Ship

A ship is a large watercraft designed for travel across the surface of a body of water, carrying cargo or passengers, or in support of specialized tasks such as warfare, oceanography and fishing. Ships are generally distinguished from boats, based on size, shape, load capacity and purpose. Ships have supported exploration, trade, warfare, migration, colonization, and science. Ship transport is responsible for the largest portion of world commerce.

The word ship has meant, depending on era and context, either simply a large vessel or specifically a full-rigged ship with three or more masts, each of which is square rigged.

The earliest historical evidence of boats is found in Egypt during the 4th millennium BC. In 2024, ships had a global cargo capacity of 2.4 billion tons, with the three largest classes being ships carrying dry bulk (43%), oil tankers (28%) and container ships (14%).

Nomenclature

thumb|upright=1.42|Main parts of ship. 1:  [[Funnel (ship)|Funnel; 2: Stern; 3: Propeller and Rudder; 4: Portside (the right side is known as starboard); 5: Anchor; 6: Bulbous bow; 7: Bow; 8: Deck; 9: Superstructure ]]

Ships are typically larger than boats, but there is no universally accepted distinction between the two. Ships generally can remain at sea for longer periods of time than boats. A legal definition of ship from Indian case law is a vessel that carries goods by sea. A US Navy rule of thumb is that ships heel towards the outside of a sharp turn, whereas boats heel towards the inside

Starting around the middle of the 18th century, sailing vessels started to be categorised by their type of rig. (Previously they were described by their hull typefor example pink, cat.) Alongside the other rig types such as schooner and brig, the term "ship" referred to the rig type. In this sense, a ship is a vessel with three or more masts, all of which are square-rigged. For clarity, this may be referred to as a full-rigged ship or a vessel may be described as "ship-rigged". Alongside this rig-specific usage, "ship" continued to have the more general meaning of a large sea-going vessel. Often the meaning can only be determined by the context.

Some large vessels are traditionally called boats, notably submarines. Others include Great Lakes freighters, riverboats, and ferryboats, which may be designed for operation on inland or protected coastal waters. The Imperial War Museum stated that this may have originated from "far more ancient traditions" which included using a female grammatical gender for ships, and that there is a tradition that "relates to the idea of a female figure such as a mother or goddess guiding and protecting a ship and crew." By 2019, the Lloyd's Register of Shipping switched to referring to ships as "it".

Examples of the consequences of this include the large grain trade in the Mediterranean during the classical period. Cities such as Rome were totally reliant on the delivery by sailing and human powered (oars) ships of the large amounts of grain needed. It has been estimated that it cost less for a sailing ship of the Roman Empire to carry grain the length of the Mediterranean than to move the same amount 15 miles by road. Rome consumed about 150,000 tons of Egyptian grain each year over the first three centuries AD.

Until recently, it was generally the case that ships were the most advanced representations of the technology available to the societies that produced them.

Prehistory and antiquity

Asian developments

thumb|[[Fiji#Early settlement|Fijian voyaging outrigger boat with a crab claw sail ]]

thumb|One of the sailing vessels depicted in [[Borobudur temple, c. 8th century AD in Java, Indonesia ]]

The earliest attestations of ships in maritime transport in Mesopotamia are model ships, which date back to the 4th millennium BC. In archaic texts in Uruk, Sumer, the ideogram for "ship" is attested, but in the inscriptions of the kings of Lagash, ships were first mentioned in connection to maritime trade and naval warfare at around 2500–2350 BC.

Austronesian peoples originated in what is now Taiwan. From here, they took part in the Austronesian Expansion. Their distinctive maritime technology was integral to this movement and included catamarans and outriggers. It has been suggested that they had sails some time before 2000 BC. Their crab claw sails enabled them to sail for vast distances in open ocean. 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. In the 11th century, a new type of ship called djong or jong was recorded in Java and Bali. This type of ship was built using wooden dowels and treenails, unlike the kunlun bo which used vegetal fibres for lashings.

In China, miniature models of ships that feature steering oars have been dated to the Warring States period (c. 475–221 BC). The Chinese only acquired sea-going ship technologies in the 10th-century AD Song dynasty after contact with Southeast Asian k'un-lun po trading ships, leading to the development of the junks.

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

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

By 1200 BC, the Phoenicians were building large merchant ships. In world maritime history, declares Richard Woodman, they are recognized as "the first true seafarers, founding the art of pilotage, cabotage, and navigation" and the architects of "the first true ship, built of planks, capable of carrying a deadweight cargo and being sailed and steered."

Medieval and early modern periods

Asian developments

thumb|right|A Japanese [[atakebune from the 16th century]]

During the 15th century, China's Ming dynasty assembled one of the largest and most powerful naval fleets in the world for the diplomatic and power projection voyages of Zheng He. Elsewhere in Japan in the 15th century, one of the world's first iron-clads, "Tekkōsen" (鉄甲船), literally meaning "iron ships", was also developed. In Japan, during the Sengoku era from the 15th century to 17th century, the great struggle for feudal supremacy was fought, in part, by coastal fleets of several hundred boats, including the atakebune. In Korea, in the early 15th century during the Joseon era, "Geobukseon"(거북선), was developed.

The empire of Majapahit used large ships called jong, built in northern Java, for transporting troops overseas. The jongs were transport ships which could carry 100–2000 tons of cargo and 50–1000 people, 28.99–88.56 meter in length. The exact number of jong fielded by Majapahit is unknown, but the largest number of jong deployed in an expedition is about 400 jongs, when Majapahit attacked Pasai, in 1350.

European developments

thumb|Replica of Magellan's [[Victoria (ship)|Victoria. Ferdinand Magellan and Juan Sebastián Elcano led the first expedition that circumnavigated the globe in 1519–1522.]]

Until the late 13th or early 14th century, European shipbuilding had two separate traditions. In Northern Europe clinker construction predominated. In this, the hull planks are fastened together in an overlapping manner. This is a "shell first" construction technique, with the hull shape being defined by the shaping and fitting of the hull planks. The reinforcing s (or ribs) are fitted after the planks. Clinker construction in this era usually used planks that were cleft (split radially from the log) and could be made thinner and stronger per unit of thickness than the sawn logs, thanks to preserving the radial integrity of the grain.

An exception to clinker construction in the Northern European tradition is the bottom planking of the cog. Here, the hull planks are not joined to each other and are laid flush (not overlapped). They are held together by fastening to the frames but this is done after the shaping and fitting of these planks. Therefore, this is another case of a "shell first" construction technique.

These Northern European ships were rigged with a single mast setting a square sail. They were steered by rudders hung on the .]]

thumb|[[Italy|Italian full-rigged ship Amerigo Vespucci in New York Harbor ]]

thumb|[[RMS Titanic|RMS Titanic departs from Southampton. Her sinking led to tighter safety regulations.]]

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. Canal barges, towed by draft animals on an adjacent towpath, contended with the railway up to and past the early days of the Industrial Revolution. Flat-bottomed and flexible scow boats also became widely used for transporting small cargoes. Mercantile trade went hand-in-hand with exploration, self-financed by the commercial benefits of exploration.

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 long and their construction required 2,800 oak trees and 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. Ships and their owners grew with the 19th century Industrial Revolution across Europe and North America, leading to increased numbers of oceangoing ships, as well as other coastal and canal based vessels.

Through more than half of the 19th century and into the early years of the 20th century, steam ships coexisted with sailing vessels. Initially, steam was only viable on shorter routes, typically transporting passengers who could afford higher fares, and mail. Steam went through many developmental steps that gave greater fuel efficiency, thereby increasingly making steamships commercially competitive with sail. Screw propulsion worked better than paddle wheels, but relied, among other things, on the invention of an effective stern gland for the propeller shaft. Higher boiler pressures of powering compound engines, were introduced in 1865, making long-distance steam cargo vessels commercially viable on the route from England to Chinaeven before the opening of the Suez Canal in 1869. Within a few years, steam had replaced many of the sailing ships that had served this route. Even greater fuel efficiency was obtained with triple-expansion steam enginesbut this had to wait for higher quality steel to be available to make boilers running at in SS Aberdeen (1881). By this point virtually all routes could be served competitively by steamships. Sail continued with some cargoes, where low costs were more important to the shipper than a predictable and rapid journey time.

The Second Industrial Revolution in particular led to new mechanical methods of propulsion, and the ability to construct ships from metal triggered an explosion in ship design. These led to the development of long-distance commercial ships and Ocean liners, as well as technological changes including the Marine steam engine, screw propellers, triple expansion engines and others. Factors included the quest for more efficient ships, the end of long running and wasteful maritime conflicts, and the increased financial capacity of industrial powers created more specialized ships and other maritime vessels. Ship types built for entirely new functions that appeared by the 20th century included research ships, offshore support vessels (OSVs), Floating production storage and offloading (FPSOs), Pipe and cable laying ships, drill ships and Survey vessels.

The late 20th century saw changes to ships that included the decline of ocean liners as air travel increased. The rise of container ships from the 1960s onwards dramatically changed the nature of commercial merchant shipping, as containerization led to larger ship sizes, dedicated container routes and the decline of general cargo vessels as well as tramp steaming. The late 20th century also saw a rise in cruise ships for tourism around the world.

21st century

thumb|[[Colombo Express, a 8749 TEU container ship owned and operated by Hapag-Lloyd of Germany ]]

In 2016, there were more than 49,000 merchant ships, totaling almost 1.8 billion deadweight tons. Of these 28% were oil tankers, 43% were bulk carriers, and 13% were container ships. Such ships carried 11 billion tons of cargo in 2018, a sum that grew by 2.7% over the previous year. In terms of tonnage, 29% of ships were tankers, 43% are bulk carriers, 13% container ships and 15% were other types.

In 2008, 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. caught of fish and shellfish that year.

In 2023, the number of ships globally grew by 3.4%.

As of 2024, wind power for ships had received renewed interest for its potential to mitigate greenhouse gas emissions.

Types of ships

thumb|Various vessel types in the [[Port of Rotterdam ]]

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, which requires modification of the components. The categories accepted in general by naval architects are:

High-speed craft – Multihulls including wave piercers, small-waterplane-area twin hull (SWATH), surface effect ships and hovercraft, hydrofoil, wing in ground effect craft (WIG).
Off shore oil vessels – Platform supply vessels, pipe layers, accommodation and crane barges, non and semi-submersible drilling rigs, drill ships, production platforms, floating production storage and offloading units.
Fishing vessels
Motorised fishing trawlers, trap setters, seiners, longliners, trollers & factory ships.
Traditional sailing and rowed fishing vessels and boats used for handline fishing
Harbour work craft
Cable layers
Tugboats, dredgers, salvage vessels, tenders, pilot boats.
Floating dry docks, crane vessels, lighterships.
Dry cargo ships – tramp freighters, bulk carriers, cargo liners, container vessels, barge carriers, Ro-Ro ships, refrigerated cargo ships, timber carriers, livestock carriers & light vehicle carriers.
Liquid cargo ships – tankers, oil tankers, liquefied gas carriers, LNG carriers, chemical carriers.
Passenger ships
Liners, cruise and special trade passenger (STP) ships
Cross-channel, coastal and harbour ferries
Luxury and cruising yachts and superyachts
Sail training and sailing ships
Galleys – biremes, triremes and quinqueremes
Recreational boats and craft – rowed, masted and motorised craft
Special-purpose vessels – weather and research vessels, deep sea survey vessels, and icebreakers.
Submarines – watercraft capable of independent operation underwater.
Naval ships
Warships – aircraft carriers, amphibious warfare ships, battleships, battlecruisers, coastal defence ships, cruisers, destroyers, frigates, corvettes, patrol ships, minesweepers, etc.
Auxiliary ships – ammunition ships, replenishment oilers, repair ships, storeships, troopships, etc.
Hospital ships

Some of these are discussed in the following sections.

Inland vessels

thumb|Passenger ship of [[Köln-Düsseldorfer on the river Rhine ]]

thumb|Hurma, Hans and Voima at the [[Lake Saimaa in the harbour of Imatra, Finland, at a heritage ship meeting in 2009]]

Freshwater shipping may occur on lakes, rivers and canals. Ships designed for those body of waters may be specially adapted to the widths and depths of specific waterways. Examples of freshwater waterways that are navigable in part by large vessels include the Danube, Mississippi, Rhine, Yangtze and Amazon Rivers, and the Great Lakes.

Great Lakes

Lake freighters, also called lakers, are cargo vessels that ply the Great Lakes. The most well-known is , 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.

, 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 ship

thumb|Two modern [[container ships in San Francisco ]]

Merchant ships are ships used for commercial purposes and can be divided into four broad categories: fishing vessels, cargo ships, passenger ships, and special-purpose ships. 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". but until the mid-19th century they were predominantly square sail rigged. The fastest vessels may use pump-jet engines. Most commercial vessels such as container ships, have full hull-forms (higher Block coefficients) to maximize cargo capacity. Merchant ships and fishing vessels are usually made of steel, although aluminum can be used on faster craft, and fiberglass or wood on smaller 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 but up to 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, of fish were caught in the marine capture fishery. Anchoveta represented the largest single catch at . Of these, 1.3 million were decked vessels with enclosed areas and the rest were open vessels.

Special purpose vessels

thumb|The weather ship [[MS Polarfront|MS Polarfront at sea]]

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. 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. The removal of a weather ship became a negative factor in forecasts leading up to the Great Storm of 1987. Beginning in the 1970s, their role became largely superseded by weather buoys due to the ships' significant cost.

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.

Fast combat vessels such as cruisers and destroyers usually have fine hulls to maximize speed and maneuverability. 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. 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.

Hull

thumb|right|A ship's hull endures harsh conditions at sea, as illustrated by this [[reefer ship in bad weather.]]

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 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. The bow is the foremost part of the hull. Many ships feature a bulbous bow. The keel is 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

thumb|right|A ship's engine room

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 use 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. Most vessels have a single propeller, but some large vessels may have up to four propellers supplemented with transverse thrusters for maneuvring at ports. The propeller is connected to the main engine via a propeller shaft and, in case of medium- and high-speed engines, a reduction gearbox. Some modern vessels have a diesel–electric powertrain in which the propeller is turned by an electric motor powered by the ship's generators.

As environmental sustainability becomes a paramount concern, the maritime industry is exploring cleaner propulsion technologies. Alternatives like LPG (Liquefied Petroleum Gas), ammonia, and hydrogen are emerging as viable options. LPG is already utilized as fuel for long-distance shipping, offering a cleaner option with a lower carbon footprint. Meanwhile, hydrogen and ammonia technologies are in development stages for long-haul applications, promising even more significant reductions in emissions and a step closer to achieving carbon-neutral shipping.

Steering systems

thumb|right|The rudder and propeller on a newly built [[Ferryboat|ferry ]]

For ships with independent propulsion systems for each side, such as manual oars or some paddles, 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. Examples include the outboard motor, the bow thruster, and the azimuth thruster.

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 . 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.

Equipment

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 tackle comprises the anchor, its chain or cable, and connecting fittings.
Cargo equipment such as cranes and cargo booms may be 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

Hydrostatics

Ships float in the water at a level where mass of the displaced water equals the mass of the vessel, so 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.

Hydrodynamics

thumb|right|Aerial view of the , showing a 39° [[Wake (physics)|wake, characteristic of vessels passing through water]]

thumb|Vessels move along the three axes: 1. heave, 2. sway, 3. surge, 4. yaw, 5. pitch, 6. roll

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. Antifouling paint is commonly used to assist in this. Advanced designs such as the bulbous bow assist 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.

This hull speed is found by the formula:

</math>

or, in metric units:

</math>

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.

Lifecycle

thumb|right|Lines plan for the hull of a basic [[cargo ship ]]

thumb|[[MS Freedom of the Seas|MS Freedom of the Seas under construction in a shipyard in Turku ]]

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 ship to the scrapyard.

Design

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. Designs for larger or more complex vessels may also include sail plans, electrical schematics, and plumbing and ventilation plans.

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.

Construction

thumb|right|A [[Ship naming and launching|ship launching at the Northern Shipyard in Gdańsk, Poland ]]

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. 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

thumb|right| The tanker [[Exxon Valdez oil spill|Exxon Valdez spilled of oil into Alaska's Prince William Sound.]]

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 sediment and marine environment.

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

Nomenclature

Prehistory and antiquity

Asian developments

Medieval and early modern periods

Asian developments

European developments

21st century

Types of ships

Inland vessels

Great Lakes

Merchant ship

Special purpose vessels

Architecture

Hull

Propulsion systems

Steering systems

Holds, compartments, and the superstructure

Equipment

Design considerations

Hydrostatics

Hydrodynamics

Lifecycle

Design

Construction

Oil spills

See also

Notes

References

Citations

Sources