Submersible Craft

I

Introduction

Submersible Craft, undersea vehicle used for researching the ocean and ocean floor, salvaging military and civilian ships and planes on the sea floor, rescuing submarines, or performing other specialized tasks. Submersible craft are smaller than submarines and are designed for specific underwater tasks. Submarines are full-sized warships built to carry out a variety of military missions. Contemporary submersible craft fall into several categories, including crewed and remote-controlled craft. Submersible craft are sophisticated machines, and are usually equipped with cameras and mechanical devices such as movable arms. These tools can record undersea wildlife, measure geologic formations such as hydrothermal vents, or retrieve artifacts from shipwrecks such as the Titanic (see Titanic Disaster).

II

Submersible Uses

Submersible craft are useful in situations where unprotected divers would be at risk from such dangers as predators (like sharks), the pressures of very deep water, or strong currents. Submersibles are routinely put to work on industrial, scientific, and military tasks. They aid industry in conducting undersea surveys, searching for new mineral deposits, performing salvage, and monitoring installations such as oil rigs and dams. Scientists use submersibles to explore geologic sites and areas of activity between tectonic plates (areas where the large plates that make up the earth’s surface are moving). Scientists also use submersibles to explore marine biology and perform undersea archaeology. Some small submersibles have been built for tourism. These range greatly in size, but most hold from 15 to 50 passengers.

The United States military remains the most active sponsor and operator of advanced submersible craft. United States Navy submersibles are used for salvage operations, submarine rescues, delivering navy commandos underwater, and minesweeping (detecting explosive underwater mines). Since the 1950s there has been a close relationship between U.S. Navy organizations responsible for developing deep-ocean submersible craft and civilian scientists who have used the same craft for scientific and historical research. New technology has also allowed a number of new civilian firms to develop and market ready-to-use submersible technology for commercial purposes.

III

Types of Submersibles

There are many types of submersible craft, and each are designed for different uses. Wet submersibles and tourist submarines give amateurs underwater access, while pressurized submersibles and remotely operated vehicles are used by professionals for research and exploration.

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Wet submersibles are relatively simple vehicles that are mostly propelled by battery-powered electric motors. They are used at shallow depths to carry scuba divers. Divers using wet submersibles can cover area more easily than by swimming. Types of wet submersibles vary; some are shaped like sleds, while others are steered much like underwater bicycles or jet skis. All wet submersibles are open to the sea, which limits their operating depth to 76m (250 ft), the depth to which scuba divers can descend with compressed air tanks. Some wet submersibles contain a small Plexiglas dome, filled with air, that covers just the user’s head, so extra breathing tanks are not needed. Other styles of wet submersibles require the user to carry an oxygen supply, such as a scuba tank. See also Diving (underwater).

Pressurized submersibles are piloted mini-submarines designed to withstand the crushing pressure of deep dives. They are used for research and salvage. The earliest submersible was the bathysphere, a simple spherical chamber lowered by a cable from a ship and used for deep-ocean exploration. Contemporary pressurized submersibles have ballast tanks for diving and surfacing, small propellers called thrusters for maneuvering, and mounts that can be fitted with cameras and other research equipment. These craft carry their own supplies of breathing air, and the hulls of some can withstand pressure at undersea depths as great as 6,000 m (20,000 ft). The U.S. Navy operates mini-subs such as the nuclear-powered NR-1 mini-sub, which was used to locate wreckage from the U.S. space shuttle Challenger disaster. The Navy also maintains the deep submergence rescue vehicle (DSRV) Mystic, which is used for submarine rescues. It can descend to a depth of several hundred meters (its exact capability is classified).

The U.S. Navy and the Central Intelligence Agency (CIA) have also developed systems for retrieving large objects from the ocean floor. In 1968 the American submarine USS Halibut explored a sunken submarine that belonged to the Union of Soviet Socialist Republics (USSR). Several years later the research ship Glomar Explorer attempted to raise the entire hull of the sunken sub using a massive clawlike device deployed from within a vast compartment in the center of the 188 m (618 ft) ship.

Towed submersibles have been a mainstay of deep-ocean exploration and salvage for many years. They are large, pilotless platforms loaded with instruments. Towed submersibles do not have thrusters. They are submerged to a few feet above the ocean floor, and simply pulled behind a surface ship. The U.S. Navy located the wrecks of the submarines USS Thresher and USS Scorpion during the 1960s by trolling a submersible mounted with cameras, sonar, and magnetic detectors over the general area in which the subs sank. The wreck of the Titanic was located in 1985 by a towed submersible. The Titanic was later explored in Alvin by oceanographer Robert Ballard, with the use of a prototype remote camera called Jason Jr., which was tethered to Alvin.

Remotely operated vehicles, or ROVs, are small, maneuverable craft that are piloted by remote control. Most ROVs are tethered to a surface ship by a cable that is used to hoist and lower the vehicle, but some can be tethered to piloted submersibles as well. The cable connecting the ROV to the mother ship also transmits electrical power, instructions from the pilot, and research information. These highly maneuverable remote craft are fitted with thrusters, video and still cameras, lights, and sensors. Some ROVs have small remote arms that can grasp and retrieve objects.

IV

History

The first recorded submersible was reportedly a primitive diving bell, probably made of wood, in which the ancient Greek leader and general Alexander the Great (356-323 bc) was briefly lowered into the Mediterranean Sea. Diving bells are small, dome-shaped chambers that hold a limited amount of air. They are still occasionally used by divers. The modern era of submersibles began with the American ocean scientist Charles William Beebe in 1930. Along with American engineer Otis Barton, Beebe pioneered the use of a tethered, manned submersible, which he named the bathysphere. It was a spherical metal ball, constructed of steel, with two viewing windows, and was able to withstand the high pressure of undersea exploration. Beebe and Barton reached a depth of 435 m (1,427 ft) in 1930, and a depth of 923 m (3,028 ft) in 1934.

Swiss physicist Auguste Piccard created the second generation of deep-diving exploration vehicles. An acquaintance of Beebe, Piccard was a reputable inventor who had devised a number of designing instruments for Albert Einstein. In 1947 Piccard designed a bathysphere-type hull for a human crew, but added a massive buoyancy tank filled with lighter-than-water gasoline. Piccard called the submersible the bathyscaphe. Lead pellets and tanks filled with water provided the necessary weight to sink the craft. To resurface, the pellets were released and the water expelled, enabling the vehicle to surface without being tethered to a host ship. Using the bathyscaphe, Piccard reached a depth of 4,000 m (13,125 ft).

In 1958 the Navy purchased Piccard’s deep-diving submersible and assigned it to a research unit that handled other Navy submersibles, such as the DSRV rescue submersibles. Jacques Piccard, Auguste Piccard’s son, worked with the Navy unit. On January 23, 1960, he and Navy Lieutenant Don Walsh descended to a record depth of 10,915 m (35,810 ft) in the bathyscaphe Trieste. The dive took place in the Pacific Ocean in the Challenger Deep, which is located in a deep depression known as the Mariana Trench on the ocean floor. The Challenger Deep is the deepest place on the earth. At that depth, Trieste withstood pressures as high as 1.17 metric tons/sq cm.

From the 1950s to the 1980s the U.S. Navy led the way in deep-ocean exploration. The Navy was motivated by the need to track Soviet submarines and to improve underwater navigation and antisubmarine warfare tactics. The Navy’s efforts accelerated after a malfunction caused the loss of the submarine USS Thresher during a 1963 test run. After the accident, the Navy developed deep-sea rescue vehicles that could descend and dock with damaged submarines. The Navy has also used its deep-sea technology for other purposes. After the fall of the USSR in 1991, the United States revealed a number of secret missions carried out by its submarines. One operation, code-named Ivy Bells, used submarines and submersibles to install a listening device on an underwater Soviet communications cable in the Sea of Okhotsk.

As international tensions subsided in the 1980s, civilian researchers gained access to the Navy's fleet of submersibles for a number of scientific and archaeological expeditions. One of the most famous expeditions was the 1986 discovery and survey of the Titanic in the North Atlantic. Popular interest in oceanographic exploration was also enhanced by the work of French explorer Jacques-Yves Cousteau, who is credited with the invention of the aqualung, an underwater breathing device (also referred to as scuba gear). Cousteau built a number of small piloted submersibles capable of shallow-water dives.

A growing civilian industry has adapted the Navy’s once-classified machinery and techniques for commercial uses. ROVs were first used to locate Navy submarine wrecks, but are now used by commercial and scientific groups. ROVs, alongside human divers, were used to salvage debris from Trans World Airlines Flight 800, which crashed off Long Island, New York, in 1996. The latest submersibles in development are robotic vehicles called autonomous underwater vehicles, or AUVs. These untethered craft are designed to operate individually according to a preprogrammed set of instructions. This preprogramming allows AUVs to perform simple routine tasks without the need for people to control them. Possible uses for AUVs include the periodic monitoring of seabeds for changes in biological growth and the provision of security for underwater areas.

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