ship
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What is a ship?
A ship is a large floating vessel designed for crossing open waters, in contrast to a boat, which is generally smaller. Since 4000 BCE, ships have been vital for movement, with early designs changing slowly until about 150 years ago.
Initially, ships primarily sailed with the wind behind them, but innovations allowed them to "sail into the wind." By 1600, merchant ships had grown significantly, leading to efforts to minimize crew sizes for oceanic navigation due to the high costs of payment and provisions.
The rise of eastern trade around 1600 saw impressive growth in merchant ships. The English understood their ships needed cannons to defend their factories and ward off pirates. Scientific construction improved ships, but operational efficiency was lost in the effort to make them secure against attack.
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How is a ship different from a boat?
The primary distinction between a ship and a boat lies in their size and capacity. A ship is a large floating vessel capable of traversing open waters, whereas a boat is generally a smaller craft. Ships often have the capacity to carry boats on board.
The point at which a boat becomes a ship isn't precisely defined, but the term ship typically denotes a vessel of more than 500 tons of displacement.3 Britannica SourcesCreated from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles. -
What are the main parts of a ship?
A ship's main components include the hull, which is the primary structural body designed to support its weight and resist forces. The deck serves as a platform and floor. The machinery for propulsion is often located at the stern (rear) to keep cargo spaces clear. The bridge is a structure above the main deck that houses navigating spaces. Additionally, ships have watertight closures for openings like doors and cargo hatches to prevent water from entering the hull. These components ensure structural integrity, efficient operation, and safety at sea.
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What are some common types of ships and their uses?
Ships serve various purposes, and most non-military and non-yacht vessels fall into categories like cargo, passenger, industrial, service, and miscellaneous types.
- Cargo ships are designed to carry goods, with specialized designs for different cargo types, such as container ships that transport goods in standardized containers.
- Tankers are cargo ships that carry liquids like petroleum.
- Cruise ships function as floating resorts, offering leisure activities and transportation.
- Industrial ships perform industrial processes at sea, like fish processing or waste incineration.
- Naval ships include aircraft carriers, cruisers, and submarines, which enable a nation to extend its military power onto the seas.
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How do ships float and move through water?
A ship floats due to buoyancy, which is an upward force that opposes the ship's weight. According to Archimedesâ principle, a ship sinks until it displaces an amount of water equal to its own weight, achieving equilibrium and remaining afloat. The center of buoyancy is the center of mass of the volume of water the ship displaces.
To move through water, a ship uses a propulsion device to thrust against the water. The most efficient propulsion occurs when a large mass of water is acted upon with a small acceleration. Modern ships use screw propellers, which may be surrounded by fixed shrouding, such as the Kort nozzle, for producing high thrusts at low ship speeds.
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How have ships changed throughout history?
From ancient rowed vessels to today's modern ships, ships have undergone significant changes throughout history.
Early boats, dating back to 4000 BCE, were essential for movement, and their designs depended on available materials like timber, reeds, and animal skins. Ancient Egyptian boats featured sails and oars, while the Romans used two and three-level oared galleys.
The rise of the full-rigged ship in the 15th century, with multiple masts and sails, enabled ships to navigate against the wind, facilitating global trade. In the 16th and 17th centuries, oar propulsion was replaced by sails, and cannons were introduced, leading to the development of galleons and the distinction between warships and trading ships.
The 19th century saw the transition to steam-powered iron ships, revolutionizing naval design and tactics. Modern combat ships include aircraft carriers, missile-equipped cruisers, destroyers, battleships, and submarines. Today, ships are constructed using various materials, including wood, steel, aluminum alloys, and reinforced plastics.
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ship, any large floating vessel capable of crossing open waters, as opposed to a boat, which is generally a smaller craft. The term formerly was applied to sailing vessels having three or more masts; in modern times it usually denotes a vessel of more than 500 tons of displacement. Submersible ships are generally called boats regardless of their size.
Naval architecture
The design of ships employs many technologies and branches of engineering that also are found ashore, but the imperatives of effective and safe operation at sea require oversight from a unique discipline. That discipline is properly called marine engineering, but the term naval architecture is familiarly used in the same sense. In this section the latter term is used to denote the hydrostatic and aesthetic aspects of marine engineering.
The measurements of ships are given in terms of length, breadth, and depth. The length between perpendiculars is the distance on the summer (maximum) load waterline, from the forward side of the stem at the extreme forward part of the vessel to the after side of the rudder post at the extreme rear, or to the centre of the rudder stock, if there is no rudder post. The beam is the greatest breadth of the ship. The depth is measured at the middle of the length, from the top of the keel to the top of the deck beam at the side of the uppermost continuous deck. Draft is measured from the keel to the waterline, while freeboard is measured from the waterline to the deck edge. These terms, together with several others of importance in ship design, are given in the .
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Hydrostatics
The basis of naval architecture is found in Archimedesâ principle, which states that the weight of a statically floating body must equal the weight of the volume of water that it displaces. This law of buoyancy determines not only the draft at which a vessel will float but also the angles that it will assume when in equilibrium with the water.
A ship may be designed to carry a specified weight of cargo, plus such necessary supplies as fuel, lubricating oil, crew, and the crewâs life support). These combine to form a total known as deadweight. To deadweight must be added the weight of the shipâs structure, propulsion machinery, hull engineering (nonpropulsive machinery), and outfit (fixed items having to do with crew life support). These categories of weight are known collectively as lightship weight. The sum of deadweight and lightship weight is displacementâthat is, the weight that must be equaled by the weight of displaced water if the ship is to float. Of course, the volume of water displaced by a ship is a function of the size of that ship, but in turn the weight of water that is to be matched by displacement is also a function of the shipâs size. The early stages of ship design, therefore, are a struggle to predict the size of the ship that the sum of all weights will require. The naval architectâs resources include experience-based formulas that provide approximate values for making such predictions. Subsequent refinements usually produce accurate predictions of the shipâs draftâthat is, the depth of water in which the finished ship will float.
In some cases a ship may be intended for cargo of such a high stowage factor (i.e., volume per weight unit) that providing for the required internal volume is more of a problem than providing for a specific deadweight. Nevertheless, the problem of designing for a displacement that matches the weight of the ship is essentially the same.
Static stability
Accurately predicting a shipâs draft is a necessary result of correctly applied hydrostatic principles but is far from sufficient. If the many items of weight on a ship are not distributed with considerable precision, the ship will float at unwanted angles of heel (sideways inclination) and trim (endwise inclination). Nonzero trim angles may lift the tips of propeller blades above the surface, or they may increase the possibility that the bow will slam into waves during heavy weather. Nonzero heel angles (which tend to be much greater than trim angles) may make all human activity aboard difficult; moreover, they are dangerous because they reduce the margin against capsizing. In general, the avoidance of such inclinations requires an extension of Archimedesâ principle to the first moments of weights and volumes: the collective first moment of all weights must equal the first weight moment of the water displaced.
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The shows the cross section of a ship that is floating at heel angle θ, caused by the placement of a weight (w) a certain distance (d) from the centre line. At this angle, the upsetting moment, calculated as w Ă d Ă cos θ, is equaled by the righting moment Î Ă GZ, (Î is the symbol for displacement, and GZ is the distance from the centre of gravity [G] to the centre of buoyancy [Z]). Under these conditions, the ship is said to be in static equilibrium. If w is removed, the upsetting moment will become zero, and the righting moment will return the ship to its upright position. The ship is therefore judged to be stable. The moment will act in the stable direction only as long as the point M (the âmetacentre,â the point where the buoyant force intersects the midplane) is above G (the centre of gravity of the ship and its contents). If M is below G, the forces of weight and buoyancy will tend to increase the angle of heel, and the equilibrium will be unstable. The distance from G to M, taken to be positive if M is above G, is called the transverse metacentric height.
A value for metacentric height is usually found only for the zero heel condition; hence, it is an accurate measure of stability only for small disturbancesâfor example, ones that cause heeling of no more than about 10°. For larger angles, the ârighting arm,â GZ, is used to measure stability. In any stability analysis, the value of GZ is plotted over the entire range of heel angles for which it is positive, or restoring. The resultant curve of statical stability shows thereby the angle beyond which the ship cannot return to upright and the angle at which the restoring moment is at a maximum. The area of the curve between its origin and any specified angle is proportional to the energy required to heel the ship to that angle.