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A submarine is a watercraft that can operate underwater at pressures beyond the range of unaided human survivability. Submarines were first widely used in World War I and are used by all major navies today. Civilian submarines and submersibles are used for marine and freshwater science and for work at depths too great for human divers. Submarines are typically referred to as "boats" even though most modern submarines should technically be called "ships". The term U-Boat is sometimes used for German submarines in English. This comes from the German word for submarine, 'U-Boot', itself an abbreviation for Unterseeboot ('undersea boat'). The vertical structure, usually located amidships, houses communications and sensing devices as well as periscopes. In the United States Navy it is called the "sail", not the "conning tower", a term associated with German submarines. (Actually, even US submarines until the advent of nuclear powered boats used conning towers, primarily for periscope depth torpedo attacks)
Submarines encompass one of the largest ranges in capabilities of any vessel. They range from small one- or two-man vessels that can examine the sea floor for a few hours to the Russian Typhoon class, which can remain submerged for 6 months and carry nuclear missiles capable of destroying multiple cities. There are also specialized submarines such as rescue submarines (like the DSRV or Priz) and tiny one-person human powered subs intended for competitions between universities. An older device for use in underwater exploration, salvage, construction and rescue is the diving bell. A specialized form of submarine capable of extremely deep dives is the bathyscaphe.
The word submarine was originally an adjective meaning "under the sea". Some firms who make diving gear but not parts for submarines, called their work "submarine engineering". "Submarine" as a noun meaning a submersible craft originated as short for "submarine boat" and older books such as Twenty Thousand Leagues Under the Sea always use this term. Also, some people simply say 'sub' instead of saying the entire word 'submarine'.
[edit] Military usage
The roles of military submarines are almost limitless. From delivering supplies and facilitating troop movements undetected, to launching a surprise nuclear attack from just a few miles off of the coast. Submarines have been used as spy platforms and as underwater research vessels.
Submarines are useful militarily because of their ability to remain concealed: they are difficult to find and destroy when deep below the surface. Because water's dense molecular structure makes it an excellent conductor of sound, a submarine is more likely to be detected from its sound patterns than its visual appearance. To maintain stealth, a great deal of attention in the design of a submarine is devoted to making it travel through the water as silently as possible. Some submarines conceal their sound so well that they actually create a silent area in their environment, which can be detected if it blocks other ambient sounds. If a submarine remains undetected, it is able to strike at close range.
A concealed submarine can force an enemy Navy to waste resources defending large areas of ocean against possible attack, while in reality only threatening a small area. This advantage was vividly demonstrated in the 1982 Falklands war when the British SSN HMS Conqueror sank the General Belgrano. After the sinking of the 'Belgrano', the Argentine Navy realised that they were vulnerable to submarine attack, and that they had no defense from it. Thus the Argentinian fleet remained in port for the remainder of the war.
[edit] Technology
[edit] Submersion and navigation
All surface ships, as well as surfaced submarines, are in a positively buoyant condition, weighing less than the volume of water they displace. To submerge hydrostatically, a ship must gain negative buoyancy, either increasing its own weight or decreasing displacement of the water. To control their weight, submarines are equipped with ballast tanks, which can be filled with either outside water or pressurized air.
For general submersion or surfacing, submarines use the forward and aft tanks, called Main Ballast Tanks or MBTs, which are opened and completely filled with water to submerge, or filled by pressurized air to surface. Under submerged conditions, MBTs generally always stay flooded, which simplifies their design, so on many submarines these tanks are simply a section of interhull space. For more precise and quick control of depth, submarines use smaller Depth Control Tanks or DCTs, also called hard tanks due to their ability to withstand higher pressure. The amount of water in depth control tanks can be controlled either to reflect changes in outside conditions or change submersion depth. Depth control tanks can be located either near the submarine's center of gravity, or separated along the submarine body to prevent affecting trim.
When submerged, the water pressure on submarine's hull can reach 4 MPa for steel submarines and up to 10 MPa for titanium submarines like Komsomolets, while the pressure inside stays the same. This difference results in hull compression, which decreases displacement. Water density also increases, as the salinity and pressure are higher, but this does not compensate for hull compression, so buoyancy falls with depth. A submerged submarine is in an unstable equilibrium, having a tendency to either fall down to the ocean floor or float up to the surface. Keeping a constant depth requires continual operation of either the depth control tanks or control surfaces.[1]
Submarines in a neutral buoyancy condition are not intrinsically stable in trim. To sustain desired trim, submarines use specialized forward and aft trim tanks. Pumps can move water between these tanks, changing the weight distribution and therefore creating a moment to turn the sub upwards or downwards. A similar system is sometimes used to maintain stability.
The hydrostatic effect of variable ballast tanks is not the only way to control the submarine underwater. Hydrodynamic maneuvering is done by several surfaces, which can be turned to create corresponding hydrodynamic forces when a submarine moves at sufficient speed. The stern planes, located near the propeller and normally oriented horizontally, serve the same purpose as the trim tanks, controlling the trim, and are commonly used, while other control surfaces may not be present on many submarines. The fairwater planes on the sail and/or bow planes on the main body, both also horizontal, are located closer to the centre of gravity, and are used to control depth with less effect on the trim.
When a submarine performs an emergency surfacing, all depth and trim methods are used simultaneously, together with propelling the boat upwards. Such surfacing is very quick, so the sub may even partially jump out of the water, but it inflicts serious damage on some submarine systems, primarily pipes.
Modern submarines use an inertial guidance system for navigation while submerged, but drift error unavoidably builds up over time. To counter this, the Global Positioning System will occasionally be used to obtain an accurate position. The periscope - a retractable tube with prisms allowing a view to the surface - is only used occasionally in modern submarines, since the range of visibility is short. The Virginia-class submarines have "photonics masts" rather than hull-penetrating optical tube periscopes. These masts must still be hoisted above the surface, and employ electronic sensors for visible light, infrared, laser range-finding, and electromagnetic surveillance.
[edit] Ship hull
[edit] Overview
Modern submarines are usually cigar-shaped. This design, already visible on very early submarines (see below) is sometimes called a "teardrop hull". It significantly reduces the hydrodynamic drag on the sub when submerged, but decreases the sea-keeping capabilities and increases the drag while surfaced. Since the limitations of the propulsion systems of early military submarines forced them to operate on the surface most of the time, their hull designs were a compromise. Because of the slow submerged speeds of those subs, usually well below 10kt (18 km·h−1), the increased drag for underwater travel was considered acceptable. Only late in World War II, when technology allowed faster and longer submerged operations and increased surveillance by enemy aircraft forced submarines to stay submerged, did hull designs become teardrop shaped again, to reduce drag and noise. On modern military submarines the outer hull is covered with a thick layer of special sound-absorbing rubber, or anechoic plating, to make the submarine quieter.
A raised tower on top of a submarine accommodates the length of the periscope and electronics masts, which can include radio, radar, electronic warfare, and other systems. In many early classes of submarines (see history), the Control Room, or "Conn", was located inside this tower, which was known as the "conning tower". Since that time, however, the Conn has been located within the hull of the submarine, and the tower is more commonly called the "sail" today. The Conn should not be confused with the "bridge", which is a small, open platform set into the top of the sail used for visual observation while operating on the surface. There may also be an additional closed platform below this with windows and wipers for bad weather.
[edit] Double hull
Modern submarines and submersibles, as well as the oldest ones, have a single hull. Large submarines generally have an additional hull or hull sections outside. This external hull, which actually forms the shape of submarine, is called the outer hull or light hull, as it does not have to hold any pressure difference. Inside the outer hull there is a strong hull, or pressure hull, which withstands sea pressure and has normal atmospheric pressure inside.
As early as World War I, it was realized that the optimal shape for withstanding pressure conflicted with the optimal shape for seaworthiness and minimized water resistance, and construction difficulties further complicated the problem. This was solved either by a compromise shape, or by using two hulls; internal for holding pressure, and external for optimal shape. Until the end of World War II, most submarines had an additional partial cover on the top, bow and stern, built of thinner metal, which was flooded when submerged. Germany went further with the Type XXI, the general predecessor of modern submarines, in which the pressure hull was fully enclosed inside the light hull, but optimised for submerged navigation, unlike earlier designs.
After World War II, approaches split. The Soviet Union changed its designs, basing them on the latest German developments. All post-WWII heavy Soviet and Russian submarines are built with a double hull structure. American and most other Western submarines retain a single-hull approach. They still have light hull sections in the bow and stern, which house main ballast tanks and provide a hydrodynamically optimized shape, but the main cylindrical hull section has only a single plating layer.
Despite being no longer needed for different shapes, the double-hull approach still has a number of advantages. The ring stiffeners and longitudinals are located between hulls, and the light hull can also be used to mount certain equipment that does not require constant pressure to operate, while attaching it directly to the pressure hull could cause dangerous local stress. These measures save a lot of space inside the pressure hull, which is much heavier and takes longer to build than the light hull. In case the submarine is damaged, the light hull can take most of the damage, which does not compromise the boat's integrity, as long as the strong hull is intact. A light hull can also be acoustically decoupled from the pressure hull, which significantly reduces noise from internal equipment, improves stealth or allows the use of a simpler internal layout and equipment mounting.
The major downside of double-hull structure is the significantly greater amount of manual work required to construct it. The Soviet Union had implemented the requisite welding technology earlier and had enough cheap qualified workers available, but the high cost of manual labor in the United States made the less expensive single-hull approach preferable. Another reason for double-hull construction in the Soviet Union was operation under the Arctic Ocean, where submarines had to break thick ice to launch their missiles, which could damage the hull. However, the double-hull approach is today being considered for future submarines in the United States as a means to improve payload capacity, stealth and operational reach.[2]
[edit] Pressure hull
The pressure hull is generally constructed of thick high-strength steel with a complex structure and high strength reserve, and is separated with watertight bulkheads into several compartments. There are also examples of more than two hulls in a submarine, like the Typhoon class, which has two main pressure hulls and three smaller ones for control room, torpedoes and steering gear, while the missile launch system is located between the main hulls.
The dive depth cannot be increased easily. Simply making the hull thicker increases the weight and requires reduction of the weight of onboard equipment, ultimately resulting in a bathyscaphe. This is affordable for civilian research submersibles, but not military submarines, so their dive depth was always bound by current technology.
WW1 submarines had their hulls built of carbon steel, and could not submerge below 100 meters. During World War Two, high-strength alloyed steel was introduced, allowing for dive depths of up to 200 meters. High-strength alloyed steel is still the main material for submarines today, with 250-400 meters depth limit, which cannot be exceeded on a military submarine without sacrificing other characteristics. To exceed that limit, a few submarines were built with titanium hulls. Titanium is almost as strong as steel, but lighter, and is also not ferromagnetic, which is important for stealth. Titanium submarines were favored by the Soviet Union, which developed specialized high-strength alloys and built an industry capable of producing titanium at an affordable cost. It has produced several types of titanium submarines. Titanium alloys allow a major increase in depth, but other systems need to be redesigned to cope, so test depth was limited to 1000 meters for K-278 Komsomolets, the deepest-diving military submarine. An Alfa class submarine may have successfully operated at 1300 meters,[3] though continuous operation at such depths would be an excessive stress for many submarine systems. Despite its benefits, the high cost of titanium construction led to the abandonment of titanium submarine construction as the Cold War ended.
The task of building a pressure hull is very difficult, as it must withstand a force of several million tons. When the hull is perfectly round in cross-section, the pressure is evenly distributed, and causes only hull compression. If the shape is not perfect, the hull is bent, with several points heavily strained. Inevitable minor deviations are resisted by the stiffener rings, but even a one inch (25 mm) deviation from roundness results in over 30 percent decrease of maximal hydrostatic load and consequently dive depth.[4] The hull must therefore be constructed with very high precision. All hull parts must be welded without defects, and all joints are checked several times using different methods. This contributes to the very high cost of modern submarines. (For example, each Virginia-class attack submarine costs 2.6 billion dollars, over $200,000 per ton of displacement).
[edit] Propulsion
The first mechanically driven submarine was the 1863 French Plongeur, which used compressed air for propulsion, and anaerobic propulsion was first employed by the Spanish Ictineo II in 1864. Ictineo's engine used a chemical mix containing a peroxide compound to generate heat for steam propulsion while also providing oxygen for the crew. The system was not employed again until 1940 when the German Navy tested a system employing the same principles, the Walter turbine, on the experimental V-80 submarine and later on the naval U-791 submarine.
Until the advent of nuclear marine propulsion, most 20th century submarines used batteries for running underwater and gasoline (petrol) or diesel engines on the surface and to recharge the batteries. Early submarines used gasoline, but this quickly gave way to paraffin, then diesel, because of reduced flammability. Diesel-electric became the standard means of propulsion. The diesel or gasoline engine and the electric motor, separated by clutches, were initially on the same shaft and drove the propeller. This allowed the engine to drive the electric motor as a generator to recharge the batteries and also propel the submarine if required. The clutch between the motor and the engine would be disengaged when the submarine dived so that the motor could be used to turn the propeller. The motor could have more than one armature on the shaft — these would be electrically coupled in series for slow speed and in parallel for high speed (known as "group down" and "group up", respectively).
The principle was modified for some submarine designs in the 1930s, particularly those of the U.S. Navy and the British U class submarines. The engine was no longer attached to the motor/propeller drive shaft, but drove a separate generator to drive the motors on the surface while recharging the batteries. This diesel-electric propulsion allowed much more flexibility; for example, the submarine could travel slowly while the engines were running at full power to recharge the batteries as quickly as possible, reducing time spent on the surface, or use its snorkel. It was then possible to insulate the noisy diesel engines from the pressure hull, making the submarine quieter.
Other power sources were attempted. Oil-fired steam turbines powered the British "K" class submarines built during the first World War and in the following years, but these were not very successful. The "K" class design was over-endowed with hatches, which proved troublesome in service. This was selected to give them the necessary surface speed to keep up with the British battle fleet. German Type XXI submarines attempted the application of hydrogen peroxide to provide long-term, fast air-independent propulsion, but were ultimately built with very large batteries instead.
At the end of the Second World War, the British and Russians experimented with hydrogen peroxide/kerosene (paraffin) engines which could be used both above and below the surface. The results were not encouraging enough for this technique to be adopted at the time, and although the Russians deployed a class of submarines with this engine type (codenamed Quebec by NATO), they were considered unsuccessful. Today several navies use air-independent propulsion. Notably Sweden uses Stirling technology on the Gotland class and Södermanland class series of submarines. The Stirling engine is heated by burning diesel fuel with liquid oxygen stored in cryogenic tanks. A newer development in air-independent propulsion is the use of hydrogen fuel cells, first applied in series on the German Type 212 submarine, with nine 34 kW or two 120-kilowatt cells.
Steam power was resurrected in the 1950s with the advent of the nuclear-powered steam turbine driving a generator. By removing the requirement for atmospheric oxygen, these submarines can remain submerged indefinitely. (Air is recycled and fresh water is distilled from seawater.) These vessels always have a small battery and diesel engine/generator installation for emergency use if the reactors have to be shut down.
Nuclear power is now used in all large submarines, but due to the high cost and large size of nuclear reactors, smaller submarines still use diesel-electric propulsion. The ratio of larger to smaller submarines depends on strategic needs; for instance, the US Navy operates only nuclear submarines,[5] which is usually explained by the need for overseas operations. Other major operators rely on a mix of nuclear submarines for strategic purposes and diesel-electric submarines for defensive needs. Most fleets have no nuclear submarines at all, due to the limited availability of nuclear power and submarine technology. Commercial submarines usually rely only on batteries, as they are never expected to operate independently of a mother ship.
Toward the end of the 20th century, some submarines, such as the British Vanguard class, began to be fitted with pump-jet propulsors instead of propellers. Although these are heavier, more expensive, and less efficient than a propeller, they are significantly quieter, giving an important tactical advantage.
A possible propulsion system for submarines is the magnetohydrodynamic drive, or "caterpillar drive", which has no moving parts. It was popularized in the movie version of The Hunt for Red October, written by Tom Clancy, which portrayed it as a virtually silent system. (In the book, a form of propulsor was used rather than an MHD). Although some experimental surface ships have been built with this propulsion system, speeds have not been as high as expected. In addition, the noise created by bubbles, and the higher power settings that a submarine's reactor would need, mean that it is unlikely to be considered for any military purpose.
[edit] Crew
[edit] Overview
With nuclear power, submarines can remain submerged for months at a time. Diesel submarines must periodically resurface or snorkel to recharge their batteries. Most modern military submarines are able to generate oxygen for their crew by electrolysis of water. Atmosphere control equipment includes a CO2 scrubber, which uses an amine absorbent to remove the gas from air and diffuse it into waste pumped overboard. A machine that uses a catalyst to convert carbon monoxide into carbon dioxide (removed by the CO2 scrubber) and bonds hydrogen produced from the ship's storage battery with oxygen in the atmosphere to produce water, also found its use. An atmosphere monitoring system samples the air from different areas of the ship for nitrogen, oxygen, hydrogen, R12 and R114 refrigerant, carbon dioxide, carbon monoxide, and others. Poisonous gases are removed, and oxygen is replenished by use of an oxygen bank located in a main ballast tank. Some heavier submarines have two oxygen bleed stations (forward and aft). The oxygen in the air is sometimes kept a few percent less than atmospheric concentration to reduce fire danger.
Fresh water is produced by either an evaporator or a reverse osmosis unit. It is used for showers, sinks, cooking and cleaning. Seawater is used to flush toilets, and the resulting "black water" is stored in a sanitary tank until it is blown overboard using pressurised air or pumped overboard by using a special sanitary pump. The method for blowing sanitaries overboard is difficult to operate, and the German Type VIIC boat U-1206 was lost with casualties because of a mistake with the toilet. Water from showers and sinks is stored separately in "gray water" tanks, which are pumped overboard using the drain pump.
Trash on modern large submarines is usually disposed of using a tube called a Trash Disposal Unit (TDU), where it is compacted into a galvanised steel can. At the bottom of the TDU is a large ball valve. An ice plug is set on top of the ball valve to protect it, the cans on top of the ice plug. The top breech door is shut, and the TDU is flooded and equalised with sea pressure, the ball valve is opened and the cans fall out to the ocean floor assisted by scrap iron weights inside the cans.
A typical nuclear submarine has a crew of over 120; non-nuclear boats typically have less than half as many. The conditions on a submarine can be difficult because crewmembers must work in isolation for long periods of time, without contact with their families. Submarines normally maintain radio silence to avoid detection. Operating a submarine is dangerous, even in peacetime, and many submarines have been lost in accidents.
[edit] Women as part of crew
In 1995 the Royal Norwegian Navy became the first navy in the world to appoint a female submarine captain.[6] In 1998, the Royal Australian Navy (RAN) became the second navy to allow women to serve on combat submarines. Canada and Spain followed in permitting women to serve on military submarines with seamen.[7] The usual reasons for barring women that are given are lack of privacy and "hot bunking" or "hot racking", a common practice on submarines where three sailors share two bunks on a rotating basis to save space. The US Navy, which permits women to serve on almost every other ship in the fleet, only allows three exceptions for women being on board military submarines: (1) Female civilian technicians for a few days at most; (2) Women midshipmen on an overnight during summer training for both Navy ROTC and Naval Academy; (3) Family members for one-day dependent cruises.[8] The US Navy argues it would cost $300,000 per bunk to permit women to serve on submarines versus $4,000 per bunk to allow women to serve on aircraft carriers. However, this calculation is based on the assumption of semi segregation of the female crew, possibly to the extent of structural redesign of the vessel.[9] No studies of the feasibility of an all-female crew, which would circumvent the US Navy's objections, are known to have been carried out.
[edit] History of submarines
[edit] Early history of submarines and the first submersibles
The first submersible with reliable information on its construction was built in 1620 by Cornelius Jacobszoon Drebbel, a Dutchman in the service of James I of England. It was built to the standards of the design outlined by William Bourne, the inventor of the submarine. It was propelled by means of oars. The precise nature of the submarine type is a matter of some controversy; some claim that it was merely a bell towed by a boat. Two improved types were tested in the Thames between 1620 and 1624.
Though the first submersible vehicles were tools for exploring under water, it did not take long for inventors to recognize their military potential. The strategic advantages of submarines were set out by Bishop John Wilkins of Chester, England, in Mathematicall Magick in 1648.
- Tis private: a man may thus go to any coast in the world invisibly, without discovery or prevented in his journey.
- Tis safe, from the uncertainty of Tides, and the violence of Tempests, which do never move the sea above five or six paces deep. From Pirates and Robbers which do so infest other voyages; from ice and great frost, which do so much endanger the passages towards the Poles.
- It may be of great advantages against a Navy of enemies, who by this may be undermined in the water and blown up.
- It may be of special use for the relief of any place besieged by water, to convey unto them invisible supplies; and so likewise for the surprisal of any place that is accessible by water.
- It may be of unspeakable benefit for submarine experiments.
[edit] The first military submarines
The first military submarine was Turtle (1775), a hand-powered egg-shaped device designed by the American David Bushnell, to accommodate a single man. It was the first verified submarine capable of independent underwater operation and movement, and the first to use screws for propulsion. During the American Revolutionary War, Turtle (operated by Sgt. Ezra Lee, Continental Army) tried and failed to sink a British warship, HMS Eagle (flagship of the blockaders) in New York harbor on September 7, 1776.
In 1800, France built a human-powered submarine designed by Robert Fulton, the Nautilus. The French eventually gave up with the experiment in 1804, as did the British when they later considered Fulton's submarine design.
During the War of 1812, in 1814, Silas Halsey lost his life while using a submarine in an unsuccessful attack on a British warship stationed in New London harbor.
In 1851, a Bavarian artillery corporal, Wilhelm Bauer, took a submarine designed by him called the Brandtaucher (incendiary-diver) to sea in Kiel Harbour. This submarine was built by August Howaldt and powered by a treadwheel. It sank but the crew of 3 managed to escape. The submarine was raised in 1887 and is on display in a museum in Dresden.
[edit] Submarines in the American Civil War
During the American Civil War, the Union was the first to field a submarine. The French-designed Alligator was the first U.S. Navy sub and the first to feature compressed air (for air supply) and an air filtration system. It was the first submarine to carry a diver lock which allowed a diver to plant electrically detonated mines on enemy ships. Initially hand-powered by oars, it was converted after 6 months to a screw propeller powered by a hand crank. With a crew of 20, it was larger than Confederate submarines. Alligator was 47 feet (14.3 m) long and about 4 feet (1.2 m) in diameter. It was lost in a storm off Cape Hatteras on April 1, 1863 while uncrewed and under tow to its first combat deployment at Charleston.
The Confederate States of America fielded several human-powered submarines including H. L. Hunley (named for one of its financiers, Horace Lawson Hunley) . The first Confederate submarine was the 30-foot long Pioneer which sank a target schooner using a towed mine during tests on Lake Pontchartrain but it was not used in combat. It was scuttled after New Orleans was captured and in 1868 was sold for scrap.
Hunley was intended for attacking the North's ships, which were blockading the South's seaports. The submarine had a long pole with an explosive charge in the bow, called a spar torpedo. The sub had to approach an enemy vessel, attach the explosive, move away, and then detonate it. It was extremely hazardous to operate, and had no air supply other than what was contained inside the main compartment. On two occasions, the sub sank; on the first occasion half the crew died and on the second, the entire eight-man crew (including Hunley himself) drowned. On February 18, 1864 Hunley sank USS Housatonic off the Charleston Harbor, the first time a submarine successfully sank another ship, though it sank in the same engagement shortly after signaling its success. Another Confederate submarine was lost on its maiden voyage in Lake Pontchartrain; it was found washed ashore in the 1870s and is now on display at the Louisiana State Museum. Submarines did not have a major impact on the outcome of the war, but did portend their coming importance to naval warfare and increased interest in their use in naval warfare.
[edit] Latin America
The first
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