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A submarine hull has two major components, the light hull and the pressure hull. The light hull (casing in British usage) of a submarine is the outer non-watertight hull which provides a hydrodynamically efficient shape. The pressure hull is the inner hull of a submarine that maintains structural integrity with the difference between outside and inside pressure at depth.
Modern submarines are usually cigar-shaped. This design, already visible on very early submarines, is called a "teardrop hull". It is structurally efficient for withstanding external pressure, and significantly reduces the hydrodynamic drag on the sub when submerged, but decreases the sea-keeping capabilities and increases drag while surfaced.
The concept of an outer hydrodynamically streamlined light hull separated from the inner pressure hull was first introduced in the early pioneering submarine Ictineo I designed by the Spanish inventor Narcís Monturiol in 1859. [1] [2] However, when military submarines entered service in the early 1900s, the limitations of their propulsion systems forced them to operate on the surface most of the time; their hull designs were a compromise, with the outer hulls resembling a ship, allowing for good surface navigation, and a relatively streamlined superstructure to minimize drag under water. Because of the low submerged speeds of these submarines, usually well below 10 knots (19 km/h), the increased drag for underwater travel by the conventional ship-like outer hull was considered acceptable.[ citation needed ] Only late in World War II, when technology enhancements allowed faster and longer submerged operations and increased surveillance by enemy aircraft forced submarines to spend most of their times below the surface, did hull designs become teardrop shaped again, to reduce drag and noise. USS Albacore (AGSS-569) was a unique research submarine that pioneered the American version of the teardrop hull form (sometimes referred to as an "Albacore hull") of modern submarines. On modern military submarines the outer hull (and sometimes also the propeller) is covered with a thick layer of special sound-absorbing rubber, or anechoic plating, to make the submarine more difficult to detect by active and passive sonar.[ citation needed ]
All small modern submarines and submersibles, as well as the oldest ones, have a single hull.[ citation needed ] However, for large submarines, the approaches have separated. All Soviet heavy submarines are built with a double hull structure, but American submarines usually are single-hulled. They still have light hull sections in bow and stern, which house main ballast tanks and provide hydrodynamically optimized shape, but the main, usually cylindrical, hull section has only a single plating layer.
The double hull of a submarine is different from a ship's double hull. The external hull, which actually forms the shape of submarine, is called the outer hull, casing or light hull. It defines the hydrodynamic performance of submarine, which affects the amount of power required to drive the vessel through the water. This term is especially appropriate for Russian submarine construction, where the light hull is usually made of thin steel plate, as it has the same pressure on both sides. The light hull can be used to mount equipment, which if attached directly to the pressure hull could cause unnecessary stress. The double hull approach also saves space inside the pressure hull, as the ring stiffeners and longitudinals can be located between the hulls. These measures help minimise the size of the pressure hull, which is much heavier than the light hull. Also, in case the submarine is damaged, the light hull takes some of the damage and does not compromise the vessel's integrity, as long as the pressure hull is intact.
Inside the outer hull there is a strong hull, or pressure hull, which withstands the outside pressure and has normal atmospheric pressure inside. The pressure hull is generally constructed of thick high-strength steel with a complex stiffening structure and high strength reserve, and is divided by watertight bulkheads into several compartments. The pressure and light hulls are separated by a gap in which numerous steel structural elements connect the light hull and pressure hull and form a three-dimensional structure which provides increased strength and buckling stability. The interhull space is used for some of the equipment which can tolerate the high external pressure at maximum depth and exposure to the water. This equipment significantly differs between submarines, and generally includes various water and air tanks. In a single-hull submarine, the light hull is discontinuous and exists mainly at the bow and stern.
Pressure hulls have a circular cross section as any other shape would be substantially weaker. The construction of a pressure hull requires a high degree of precision. This is true irrespective of its size. Even a one-inch (25 mm) deviation from cross-sectional roundness results in over 30 percent decrease of hydrostatic load capacity. [3] Minor deviations are resisted by the stiffener rings, and the total pressure force of several million longitudinally-oriented tons must be distributed evenly over the hull by using a hull with a circular cross section.[ clarification needed ] This design is the most resistant to compressive stress and without it no material could resist water pressure at submarine depths. A submarine hull requires expensive transverse framing construction, with ring frames closely spaced to stiffen against buckling instability. No hull parts may contain defects, and all welded joints are checked several times using different methods.
Typhoon-class submarines feature multiple pressure hulls that simplify internal design[ clarification needed ] while making the vessel much wider than a normal submarine. In the main body of the sub, two long pressure hulls lie parallel side by side, with a third, shorter pressure hull above and partially between them (which protrudes just below the sail), and two other centreline pressure hulls, for torpedoes at the bow, and steering gear at the stern. This also greatly increases their survivability – even if one pressure hull is breached, the crew members in the others are relatively safe if the submarine can be prevented from sinking, and there is less potential for flooding.[ citation needed ]
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 bounded by current technology.
World War One submarines had their hulls built of carbon steel, and usually had test depths of no more than 100 metres (330 ft). During World War Two, high-strength alloyed steel was introduced, allowing for depths up to 200 metres (660 ft); post-war calculations have suggested crush depths exceeding 300 metres (980 ft) for late-war German Type VII U-boats. High-strength alloyed steel is still the main material for submarines today, with 250 to 350 metres (820 to 1,150 ft) 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 has a better strength to weight ratio and durability than most steels, and is non-magnetic. Titanium submarines were especially favoured by the Soviets, as they had developed specialized high-strength alloys, built an industry for producing titanium with affordable costs, and have several types of titanium submarines. Titanium alloys allow a major increase in depth, but other systems need to be redesigned as well, so test depth was limited to 1,000 metres (3,300 ft) for the Soviet submarine Komsomolets, the deepest-diving military submarine. Despite its benefits, the high costs of titanium submarine construction led to its abandonment as the Cold War ended.
There are examples of more than two hulls inside a submarine. The light hull of Typhoon-class submarines houses two main pressure hulls, a smaller third pressure hull constituting most of the sail, two other for torpedoes and steering gear, and between the main hulls 20 MIRV SLBMs along with ballast tanks and some other systems. The Royal Netherlands Navy Dolfijn- and Potvis-class submarines housed three main pressure hulls. The Russian submarine Losharik is able to dive over 2000 m with its multi-spherical hull.
A submarine is a watercraft capable of independent operation underwater. It differs from a submersible, which has more limited underwater capability. The term is also sometimes used historically or colloquially to refer to remotely operated vehicles and robots, as well as medium-sized or smaller vessels, such as the midget submarine and the wet sub. Submarines are referred to as boats rather than ships irrespective of their size.
Alvin (DSV-2) is a crewed deep-ocean research submersible owned by the United States Navy and operated by the Woods Hole Oceanographic Institution (WHOI) in Woods Hole, Massachusetts. The vehicle was built by General Mills' Electronics Group in Minneapolis, Minnesota. Named to honor the prime mover and creative inspiration for the vehicle, Allyn Vine, Alvin was commissioned on June 5, 1964. The submersible is launched from the deep submergence support vessel RV Atlantis (AGOR-25), which is also owned by the U.S. Navy and operated by WHOI. The submersible has made more than 5,000 dives, carrying two scientists and a pilot, to observe the lifeforms that must cope with super-pressures and move about in total darkness, as well as exploring the wreck of Titanic. Research conducted by Alvin has been featured in nearly 2,000 scientific papers.
An underwater environment is a environment of, and immersed in, liquid water in a natural or artificial feature, such as an ocean, sea, lake, pond, reservoir, river, canal, or aquifer. Some characteristics of the underwater environment are universal, but many depend on the local situation.
A submersible is an underwater craft which needs to be transported and supported by a surface vessel or platform. This distinguishes submersibles from submarines, which are self-supporting and capable of independent operation.
A deep-submergence vehicle (DSV) is a deep-diving crewed submersible that is self-propelled. Several navies operate vehicles that can be accurately described as DSVs. DSVs are commonly divided into two types: research DSVs, which are used for exploration and surveying, and DSRVs, which are intended to be used for rescuing the crew of a sunken navy submarine, clandestine (espionage) missions, or both. DSRVs are equipped with docking chambers to allow personnel ingress and egress via a manhole.
The SP-350 Denise, famous as the "Diving saucer", is a small submarine designed to hold two people, and is capable of exploring depths of up to 400 metres (1,300 ft). It was invented by Jacques-Yves Cousteau and engineer Jean Mollard at the French Centre for Undersea Research. It was built in the year 1959 and usually operated from Cousteau's ship, the Calypso.
A diving chamber is a vessel for human occupation, which may have an entrance that can be sealed to hold an internal pressure significantly higher than ambient pressure, a pressurised gas system to control the internal pressure, and a supply of breathing gas for the occupants.
Mir was a class of two self-propelled deep-submergence vehicles. The project was initially developed by the USSR Academy of Sciences along with Lazurit Central Design Bureau, and two vehicles were ordered from Finland. The Mir-1 and Mir-2, delivered in 1987, were designed and built by the Finnish company Rauma-Repola's Oceanics subsidiary. The project was carried out under the supervision of constructors and engineers of the Shirshov Institute of Oceanology.
Depth ratings are primary design parameters and measures of a submarine's ability to operate underwater. The depths to which submarines can dive are limited by the strengths of their hulls.
A diving watch, also commonly referred to as a diver's or dive watch, is a watch designed for underwater diving that features, as a minimum, a water resistance greater than 1.1 MPa (11 atm), the equivalent of 100 m (330 ft). The typical diver's watch will have a water resistance of around 200 to 300 m, though modern technology allows the creation of diving watches that can go much deeper. A true contemporary diver's watch is in accordance with the ISO 6425 standard, which defines test standards and features for watches suitable for diving with underwater breathing apparatus in depths of 100 m (330 ft) or more. Watches conforming to ISO 6425 are marked with the word DIVER'S to distinguish ISO 6425 conformant diving watches from watches that might not be suitable for actual scuba diving.
A teardrop hull is a submarine hull design which emphasizes submerged performance over surfaced performance. It was somewhat commonly used in the early stages of submarine development, but was gradually abandoned in the early 20th century in favour of designs optimized for high performance on the surface as a result of changes in operational doctrine. Although naval doctrine changed, design practices remained until the later parts of World War II when the German Kriegsmarine suffered ever-growing losses of submarines in the Battle of the Atlantic.
Deep-sea exploration is the investigation of physical, chemical, and biological conditions on the ocean waters and sea bed beyond the continental shelf, for scientific or commercial purposes. Deep-sea exploration is an aspect of underwater exploration and is considered a relatively recent human activity compared to the other areas of geophysical research, as the deeper depths of the sea have been investigated only during comparatively recent years. The ocean depths still remain a largely unexplored part of the Earth, and form a relatively undiscovered domain.
Ictíneo I was a pioneering submarine constructed in Barcelona, Spain in 1858–1859 by engineer Narcís Monturiol.
The Sea Pole class bathyscaphe is a class of bathyscaphe of the People's Republic of China (PRC). They are capable of diving up to 7,000 meters, covering 99.8% of the oceanic floor of the world. Two units of this class are planned, with derivatives to follow and are used by both the civilian and military establishments in China.
The Shinkai (しんかい) is a crewed research submersible that can dive up to a depth of 600 m. It was completed in 1970, and until 1981 it had the greatest depth range of any crewed research vehicle in Japan. The Shinkai is owned and run by the Japan Coast Guard and it is launched from the support vessel Otomemaru (乙女丸).
DeepFlight Challenger is a one-person personal submarine deep submergence vehicle with full ocean depth capability. It is an "aero-submarine" which uses hydrodynamic forces to descend, as the sub has positive buoyancy, utilizing DeepFlight technology from Hawkes Ocean Technologies. The submarine is currently owned by Virgin Oceanic.
HY-80 is a high-tensile, high yield strength, low alloy steel. It was developed for use in naval applications, specifically the development of pressure hulls for the US nuclear submarine program and is still currently used in many naval applications. It is valued for its strength to weight ratio.
The Shinkai 2000 (しんかい) was a crewed research submersible that could dive up to a depth of 2,000 meters. It was completed in 1981 and until 1991 it had the greatest depth range of any crewed research vehicle in Japan. The Shinkai 2000 was owned and run by the Japan Agency for Marine-Earth Science and Technology (JAMSTEC) and it was launched from the support vessel Natsushima.
Ictineu 3 is a crewed submersible capable of reaching depths of 1,200 m (3,900 ft), which makes it the ninth deepest submersible, owned by Ictineu submarins SL. Commissioned in 2013, the submersible can carry one pilot and two passengers for 10 hours using all the equipment.
Limiting Factor is a crewed deep-submergence vehicle (DSV) manufactured by Triton Submarines and owned and operated by Gabe Newell’s Inkfish ocean-exploration research organization. It currently holds the records for the deepest crewed dives in all five oceans. Limiting Factor was commissioned by Victor Vescovo for $37 million. It is commercially certified by DNV for dives to full ocean depth, and is operated by a pilot, with facilities for an observer.