| MadSci Network: Engineering |
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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