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Undersea Cable Repair Via 19th Century Tech
An anonymous reader writes to mention a story going across the wires about an old-fashioned way to fix a modern convenience. Taiwanese boaters are using simple hooks to fish up the fiber-optic cables damaged in an earthquake late last year. The outage that resulted kept millions of users offline in half a dozen countries around the Pacific rim. From the article: "They work 24 hours a day but the weather can hinder their progress. Walters said one ship is waiting for 30 to 40 mile-an-hour winds (48 to 64 kilometres- an-hour) to die down in the Bashi Channel. The winds have stirred up 10 to 12 metre waves ... After arriving at the scene they survey the ocean bottom to assess whether the contour has changed, and the degree of sediment movement. Then the traditional tools are brought out. A rope with a grapnel on the end is played out, down into the depths, and towed over the sea floor until tension registers on a graph on the ship, indicating contact has been made with the cable. Today's fibre optic cables are just 21 millimetres in diameter."
Correct me if I'm wrong, I'm no expert on this subject, but undersea cables certainly aren't 21 mm wide. Certainly they are run in bundles of dozens (maybe hundreds) for a total width of several inches. At work we had fiber cable installed that has 16 or so strands and it was half an inch thick.
:)
I guess it's just bad writing and I shouldn't be so nitpicky.
Anyway, with all this wind and water moving, how do they find a 21mm cable 2.5 miles down? A rope that far would bend under air resistance, let alone water resistance. I think some high technology went into this somewhere. Kudos on not making it too complicated. KISS at work.
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It's reasonably easy to find a cable. At those depths the cables lie directly on the sea floor, and if you run a hook across the sea floor from one side of the cable to the other, you'll cross it by definition. Sure you might then end up some distance from the break, but they are apparently reasonably good at handling that. Such techniques don't work with shipwrecks -- and even if they did, there may not be anything the right shape for a hook to catch.
Anyway, there's an old but interesting article on undersea cables by Neal Stephenson.
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When a method works well, there is not really a need for something else, it will only be used when it is superior. So what would those alternatives be, that are cheaper overall?
A submarine robot repairing on site is probably not possible (I have problems believing it would be able to fuse the fibers), so you only could use it to more quickly find the cable and perhaps make it easier to get the hook onto it as you can see what you are doing. But honestly, how much faster would it be, I guess a hook and the cable for it can just be tossed into the water, an expensive robot probably would take a bit longer to reach the ground. And it probably has limitations on the depth it can operate. Additionally I am quite sure they don't just drive out there and plow the sea bed, they probably have a very good idea where the cable is supposed to be. And don't forget, to find a very long cable is much simpler than finding a wreck. I don't have to find a particular piece, any piece before and after the break is ok, as I can just pull the part up and then follow it, no need to exactly grab the end.
Also the strong winds and high waves probably would make fusing the cables very hard as well, even if they could bring up the cable. So the only thing 'old fashioned' I can see is, that they use a hook. The rest is probably quite up to date and the hook is simply the easiest, most reliable and cheapest way. Why use expensive technology if something simple is perfectly adequate?
Well, I provide support for a retail chain who has stores located in the Asia Pacific. Since the earthquake 75% of all calls to Asia result in a 103T error. Asia has had no issue calling us although its always fun to try to explain "We can't call you back" without an interpreter.
Thankfully, it has gotten better over the past week or so. The funniest thing to come out of this is the director of IT for Asia operations lives in Singapore. Every night when I send my report to notify that we still can't contact the stores I get a nice message back stating "Well I had no problem, please try again". It has taken a lot of patience to not reply back "Well yeah dumbass... you're on the same side of the pond. Your calls don't have to cross the pacific."
Disclaimer: My father worked for several firms involved in the manufacture, laying, and operation of submarine cable systems in the 80s and 90s. I've seen and handled the cables and have toured the type of ship shown in the photo.
The cable size (21mm) sounds correct. They are much smaller than the repeaters. I've seen some samples mounted on display plaques so that you can see how they are constructed. Each cable contains a small number of tiny fibers (the ones I've seen had 6). The construction is a solid metal (steel?) core for strength, then some sort of thicker plastic layer around it that contains the fibers embedded within it, then a copper shield layer, and then more of the plastic material. I've probably missed a layer or two.
On the deep sea floor, that's all there is. Just one of those cables (not bundled or armored) with the big repeater casings every so often. At shallower depths, they can be armored to prevent damage from sharks. (Sharks like them, don't know why.)
The ships are pretty amazing. They have large bow and stern thrusters and can hold position in some pretty rough water. They have huge, round vertical cylindrical holds into which the cable and inline repeaters are fed in and spooled from the factory, and then fed back out when laying them at sea. There's a giant conveyor mechanism that runs from bow to stern to facilitate deployment or recovery of the cable and repeaters. This conveyor clamps onto the cable from above and below it, but it can also widen dramatically to accommodate the repeaters as they pass through.
Interesting that they use a line and a grapple to find and recover the cable, but they do have very precise survey maps to work from that were created when the cable was originally laid, so they probably don't have to look very far to locate it.
My father worked in the cable industry in the 1950s and 1960s. He tells an interesting story from the start of the second world war.
Immediately after Britain declared war in 1939, a cable ship was sent out into the North Sea to dredge up the German cables, which ran from Hamburg through the North Sea and out into the Atlantic. They found the cables using a hook, exactly as described in this story, and cut through them.
Of course it would be easy for the Germans to go out with their cable ship, dredge up the two ends, and join them back together again - if they knew where to look for the break. And it's not hard to find out how far along the cable the cut is, as a pulse will be reflected from the break. This had been well understood for a hundred years.
Knowing this, the British engineers made some sort of contraption full of capacitors and coils that they could fix on to the end of the severed cable before dropping it back into the sea. This would add some extra delay to the reflection, causing the Germans to miscalculate where the break was, and send their cable ship to the wrong place.
Ive always wondered how, or if, they repair cables which are located several miles underwater and continue for a thousand miles. How would you ever hook onto such a cable, and pulling it to the surface seems rather difficult to me and would put a lot of stress on the cable. I just assumed if the cable went bad, they would have to lay all new cable.