Silicon Valley goes under water

By CHRIS DANIELS

It starts in California and snakes along the Pacific Ocean seabed until it strikes New Zealand.

Then it takes off again, crossing the Tasman before looping back to North America.

The revolutionary 30,500km Southern Cross cable kicks into life today. Its arrival signals a big leap in transpacific communications between New Zealand, Australia, Fiji and the United States.

Laying submarine telegraph cables between continents was once described as the Victorian equivalent of the Apollo space programme that landed men on the moon.

Now, more than 130 years since the Great Eastern company laid the first successful telegraph cable across the Atlantic, New Zealand money and expertise are leading the way with the $2.2 billion fibre-optic submarine cable ring across the Pacific Ocean floor.

Half-owned by Telecom New Zealand, the cable has been promoted as an internet, voice and data communication ring with the important West Coast of the United States.

The first international submarine cable to reach New Zealand came ashore at Nelson in 1876. Many cables have since been laid, operated and either broken down or become obsolete.

As the space age dawned, satellites took over and were promoted as the future of global communications. But the development of fibre-optic cables, where signals travel at the speed of light along hair's-width glass strands, has taken technological innovation down from outer space and back into Davy Jones' locker.

With just six strands of fibre, the Southern Cross cable has 120 times the capacity of the existing "PacRim" cable, laid in 1992.

This means two full-length movies can be transmitted along Southern Cross every two seconds, with a one-way transmission delay between New Zealand and the US of just 70-thousandths of a second.

The marine operation begins with the landing of the cable from a cable ship. It is normally floated ashore, suspended by buoys to avoid damage on the ocean floor. Once it is secured, the buoys are removed so it can settle on the ocean floor.

New Zealander Dave Hercus, marine manager of the entire Southern Cross operation, said that in most parts of its journey the cable was buried on the seafloor at an average depth of 0.9m.

During the laying of Southern Cross, a world record was set for the deepest "plough-buried" submarine cable.

Where the seafloor permits, a huge plough is attached to the cable and digs it down into the mud and sediment.

On February 21 this year, a record was set when the ship CS Vercors buried the cable in water 1610m deep. This was done on the eastern side of Lord Howe Rise, 1300km out of Sydney, as the ship sailed towards Fiji.

Mr Hercus said it was becoming increasingly important to protect the cable by burying it into the seabed.

"As the fishing vessels of the world get bigger and fish in deeper and deeper waters, cable companies like Southern Cross have to act to future-proof their cables and the information that flows along them."

A detailed marine survey was done to make sure the cable would take the quickest route, but to avoid deep ridges and gullies and rocky seabeds where possible.

A remote-operated vehicle, worth around $10 million, linked to the mother ship by an umbilical cord, can be lowered to the cable. It can hover above the cable or move along the seafloor on tracks.

The cable's optical fibres are set in a steel tube and coated in jelly to protect them from water penetration and hydrogen. The tube is protected by high-strength steel and surrounded in seam-welded copper to form the "composite conductor."

The cable is only 18mm in diameter for most of its length, but every 40km to 70km is encased by a booster station, a 2m-long box filled with monitors and amplification equipment.

Special self-repair software means signals will not be lost if there is any problem with the cable itself.

The Southern Cross cable has removed a global communications bottleneck, say the experts, taking our little South Pacific a lot closer to Silicon Valley.