TRACKING OF CABLE

Hawke's Bay Herald-Tribune, Issue 117, 3 June 1937, Page 10

TRACKING OF CABLE

Under-Water Detector 2n laying tbe beavily protected sbore-end of tbe new Cook Strait cahle froni Lyall Bay last week, Post Offico engineers utilised an ingenious electrical detector to track tbe course of anotber cable laid thirty years ago and now disused. Tbis cable had found for itself a thorougbly safe bed wbere it bad rested witbout damage tbrougbout its useful life. Tbereiore, the engineers came to tbe conclueion tbat tb© route would be ideal for tbe new cable. To track tbe exact course of au old cable covered witb sand dnvolved tbe use of an ingenious electrical detector. Tbe disused cable was electricaily energised, regular signals being seut out and, at tbe samo time, tbe motor ■vessel Hokitika cruised a zig-zag course over the probable route trailing a submerged electrode. Wben tbe eleetrode passed over tbe cable its signals were picked up, and tbis process gave sucb clear indications of tbe position that tbe safest possible route fo'r the new cable was quickly marked by a line of buoys f rom the shore. to a point two and a half milos 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 a'ong a earefully surveyed course across the fcitrait south-east to the moutb of Blind River, Marlborougn. This principle is utilised m sorne parts to guide shipping during foggy conditionsj a cable being laid in the centrc of the navigable cnannel and its course being followed by ships ,which keep in electrical contact With the signals sent out beneath the water. The New Zealand Post Office regular ly uses the same method for locating faults in telephone cables. >Some of them cairy in their lead eovering as many as 1000 pairs of telephone wires insulated with paper. When a breakdown in the insulation occurs, an electrical ' 'trailer " is run over th'e cable picking up a series of morse signals where the circuit is normal. Ijnmediately the fault is reached the signals become iudislinct or disappear, and this enablcs tbe point of action to be located by the repair gang to within a few anches.