On standby · CS Helford
Cable down?
BIGHT keeps one cable ship ready in Falmouth. Call the duty line and CS Helford sails within 24 hours to find the break, lift both ends and splice in new cable.
Duty line · 24 h+44 1632 960 418
The cable
Cables on the seabed carry 99% of the data that crosses an ocean
Modern deep-sea cable is about 25 mm across and weighs 1.4 tonnes a kilometre. Near the shore it gets heavier armour against anchors and fishing gear.
Most systems can send traffic another way round a break. The break itself stays on the seabed until a ship comes to lift it.
Shore-end cable, cut back for jointing
Inside the armour
- 01
Fibres
Glass fibres in pairs, one each way. Conventional cables carry up to eight pairs; newer ones up to 24.
- 02
Tube and jelly
Water-repellent jelly keeps the sea off the glass. The fibres lie in it in a helix, so the cable can stretch without stretching them.
- 03
Copper
The conductor near the centre. The shore stations feed it 3,000–15,000 V DC to power every repeater on the line.
- 04
Polyethylene
Insulation between the copper and the sea. Gutta-percha did this job until 1945, when the first polyethylene cable crossed the Channel.
- 05
Armour wires
Steel wires added near the shore, where anchors and trawls find cables. Deep-sea cable goes without.
Find the break
Most breaks are trawls and anchors, not earthquakes or sharks
- <9%
- of the Atlantic and Caribbean breaks surveyed from 1959 to 1996 had natural causes
- 50+
- repairs a year in the Atlantic alone
- 3.70.44
- faults per 1,000 km a year, before and after cables were buried from 1980
Your shore station sends a pulse of light down a fibre and times what comes back, the way radar does. The reflection from the break gives its distance. Send us that distance with the cable's route positions and we have a place on the chart before we leave the quay.
Example: a deep-water repair
Lift ·
splice ·
lay
01 / 08
On station
CS Helford arrives over the position from your trace. Depth here: 3,800 m.
On station
CS Helford arrives over the position from your trace. Depth here: 3,800 m.
Mark it
A marker buoy goes down near the break, so every pass that follows starts from the same point.
Grapnel
We drag a grapnel across the route on its rope. Rigid prongs plough through sand; on rock we use one with hooks along its length.
First end
At this depth the cable is too heavy to lift as one loop, so a cutting grapnel cuts it and one end comes up to the bow.
Seal and buoy
On deck we test back toward the shore station, seal the end and hang it off a buoy while the ship moves on.
Second end
The same again on the far side of the break, until both ends are in the jointing room.
Splice
Fibre by fibre, an electric arc melts each pair of ends together. New cable from our tanks makes up the length.
Lay
The joined cable is longer than the one that broke, so we lower it and lay the spare on the seabed in a U.
CS Helford
One repair ship, ready in Falmouth, the nearest large harbour to the mouth of the Channel
- Call-out to sailing
- 24 h
- Grapnel work to
- 6,000 m
- Spare cable aboard
- 60 km
- Length
- 98 m
Report
a fault
Duty line, 24 hours +44 1632 960 418
A finished repair leaves the cable longer than it was, with the spare laid on the seabed in a U. A slack curve in a line is called a bight. That is the name on the hull.