This raises two questions, one simple and one nauseatingly difficult and complex. First, how does one repair a cable if it's too tight to haul up?
The answer is that it must first be pulled slightly off the seafloor by a detrenching grapnel, which is a device, meant to be towed behind a ship, that rolls across the bottom of the ocean on two fat tractor tires. Centered between those tires is a stout, wicked-looking, C-shaped hook, curving forward at the bottom like a stinger. It carves its way through the muck and eventually gets under the cable and lifts it up and holds it steady just above the seafloor. At this point its tow rope is released and buoyed off.
The ship now deploys another towed device called a cutter, which, seen from above, is shaped like a manta ray. On the top and bottom surfaces it carries V-shaped blades. As the ship makes another pass over the detrenching grapnel, one of these blades catches the cable and severs it.
It is now possible to get hold of the cut ends, using other grapnels. A cable repair ship carries many different kinds of grapnels and other hardware, and keeping track of them and their names (like "long prong Sam") is sort of like taking a course in exotic marine zoology. One of the ends is hauled up on board ship, and a new length of cable is spliced onto it solely to provide excess slack. Only now can both ends of the cable be brought aboard the ship at the same time and the final splice made.
But now the cable has way too much slack. It can't just be dumped overboard, because it would form an untidy heap on the bottom, easily snagged. Worse, its precise location would not be known, which is suicide from a legal point of view. As long as a cable's position is precisely known and marked on charts, avoiding it is the responsibility of every mariner who comes that way. If it's out of place, any snags are the responsibility of the cable's owners.
So the loose loop of cable must be carefully lowered to the bottom on the end of a rope and arranged into a sideways bight that lies alongside the original route of the cable something like an oxbow lake beside a river channel. The geometry of this bight is carefully recorded with sidescan sonar so that the information can be forwarded to the people who update the world's nautical charts.
One problem: now you have a rope between your ship's winch and the recently laid cable. It looks like an old-fashioned, hairy, organic jute rope, but it has a core of steel. It is a badass rope, extremely strong and heavy and expensive. You could cut it off and drop it, but this would waste money and leave a wild rope trailing across the seafloor, inviting more snags.
So at this point you deploy your submersible remotely operated vehicle (ROV) on the end of an umbilical. It rolls across the seabed on its tank tracks, finds the rope, and cuts it with its terrifying hydraulic guillotine.
Sad to say, that was the answer to the easy question. The hard one goes like this: You are the master of a cable ship just off Songkhla, and you have taken on 2,525 kilometers of cable which you are about to lay along the 2500-kilometer route between there and Tong Fuk Beach on Lan Tao Island. You have the 1 percent of slack required. But 1 percent is just an average figure for the whole route. In some places the seafloor is rugged and may need 5 percent slack; in others it is perfectly flat and the cable may be laid straight as a rod. Here's the question: How do you ensure that the extra 25 kilometers ends up where it's supposed to?
Remember that you are on a ship moving up and down on the waves and that you will be stretching the cable out across a distance of several kilometers between the ship and the contact point on the ocean floor, sometimes through undersea currents. If you get it wrong, you'll get suspensions in the cable, which will eventually develop into faults, or you'll get loops, which will be snagged by trawlers. Worse yet, you might actually snap the cable. All of these, and many more entertaining things, happened during the colorful early years of the cable business.
The answer has to do with slack control. And most of what is known about slack control is known by Cable & Wireless Marine. AT&T presumably knows about slack control too, but Cable & Wireless Marine has twice as many ships and dominates the deep-sea cable-laying industry. The Japanese can lay cable in shallow water and can repair it anywhere. But the reality is that when you want to slam a few thousand kilometers of state-of-the-art optical fiber across a major ocean, you call Cable & Wireless Marine, based in England. That is pretty much what FLAG did several years ago.
In which the Hacker Tourist treks to Land's end, the haunt of Druids, Pirates, and Telegraphers.
An idyllic hike to the tiny Cornish town of Porthcurno. More flagon hoisting at the Cable Station. Lord Kelvin's handiwork examined and explained. Early bits. The surveyors of the oceans in Chelmsford, and how computers play an essential part in their work. Alexander Graham Bell, the second Supreme Ninja Hacker Mage Lord, and his misguided analog detour. Legacy of Kelvin, Bell, and FLAG to the wired world.
50° 3.965' N, 5° 42.745 WLand's End, Cornwall, England
As anyone can see from a map of England, Cornwall is a good jumping-off place for cables across the Atlantic, whether they are laid westward to the Americas or southward to Spain or the Azores. A cable from this corner of the island needs to traverse neither the English Channel nor the Irish Sea, both of which are shallow and fraught with shipping. Cornwall also possesses the other necessary prerequisite of a cable landing site in that it is an ancient haunt of pirates and smugglers and is littered with ceremonial ruins left behind by shadowy occult figures. The cable station here is called Porthcurno.
Not knowing exactly where Porthcurno is (it is variously marked on maps, if marked at all), the hacker tourist can find it by starting at Land's End, which is unambiguously located (go to England; walk west until the land ends). He can then walk counterclockwise around the coastline. The old fractal question of "How long is the coastline of Great Britain" thus becomes more than a purely abstract exercise. The answer is that in Cornwall it is much longer than it looks, because the fractal dimension of the place is high - Cornwall is bumpy. All of the English people I talked to before getting here told me that the place was rugged and wild and beautiful, but I snidely assumed that they meant "by the standards of England." As it turns out, Cornwall is rugged and wild and beautiful even by the standards of, say, Northern California. In America we assume that any place where humans have lived for more than a generation has been pretty thoroughly screwed up, so it is startling to come to a place where 2,000-year-old ruins are all over the place and find that it is still virtually a wilderness.
From Land's End you can reach Porthcurno in two or three hours, depending on how much time you spend gawking at views, clambering up and down cliffs, exploring caves, and taking dips at small perfect beaches that can be found wedged into clefts in the rock.
Cables almost never land in industrial zones, first because such areas are heavily traveled and frequently dredged, second because of pure geography. Industry likes rivers, which bring currents, which are bad for cables. Cities like flat land. But flat land above the tide line implies a correspondingly gentle slope below the water, meaning that the cable will pass for a greater distance through the treacherous shallows. Three to thirty meters is the range of depth where most of the ocean dynamics are and where cable must be armored. But in wild places like Porthcurno or Lan Tao Island, rivers are few and small, and the land bursts almost vertically from the sea. The same geography, of course, favors pirates and smugglers.