Difference between revisions of "Ship"

Revision as of 17:17, 15 June 2007

Italian ship-rigged vessel Amerigo Vespucci in New York Harbor, 1976

A ship is a large, sea-going watercraft, sometimes with multiple decks. A ship usually has sufficient size to carry its own boats, such as lifeboats, dinghies, or runabouts. A rule of thumb saying (though it doesn't always apply) goes: "a boat can fit on a ship, but a ship can't fit on a boat". Often local law and regulation will define the exact size (or the number of masts) which a boat requires to become a ship. (Note that one refers to submarines as "boats"). Compare vessel.

During the age of sail, ship signified a ship-rigged vessel, that is, one with three or more masts, usually three, all square-rigged. Such a vessel would normally have one fore and aft sail on her aftermost mast which was usually the mizzen. Almost invariably she would also have a bowsprit but this was not part of the definition. The same economic pressures which increased sizes to the point of carrying four or five masts, also introduced the fore and aft rig to larger vessels, so few ship-rigged vessels were built with more than three masts. The five-masted Preussen was the outstanding example but the big German ships and barques were built partly for prestige reasons.

Nautical means related to sailors, particularly customs and practices at sea. Naval is the adjective pertaining to ships though in common usage, it has come to be more particularly associated with the noun 'navy'.

Measuring ships

One can measure ships in terms of overall length, length of 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; most measure volume rather than weight and are used when describing merchant ships.

Gross tonnage is a measure of the total internal volume of the ship.
Net tonnage is expresses a merchant vessel's earning capacity and gives the internal capacity of that part of the ship available for cargo or passengers.
Thames measurement tonnage was used for smaller vessels and worked to a formula: (length - beam) x beam x ½beam / 94
Displacement tonnage is normally applied to warships and equals the actual weight of a ship complete with crew, fuel, stores and water.
Light ship tonnage measures the actual weight of the ship with no fuel, no persons, no cargo, no water on board is not usually quoted.
Deadweight tonnage is the weight of cargo, stores, passengers etc. which when added to the weight of the ship's structure and equipment, will bring the vessel down to her designed waterline.

The word "displacement" arises from the basic physical law, discovered by Archimedes, that the weight of a floating object equates exactly to that of the water which would otherwise occupy the "hole in the water" displaced by the ship.

In Britain, until the Merchant Shipping Act of 1876, ship-owners could load their vessels until their decks were almost awash, resulting in a dangerously unstable condition. Additionally, anyone who signed onto such a ship for a voyage and, upon realizing the danger, chose to leave the ship, could end up in jail.

Samuel 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 Mark", exists on ships' sides, and consists of a circle with a horizontal line through the center. 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.

Propulsion

Until the application of the steam engine to 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 warfare depended 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 War used triremes, as did the Romans contesting the Battle of Actium. The use of large numbers of cannon from the 16th century meant that maneuverability took second place to broadside weight; this led to the dominance of the sail-powered warship.

The development of the steamship became a complex process, the first commercial success accruing to Robert Fulton's North River Steamboat (often called Clermont) in the USA in 1807, followed in Europe by the 45-foot PS Comet of 1812. Steam propulsion progressed considerably over the rest of the 19th century. Notable developments included the condenser, which reduced the requirement for fresh water, and the multiple expansion engine, which improved efficiency. As the means of transmitting the engine's power, the paddle wheel gave way to the more efficient screw propeller. The marine steam turbine developed by Sir Charles Algernon Parsons, brought the power to weight ratio down. He had achieved publicity by demonstrating it unofficially in the 100-foot Turbinia at the Spithead Naval 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 out of date, in warships.

The marine diesel engine first came into use around 1912: either the Vulcanus or the Selandia (depending upon who you talk to) first deployed it. It soon offered even greater efficiency than the steam turbine but for many years had an inferior power-to-space ratio. About this period too, heavy fuel oil came into more general use and began to replace coal as the fuel of choice in steamships. Its great advantages were the convenience and the reduction in manning owing to the removal of the need for trimmers and of stokers in the old-fashioned numbers.

Most ships built since around 1960 have used diesel power or motors; one exception, Queen Elizabeth 2 of 1968, started with steam turbines but subsequently converted to diesel as a cost-saving measure.

A few ships have used nuclear reactors, but this is not a separate form of propulsion. It merely makes steam to drive the turbines. Nonetheless, it has caused concerns about safety and waste disposal. It has become usual only in large aircraft carriers and in submarines, where the ability to run submerged for long periods holds obvious advantage. In such long-endurance vessels, the saving in bunkerage too, is an important consideration.

General terminology

Ships may occur collectively as fleets, flotillas or squadrons. Convoys of ships commonly occur.

A collection of ships for military purposes may compose a navy or a task force.

In the past, people counting or grouping disparate types of ship may refer to the individual vessels as bottoms. Groups of sailing ships could constitute, say, a fleet of 40 sail. Groups of submarines (particularly German U-boats in the 1940s) may hunt in packs (often erroneously called wolf packs).

Shipboard terminology

See also: Glossary of nautical terms. The complexity of ships, particularly of sailing ships, led to the development of a rich and various vocabulary. Many of the following terms link to more detailed discussions of nautical terminology.

Amidships - toward the middle of the vessel.
Bow - strictly, one of the two curved structures where the hull broadens out from the stem (the pointed end). The bows is a term for the head of the vessel or front of the ship. Compare prow, a more poetical term for the ship's head.
Stern - the after end of the ship.
Aft - towards the stern when the relationship is within the ship.
Astern beyond the stern where the relationship is outside the vessel.
Starboard - the side of the ship which lies to the right when an observer within the ship faces forward.
Port - the side of the ship which lies to the left when an observer within the ship faces forward. (A mnemonic to distinguish port and starboard notes that left and port both have four letters. Another incorporates the navigation light: Is there any red port left?)
(Navigation) Bridge - A structure above the weather deck, extending the full width of the vessel, which houses a command centre, itself called by association, the bridge. A bridge usually extends a little beyond the ship's side to enable observation of boats alongside, or the proximity of a dock or lock gate; these projections are called bridge wings. In big vessels, a docking bridge used to be found aft. (See Lord, Walter. A Night to Remember (1976) p.96). It enabled an officer to observe docking manoeuvres before giving orders. RMS Titanic had one but they have been superseded by closed circuit television cameras.
Bulkheads - internal "walls" in a ship. Bulkheads are the vertical equivalent of decks. They have a structural function as well as dividing spaces. They serve to prevent collapse of the hull under stress, to maintain stability, in the event of flooding, and to contain fire. Many bulkheads feature watertight doors which, in the case of certain types of ships, the crew may close remotely. An internal "wall" that is not load-bearing is usually referred to as a "partition". It is to a bulkhead as a flat is to a deck.
Cabin - an enclosed room on a deck or flat.
Capstan - a winch with a vertical axis.
Coaming - Raised edges of hatches in decks for keeping water and articles free on the deck from falling into the hold.
Decks - the structures forming the approximately horizontal surfaces in the ship's general structure. Unlike flats, they are a structural part of the ship.
Deck Head - The under-side of the deck above. Sometimes panelled over to hide the pipe work. This panelling, like that lining the bottom and sides of the holds, is the ceiling.
Draft - The vertical distance from the current waterline to the lowest point of the ship or in the part of the ship under consideration.
Figurehead - symbolic image at the head of a traditional sailing ship or early steamer.
Forecastle - a partial deck, above the upper deck and at the head of the vessel; traditionally the sailors' living quarters.
Freeboard - The vertical distance from the current waterline to the highest continuous watertight deck. This usually varies from one part to another.
Galley - the kitchen of the ship
Gunwale - Formerly a fabricated band placed for strengthening around the ship at the main or upper deck level to accommodate the stresses imposed by the use of artillery. In later use it is the angle between the ship’s side and upper deck. It remained as a structural member, in wooden boats where it was mounted inboard of the sheer strake regardless of the need for gunnery.
Bulwark - the extension of the ship's side above the level of the weather deck.
Hold - In earlier use, below the orlop deck, the lower part of the interior of a ship's hull, especially when considered as storage space, as for cargo. In later merchant vessels it extended up through the decks to the underside of the weather deck.
Hull - the shell and framework of the basic flotation-oriented part of a ship
Keel - the central structural basis of the hull
Kelson - the timber immediately above the keel of a wooden ship.
Mast - a spar (in a ship, a very heavy one stepped in the keelson) formerly designed for the support of one or more sails. In modern ships, it is a steel or aluminium fabrication which carries navigation lights, radar antennae etc.
Prow - a poetical alternative term for bows.
Scupper - a drainage waterway at the edge of a deck, is drained by a pipe or, on the weather deck, a small opening in the bulwarks, leading overboard. It is called a scupper which is distinct from larger openings with hinged covers on the bulwarks, designed for relieving the ship of large quantities of water in a seaway. These are called freeing ports or wash ports..
Windlass - A winch mechanism, usually with a horizontal axis. used where mechanical advantage greater than that obtainable by block and tackle was needed.
Weather deck - whichever deck is that exposed to the weather – usually either the main deck or, in larger vessels, the upper deck.

Some types of ships and boats

Some historical types of ships and boats

A two-masted schooner

Barque A sailing vessel with three or more masts, fore-and-aft rigged on only the aftermost.
Barquentine A sailing vessel with three or more masts, square-rigged only on the foremast.
Battle cruiser A light battleship.
Battleship a large, heavily-armoured and heavily-gunned warship. A term which generally post-dates sailing warships.
Bilander
Bireme An ancient vessel, propelled by two banks of oars.
Birlinn
Blockade runner A ship whose current business is to slip past a blockade.
Brig A two-masted, square-rigged vessel.
Brigantine A two-masted vessel, square-rigged on the foremast and fore-and-aft rigged on the main.
Caravel
Carrack
Clipper
Cog
Collier A vessel designed for the coal trade.
Dreadnought An early twentieth century class of battleship.
Dromons are the precursors to galleys.
East Indiaman An armed merchantman belonging to one of the East India companies (Dutch, British etc.)
Fire ship A vessel of any sort, set on fire and sent into an anchorage with the aim of causing consternation and destruction. The idea is generally that of forcing an enemy fleet to put to sea in a confused, therefore vulnerable state.
Galleass A sailing and rowing warship, equally well suited to sailing and rowing.
Galleon A sixteenth century sailing warship.
Galley A warship propelled by oars with a sail for use in a favourable wind.
Galliot
Ironclad A wooden warship with external iron plating.
Knarr A type of Viking trade ship
Liberty ship An American merchant ship of the late Second World War period, designed for rapid building in large numbers. (The earliest class of welded ships.)
Longship A Viking raiding ship
Man of war A sailing warship.
Monitor A small, very heavily gunned warship with shallow draft. Designed for land bombardment.
Paddle steamer A steam-propelled, paddle-driven vessel, a name commonly applied to nineteenth century excursion steamers.
Pantserschip A Dutch ironclad. By the end of the nineteenth century, the name was applied to a heavy gunboat designed for colonial service.
Penteconter An ancient warship propelled by 50 oars, 25 on each side.
Pram A small dinghy, originally of a clinker construction and called in English, as in Danish, a praam. The Danish orthography has changed so that it would now be a pråm in its original language. It has a transom at both ends, the forward one usually small and steeply raked in the traditional design.
Q-ship A commerce raider camouflaged as a merchant vessel.
Quinquereme An ancient warship propelled by three banks of oars. On the upper row three rowers hold one oar, on the middle row - two rowers, and on the lower row - one man to an oar.
Schooner A fore and aft-rigged vessel with two or more masts of which the foremast is shorter than the main.
Shallop A large, heavily built, sixteenth century boat. Fore and aft rigged. More recently it has been a poetically frail open boat.
Small Waterplane Area Twin Hull (SWATH) A modern ship design used for Research Vessels and other purposes needing a steady ship in rough seas.
Steamship A ship propelled by a steam engine.
Ship of the line A sailing warship of first, second or third rate. That is, with 64 or more guns. Before the late eighteenth century, fourth rates (50-60 guns) also served in the line of battle.
Torpedo boat A small, fast surface vessel designed for launching torpedoes.
Tramp steamer A steamer which takes on cargo when and where it can find it.
Trireme An ancient warship propelled by three banks of oars.
Xebec
Victory ship

Quotations

I must go down to the sea again, to the lonely sea and the sky,

And all I ask is a tall ship, and a star to steer her by...

-John Masefield

External links

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 A '''ship''' is a large, sea-going [[watercraft]], sometimes with multiple decks. A ship usually has sufficient size to carry its own [[boat]]s, such as [[lifeboat]]s, [[dinghy|dinghies]], or [[runabout]]s. A [[rule of thumb]] saying (though it doesn't always apply) goes: "a boat can fit on a ship, but a ship can't fit on a boat". Often local [[law]] and regulation will define the exact size (or the number of [[mast (sailing)|mast]]s) which a boat requires to become a ship. (Note that one refers to [[submarine]]s as "boats"). Compare [[vessel]].