TRACING "A CABLE

Evening Post, Volume CXXIII, Issue 130, 3 June 1937, Page 11

TRACING "A CABLE

SUBMARINE DETECTOR

INGENIOUS METHOD

In laying the heavily-protected shoreend of the new Cook Strait cable from Lyall Bay last week,' Post' Office engineers utilised an' ingenious electrical detector to track the course of another cable laid thirty years ago and'now disused. This cable had found a thoroughly. safe ; bed where it had rested without damage throughout its useful life. The engineers, therefore, came to the.conclusion that the route would be ideal for the' new cable. To track its exact course, the disused cable was electrically energised, regular signals being sent out, and, at the same time, the motor, vessel Hokitika cruised a zig-zag course pver the probable route trailing a submerged electrode. When the electrode passed over the cable its signals were picked up, and this'process gave such clear indications of the position that the route was quickly marked by a line of buoys from the shore to a point two and a half miles out; from Lyall Bay, where the cable ship Recorder, will eventually pick up the shore end, join it to the deep-sea section, and proceed along a carefully surveyed , course across the , Strait to the mouth- of 'Blind River, .Marlborough. . ' ■ • .

This principle is utilised in some ports to guide . shipping during foggy conditions. A cable is laid in the middle of the navigable channel and its course is followed by'ships which pick 'up electrical signals sent out be-, neath the water. The New Zealand Post Office regularly uses the same method for locating faults in telephone cables. Some of them carry within their lead, coverings as many as 1000 pairs of telephone wires .insulated \yith paper. When, a breakdown' in the insulation occurs, an electrical "trailer" is run over the cable, picking up a series of morse signals where the circuit is normal. Immediately the fault is reached the signals become indistinct or disappear,, and this enables, the fault -to .be located .to within; a few inches. .'' .. '. ;