Locating and repairing a cable fault

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The sequence by which a break in a hose-thick object lying thousands of metres below a ship is found and mended, and the reason an outage is measured in weeks rather than hours. Location comes first and is done from shore without anyone going to sea: the fibres are interrogated optically — a pulse is sent and the reflection from the fault timed — and the copper conductor is measured electrically, and the two together place the fault along the cable's route to within a comparatively small distance. A cable ship is then mobilised, which is where the delay begins, because the ship must be available, must reach the position, and must hold station in whatever weather it finds. In deep water the ship drags a grapnel across the route to cut and recover the cable, brings one end aboard, tests it, buoys it off, recovers the other end and splices in a fresh length long enough to reach the seabed and lie there as a slack loop; in shallow water a remotely operated vehicle does the same work with better precision and less damage to the seabed. Every splice is a hand operation on glass in a clean cabin on a moving ship. A single repair is commonly described in the industry as taking about two weeks once the ship is on site, and the wait for the ship, for weather and — inside a coastal state's waters — for a permit, is routinely longer than the work.

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