RIASSUNTO
ABSTRACT
This paper presents a review in narrative form of the various main elements of submarine telephone cable repair work at sea. Generally well known techniques are mentioned only in passing; specific techniques peculiar to cable work are described more fully, but with no mathematical treatment. Elements discussed are the need for repair and maintenance, an outline of a simple repair, grapnels, cable-detection, testing and fault-localization, navigation, communications, ship design and deck gear, splicing and submersibles. Line Sketches are stylized for the sake of clarity.
INTRODUCTION
The Need for Repair and Maintenance
Submarine cables are subject to the following hazards: man-made interruptions caused by fishing and by ships' anchors; mechanical or electrical breakdown resulting from faulty engineering; natural phenomena, which include iceberg-scour, turbidity currents, earthquakes, rock-chafe and chemical spoliation; and animal depredation such as fish bites and worm-boring.
New cable systems are carefully designed to reduce the risk of damage. Sea-bed problem areas are detoured wherever possible. Engineering specification requirements are extremely high, the components of the submerged plant being designed for an uninterrupted working life of between 20 and 25 years.
Much of the repair and maintenance effort is directed toward coping with the man-made interruptions. For while 90 percent of all submarine cable systems are safely located in deep ocean depths, the remaining 10 percent, that in the coastal and shelf waters, requires some 90 percent of the repair effort.
Nevertheless, cable ships must be fitted with all the tools and techniques required for repairs in any depth at which cables lie. And they must be based strategically to cover those areas of highest risk as efficiently as possible.
Fishing Activity
Continental shelves are prime fishing areas in most of the world's oceans. Much of the fishing is done by side and stern-trawlers. Scallopers and clam dredgers are active close inshore. The deepest known trawler-activated damage to cause a cable interruption was logged in 725 fathoms (Fig. 1).
In the North Atlantic, on the shelves and slopes of the North American continent, there are 13 working commercial cable systems. They contain some 2,500 nautical miles of cable laid in ""fishing"" depths. Without some form of protection all this cable is at risk.
Ship' s Anchors
Cable tracks are clearly marked on hydrographic charts, as are anchoring prohibitions. Even so, when the prohibitions are observed, any ship at anchor in the vicinity of cable is likely to drag, fetch up on a cable, and cause damage; Mother ships of large fishing fleets are well able to anchor on the shelf in some 45 fathoms. The increasing numbers of these parent vessels create increasing risks to cable.
Oil rigs moored without consultation with the cable owners could prove another source of danger, though experience to date shows the oil companies ready to protect our mutual interests by plotting the line of cable, and placing their ground moorings no closer than 800 m to the cable track.