MadSci Network: Engineering Query:

Greetings: Undersea communications cables are laid from specially designed ships that can carry many thousands of kilometers (miles) of coiled cable in their holds. The cables also have special amplifiers within them that are spaced about 40 km (25 miles) apart. These amplifiers boost up the voltage of the signals carried in them to make up for the losses in the cable. These cables must operate for many tens of years under the sea so the cables are constructed and tested on shore and the coiled up in the ship. The ship must be very careful when laying out the cable so that the cable does not break and the amplifiers are not damaged. This takes very special controls on the ship. In the past the electrical cables that crossed the oceans were very thick and heavy; however the new fiber optic cables are only about 2.54 cm (1 inch) in diameter. The fiber optics are enclosed in a central metal tube about 60 millimeters (1/8 inch) in diameter and they are surrounded by an outer layers of steel cable and plastic to provide strength during the laying of the cable which may end up thousands of meters (yards) below on the ocean floor. The first small diameter fiberoptic cables were damaged by fishing boats with drag nets and by sharks chewing on them on the ocean floor. Scientists found that the sharks were attracted by the magnetic fields around the cabled produced by the electrical current supplying power the amplifiers. To reduce these problems, today the cables are buried in the floor of the ocean using special under sea ploughs. However, in rocky bottoms and over undersea cliffs the cables are still exposed. Special unmanned robot submarines with TV cameras and repair arms are used to inspect the cables and to help bring up cables sections that have been damaged. These repairs are performed on the special cable ships. You can see pictures of the cable ships at the following web site: http://www.submarinesystems.com/tssl/marineservices/sail.htm One of the most famous cable ships in the pictures was the SS Long Lines that was built for AT&T. Recently the ship was sold to a special cable laying company. The following news release tells about another AT&T ship the Global Link. QUOTE: FOR RELEASE THURSDAY, APRIL 2, 1992 SOUTHAMPTON, England -- AT&T's new cable ship, the Global Link, will complete its maiden voyage here Friday after battling snow squalls, rough seas and the threat of waterspouts in the wintry North Atlantic to complete the longest, fastest single installation of transoceanic Communications cable. The Global Link installed 5,621 kilometers (3,500 miles) of the next transatlantic fiber optic cable system, TAT-10, in 21 days. This tops the record set by AT&T's cable ship, the Long Lines, in 1988, when it installed 5,224 kilometers (3,250 miles) of fiber optic cable for the transpacific system, TPC-3. The fleet of five cable ships that AT&T operates holds the world's record for installing undersea telecommunications cable-- more than double its nearest competitors. "We've installed about 177,000 kilometers (109,900 miles) of undersea cable- -51,000 kilometers (32,000 miles) of which is fiber optic cable. Altogether that's enough to wrap around the equator about four times," said Jim Barrett, vice president of engineering and operations for AT&T Submarine Systems, Inc. AT&T also owns four sea plows and a seabed tractor, and has ownership interest in three unmanned remotely operated submersible vehicles used for cable burial and repair operations around the world. "We're the leading full-service provider of undersea communications cable systems," he said. "We design and install cable routes worldwide, and we maintain and repair them as well. And our Bell Labs-designed cables and repeaters have a 25-year lifespan." In addition, both the Global Link and the Long Lines have the unique AT&T Bell Laboratories-designed linear cable engine that permits the fastest cable-laying speeds in the industry. The Global Link, for example, averaged 6.2 knots on its historic voyage. Most cable ships install undersea cable at speeds around 5 knots. The TAT-10 fiber optic route will directly link the United States with Germany and the Netherlands for the first time. Service on the U.S.-Germany segment is slated for late August, with service on the Netherlands leg of the route due for service in October. AT&T announced service on the TAT-9 fiber optic route, which links the United States and Canada with the United Kingdom, France and Spain, on March 2. From start to finish, the TAT-10 undersea fiber optic route will be completed in less than half the time a project of this size normally requires. In addition, the Global Link's operations were planned so carefully that the TAT-10 project has required fewer people than usual. A typical transoceanic cable operation requires about 110 people, but the Global Link had only 10 AT&T engineers on board, along with 22 ship officers and 57 crew. With the Global Link's deep sea cable operations accomplished, AT&T will now deploy another cable ship it operates to complete the remaining segment of the North Sea undersea cable operations. The AT&T-operated cable ship, the Dock Express 20, will begin working with other vessels to connect with the cable segment left off the northern coast of Scotland by the Global Link. This final leg will require the installation of specially armored cable over 11 natural gas and oil pipelines in the North Sea. Another new record is expected during this phase. "We will need to bury more cable on the northern European continental shelf than on any other route in history," Barrett said. "We need to bury about 1,000 kilometers (620 miles) of cable using our sea plow, because of the shallowness of the sea in this particular area. This is nearly double the seabed plowing record AT&T set on the Meridian undersea cable route from Spain to Denmark." AT&T initiated the industry practice of burying communications cable beneath the seabed in 1967, to protect the cable from fishing activities and ship anchor snags. AT&T holds the record for the most cable buried worldwide--more than 6,500 kilometers (4,000 miles). Undersea fiber optic cable activities area also under way in the Pacific. AT&T's second new cable ship, the Global Sentinel, will begin installing the next fiber optic transpacific cable, TPC-4, in June. TPC-4, which will link the United States and Canada with Japan, is slated for service this fall. In addition, the Long Lines will begin installing a new fiber optic route between Hawaii and New Zealand later this year. END QUOTE Best Regards, Your Mad Scientist Adrian Popa

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