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<a href="/content/Container_ship" style="color:blue">Container ship</a> on the <a href="/content/Black_Sea" style="color:blue">Black Sea</a> near <a href="/content/Constan%C8%9Ba,_Romania" style="color:blue">Constanța, Romania</a>.
Container ship on the Black Sea near Constanța, Romania.

A ship is a large watercraft that travels the world's oceans and other sufficiently deep waterways, carrying passengers or goods, or in support of specialized missions, such as defense, research and fishing. Historically, a "ship" was a sailing vessel with at least three square-rigged masts and a full bowsprit. Ships are generally distinguished from boats, based on size, shape, load capacity, and tradition.

Ships have been important contributors to human migration and commerce.

As of 2016, there were more than 49,000 merchant ships, totaling almost 1.8 billion dead weight tons. Of these 28% were oil tankers, 43% were bulk carriers, and 13% were container ships.[2]

Nomenclature


Ships are generally larger than boats, but there is no universally accepted distinction between the two.

In the Age of Sail, a full-rigged ship was a sailing vessel with at least three square-rigged masts and a full bowsprit; other types of vessel were also defined by their sailplan, e.g. barque, brigantine, etc.[10]

A number of large vessels are usually referred to as boats.

In most maritime traditions ships have individual names, and modern ships may belong to a ship class often named after its first ship.

In the northern parts of Europe and America a ship is traditionally referred to with a female grammatical gender, represented in English with the pronoun "she", even if named after a man. This is not universal usage and some English language journalistic style guides advise using "it" as referring to ships with female pronouns can be seen as offensive and outdated.[12][13] In many documents the ship name is introduced with a ship prefix being an abbreviation of the ship class, for example "MS" (motor ship) or "SV" (sailing vessel), making it easier to distinguish a ship name from other individual names in a text.

History


The first known vessels date back about 10,000 years ago, but could not be described as ships.

The first sea-going sailing ships were developed by the Austronesian peoples from what is now Southern China and Taiwan. Their invention of catamarans, outriggers, and crab claw sails enabled their ships to sail for vast distances in open ocean. It led to the Austronesian Expansion at around 3000 to 1500 BC. From Taiwan, they rapidly colonized the islands of Maritime Southeast Asia, then sailed further onwards to Micronesia, Island Melanesia, Polynesia, and Madagascar, eventually colonizing a territory spanning half the globe.[16][17][15]

Austronesian rigs were distinctive in that they had spars supporting both the upper and lower edges of the sails (and sometimes in between), in contrast to western rigs which only had a spar on the upper edge.[16][17][15] The sails were also made from woven leaves, usually from pandan plants.[18][19] These were complemented by paddlers, who usually positioned themselves on platforms on the outriggers in the larger boats.[17][20] Austronesian ships ranged in complexity from simple dugout canoes with outriggers or lashed together to large edge-pegged plank-built boats built around a keel made from a dugout canoe. Their designs were unique, evolving from ancient rafts to the characteristic double-hulled, single-outrigger, and double-outrigger designs of Austronesian ships.[15][20]

Early Austronesian sailors influenced the development of sailing technologies in Sri Lanka and Southern India through the Austronesian maritime trade network of the Indian Ocean, the precursor to the spice trade route and the maritime silk road, which was established at around 1500 BC.[22] Some scholars believe that the triangular Austronesian crab claw sail may have influenced the development of the lateen sail in western ships due to early contact.[15] The junk rigs of Chinese ships is also believed to be originally Javanese in origin.[23]Maritime%20Southeast%20]] [25]

Also in 3000 BC, Ancient Egyptians learned how to assemble wooden planks into a hull.[26] They used woven straps to lash the planks together,[26] and reeds or grass stuffed between the planks helped to seal the seams.[26][27] The Greek historian and geographer Agatharchides had documented ship-faring among the early Egyptians: "During the prosperous period of the Old Kingdom, between the 30th and 25th centuries BC, the river-routes were kept in order, and Egyptian ships sailed the Red Sea as far as the myrrh-country." [28] Sneferu's ancient cedar wood ship Praise of the Two Lands is the first reference recorded (2613 BC) to a ship being referred to by name.[29]

The ancient Egyptians were perfectly at ease building sailboats. A remarkable example of their shipbuilding skills was the Khufu ship, a vessel 143 feet (44 m) in length entombed at the foot of the Great Pyramid of Giza around 2500 BC and found intact in 1954.

It is known that ancient Nubia/Axum traded with India, and there is evidence that ships from Northeast Africa may have sailed back and forth between India/Sri Lanka and Nubia trading goods and even to Persia, Himyar and Rome.[30] Aksum was known by the Greeks for having seaports for ships from Greece and Yemen.[31]

Elsewhere in Northeast Africa, the Periplus of the Red Sea reports that Somalis, through their northern ports such as Zeila and Berbera, were trading frankincense and other items with the inhabitants of the Arabian Peninsula well before the arrival of Islam as well as with then Roman-controlled Egypt.[32]

The oldest discovered sea faring hulled boat is the Late Bronze Age Uluburun shipwreck off the coast of Turkey, dating back to 1300 BC.[33]

The Phoenicians, the first to sail completely around Africa, and Greeks gradually mastered navigation at sea aboard triremes, exploring and colonizing the Mediterranean via ship. Around 340 BC, the Greek navigator Pytheas of Massalia ventured from Greece to Western Europe and Great Britain.[34] In the course of the 2nd century BC, Rome went on to destroy Carthage and subdue the Hellenistic kingdoms of the eastern Mediterranean, achieving complete mastery of the inland sea, that they called Mare Nostrum. The monsoon wind system of the Indian Ocean was first sailed by Greek navigator Eudoxus of Cyzicus in 118 BC.[35]

In the 1st century AD, the people from Nusantaran archipelago already made large ships over 50 m long and stood out 4–7 m out of the water. They could carry 700-1000 people and 260 ton cargo. These ships known as kunlun bo or k'unlun po (崑崙舶, lit. "ship of the Kunlun people") by the Chinese and kolandiaphonta by the Greeks. It has 4-7 masts and able to sail against the wind due to the usage of tanja sails. These ships reaching as far as Ghana.[36]

In China, miniature models of ships that feature steering oars have been dated to the Warring States period (c. 475–221 BC).[37] By the Han dynasty, a well kept naval fleet was an integral part of the military. Sternpost-mounted rudders started to appear on Chinese ship models starting in the 1st century AD.[37]Echoes%20from%20Old%20China%3A%20Life%2C%20Le]]owever, these early Chinese ships were fluvial (riverine), and were not seaworthy.[39]Song Dynasty djong elopment of the junks.[23]Maritime%20Southeast%20]] [25]

A panel found at Mohenjodaro depicted a sailing craft. Vessels were of many types; their construction is vividly described in the Yukti Kalpa Taru, an ancient Indian text on shipbuilding. This treatise gives a technical exposition on the techniques of shipbuilding. It sets forth minute details about the various types of ships, their sizes, and the materials from which they were built. The Yukti Kalpa Taru sums up in a condensed form all the available information. The Yukti Kalpa Taru gives sufficient information and dates to prove that, in ancient times, Indian shipbuilders had a good knowledge of the materials which were used in building ships. In addition to describing the qualities of the different types of wood and their suitability for shipbuilding, the Yukti Kalpa Taru gives an elaborate classification of ships based on their size.

The Swahili people had various extensive trading ports dotting the coast of medieval East Africa and Great Zimbabwe had extensive trading contacts with Central Africa, and likely also imported goods brought to Africa through the Southeast African shore trade of Kilwa in modern-day Tanzania.[41]

It is known by historians that at its height the Mali Empire built a large naval fleet under Emperor Mansa Musa in the late 13th and early 14th century.[42] Arabic sources describe what some consider to be visits to the New World by a Mali fleet in 1311.[43]

Before the introduction of the compass, celestial navigation was the main method for navigation at sea. In China, early versions of the magnetic compass were being developed and used in navigation between 1040 and 1117.[44] The true mariner's compass, using a pivoting needle in a dry box, was developed in Europe no later than 1300.[45][46]

Until the Renaissance, navigational technology remained comparatively primitive. This absence of technology did not prevent some civilizations from becoming sea powers. Examples include the maritime republics of Genoa and Venice, Hanseatic League, and the Byzantine navy. The Vikings used their knarrs to explore North America, trade in the Baltic Sea and plunder many of the coastal regions of Western Europe.

Towards the end of the 14th century, ships like the carrack began to develop towers on the bow and stern. These towers decreased the vessel's stability, and in the 15th century, the caravel, designed by the Portuguese, based on the Arabic qarib which could sail closer to the wind, became more widely used. The towers were gradually replaced by the forecastle and sterncastle, as in the carrack Santa María of Christopher Columbus. This increased freeboard allowed another innovation: the freeing port, and the artillery associated with it.

In the 16th century, the use of freeboard and freeing ports became widespread on galleons.

At this time, ships were developing in Asia in much the same way as Europe.

During the Age of the Ajuran, the Somali sultanates and republics of Merca, Mogadishu, Barawa, Hobyo and their respective ports flourished, enjoying a lucrative foreign commerce with ships sailing to and coming from Arabia, India, Venetia,[48] Persia, Egypt, Portugal and as far away as China. In the 16th century, Duarte Barbosa noted that many ships from the Kingdom of Cambaya in what is modern-day India sailed to Mogadishu with cloth and spices, for which they in return received gold, wax and ivory. Barbosa also highlighted the abundance of meat, wheat, barley, horses, and fruit on the coastal markets, which generated enormous wealth for the merchants.[49]

Middle Age Swahili Kingdoms are known to have had trade port bullship and trade routes[50] with the Islamic world and Asia and were described by Greek historians as "metropolises".[51] Famous African trade ports such as Mombasa, Zanzibar, and Kilwa[52] were known to Chinese sailors such as Zheng He and medieval Islamic historians such as the Berber Islamic voyager Abu Abdullah ibn Battua.[53] In the 14th century AD, King Abubakari I, the brother of King Mansa Musa of the Mali Empire, is thought to have had a great armada of ships sitting on the coast of West Africa.[54] This is corroborated by ibn Battuta himself who recalls several hundred Malian ships off the coast.[55] This has led to great speculation, with historical evidence, that it is possible that Malian sailors may have reached the coast of Pre-Columbian America under the rule of Abubakari II, nearly two hundred years before Christopher Columbus[56] and that black traders may have been in the Americas before Columbus.[43] Fifty years before Christopher Columbus, Chinese navigator Zheng He traveled the world at the head of what was for the time a huge armada. The largest of his ships had nine masts, were 130 metres (430 ft) long and had a beam of 55 metres (180 ft). His fleet carried 30,000 men aboard 70 vessels, with the goal of bringing glory to the Chinese emperor.

At the same time Zheng He made his expedition, Portuguese explorer Gil Eanes sailed on a square-rigged caravel beyond Cape Bojador the end of what was then considered the known world opening the route to deep sea exploration, continental sea communication technology and the spherical earth principle.

The carrack and then the caravel were developed in Portugal. After Columbus, European exploration rapidly accelerated, and many new trade routes were established.[58] In 1498, by reaching India, Vasco da Gama proved that the access to the Indian Ocean from the Atlantic was possible. These explorations in the Atlantic and Indian Oceans were soon followed by France, England and the Netherlands, who explored the Portuguese and Spanish trade routes into the Pacific Ocean, reaching Australia in 1606 and New Zealand in 1642.[59] In the 17th century Dutch and Spanish explorers such as Abel Tasman and Luís Vaz de Torres explored the coasts of Australia, while in the 18th century it was British explorer James Cook who mapped much of Polynesia.

Parallel to the development of warships, ships in service of marine fishery and trade also developed in the period between antiquity and the Renaissance.

Maritime trade was driven by the development of shipping companies with significant financial resources.

During the first half of the 18th century, the French Navy began to develop a new type of vessel known as a ship of the line, featuring seventy-four guns. This type of ship became the backbone of all European fighting fleets. These ships were 56 metres (184 ft) long and their construction required 2,800 oak trees and 40 kilometres (25 mi) of rope; they carried a crew of about 800 sailors and soldiers.

During the 19th century the Royal Navy enforced a ban on the slave trade, acted to suppress piracy, and continued to map the world. A clipper was a very fast sailing ship of the 19th century. The clipper routes fell into commercial disuse with the introduction of steam ships with better fuel efficiency, and the opening of the Suez and Panama Canals.

Ship designs stayed fairly unchanged until the late 19th century.

In light of this, classification of vessels by type or function can be difficult.

In 2007, the world's fleet included 34,882 commercial vessels with gross tonnage of more than 1,000 tons,[61] totaling 1.04 billion tons.[62] These ships carried 7.4 billion tons of cargo in 2006, a sum that grew by 8% over the previous year.[62] In terms of tonnage, 39% of these ships are tankers, 26% are bulk carriers, 17% container ships and 15% were other types.[62]

In 2002, there were 1,240 warships operating in the world, not counting small vessels such as patrol boats. The United States accounted for 3 million tons worth of these vessels, Russia 1.35 million tons, the United Kingdom 504,660 tons and China 402,830 tons. The 20th 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 Kingdom in the Falkland Islands and the United States in Iraq.

The size of the world's fishing fleet is 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 Organization estimated 4 million fishing vessels were operating worldwide.[63] The same study estimated that the world's 29 million fishermen[64] caught 85,800,000 tonnes (84,400,000 long tons; 94,600,000 short tons) of fish and shellfish that year.[65]

Types of ships


Because ships are constructed using the principles of naval architecture that require same structural components, their classification is based on their function such as that suggested by Paulet and Presles,[66] which requires modification of the components. The categories accepted in general by naval architects are:[67]

  • Dry cargo ships – tramp freighters, bulk carriers, cargo liners, container vessels, barge carriers, Ro-Ro ships, refrigerated cargo ships, timber carriers, livestock & light vehicle carriers.
  • Liquid cargo ships – Oil tankers, liquefied gas carriers, chemical carriers.
  • Passenger vessels

Some of these are discussed in the following sections.

Freshwater shipping may occur on lakes, rivers and canals.

Lake freighters, also called lakers, are cargo vessels that ply the Great Lakes. The most well-known is 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." Because of their additional beam, very large salties are never seen inland of the Saint Lawrence Seaway. Because the smallest of the Soo Locks is 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 Canal that bypasses the Niagara River.

Since the freshwater lakes 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.[68]

SS St. Marys Challenger, built in 1906 as William P Snyder, was the oldest laker still working on the Lakes until its conversion into a barge starting in 2013. Similarly, E.M. Ford, built in 1898 as Presque Isle, was sailing the lakes 98 years later in 1996. As of 2007 E.M. Ford was still afloat as a stationary transfer vessel at a riverside cement silo in Saginaw, Michigan.

Merchant ships are ships used for commercial purposes and can be divided into four broad categories: fishing, cargo ships, passenger ships, and special-purpose ships.[69] The UNCTAD review of maritime transport categorizes ships as: oil tankers, bulk (and combination) carriers, general cargo ships, container ships, and "other ships", which includes "liquefied petroleum gas carriers, liquefied natural gas carriers, parcel (chemical) tankers, specialized tankers, reefers, offshore supply, tugs, dredgers, cruise, ferries, other non-cargo". General cargo ships include "multi-purpose and project vessels and roll-on/roll-off cargo".[2]

Modern commercial vessels are typically powered by a single propeller driven by a diesel or, less usually, gas turbine engine., but until the mid-19th century they were predominantly square sail rigged. The fastest vessels may use pump-jet engines. Most commercial vessels have full hull-forms to maximize cargo capacity. Hulls are usually made of steel, although aluminum can be used on faster craft, and fiberglass on the smallest service vessels. Commercial vessels generally have a crew headed by a sea captain, with deck officers and engine officers on larger vessels. Special-purpose vessels often have specialized crew if necessary, for example scientists aboard research vessels.

Fishing boats are generally small, often little more than 30 meters (98 ft) but up to 100 metres (330 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, 85,800,000 tonnes (84,400,000 long tons; 94,600,000 short tons) of fish were caught in the marine capture fishery.[70] Anchoveta represented the largest single catch at 10,700,000 tonnes (10,500,000 long tons; 11,800,000 short tons).[70] 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.[70] Other species including salmon, shrimp, lobster, clams, squid and 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 fishing and hand-line fishing. Another method is the use of fishing trap.

Cargo ships transport dry and liquid cargo.[71] Dry cargo can be transported in bulk by bulk carriers, packed directly onto a general cargo ship in break-bulk, packed in intermodal 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 which may include both crude and finished products of oil, chemical tankers which may also carry vegetable oils other than chemicals and LPG/LNG tankers, although smaller shipments may be carried on container ships in tank containers.

Passenger ships range in size from small river ferries to very large cruise ships. This type of vessel includes ferries, which move passengers and vehicles on short trips; ocean liners, which carry passengers from one place to another; and cruise ships, which carry passengers on voyages undertaken for pleasure, visiting several places and with leisure activities on board, often returning them to the port of embarkation. 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.

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.[63] Of these, 1.3 million were decked vessels with enclosed areas and the rest were open vessels.[63] Most decked vessels were mechanized, but two-thirds of the open vessels were traditional craft propelled by sails and oars.[63] More than 60% of all existing large fishing vessels[72] were built in Japan, Peru, the Russian Federation, Spain or the United States of America.[73]

A weather ship was a ship stationed in the ocean as a platform for surface and upper air meteorological observations for use in marine weather forecasting. Surface weather observations were taken hourly, and four radiosonde releases occurred daily.[74] It was also meant to aid in search and rescue operations and to support transatlantic flights.[74][75] Proposed as early as 1927 by the aviation community,[76] the establishment of weather ships proved to be so useful during World War II that the International Civil Aviation Organization (ICAO) established a global network of weather ships in 1948, with 13 to be supplied by the United States.[75] This number was eventually negotiated down to nine.[77]

The weather ship crews were normally at sea for three weeks at a time, returning to port for 10-day stretches.[74] Weather ship observations proved to be helpful in wind and wave studies, as they did not avoid weather systems like other ships tended to for safety reasons.[78] They were also helpful in monitoring storms at sea, such as tropical cyclones.[79] The removal of a weather ship became a negative factor in forecasts leading up to the Great Storm of 1987.[80] Beginning in the 1970s, their role became largely superseded by weather buoys due to the ships' significant cost.[81] The agreement of the use of weather ships by the international community ended in 1990. The last weather ship was Polarfront, known as weather station M ("Mike"), which was put out of operation on 1 January 2010. Weather observations from ships continue from a fleet of voluntary merchant vessels in routine commercial operation.

Naval vessels are those used by a navy for military purposes. There have been many types of naval vessel. Modern naval vessels can be broken down into three categories: surface warships, submarines, and auxiliary ships.

Modern warships are generally divided into seven main categories: aircraft carriers, cruisers, destroyers, frigates, corvettes, submarines and amphibious assault ships. The distinction between cruisers, destroyers, frigates, and corvettes is not rigorous; the same vessel may be described differently in different navies. Battleships were used during the Second World War and occasionally since then (the last battleships were removed from the U.S. Naval Vessel Register in March 2006), but were made obsolete by the use of carrier-borne aircraft and guided missiles.[82]

Most military submarines are either attack submarines or ballistic missile submarines. Until the end of World War II 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 sonar systems, and nuclear propulsion, submarines also became able to effectively hunt each other. The development of submarine-launched nuclear and cruise missiles gave submarines a substantial and long-ranged ability to attack both land and sea targets with a variety of weapons ranging from cluster munitions to nuclear weapons.

Most navies also include many types of support and auxiliary vessel, such as minesweepers, patrol boats, offshore patrol vessels, replenishment ships, and hospital ships which are designated medical treatment facilities.[83]

Fast combat vessels such as cruisers and destroyers usually have fine hulls to maximize speed and maneuverability.[84] They also usually have advanced marine electronics and communication systems, as well as weapons.

Architecture


Some components exist in vessels of any size and purpose.

For a ship to float, its weight must be less than that of the water displaced by the ship's hull.[85] There are many types of hulls, from logs lashed together to form a raft to the advanced hulls of America's Cup sailboats. 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.

Hulls are subject to various hydrostatic and hydrodynamic constraints.

Older ships and pleasure craft often have or had wooden hulls.

Propulsion systems for ships fall into three categories: human propulsion, sailing, and mechanical propulsion. Human propulsion includes rowing, which was used even on large galleys. 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 19th century. They are now generally used for recreation and competition, although experimental sail systems, such as the turbosails, rotorsails, and wingsails have been used on larger modern vessels for fuel savings.

Mechanical propulsion systems generally consist of a motor or engine turning a propeller, or less frequently, an impeller or wave propulsion fins. 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. Nuclear reactors producing steam are used to propel warships and icebreakers, and there have been attempts to utilize them to power commercial vessels (see NS Savannah

In addition to traditional fixed and controllable pitch propellers there are many specialized variations, such as contra-rotating and nozzle-style propellers.

For ships with independent propulsion systems for each side, such as manual oars or some paddles,[86] steering systems may not be necessary. In most designs, such as boats propelled by engines or sails, a steering system becomes 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. Autopilot systems combine mechanical rudders with navigation systems. Ducted propellers are sometimes used for steering.

Some propulsion systems are inherently steering systems.

Larger boats and ships generally have multiple decks and compartments.

Superstructures are found above the main deck.

Shipboard equipment varies from ship to ship depending on such factors as the ship's era, design, area of operation, and purpose.

  • Masts can be the home of antennas, navigation lights, radar transponders, fog signals, and similar devices often required by law.
  • Ground tackle includes 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, and survival suits are carried aboard many vessels for emergency use.

Design considerations


Ships float in the water at a level where mass of the displaced water equals the mass of the vessel, such that the downwards force of gravity equals the upward force of buoyancy. As a vessel is lowered into the water its weight remains constant but the corresponding weight of water displaced by its hull increases. If the vessel's mass is evenly distributed throughout, it floats evenly along its length and across its beam (width). 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.

A simple way of considering wave-making resistance is to look at the hull in relation to its wake.

This hull speed is found by the formula:

or, in metric units:

where L is the length of the waterline in feet or meters.

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 swell as well as effects of wind and 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.

How it has been convincingly shown in scientific studies of the 21st century,[87][88] controllability of some vessels decreases dramatically in some cases that are conditioned by effects of the bifurcation memory. This class of vessels includes ships with high manoeuvring capabilities, aircraft and controlled underwater vehicles designed to be unstable in steady-state motion that are interesting in terms of applications. These features must be considered in designing ships and in their control in critical situations.

Lifecycle


A ship will pass through several stages during its career.

A vessel's design starts with a specification, which a naval architect uses 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.

As environmental laws are becoming more strict, ship designers need to create their design in such a way that the ship, when it nears its end-of-term, can be disassembled or disposed easily and that waste is reduced to a minimum.

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. During World War II, the need for cargo ships was so urgent that construction time for Liberty Ships went from initially eight months or longer, down to weeks or even days. Builders employed production line and prefabrication techniques such as those used in shipyards today.[89]The%20Liberty%20Ships]] [91]

Hull materials and vessel size play a large part in determining the method of construction.

Generally, construction starts with the hull, and on vessels over about 30 meters (98 ft), by the laying of the keel.

Once completed, the vessel is delivered to the customer.

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 drydock at regular intervals. Tasks often done at drydock include removing biological growths on the hull, sandblasting and 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.

Some vessels that sustain major damage at sea may be repaired at a facility equipped for major repairs, such as a shipyard.

Most ocean-going cargo ships have a life expectancy of between 20 and 30 years.

As ships age, forces such as corrosion, osmosis, and rotting compromise hull strength, and a vessel becomes too dangerous to sail.

Many ships do not make it to the scrapyard, and are lost in fires, collisions, grounding, or sinking at sea. The Allies lost some 5,150 ships during World War II.[92]

Measuring ships


One can measure ships in terms of overall length, length between perpendiculars, 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 formula to 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 circle with 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 pollution


Ship pollution is the pollution of air and water by shipping. It is a problem that has been accelerating as trade has become increasingly globalized, posing an increasing threat to the world’s oceans and waterways as globalization continues. It is expected that "shipping traffic to and from the United States is projected to double by 2020."[93] 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.

Oil spills have devastating effects on the environment.

By the sheer amount of oil carried, modern oil tankers must be considered something of a threat to the environment.

The International Tanker Owners Pollution Federation has researched 9,351 accidental spills since 1974.[96] According to this study, most spills result from routine operations such as loading cargo, discharging cargo, and taking on fuel oil.[96] 91% of the operational oil spills were small, resulting in less than 7 tons per spill.[96] Spills resulting from accidents like collisions, groundings, hull failures, and explosions are much larger, with 84% of these involving losses of over 700 tons.[96]

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 Erika (1999) and Prestige (2002), the European Union passed 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".[97]

When a large vessel such as a container ship or an oil tanker unloads cargo, seawater is pumped into other compartments in the hull to help stabilize and balance the ship. During loading, this ballast water is pumped out from these compartments.[98]

One of the problems with ballast water transfer is the transport of harmful organisms.

Ballast and bilge discharge from ships can also spread human pathogens and other harmful diseases and toxins potentially causing health issues for humans and marine life alike.[100] 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 hormone cycles, birth defects, suppression of the immune system, and disorders resulting in cancer, tumors, and genetic abnormalities or even death.[95]

Exhaust emissions 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."[95] In Europe ships make up a large percentage of the sulfur introduced to the air, "as much sulfur as all the cars, lorries and factories in Europe put together".[101] "By 2010, up to 40% of air pollution over land could come from ships."[101] Sulfur in the air creates acid rain which damages crops and buildings. When inhaled, sulfur is known to cause respiratory problems and increase the risk of a heart attack.[101]

Ship breaking or ship demolition is a type of ship disposal involving the breaking up of ships for scrap recycling, with the hulls being discarded in ship graveyards. Most ships have a lifespan of a few decades before there is so much wear that refitting and repair becomes uneconomical. Ship breaking allows materials from the ship, especially steel, to be reused.

In addition to steel and other useful materials, however, ships (particularly older vessels) can contain many substances that are banned or considered dangerous in developed countries. Asbestos and polychlorinated biphenyls (PCBs) are typical examples. Asbestos was used heavily in ship construction until it was finally banned in most of the developed world in the mid 1980s. Currently, the costs associated with removing asbestos, along with the potentially expensive insurance and health risks, have meant that ship-breaking in most developed countries is no longer economically viable. Removing the metal for scrap can potentially cost more than the scrap value of the metal itself. In most of the developing world, however, shipyards can operate without the risk of personal injury lawsuits or workers' health claims, meaning many of these shipyards may operate with high health risks. Furthermore, workers are paid very low rates with no overtime or other allowances. Protective equipment is sometimes absent or inadequate. Dangerous vapors and fumes from burning materials can be inhaled, and dusty asbestos-laden areas around such breakdown locations are commonplace.

Aside from the health of the yard workers, in recent years, ship breaking has also become an issue of major environmental concern. Many developing nations, in which ship breaking yards are located, have lax or no environmental law, enabling large quantities of highly toxic materials to escape into the environment and causing serious health problems among ship breakers, the local population and wildlife. Environmental campaign groups such as Greenpeace have made the issue a high priority for their campaigns.[102]

See also


Model ships

Lists

Ship sizes

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