
May 5, 1998

Communication follows the hydroplow

BY JON SAVELLE
Journal staff reporter

With much ado these days about the explosion in telecommunications, including the Internet, wireless satellite networks and multiple home telephone lines, it is easy to forget that it is still necessary to lay communications cables on the seabed.

In fact, as the world demands ever more bandwidth, and hence higher-capacity cables, those companies that install subsea cables are in great demand.

Just ask Mark Jacobson, senior project manager with Pirelli Jacobson in Seattle. His company, formerly family owned but now a subsidiary of the Italian industrial giant Pirelli Cables and Systems, operates worldwide installing fiber-optic communications cables and copper power cables.

This year, however, the company has the rare treat of working close to home. Jacobson said his firm will be installing cables in north Puget Sound, linking communities in British Columbia and Washington state.

Pirelli Jacobson will be using a "hydroplow," or waterjet excavating device, to dig a trench in bottom sediments where the cable will be laid. The wheeled device, towed by a surface ship, travels slowly across the bottom where it simultaneously trenches and places the cable.

Pirelli Jacobson's Puget Sound assignment is to install 48-strand fiber-optic cable -- it has twice the capacity of standard 24-strand cable -- from Seattle to Whidbey Island; from Whidbey to Victoria, B.C.; and from Victoria to Point Roberts, Wash., for a total installed length of about 300 kilometers.

Each link will be capable of carrying 770,000 simultaneous telephone conversations.

Jacobson

Mark Jacobson shows off the containerized equipment his Seattle firm uses to lay subsea cable for clients around the world.
Photo by Jon Savelle

Although Jacobson declined to name the firm's client for that project, he said in the past the company has done work for such familiar names as GTE, TCI, Puget Power and Orcas Power and Light.

The power companies, of course, need power cables. Pirelli makes cables that can carry both electricity and communications, using copper for the electricity and fiber for communications.

In either case, demand is increasing rapidly worldwide. And that is spurring development of cable technology.

"America is pushing it," Jacobson said. "We call Italy and say, 'Have you got a 148-strand cable?' and they say, 'Are you crazy? Only America would ask for that.' "

Just as cable technology is advancing rapidly, so are methods for installing them. Pirelli Jacobson has developed a transportable system in which all their equipment and supplies are packed in shipping containers, then reassembled at their destination. The firm then leases a "vessel of opportunity" on site to carry its equipment and crew.

But laying subsea cable is not simply a matter of unrolling a spool as the vessel steams off to some distant point. The route must be carefully planned, using accurate charts of bottom features such as rocks, wrecks, pipelines and other cables. Then the vessel, towing its hydroplow, must follow that route exactly.

To accomplish such a feat, Pirelli Jacobson makes use of the Global Positioning System, the U.S. Government's satellite navigation network that can pinpoint a vessel's location anywhere on the globe. Data from the satellites enables Pirelli Jacobson to closely monitor the position of its cable-laying vessel, and to adjust its path accordingly.

The position data is fed into computers that control thrusters, like giant outboard motors, that Pirelli Jacobson attaches to its vessel. Depending on the operator's wishes, the system can hold the vessel at one point, counteracting the effects of winds and currents, or direct it to follow any programmed path.

This technique will be used in Puget Sound, exactly as Pirelli Jacobson has used it in Malaysia, Mexico, the Bahamas, South Korea, Saudi Arabia, Cyprus, Syria, Holland, England and France.

On every job, installation engineers must account for not only the route but the depth of the bottom, the amount of shielding necessary to protect the cable, and whether it must be buried or not.

The Puget Sound project, for example, calls for buried cable to a depth of 150 feet. At greater depths the cable will lie on the bottom. The hydroplow, using pressurized water from a large diesel-powered pump on the surface, can excavate a trench in bottom sediments that can be as much as three meters deep yet only a few inches wide.

Jacobson said no backfilling is necessary when using the hydroplow. The sediments are liquefied by the process and simply settle back into the slot above the cable. Cable can be installed at a rate of 200 to 300 meters per hour.

Though Pirelli Jacobson now practices the state of the art in subsea cable installation -- and also does cable jobs on land -- Jacobson said the company's origins were in a different kind of undersea work.

"We used to recover torpedoes for the Navy," he said. Founded by his grandfather, the company eventually diversified into cables, then got out of the torpedo business.

The firm was purchased by Pirelli 10 years ago and has been busy ever since.

"Every job we do, we improve," Jacobson said. "It's an ongoing, changing technology."