Earlier this month the undersea cable carrying broadband to Northern Ireland broke, slowing internet speeds down to a crawl. It took a specially designed ship and two crews of 30 people a fortnight to get broadband speeds back to normal. But how do you go about fixing a cable that's just six centimetres in diameter, lying over 100 metres down at the bottom of the stormy Irish Sea? You use a robot. A really big one.
Breaks in undersea broadband cables are fixed by inserting a new piece of cable and connecting it either side of the break / Yannick Le Bris
Breaks in undersea cables are nearly always caused by fishing trawlers or anchors being dropped in the wrong location and dragged across the sea floor. Earthquakes have also been known to damage cables in Asia -- while shark attacks are something of an industry myth.
The cable that broke in the Irish Sea is one of two owned by Virgin Media, which connect the countries of the United Kingdom with Ireland. Finding and fixing the fault is the job of Peter Jamieson, Virgin Media's principalengineer and chairman of industry organisation Subsea Cables UK.
"Fixing a cable at sea is no easy task," he tells WIRED.co.uk. "There are many variables in play and it requires a steady hand and even steadier ship, plus expert teams who work round the clock to get the job done."
Once the repair is made the ROV uses a high-pressure water jet to bury the cable up to 1.5 below the seabed/Yannick Le Bris
As well as being incredibly small, fibre optic cables are also very complicated. Virgin's contain 48 optical fibres, each capable of carrying huge amounts of data. A poor repair job can reduce the capacity of a fibre, so it has to be done just right. To complete the fiddly job some seriously hefty machinery is required.The Pierre de Fermat, a ship specially designed for undersea cable repair jobs, uses GPS and manoeuvrable thrusters to stay in exactly the right position
Jamieson and his team chartered the Pierre de Fermat, a ship specially designed to manage the installation and maintenance of all kinds of undersea cables. The ship, which measures 100 metres long and 21.5 metres across, uses GPS and manoeuvrable thrusters to keep it in the same position, even in the stormiest seas.
"The first job is carried out by onshore Virgin Media engineers, who are sent to both ends of the cable as soon as a network alarm has alerted us that there's been a break," Jamieson explains. The teams then use laser pulses to identify exactly where the break is and dispatch the repair ship to the location. Once on site, the ship launches a remotely operated vehicle (ROV), which hunts down and retrieves the cable.
"The ROV is an innovative piece of machinery that enables us to dive down onto the seabed, inspect the damage and bring up the cable to the ship. Don't let the pictures fool you, it's not like anything on Robot Wars; it's actually the size of a large van."
Once the cable has been found and returned to the ship a new piece of undamaged cable is attached. The ROV then returns to the seabed, finds the other end of the cable and makes the second join. It then uses a high-pressure water jet to bury the cable up to 1.5 metres under the seabed.
Repairs normally take around ten days from the moment the ship is launched, with four to five days spent at the location of the break. Fortunately, such incidents are rare -- Virgin Media has only had to deal with two in the past seven years.
"These days I manage the process from dry land. The repair operation has to be perfect every time -- once it's done you never want to go back," Jamieson says.
26 FEBRUARY 15 by JAMES TEMPERTON