colonizing the Mediterraneanvia ship. Around 340 BC, the Greek navigator Pytheas of Massaliaventured from Greece to Western Europeand Great Britain.Chisholm, 1911:703.]
Before the introduction of the compass,
celestial navigationwas the main method for navigation at sea. In China, early versions of the magnetic compasswere being developed and used in navigation between 1040 and 1117. [Li Shu-hua, “Origine de la Boussole 11. Aimant et Boussole,” "Isis", Vol. 45, No. 2. (Jul., 1954), p.181] The true mariner's compass, using a pivoting needle in a dry box, was invented in Europe no later than 1300. [Frederic C. Lane, “The Economic Meaning of the Invention of the Compass,” "The American Historical Review", Vol. 68, No. 3. (Apr., 1963), p.615ff.] Chisholm, 1911:284.]
Through the Renaissance
Renaissance, navigational technology remained comparatively primitive. This absence of technology didn't prevent some civilizations from becoming sea powers. Examples include the maritime republics of Genoa and Venice, and the Byzantine navy. The Vikings used their knarrs to explore North America, trade in the Baltic Seaand plunder many of the coastal regions of Western Europe.
Towards the end of the fourteenth century, ships like the
carrackbegan to develop towers on the bow and stern. These towers decreased the vessel's stability, and in the fifteenth century, caravels became more widely used. The towers were gradually replaced by the forecastleand sterncastle, as in the carrack "Santa María" of Christopher Columbus. This increased freeboardallowed another innovation: the freeing port, and the artillery associated with it.
In the sixteenth century, the use of freeboard and freeing ports become widespread on
galleons. The English modified their vessels to maximize their firepower and demonstrated the effectiveness of their doctrine, in 1588, by defeating the Spanish Armada.
Fifty years before Christopher Columbus, Chinese navigator
Zheng Hetraveled the world at the head of what was for the time a huge armada. The largest of his ships had nine masts, were convert|130|m|ft long and had a beam of convert|55|m|ft. His fleet carried 30,000 men aboard 70 vessels, with the goal of bringing glory to the Chinese emperor.
pecialization and modernization
Parallel to the development of warships, ships in service of marine fishery and trade also developed in the period between antiquity and the Renaissance. Still primarily a coastal endeavor, fishing is largely practiced by individuals with little other money using small boats.
Maritime trade was driven by the development of shipping companies with significant financial resources. Canal barges, towed by draft animals on an adjacent
towpath, contended with the railwayup to and past the early days of the industrial revolution. Flat-bottomed and flexible scowboats also became widely used for transporting small cargoes. Mercantile trade went hand-in-hand with exploration, which is self-financing by the commercial benefits of exploration.
During the first half of the eighteenth century, the
French Navybegan to develop a new type of vessel, featuring seventy-four guns. This type of ship became the backbone of all European fighting fleets. These ships were convert|56|m|ft long and their construction required 2,800 oak trees and convert|40|km|mi of rope; they carried a crew of about 800 sailors and soldiers.
Ship designs stayed fairly unchanged until the late nineteenth century. The industrial revolution, new mechanical methods of propulsion, and the ability to construct ships from metal triggered an explosion in ship design. Factors including the quest for more efficient ships, the end of long running and wasteful maritime conflicts, and the increased financial capacity of industrial powers created an avalanche of more specialized boats and ships. Ships built for entirely new functions, such as firefighting, rescue, and research, also began to appear.
In light of this, classification of vessels by type or function can be difficult. Even using very broad functional classifications such as fishery, trade, military, and exploration fails to classify most of the old ships. This difficulty is increased by the fact that the terms such as sloop and frigate are used by old and new ships alike, and often the modern vessels sometimes have little in common with their predecessors.
In 2007, the world's fleet included 34,882 commercial vessels with
gross tonnageof more than 1,000 tons,UNCTAD 2007, p. 32.] totaling 1.04 billion tons.UNCTAD 2007, p. "x".] These ships carried 7.4 billion tons of cargo in 2006, a sum that grew by 8% over the previous year. In terms of tonnage, 39% of these ships are tankers, 26% are bulk carriers, 17% container shipsand 15% were other types.
In 2002, there were 1,240
warships operating in the world, not counting small vessels such as patrol boats. The United Statesaccounted for 3 million tons worth of these vessels, Russia1.35 million tons, the United Kingdom504,660 tons and China402,830 tons. The twentieth century saw many naval engagements during the two world wars, the Cold War, and the rise to power of naval forces of the two blocs. The world's major powers have recently used their naval power in cases such as the United Kingdomin the Falkland Islandsand the United Statesin Iraq. Warships were also key in history's great explorations and scientific and technological development. Navigators such as Zheng Hespread such inventions as the compassand gunpowder. On one hand, ships have been used for colonizationand the slave trade. On the other, they also have served scientific, cultural, and humanitarian needs.
The size of the world's
fishing fleetis more difficult to estimate. The largest of these are counted as commercial vessels, but the smallest are legion. Fishing vessels can be found in most seaside villages in the world. As of 2004, the United Nations Food and Agriculture Organizationestimated 4 million fishing vessels were operating worldwide. The same study estimated that the world's 29 million fishermenUNFAO 2005, p.6.] caught 85.8 million metric tons of fish and shellfish that year.UNFAO 2005, p.9.]
Types of ships
Ships are difficult to classify, mainly because there are so many criteria to base classification on. One classification is based on propulsion; with ships categorised as either a
sailing shipor a motorship. Sailing ships are ships which are propelled solely by means of sails. Motorships are ships which are propelled by mechanical means to propell itself. Motorships include ships that propel itself trough the use of both sail and mechanical means.
Other classification systems exist that use criteria such as:
* The number of hulls, giving categories like monohull, catamaran, trimaran.
* The shape and size, giving categories like dinghy, keelboat, and icebreaker.
* The building materials used, giving steel, aluminum, wood, fiberglass, and plastic.
* The type of propulsion system used, giving human-propelled, mechanical, and sails.
* The epoch in which the vessel was used, triremes of Ancient Greece, man' o' wars, eighteenth century.
* The geographic origin of the vessel, many vessels are associated with a particular region, such as the
pinnaceof Northern Europe, the gondolas of Venice, and the junks of China.
* The manufacturer, series, or class.
Another way to categorize ships and boats is based on their use, as described by Paulet and Presles.cite book |last=Paulet |first=Dominique |coauthors=Presles ,Dominique |editor= |others= |title=Architecture navale, connaissance et pratique |origdate= |origyear= |accessyear= |year=1999 |publisher=Éditions de la Villette |location=Paris |language=Français |isbn=2-903539-46-4 ] This system includes military ships, commercial vessels, fishing boats, pleasure craft and competitive boats. In this section, ships are classified using the first four of those categories, and adding a section for lake and river boats, and one for vessels which fall outside these categories.
Commercial vessels or
merchant ships can be divided into three broad categories: cargo ships, passenger ships, and special-purpose ships.UNCTAD 2007, p. "xii" uses a similar, but slightly more detailed classification system.] Cargo ships transport dry and liquid cargo. Dry cargo can be transported in bulk by bulk carriers, packed directly onto a general cargo shipin break-bulk, packed in shipping containers as aboard a container ship, or driven aboard as in roll-on roll-off ships. Liquid cargo is generally carried in bulk aboard tankers, such as oil tankers, chemical tankers and LNG tankers.
Passenger ships range in size from small river ferries to giant
cruise ships. This type of vessel includes ferries, which move passengers and vehicles on short trips; ocean liners, which carry passengers on one-way trips; and cruise ships, which typically transport passengers on round-trip voyages promoting leisure activities onboard and in the ports they visit.
Special-purpose vessels are not used for transport but are designed to perform other specific tasks. Examples include
tugboats, pilot boats, rescue boats, cable ships, research vessels, survey vessels, and ice breakers.
Most commercial vessels have full hull-forms to maximize cargo capacity.Fact|date=April 2008 Hulls are usually made of steel, although aluminum can be used on faster craft, and fiberglass on the smallest service vessels.Fact|date=April 2008 Commercial vessels generally have a crew headed by a captain, with
deck officers and marine engineers on larger vessels. Special-purpose vessels often have specialized crew if necessary, for example scientists aboard research vessels. Commercial vessels are typically powered by a single propeller driven by a diesel engine.Fact|date=April 2008 Vessels which operate at the higher end of the speed spectrum may use pump-jet engines or sometimes gas turbine engines.Fact|date=April 2008
Modern warships are generally divided into seven main categories, which are:
aircraft carriers, cruisers, destroyers, frigates, corvettes, submarines and amphibious assault ships. Battleships encompass an eighth category, but are not in current service with any navy in the world.With the addition of corvettes, this is the categorization used at cite web |url=http://www.navy.mil/navydata/our_ships.asp |title=U.S. Navy Ships |accessdate=2008-04-20 |author=United States Navy |authorlink=United States Navy |publisher=United States Navy ]
Most military submarines are either
attack submarines or ballistic submarines. Until World War Two, the primary role of the diesel/electric submarine was anti-ship warfare, inserting and removing covert agents and military forces, and intelligence-gathering. With the development of the homing torpedo, better sonarsystems, and nuclear propulsion, submarines also became able to effectively hunt each other. The development of submarine-launched nuclear missiles and submarine-launched cruise missilesgave submarines a substantial and long-ranged ability to attack both land and sea targets with a variety of weapons ranging from cluster bombs to nuclear weapons.
Most navies also include many types of support and auxiliary vessels, such as minesweepers,
patrol boats, offshore patrol vessels, replenishment ships , and hospital ships which are designated medical treatment facilities. [ [http://wordnet.princeton.edu/perl/webwn?s=hospital%20ship Hospital Ship] (definition via WordNet, Princeton University)]
Combat vessels like cruisers and destroyers usually have fine hulls to maximize speed and maneuverability.Cutter, 1999, p. 224.] They also usually have advanced electronics and communication systems, as well as weapons.
Fishing vessels are a subset of commercial vessels, but generally small in size and often subject to different regulations and classification. They can be categorized by several criteria: architecture, the type of fish they catch, the fishing method used, geographical origin, and technical features such as rigging. As of 2004, the world's fishing fleet consisted of some 4 million vessels.UNFAO, 2007, p. 25.] Of these, 1.3 million were decked vessels with enclosed areas and the rest were open vessels. Most decked vessels were mechanized, but two-thirds of the open vessels were traditional craft propelled by sails and oars. More than 60% of all existing large fishing vessels [UNFAO defines a large fishing vessel as one with
gross tonnageover 100 GT.] were built in Japan, Peru, the Russian Federation, Spain or the United States of America.UNFAO, 2007, p. 28.]
Fishing boats are generally small, often little more than convert|30|m|ft but up to convert|100|m|ft for a large tuna or
whaling ship. Aboard a fish processing vessel, the catch can be made ready for market and sold more quickly once the ship makes port. Special purpose vessels have special gear. For example, trawlers have winches and arms, stern-trawlers have a rear ramp, and tuna seiners have skiffs.
In 2004, 85.8 million metric tons of fish were caught in the marine capture fishery.UNFAO, 2007, p. 11.]
Anchovetarepresented the largest single catch at 10.7 million metric tons. That year, the top ten marine capture species also included Alaska pollock, Blue whiting, Skipjack tuna, Atlantic herring, Chub mackerel, Japanese anchovy, Chilean jack mackerel, Largehead hairtail, and Yellowfin tuna. Other species including salmon, shrimp, lobster, clams, squidand crab, are also commercially fished.
Modern commercial fishermen use many methods. One is fishing by nets, such as purse seine,
beach seine, lift nets, gillnets, or entangling nets. Another is trawling, including bottom trawl. Hooks and lines are used in methods like long-line fishingand hand-line fishing). Another method is the use of fishing trap.
Inland and coastal boats
Many types of boats and ships are designed for inland and coastal waterways. These are the vessels that trade upon the lakes, rivers and canals.
Barges are a prime example of inland vessels. Flat-bottomed
boats built to transport heavy goods, most barges are not self-propelled and need to be moved by tugboats towing or towboatspushing them. Barges towed along canals by draft animals on an adjacent towpathcontended with the railwayin the early industrial revolutionbut were outcompeted in the carriage of high value items due to the higher speed, falling costs, and route flexibility of rail transport. Riverboats and inland ferries are specially designed to carry passengers, cargo, or both in the challenging river environment. Rivers present special hazards to vessels. They usually have varying water flows that alternately lead to high speed water flows or protruding rock hazards. Changing siltation patterns may cause the sudden appearance of shoal waters, and often floating or sunken logs and trees (called snags) can endanger the hulls and propulsion of riverboats. Riverboats are generally of shallow draft, being broad of beam and rather square in plan, with a low freeboard and high topsides. Riverboats can survive with this type of configuration as they do not have to withstand the high winds or large waves that are seen on large lakes, seas, or oceans. Lake freighters, also called lakers, are cargovessels that ply the Great Lakes. The most well-known is the SS|Edmund Fitzgerald, the latest major vessel to be wrecked on the Lakes. These vessels are traditionally called boats, not ships. Visiting ocean-going vessels are called "salties." Due to their additional beam, very large salties are never seen inland of the Saint Lawrence Seaway. Because the largest of the Soo Locksis larger than any Seaway lock, salties that can pass through the Seaway may travel anywhere in the Great Lakes. Because of their deeper draft, salties may accept partial loads on the Great Lakes, "topping off" when they have exited the Seaway. Similarly, the largest lakers are confined to the Upper Lakes (Superior, Michigan, Huron, Erie) because they are too large to use the Seaway locks, beginning at the Welland Canalthat bypasses the Niagara River.
freshwaterlakes are less corrosive to ships than the salt water of the oceans, lakers tend to last much longer than ocean freighters. Lakers older than 50 years are not unusual, and as of 2005, all were over 20 years of age.Office of Data and Economic Analysis, 2006, p. 2.]
The "St. Mary's Challenger", built in 1906 as the "William P Snyder", is the oldest laker still working on the Lakes. Similarly, the "E.M. Ford", built in 1898 as the "Presque Isle", was sailing the lakes 98 years later in 1996. As of 2007 the "Ford" was still afloat as a stationary transfer vessel at a riverside cement silo in
The wide variety of vessels at work on the earth's waters defy a simple classification scheme. A representative few that fail to fit into the above categories include:
* Historical boats, frequently used as
museum ships, training ships, or as good-will ambassadors of a country abroad.
Houseboats, floating structures used as dwellings.
* Scientific, technical, and industrial vessels such as mobile offshore drilling units, offshore wind farms,
survey ships, and research vessels.
Submarines, for underwater navigation and exploration
Some components exist in vessels of any size and purpose. Every vessel has a hull of sorts. Every vessel has some sort of propulsion, whether it's a pole, an ox, or a nuclear reactor. Most vessels have some sort of steering system. Other characteristics are common, but not as universal, such as compartments, holds, a superstructure, and equipment such as anchors and winches.
For a ship to float, its weight must be less than that of the water displaced by the ship's hull. There are many types of hulls, from logs lashed together to form a raft to the advanced hulls of
America's Cupsailboats. A vessel may have a single hull (called a monohull design), two in the case of catamarans, or three in the case of trimarans. Vessels with more than three hulls are rare, but some experiments have been conducted with designs such as pentamarans. Multiple hulls are generally parallel to each other and connected by rigid arms.
Hulls have several elements. The bow is the foremost part of the hull. Many ships feature a
bulbous bow. The keelis at the very bottom of the hull, extending the entire length of the ship. The rear part of the hull is known as the stern, and many hulls have a flat back known as a transom. Common hull appendages include propellers for propulsion, rudders for steering, and stabilizers to quell a ship's rolling motion. Other hull features can be related to the vessel's work, such as fishing gear and sonar domes.
Hulls are subject to various hydrostatic and hydrodynamic constraints. The key hydrostatic constraint is that it must be able to support the entire weight of the boat, and maintain stability even with often unevenly distributed weight. Hydrodynamic constraints include the ability to withstand shock waves, weather collisions and groundings.
Older ships and pleasure craft often have or had wooden hulls. Steel is used for most commercial vessels. Aluminium is frequently used for fast vessels, and
composite materials are often found in sailboats and pleasure craft. Some ships have been made with concrete hulls.
Propulsion systems for ships and boats vary from the simple paddle to the largest diesel engines in the world. These systems fall into three categories: human propulsion, sailing, and mechanical propulsion. Human propulsion includes the pole, still widely used in marshy areas, rowing which was used even on large
galleys, and the pedals. In modern times, human propulsion is found mainly on small boats or as auxiliary propulsion on sailboats.
Propulsion by sail generally consists of a sail hoisted on an erect mast, supported by stays and spars and controlled by ropes. Sail systems were the dominant form of propulsion until the nineteenth century. They are now generally used for recreation and racing, although experimental sail systems, such as the
kites/ royals, turbosails, rotorsails, wingsails and SkySails's own kite buoy-system have been used on larger modern vessels for fuel savings.
Mechanical propulsion systems generally consist of a motor or engine turning a
propeller. Steam engines were first used for this purpose, but have mostly been replaced by two-stroke or four-stroke diesel engines, outboard motors, and gas turbine engines on faster ships. Electric motors have sometimes been used, such as on submarines. Nuclear reactors are sometimes employed to propel warships and icebreakers.
There are many variations of propeller systems, including twin, contra-rotating, controllable-pitch, and nozzle-style propellers. Smaller vessels tend to have a single propeller. Aircraft carriers uses up to four propellers, supplemented with bow- and stern-thrusters. Power is transmitted from the engine to the propeller by way of a propeller shaft, which may or may not be connected to a gearbox.
Until the application of the
steam engineto ships in the early 19th century, oars propelled galleys, or the wind propelled sailing ships. Before mechanisation, merchant ships always used sail, but as long as naval warfaredepended on ships closing to ram or to fight hand-to-hand, galleys dominated in marine conflicts because of their maneuverability and speed. The Greek navies that fought in the Peloponnesian Warused triremes, as did the Romans at the Battle of Actium. The use of large numbers of cannonfrom the 16th century meant that maneuverability took second place to broadside weight; this led to the dominance of the sail-powered warship.
Reciprocating steam engines
The development of piston-engined steamships was a complex process. Early steamships were fueled by wood, later ones by coal or fuel oil. Early ships used stern or side
paddle wheels, while later ones used screw propellers.
The first commercial success accrued to
Robert Fulton's "North River Steamboat" (often called "Clermont") in the US in 1807, followed in Europeby the 45-foot "Comet" of 1812. Steam propulsion progressed considerably over the rest of the 19th century. Notable developments included the steam surface condenser, which eliminated the use of sea water in the ship's boilers. This permitted higher steam pressures, and thus the use of higher efficiency multiple expansion (compound) engines. As the means of transmitting the engine's power, paddle wheels gave way to more efficient screw propellers.
Steam turbines were fueled by
coalor, later, fuel oilor nuclear power. The marine steam turbinedeveloped by Sir Charles Algernon Parsonsraised the power to weight ratio. He achieved publicity by demonstrating it unofficially in the 100-foot " Turbinia" at the Spitheadnaval review in 1897. This facilitated a generation of high-speed liners in the first half of the 20th century and rendered the reciprocating steam engine obsolete, first in warships and later in merchant vessels.
In the early 20th century, heavy fuel oil came into more general use and began to replace coal as the fuel of choice in steamships. Its great advantages were convenience, reduced manning due to removing the need for trimmers and stokers, and reduced space needed for fuel bunkers.
In the second half of the 20th century, rising fuel costs almost led to the demise of the steam turbine. Most new ships since around 1960 have been built with
diesel engines. The last major passenger ship built with steam turbines was the "Fairsky", launched in 1984. Similarly, many steam ships were re-engined to improve fuel efficiency. One high profile example was the 1968 built " Queen Elizabeth 2" which had her steam turbines replaced with a diesel-electric propulsion plant in 1986.
Most new-build ships with steam turbines are specialist vessels such as nuclear-powered vessels, and certain merchant vessels (notably
Liquefied Natural Gas(LNG) and coal carriers) where the cargo can be used as bunker fuel.
LNG carriers (a high growth area of shipping) continue to be built with steam turbines. The natural gas is stored in a liquid state in cryogenic vessels aboard these ships, and a small amount of 'boil off' gas is needed to maintain the pressure and temperature inside the vessels within operating limits. The 'boil off' gas provides the fuel for the ship's boilers, which provide steam for the turbines, the simplest way to deal with the gas. Technology to operate internal combustion engines (modified marine two-stroke diesel engines) on this gas has improved, however, so such engines are starting to appear in LNG carriers; with their greater thermal efficiency, less gas is burnt. Developments have also been made in the process of re-liquefying 'boil off' gas, letting it be returned to the cryogenic tanks. The financial returns on LNG are potentially greater than the cost of the marine-grade fuel oil burnt in conventional diesel engines, so the re-liquefaction process is starting to be used on diesel engine propelled LNG carriers. Another factor driving the change from turbines to diesel engines for LNG carriers is the shortage of steam turbine qualified seagoing engineers. With the lack of turbine powered ships in other shipping sectors, and the rapid rise in size of the worldwide LNG fleet, not enough have been trained to meet the demand. It may be that the days are numbered for marine steam turbine propulsion systems, even though all but sixteen of the orders for new LNG carriers at the end of 2004 were for steam turbine propelled ships. [ [http://www.informare.it/news/forum/2005/brs/lng-auk.asp inforMARE - FORUM of Shipping and Logistics ] ]
Nuclear-powered steam turbines
In these vessels, the reactor heats steam to drive the turbines. Partly due to concerns about safety and waste disposal, nuclear propulsion is rare except in specialist vessels. In large
NS "Savannah" was the first nuclear-powered cargo-passenger ship
aircraft carriers, the space formerly used for ship's bunkerage could be used instead to bunker aviation fuel. In submarines, the ability to run submerged at high speed and in relative quiet for long periods holds obvious advantages. A few cruisershave also employed nuclear power; as of 2006, the only ones remaining in service are the Russian "Kirov" class. An example of a non-military ship with nuclear marine propulsionis the "Arktika" class icebreaker with 75,000 shaft horsepower. Commercial experiments such as the NS "Savannah" proved uneconomical compared with conventional propulsion.
Reciprocating diesel engines
About 99% of modern ships use diesel reciprocating enginesFact|date=May 2007. The rotating crankshaft can power the propeller directly for slow speed engines, via a gearbox for medium and high speed engines, or via an alternator and electric motor in diesel-electric vessels.
The reciprocating marine diesel engine first came into use in 1903 when the
diesel electricrivertanker "Vandal" was put in service by Branobel. Diesel engines soon offered greater efficiency than the steam turbine, but for many years had an inferior power-to-space ratio.
Diesel engines today are broadly classified according to
* Their operating cycle:
* Their construction:
Crosshead, trunk, or opposed piston
* Their speed
** Slow speed: any engine with a maximum operating speed up to 300 revs/minute, although most large 2-stroke slow speed diesel engines operate below 120 revs/minute. Some very long stroke engines have a maximum speed of around 80 revs/minute. The largest, most powerful engines in the world are slow speed, two stroke, crosshead diesels.
** Medium speed: any engine with a maximum operating speed in the range 300-900 revs/minute. Many modern 4-stroke medium speed diesel engines have a maximum operating speed of around 500 rpm.
** High speed: any engine with a maximum operating speed above 900 revs/minute.
Most modern larger merchant ships use either slow speed, two stroke, crosshead engines, or medium speed, four stroke, trunk engines. Some smaller vessels may use high speed diesel engines.
The size of the different types of engines is an important factor in selecting what will be installed in a new ship. Slow speed two-stroke engines are much taller, but the area needed, length and width, is smaller than that needed for four-stroke medium speed diesel engines. As space higher up in passenger ships and ferries is at a premium, these ships tend to use multiple medium speed engines resulting in a longer, lower engine room than that needed for two-stroke diesel engines. Multiple engine installations also give redundancy in the event of mechanical failure of one or more engines and greater efficiency over a wider range of operating conditions.
As modern ships' propellers are at their most efficient at the operating speed of most slow speed diesel engines, ships with these engines do not generally need gearboxes. Usually such propulsion systems consist of either one or two propeller shafts each with its own direct drive engine. Ships propelled by medium or high speed diesel engines may have one or two (sometimes more) propellers, commonly with one or more engines driving each propeller shaft through a gearbox. Where more than one engine is geared to a single shaft, each engine will most likely drive through a clutch, allowing engines not being used to be disconnected from the gearbox while others keep running. This arrangement lets maintenance be carried out while under way, even far from port.
Many warships built since the 1960s have used
gas turbines for propulsion, as have a few passenger ships, like the jetfoil. Gas turbines are commonly used in combination with other types of engine. Most recently, the " Queen Mary 2" has had gas turbines installed in addition to diesel engines. Due to their poor thermal efficiency at low power (cruising) output, it is common for ships using them to have diesel engines for cruising, with gas turbines reserved for when higher speeds are needed. Some warships and a few modern cruise ships have also used the steam turbines to improve the efficiency of their gas turbines in a combined cycle, where wasted heat from a gas turbine exhaust is utilized to boil water and create steam for driving a steam turbine. In such combined cycles, thermal efficiency can be the same or slightly greater than that of diesel engines alone; however, the grade of fuel needed for these gas turbines is far more costly than that needed for the diesel engines, so the running costs are still higher.
On boats with simple propulsion systems, such as paddles, steering systems may not be necessary. In more advanced designs, such as boats propelled by engines or sails, a steering system becomes more necessary. The most common is a rudder, a submerged plane located at the rear of the hull. Rudders are rotated to generate a lateral force which turns the boat. Rudders can be rotated by a
tiller, manual wheels, or electro-hydraulic systems. Autopilotsystems combine mechanical rudders with navigation systems.
Some propulsion systems are inherently steering systems. Examples include the
outboard motor, the bow thruster, and the Z-drive. Some sails, such as jibs and the mizzen sail on a ketch rig, are used more for steering than propulsion.
Holds, compartments, and the superstructure
Larger boats and ships generally have multiple decks and compartments. Separate
berthings and heads are found on sailboats over about convert|25|ft|m. Fishing boats and cargo ships typically have one or more cargo holds. Most larger vessels have an engine room, a galley, and various compartments for work. Tanks are used to store fuel, engine oil, and fresh water. Ballast tanks are equipped to change a ship's trim and modify its stability.
Superstructures are found above the main deck. On sailboats, these are usually very low. On modern cargo ships, they are almost always located near the ship's stern. On passenger ships and warships, the superstructure generally extends far forward.
Shipboard equipment varies from ship to ship depending on such factors as the ship's era, design, area of operation, and purpose. Some types of equipment that are widely found include:
Masts can be the home of antennas, navigation lights, radar transponders, fog signals, and similar devices often required by law.
Ground tackleincludes equipment such as mooring winches, windlasses, and anchors. Anchors are used to moor ships in shallow water. They are connected to the ship by a rope or chain. On larger vessels, the chain runs through a hawsepipe.
* Cargo equipment such as
cranes and cargo booms are used to load and unload cargo and ship's stores.
* Safety equipment such as
lifeboats, liferafts, fire extinguishers, and survival suits are carried aboard many vessels for emergency use.
Boats and ships are kept on (or slightly above) the water in three ways:
* For most vessels, known as displacement vessels, the vessel's weight is offset by that of the water displaced by the hull.
* For planing ships and boats, such as the hydrofoil, the lift developed by the movement of the foil through the water increases with the vessel's speed, until the vessel is foilborne.
* For non-displacement craft such as
hovercraftand air-cushion vehicles, the vessel is suspended over the water by a cushion of high-pressure air it projects downwards against the surface of the water.
A vessel is in equilibrium when the upwards and downwards forces are of equal magnitude. As a vessel is lowered into the water its weight remains constant but the corresponding weight of water displaced by its hull increases. When the two forces are equal, the boat floats. If weight is evenly distributed throughout the vessel, it floats without trim or heel.
A vessel's stability is considered in both this hydrostatic sense as well as a hydrodynamic sense, when subjected to movement, rolling and pitching, and the action of waves and wind. Stability problems can lead to excessive pitching and rolling, and eventually capsizing and sinking.
The advance of a vessel through water is resisted by the water. This resistance can be broken down into several components, the main ones being the friction of the water on the hull and
wave making resistance. To reduce resistance and therefore increase the speed for a given power, it is necessary to reduce the wetted surface and use submerged hull shapes that produce low amplitude waves. To do so, high-speed vessels are often more slender, with fewer or smaller appendages. The friction of the water is also reduced by regular maintenance of the hull to remove the sea creatures and algae that accumulate there. Antifoulingpaint is commonly used to assist in this. Advanced designs such as the bulbous bowassist in decreasing wave resistance.
A simple way of considering wave-making resistance is to look at the hull in relation to its wake. At speeds lower than the wave propagation speed, the wave rapidly dissipates to the sides. As the hull approaches the wave propagation speed, however, the wake at the bow begins to build up faster than it can dissipate, and so it grows in
amplitude. Since the water is not able to "get out of the way of the hull fast enough", the hull, in essence, has to climb over or push through the bow wave. This results in an exponential increase in resistance with increasing speed.
hull speedis found by the formula:
Or, in metric units:
When the vessel exceeds a speed/length ratio of 0.94, it starts to outrun most of its
bow wave, and the hull actually settles slightly in the water as it is now only supported by two wave peaks. As the vessel exceeds a speed/length ratio of 1.34, the hull speed, the wavelength is now longer than the hull, and the stern is no longer supported by the wake, causing the stern to squat, and the bow rise. The hull is now starting to climb its own bow wave, and resistance begins to increase at a very high rate. While it is possible to drive a displacement hull faster than a speed/length ratio of 1.34, it is prohibitively expensive to do so. Most large vessels operate at speed/length ratios well below that level, at speed/length ratios of under 1.0.
For large projects with adequate funding, hydrodynamic resistance can be tested experimentally in a hull testing pool or using tools of
computational fluid dynamics.
Vessels are also subject to
ocean surface waves and sea swellas well as effects of windand weather. These movements can be stressful for passengers and equipment, and must be controlled if possible. The rolling movement can be controlled, to an extent, by ballasting or by devices such as fin stabilizers. Pitching movement is more difficult to limit and can be dangerous if the bow submerges in the waves, a phenomenon called pounding. Sometimes, ships must change course or speed to stop violent rolling or pitching.
A ship will pass through several stages during its career. The first is usually an initial contract to build the ship, the details of which can vary widely based on relationships between the
shipowners, operators, designers and the shipyard. Then, the design phase carried out by a naval architect. Then the ship is constructed in a shipyard. After construction, the vessel is launched and goes into service. Ships end their careers in a number of ways, ranging from shipwrecks to service as a museum shipto the scrapyard.
A vessel's design starts with a specification, which a
naval architectuses to create a project outline, assess required dimensions, and create a basic layout of spaces and a rough displacement. After this initial rough draft, the architect can create an initial hull design, a general profile and an initial overview of the ship's propulsion. At this stage, the designer can iterate on the ship's design, adding detail and refining the design at each stage.
The designer will typically produce an overall plan, a general specification describing the peculiarities of the vessel, and construction blueprints to be used at the building site. Designs for larger or more complex vessels may also include sail plans, electrical schematics, and plumbing and ventilation plans.
Ship construction takes place in a
shipyard, and can last from a few months for a unit produced in series, to several years to reconstruct a wooden boat like the frigate "Hermione", to more than 10 years for an aircraft carrier. Hull materials and vessel size play a large part in determining the method of construction. The hull of a mass-produced fiberglass sailboat is constructed from a mold, while the steel hull of a cargo ship is made from large sections welded together as they are built.
Generally, construction starts with the hull, and on vessels over about 30 meters, by the laying of the keel. This is done in a
drydockor on land. Once the hull is assembled and painted, it is launched. The last stages, such as raising the superstructure and adding equipment and accommodation, can be done after the vessel is afloat.
Once completed, the vessel is delivered to the customer. Ship launching is often a ceremony of some significance, and is usually when the vessel is formally named. A typical small rowboat can cost under US$100, $1,000 for a small speedboat, tens of thousands of dollars for a cruising sailboat, and about $2,000,000 for a
Vendée Globeclass sailboat. A convert|25|m|ft trawler may cost $2.5 million, and a 1,000-person-capacity high-speed passenger ferry can cost in the neighborhood of $50 million. A ship's cost partly depends on its complexity: a small, general cargo shipwill cost $20 million, a Panamax-sized bulk carrieraround $35 million, a supertankeraround $105 million and a large LNG carriernearly $200 million. The most expensive ships generally are so due to the cost of embedded electronics: a "Seawolf" class submarine costs around $2 billion, and an aircraft carrier goes for about $3.5 billion.
Repair and conversion
Ships undergo nearly constant maintenance during their career, whether they be underway, pierside, or in some cases, in periods of reduced operating status between charters or shipping seasons.
Most ships, however, require trips to special facilities such as a
drydockat regular intervals. Tasks often done at drydock include removing biological growths on the hull, sandblastingand repainting the hull, and replacing sacrificial anodes used to protect submerged equipment from corrosion. Major repairs to the propulsion and steering systems as well as major electrical systems are also often performed at dry dock.
Vessels that sustain major damage at sea may be repaired at a facility equipped for major repairs, such as a shipyard. Ships may also be converted for a new purpose:
oil tankers are often converted into floating production storage and offloading units.
End of service
Most ocean-going cargo ships have a life expectancy of between 20 and 30 years. A sailboat made of plywood or fiberglass can last between 30 and 40 years. Solid wooden ships can last much longer but require regular maintenance. Carefully maintained steel-hulled yachts can have a lifespan of over 100 years.
As ships age, forces such as corrosion, osmosis, and rotting compromise hull strength, and a vessel becomes too dangerous to sail. At this point, it can be scuttled at sea or scrapped by
shipbreakers. Ships can also be used as museum ships, or expended to construct breakwaters or artificial reefs.
Many ships do not make it to the scrapyard, and are lost in fires, collisions, grounding, or sinking at sea.
One can measure ships in terms of overall length, length of the ship at the waterline, beam (breadth), depth (distance between the crown of the weather deck and the top of the keelson), draft (distance between the highest waterline and the bottom of the ship) and
tonnage. A number of different tonnage definitions exist and are used when describing merchant ships for the purpose of tolls, taxation, etc.
In Britain until Samuel Plimsoll's Merchant Shipping Act of 1876, ship-owners could load their vessels until their decks were almost awash, resulting in a dangerously unstable condition. Anyone who signed on to such a ship for a voyage and, upon realizing the danger, chose to leave the ship, could end up in
jail. Plimsoll, a Member of Parliament, realised the problem and engaged some engineers to derive a fairly simple formulato determine the position of a line on the side of any specific ship's hull which, when it reached the surface of the water during loading of cargo, meant the ship had reached its maximum safe loading level. To this day, that mark, called the "Plimsoll Line", exists on ships' sides, and consists of a circlewith a horizontal line through the centre. On the Great Lakes of North America the circle is replaced with a diamond. Because different types of water (summer, fresh, tropical fresh, winter north Atlantic) have different densities, subsequent regulations required painting a group of lines forward of the Plimsoll mark to indicate the safe depth (or freeboard above the surface) to which a specific ship could load in water of various densities. Hence the "ladder" of lines seen forward of the Plimsoll mark to this day. This is called the " freeboard mark" or "load line mark" in the marine industry.
Ship pollutionis the pollution of air and waterby shipping. It is a problem that has been accelerating as tradehas become increasingly globalized, posing an increasing threat to the world’s oceans and waterways as globalizationcontinues. It is expected that, “…shipping traffic to and from the USAis projected to double by 2020."Watson, T. (2004, August 30). Ship pollution clouds USA's skies. "USA Today". Retrieved November 1, 2006, from http://www.usatoday.com/news/nation/2004-08-30-ship-pollution_x.htm] Because of increased traffic in ocean ports, pollution from ships also directly affects coastal areas. The pollution produced affects biodiversity, climate, food, and human health. However, the degree to which humans are polluting and how it affects the world is highly debated and has been a hot international topic for the past 30 years.
thumb|right|_The_"Exxon Valdez" spilled 10.8 million gallons of oil into Alaska's title = Frequently asked questions about the Exxon Valdez Oil Spill|url=http://www.evostc.state.ak.us/History/FAQ.htm|publisher =State of Alaska] Oil spills have devastating effects on the environment. Crude oil contains
polycyclic aromatic hydrocarbons(PAHs) which are very difficult to clean up, and last for years in the sedimentand marine environment. Marine species constantly exposed to PAHs can exhibit developmental problems, susceptibility to disease, and abnormal reproductive cycles. By the sheer amount of oil carried, modern oil tankers must be considered something of a threat to the environment. An oil tanker can carry convert|2|Moilbbl|m3 of crude oil, or 62,000,000 gallons. This is more than six times the amount spilled in the widely known "Exxon Valdez" incident. In this spill, the ship ran aground and dumped 10.8 million gallons of oil into the ocean in March of 1989. Despite efforts of scientists, managers, and volunteers, over 400,000 seabirds, about 1,000 sea otters, and immense numbers of fish were killed.
The International Tanker Owners Pollution Federation has researched 9,351 accidental spills since 1974. [http://www.itopf.com/information-services/data-and-statistics/statistics/ International Tanker Owners Pollution Federation Statistics] ] According to this study, most spills result from routine operations such as loading cargo, discharging cargo, and taking on fuel oil. 91% of the operational oil spills were small, resulting in less than 7 tons per spill. Spills resulting from accidents like collisions, groundings, hull failures, and explosions are much larger, with 84% of these involving losses of over 700 tons.
Following the "Exxon Valdez" spill, the United States passed the
Oil Pollution Act of 1990(OPA-90), which included a stipulation that all tankers entering its waters be double-hulled by 2015. Following the sinkings of the "Erika" (1999) and "Prestige" (2002), the European Unionpassed its own stringent anti-pollution packages (known as Erika I, II, and III), which require all tankers entering its waters to be double-hulled by 2010. The Erika packages are controversial because they introduced the new legal concept of "serious negligence". [cite book |author=European Parliament |authorlink=European Parliament |coauthors= |editor= |others= |title=Directive 2005/35/EC of the European Parliament and of the Council of 7 September 2005 on ship-source pollution and on the introduction of penalties for infringements|origdate=2005 |origyear= |origmonth= |url=http://eur-lex.europa.eu/LexUriServ/LexUriServ.do?uri=OJ:L:2005:255:0011:01:EN:HTML |format= |accessdate=2008-02-22 |accessyear= |accessmonth= |edition= |series= |date= |year= |month= |publisher= |location= |language= |isbn= |oclc= |doi= |id= |pages= |chapter= |chapterurl= |quote= ]
When a large vessel such as a
container shipor an oil tanker unloads cargo, sea-water is pumped into compartments in the hull to help stabilize and balance the ship. During loading, this ballast water is pumped out from these compartments.
One of the problems with ballast water transfer is the transport of harmful organisms. MeineszMeinesz, A. (2003). Deep Sea Invasion. "The Impact of Invasive Species". PBS: NOVA. Retrieved November 26, 2006, from http://www.pbs.org/wgbh/nova/algae/impact.html] believes that one of the worst cases of a single invasive species causing harm to an ecosystem can be attributed to a seemingly harmless
jellyfish. " Mnemiopsis leidyi", a species of comb jellyfish that inhabits estuaries from the United States to the Valdés peninsula in Argentinaalong the Atlanticcoast, has caused notable damage in the Black Sea. It was first introduced in 1982, and thought to have been transported to the Black Sea in a ship’s ballast water. The population of the jellyfish shot up exponentially and, by 1988, it was wreaking havoc upon the local fishingindustry. "The anchovy catch fell from 204,000 tons in 1984 to 200 tons in 1993; sprat from 24,600 tons in 1984 to 12,000 tons in 1993; horse mackerel from 4,000 tons in 1984 to zero in 1993." Now that the jellyfish have exhausted the zooplankton, including fish larvae, their numbers have fallen dramatically, yet they continue to maintain a stranglehold on the ecosystem. Recently the jellyfish have been discovered in the Caspian Sea. Invasive species can take over once occupied areas, facilitate the spread of new diseases, introduce new genetic material, alter landscapes and jeopardize the ability of native species to obtain food. "On land and in the sea, invasive species are responsible for about 137 billion dollars in lost revenue and management costs in the U.S. each year."Panetta, L. E. (Chair) (2003). America's living oceans: charting a course for sea change [Electronic Version, CD] Pew Oceans Commission.]
bilgedischarge from ships can also spread human pathogensand other harmful diseases and toxinspotentially causing health issues for humans and marine life alike.National Research Council, Committee on the Ocean's Role in Human Health, Ocean Studies Board, Commission on Geosciences, Environment, and Resources. (1999). "From monsoons to microbes: understanding the ocean's role in human health". Washington, D.C.: National Academy Press] Discharges into coastal waters, along with other sources of marine pollution, have the potential to be toxic to marine plants, animals, and microorganisms, causing alterations such as changes in growth, disruption of hormonecycles, birth defects, suppression of the immune system, and disorders resulting in cancer, tumors, and genetic abnormalities or even death.
Exhaustemissions from ships are considered to be a significant source of air pollution. “Seagoing vessels are responsible for an estimated 14 percent of emissions of nitrogen from fossil fuels and 16 percent of the emissions of sulfur from petroleum uses into the atmosphere.” In Europe ships make up a large percentage of the sulfur introduced to the air, “…as much sulfur as all the cars, lorriesand factories in Europe put together.”Harrabin, R. (2003, June 25). EU faces ship clean-up call. "BBC News". Retrieved November 1, 2006, from http://news.bbc.co.uk/2/hi/europe/3019686.stm] “By 2010, up to 40% of air pollution over land could come from ships.” Sulfur in the air creates acid rainwhich damages crops and buildings. When inhaled sulfur is known to cause respiratoryproblems and increase the risk of a heart attack.
Ship model basin
List of world's longest ships
List of civilian nuclear ships
List of famous ships
List of fictional ships
List of historical ship types
List of shipwrecks
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* [http://www.shipspotting.com/ Photos of Ships]
* [http://ships.galutschek.at/ Video Clips of Ships]
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