Editing Submarine communications cable (section)

===== Cable repair =====
[[File:Submarine cable repair animation.gif|thumb|right|An animation showing a method used to repair submarine communications cables.]]

Shore stations can locate a break in a cable by electrical measurements, such as through [[spread-spectrum time-domain reflectometry]] (SSTDR), a type of [[Time-domain reflectometer|time-domain reflectometry]] that can be used in live environments very quickly. Presently, SSTDR can collect a complete data set in 20ms.<ref>Smith, Paul, [[Cynthia Furse|Furse, Cynthia]], Safavi, Mehdi, and Lo, Chet. "Feasibility of [http://livewiretest.com/analysis-of-spread-spectrum-time-domain-reflectometry-for-wire-fault-location/ Spread Spectrum Sensors for Location of Arcs on Live Wires] Spread Spectrum Sensors for Location of Arcs on Live Wires." ''IEEE Sensors Journal''. December, 2005. {{webarchive |url= https://web.archive.org/web/20101231231446/http://livewiretest.com/analysis-of-spread-spectrum-time-domain-reflectometry-for-wire-fault-location |date= December 31, 2010 }}</ref> Spread spectrum signals are sent down the wire and then the reflected signal is observed. It is then correlated with the copy of the sent signal and algorithms are applied to the shape and timing of the signals to locate the break.

A cable repair ship will be sent to the location to drop a marker buoy near the break. Several types of [[grapple (tool)|grapples]] are used depending on the situation. If the sea bed in question is sandy, a grapple with rigid prongs is used to plough under the surface and catch the cable. If the cable is on a rocky sea surface, the grapple is more flexible, with hooks along its length so that it can adjust to the changing surface.<ref>[https://books.google.com/books?id=TuQDAAAAMBAJ&pg=PA621 "When the ocean floor quakes"] ''Popular Mechanics'', '''vol.53''', no.4, pp.618–622, April 1930, {{ISSN|0032-4558}}, pg 621: various drawing and cutaways of cable repair ship equipment and operations</ref> In especially deep water, the cable may not be strong enough to lift as a single unit, so a special grapple that cuts the cable soon after it has been hooked is used and only one length of cable is brought to the surface at a time, whereupon a new section is spliced in.<ref>Clarke, A. C. (1959). ''Voice Across the Sea''. New York, N.Y.: Harper & Row, Publishers, Inc.. p. 113</ref> The repaired cable is longer than the original, so the excess is deliberately laid in a "U" shape on the [[seabed]]. A [[submersible]] can be used to repair cables that lie in shallower waters.

A number of ports near important cable routes became homes to specialized cable repair ships. [[Halifax Regional Municipality|Halifax]], Nova Scotia, was home to a half dozen such vessels for most of the 20th century including long-lived vessels such as the [[Cable Ship|CS]] ''Cyrus West Field'', CS ''Minia'' and ''[[CS Mackay-Bennett]]''. The latter two were contracted to recover victims from the [[sinking of the RMS Titanic|sinking of the RMS ''Titanic'']]. The crews of these vessels developed many new techniques and devices to repair and improve cable laying, such as the "[[Pipe-and-cable-laying plough|plough]]".