Ships

A ship is a large, sea-going watercraft, usually 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", because early submarines were small enough to be carried aboard a ship in

transit to distant waters.) 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 for the purpose of tolls, taxation, etc.

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.
[edit]

Propulsion
[edit]

Pre-mechanisation

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.
[edit]

Steam propulsion

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 US in 1807,

followed in Europe by the 45-foot 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.

Most new ships since around 1960 have been built with diesel engines. Rising fuel costs have

almost lead to the demise of the steam turbine, with many ships being re-engined to improve

fuel efficiency. One high profile example was the 1968 built Queen Elizabeth 2 which had her

turbines replaced with a diesel-electric propulsion plant in 1986. The last major passenger

ship built with steam turbines was the Fairsky, launched in 1984. Some specialised merchant

ships have also been built with steam turbines since then, notably Liquified Natural Gas

(LNG) and coal carriers where part of the cargo has been used as fuel for the boilers.
[edit]

LNG Carriers

LNG carriers in particular have remained a stronghold for steam , and new ships continue to

be built with steam turbines in this high growth area of shipping. This is because the

Natural Gas is stored in a liquid state in cryogenic vessels onboard these ships. A small

amount of "boil off" of gas is required to maintain the pressure and temperature inside the

vessels to within operating limits. The "boil off" gas provides the fuel for the ship's

boilers, which provide steam for the turbines- the simplest method of dealing with the gas.

Technology to operate internal combustion engines (modified marine two stroke diesel

engines) on this gas has improved however, so these engines are beginning to appear in LNG

carriers; with their greater thermal efficiency, less gas is burnt. Also, developements have

been made in the process of re-liquifying "boil off" gas, enabling it to be returned to the

cryogenic tanks. The financial returns on LNG are potentially greater than the cost of the

marine grade fuel oil burnt in conventional diesel engines, so the re-liquification process

is starting to be used on diesel engine propelled LNG carriers. Another factor driving the

switch from turbines to diesel engines for LNG carriers is the shortage of steam turbine

qualified sea going engineers. With the lack of turbine powered ships in other shipping

sectors, and the rapid increase in size of the worldwide LNG fleet, not enough have been

trained to meet the demand. It may be that the days of the last stronghold for steam turbine

propulsion systems are numbered, despite all but sixteen of the orders for new LNG carriers

at the end of 2004 being for steam turbine propelled ships. [1]
[edit]

Diesel propulsion

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, the

reduction in manning owing to the removal of the need for trimmers and stokers, and the

reduction in space required for fuel bunkers. Diesel engines today are broadly classified

according to their operating cycle (two-stroke or four-stroke), their construction

(crosshead, trunk, or opposed piston) and their speed (slow speed, medium speed or high

speed). Most modern larger merchant ships use either slow speed, two stroke, crosshead

engines, or medium speed, four stroke, trunk engines. Some smaller vessels may operate high

speed diesel engines. The operating ranges of the differant speed types are as follows;

* Slow speed- any engine with a maximum operating speed up to 300 revs/minute, although

most large 2 stroke slow speed diesel engines operate below 120 revs/minute. Some very long

stroke engines have a maximum speed of around 80 revs/minute. The largest, most powerful

engines in the world are slow speed, two stroke, crosshead diesels.
* Medium speed- any engine with a maximum operating speed in the range 300- 900 revs/

minute. Many modern 4 stroke medium speed diesel engines have a maximum operating speed of

around 500 rpm.
* High speed- any engine with a maximum operating speed above 900 revs/ minute

As modern ships' propellers are at their most efficient at the operating speed of most slow

speed diesel engines, ships with these engines do not generally require gearboxes. Usually

such propulsion systems consist of either one or two propeller shafts each with its own

direct drive engine. Ships propelled by medium or high speed diesel engines may have one or

two (sometimes more) propellers, commonly with one or more engines driving each propeller

shaft through a gearbox. Where more than one engine is geared to a single shaft, each engine

will most likely drive through a clutch, allowing engines not being used to be disconnected

from the gearbox while others continue to operate. This arrangement allows maintenance to be

carried out while under way at sea. Diesel electric is another propulsion system that has

been around for a long time, but is becoming more common. By having the engines drive

alternators, which supply electricity to motors driving the propellers, gearboxes and

clutches can be dispensed with and greater flexibility gained in the positioning of the

engines, while still providing the step down in speed required for a medium speed engine to

efficiently drive a ships propeller.

The size of the differant types of engines is an important factor in selecting what will be

installed in a new ship. Slow speed two stroke engines are much taller, but the foot print

required- length and width- is smaller than that required for four stroke medium speed

diesel engines. As space higher up in passenger ships and ferries is at a premium, these

ships tend to use multiple medium speed engines resulting in a longer, lower engine room

than that required for two stroke diesel engines. Multiple engine installations also gives

greater redundancy in the event of mechanical failure of one or more engines and greater

efficiency over a wider range of operating conditions.
[edit]

Other propulsion systems

Many warships built since the 1960s have used gas turbines for propulsion, as have a few

passenger ships. Most recently, the Queen Mary 2 has had gas turbines installed in addition

to diesel engines. Due to their poor thermal efficiency, it is common for ships using them

to have diesel engines for cruising with gas turbines reserved for when higher speeds are

required. Some warships and a few modern cruise ships have also utilised steam turbines to

improve the efficiency of gas turbines in a combined cycle. In such a combined cycle, where

waste heat from a gas turbine is used to create steam for driving a steam turbine, thermal

efficiency can be the same or slightly greater than that of diesel engines. However, the

grade of fuel required for gas turbines is much more expensive than that required for diesel

engines so running costs are higher.

A few ships have used nuclear reactors, but this is not a separate form of propulsion; the

reactor heats 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 resulting saving in bunkerage is an important consideration.
[edit]

General terminology

Ships may occur collectively as fleets, squadrons or flotillas. 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, but this generally refers only to merchant vessels. Groups of sailing

ships could constitute, say, a fleet of 40 sail. Groups of submarines (particularly German

U-boats in the 1940s) hunt in wolf packs.
[edit]

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.