Voyage to the Bottom of the Sea

 
 
By eweek  |  Posted 2001-01-08 Email Print this article Print
 
 
 
 
 
 
 

The worst thing about laying communications cables under the sea isn't the ship's food, nor the choppy waves.

The worst thing about laying communications cables under the sea isnt the ships food, nor the choppy waves. Its not the days when you have to handblast trenches in muddy sea bottoms or manipulate robot cars trundling the ocean depths.

The worst days are much worse than that. Like the day one of Alcatels 300-foot vessels got caught in Hurricane Floyd, and the crew had to abandon its trench-digging plow and sail to safety.

Or the even worse day on the North Sea in 1995, when the plow hooked onto something heavy, slowing the digging of trenches and laying of fiber-optic cable.

"The crew could feel there was something wrong," recalls Ove Smidt, director of Alcatels marine maintenance. "They pulled up the plow, and there on its penetrating point was a World War II mine. The plow had cut straight into it."

The ships captain called an explosives expert for the Dutch Marine Corps and a crew came out and exploded the 120-pound mine in the open sea as the sailors watched in astonishment from a couple of miles away.

Before fiber-optic cables are loaded aboard ships, engineers spend months planning the precise route, gauging the topography of the ocean floor and worrying about the 100 things that can go wrong.

Alcatel is the leading builder of submarine networks, its nine cable ships steering the Paris-based company to 41 percent of the world market share.

In the Atlantic alone, Alcatel has laid cable for AT&T, Cable & Wireless, France Telecom, Global Crossing, Sprint, Telefonica, WorldCom and 20 others from Telecom Eireann to Iceland Post and Telegraph.

Since the first one in 1988, 20 digital optical networks have been laid across the Atlantic. Some old analog coaxial cables still are in operation, too, including one laid in the 1920s.

Three new trans-Atlantic systems were switched on just in 2000, and five trans-Pacific networks have been switched on since 1998. None are scheduled for completion this year, but FLAG Telecoms 22,000-kilometer system connecting Canada, Japan and the U.S., is scheduled for deployment in 2002. The Federal Communications Commission late last month awarded FLAG Pacific a U.S. landing license for its project.

Undersea cables may be the most appealing option in the 21st century.

As demand for bandwidth skyrockets, satellites will have a harder time competing with fiber for transoceanic traffic, said Paul Gabla, vice president of marketing and sales for the submarine networks division at Alcatel. A fiber pair connected to Dense Wavelength Division Multiplexing equipment can carry 640 billion bits of information. With three or four fiber pairs in a cable, thats about 5 trillion bits per second.

By contrast, a satellite loaded with transponders can carry about 10 gigabits or 20 gigabits.

Ships Afloat

Alcatels fiber manufacturing capacity has quadrupled in the past two to three years, to about 100,000 kilometers annually. The company used to lease ships, but with the explosion of Internet traffic, bought nine ships, Gabla said. "Part of our turnkey offering is our installation capability."

Typically 40 to 50 people are aboard an installation ship, which can be as long as a football field.

To prepare for the project, the company starts with market analysis, gauging the traffic predicted across an ocean or sea for the next five or 10 years, Gabla said.

The next step is a desktop study, looking at maps, charts and routes, he said. "We have to determine a route suitable to lay a cable."

A scouting ship surveys the route, using sonar to scan the sea bottom along a path about 1 kilometer wide. "You want to know about any obstacles, whether its shipwrecks or something natural," Gabla said. If the sonar finds too much hard rock in shallow waters where the cable must be buried, the engineers devise a route along a softer bottom.

After the land-based engineers determine fairly accurately the path and the total length of fiber needed, the next step is to determine where the optical amplifiers go.

Whether on land or sea, the pulse of light traveling through a fiber must be reamplified about every 50 kilometers — more often if the total distance or the bit rate is great.

Every spot where the light must be reamplified, the cable also needs Wave Division Multiplexers, which increase carrying capacity by dividing light into different wavelengths. For undersea networks, the current maximum is about 64 wavelengths per fiber, each capable of carrying its own traffic.

Still working from the desktop, engineers map where the amplifiers and multiplexing equipment should be attached. They will be housed in boxes about 8 feet long and laid at the same time as the cable.

The regenerating equipment manufactured in Greenwich, England, is shipped to the cable factories in Australia, France or the U.S., where they are spliced onto the fiber cable, along with the multiplexing equipment, about every 50 kilometers.

When the ship arrives, the cable is uncoiled at the harbor and recoiled onto spools inside tanks below deck. The tedious process can take longer than laying cable on the ocean bottom.

A large ship in Alcatels fleet can carry four to eight tanks filled with fiber — enough to stretch halfway across the Atlantic Ocean.

Large ships must sit a mile or so offshore, so the first stretches of cable are pulled back into shore floating atop the water on buoys. When that first length of fiber is positioned perfectly, the buoys are removed and the fiber sinks, with luck, into the trench. The fiber is wrapped in a tube with wires and copper tape to add strength and weight.

As the ship starts moving out to sea, the fiber slowly uncoils. "We want to be able to follow the planned route to within a few tenths of a meter of accuracy," Gabla says.

Meantime, another ship starts from the other shore, with a plan to meet and splice in the middle, a wetter version of the last spike in the transcontinental railroad.

There are easy days and hard days.

Most of the way across the ocean, the water is more than 2,000 meters deep, safe from ships anchors and other threats, so the cable simply lies on the sand. If nothing goes wrong, ship crews can lay 125 miles in a single day.

Most of the hard work is within 100 miles of shore, where the ocean is typically less than a mile deep. Thats shallow enough for fishing trawlers to catch their anchors on a fiber-optic cable. And if that happens, all the soccer scores and dot-com catalogs and love letters speeding in bits and bytes between two continents get stuck in Davy Jones locker.

Well, not quite that apocalyptic. Undersea cable usually is laid in a ring configuration, so if an anchor cuts one cable, traffic automatically gets redirected the other way around the ring. Networks also write cross-restoration agreements so if they lose power they can re-route their traffic through another carriers fiber.

Still, its a potential disaster and an expensive repair job whenever a cable is snapped. So, every transoceanic cable-laying odyssey includes hundreds of miles of slow 25-kilometer-a-day trudging as a 12-foot plow cuts a trench and simultaneously lays the cable. If its done smoothly, the sand or mud will even settle nicely back over the trench and cable.

The cable also must be buried anywhere near an island, across shallow straits and along the entire route across the North Sea and the English Channel, for example.

If theyre lucky, crew members can stay dry, but there are times when the divers aboard have to get wet.

They might need to use a big chain or circular saw to cut through the rock. Or, theyll dive to the bottom with high-pressure water jets to blow the sand away, then get the cable in place and make sure the sand settles back over the cable.

Divers can only go down about 50 meters. If there is trouble deeper than that, they send down a remote-control vehicle, a sort of robot diver with tools. Its an electronic, not an optical device, and has its moods, Smidt said. If its working right, its arm can be manipulated from aboard ship to try to free fiber from snags or fix other troubles.

Those are expensive miles. But overall, laying a submarine network is cheaper than acquiring rights of way and digging a terrestrial network, Gabla said.

"International waters are public property," he said. That means no real estate costs and no real estate agents.

Sometimes, though, the waters depth is the least of the concerns.

"The major risk is weather when youre laying cable," Gabla said. "Bad weather can easily mess up operations." When winds get ferocious, they cut the cable, put it on a buoy, sail to calmer seas and come back later.

Thats what happened last year when an Alcatel ship found itself a little too close to Hurricane Floyd off the southeastern U.S. coast. They wasted no time. "You just cut the cable and run," Smidt said. After the seas calmed, they were able to find the cable and even recovered the plow. "We used a grapple that runs along the bottom," Smidt said.

 
 
 
 
 
 
 
 
 
 
 

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