DEEP SEA CABLES.

Evening Post, Volume LXXX, Issue 22, 26 July 1910, Page 3

DEEP SEA CABLES.

THEIR NATURAL ENEMIES. LAYING AND REPAIRING. The recent return of the Pacific Cable Board's steamer Iris to Wellington, after effecting repairs to on« of the Eastern Extension Company's cables, between Australia and N«w Zealand, formed the ground work of an interview with a submarine cable expert, who was in the steamer at the time the work of repair was carried out in the Tasman Sea. It was first learned that the accepted necessities for cables were threefold, i.e., commercial, strategical and sentimental. In the case of the connection between Australia and New Zealand, as in all important linos, two cables are laid. There are two cables between Lai Perouse, Sydney, and Wakapuaka, i\ elson. Their distance apart and the precise routes taken by each are kept secret. This is done in order to conceal their whereabouts from an enemy in time of war. As a general rule the terminals are near fortified positions in order to protect them as much as possible. Nevertheless cables are found, cut, and tapped, as was demonstrated in the Busso-Japanese war. Asked how cables were laid, the authority interviewed first described to a Post representative the construction of the cable and then the laying, afterwards the vicissitudes of the cable on the sea bottom, and finally the methods of repairing. CONSTRUCTION OF CABLE. "The cable," he said, "consists of two parts : — Firstly, the core, or central copper conductor, with its surrounding material, almost invariably gutta-percha for submarine cables nowadays. The core is really the cable conveying tile electric signals which form the messages. The greater the weight of copper and ! gutta-percha per mile, the higher the speed at which the cable will work. Secondly, sheathing. This is the armouring of iron or steel wires surrounding the ccrre to protect it from mechanical injury and to enable it to be lifted in deep water. The sheathing is selected to suit the cha-racter of the bottom where the cable will lie. Near anchorages or over rocky bottoms the sheathing will be ten tons to the mite, making j» cable of two inches in diameter. In deep water, where the cable will rest peacefully the ooze, the weight of the sheathing will be a ton to the mile and the diameter of the cable about one inch. It is important that the sheathing shall have greater tensile strength where the water is over 1000 fathoms deep." A THOUSAND FATHOMS DEEP. These great depths led to an enquiry of the character of the ocean bottom. The answers were to the effect that it varied in. configuration as much as tha land ; that far down below dwelt fishes anatomically so constructed (in a manner of speaking) as to resist the stupendous pressure of the great depths, that on reaching our atmosphere their eyes bulged out of their heads, they swelled to ati enormous size and burst like bombs; that shellfish were found a long way out from the coast and in very deep water. When the Iris recently repaired the cable in the Tasman Sea a small oyster-shaped shellfish was brought up from 480 fathoms. It did not measure much more thaii an inch in diameter. Small pieces of sponge, too, were brought up. ' CABLE-LAYING. But the cable steamer is not sent out for studying marine life at great depths, bne i is cruising for business— to join two lands together by cable, and this ia the way it proceeds in the work :— First a very careful survey of the adopted route is made. The depth and character of the bottom and the temperature of the water are ascertained. "Why is it necessary to ascertain the submarine temperature?" was asked. 'Because the minimum temperature at which water is at its maximum density is 39deg. Fahr. Current, however, travels quicker at a lower temperature. The normal temperature of the water at the bottom of the sea is a very important factor in cable-laying." "When a cable is laid, does it stretch from peak to peak or go up hill and down dale, following the configuration of the seabed?" ii_" Ifc I s , thou S nt *>y many people that the cable does not sink to the bottom. This is quite a mistake. If it did not it would coon break. Cables when laid out are given sufficient slack to ensuro that they follow any slight unevenness of the bottom, and to facilitate lilting for repairs. More slack should not be allowed than is absolutely necessary, as the longer the cable the slower it works. A cable of the same weight of conductor and insulator per mile throughout will have its speed reduced to one-qu3rter if its length is doubled— the speed of working follows the inverse square root of the length." FAULTS AND BREAKS. When asked how breaks and faults occuf, the reply was to the effect that breaks resulted from ships' anchors fouling the cables, the attrition of rocks, movements of the ocean bottom, and corrosion of the iron sheathing wires. The I last are galvanised, but as soon as the zinc coating- is removed the water attacks the iron itself. Corrosion is very rapid where the cable -lies on a shelly or corally bottom. "Faults," said the electrician, "are due to chemical action or by boring animals like the toredo navalis. In the Indian and China seas fish-hooks frequently puncture the cables. Again, the cable is sometimes mistaken by pre- ] datory fish for an eel, or something like it, and is bitten through. In evidence of this, fish's teeth have been found broken off in cables that have been so attacked. Faults may be sufficiently large to stop communication, or they may be no bigger than mere pin-pricks — microscopic punctures. Some are sufficient to prevent duplex working — i.e., sending messages in both directions at once. In certain cases, if they are small, they do not change, and are about the middle of the cable they are actually beneficial, as they increase the speed of working. However, as there is never any knowing when a benevolent fault will develop into a malevolent one, it is removed as soon as circumstances will permit." It was gathered that when cable-re-pairing, pieces of sunken ships that ] have gone down on the cables are i dragged up. But the deadly teredo | worm wa-s the worst enemy of all the cable companies. He bored his way into the very heart of the sheathing, and seemed to feast royally upon an unaccustomed luxury like gutta-percha. Then, after tens of thousands of pounds had been spent upon rectifying the mischief done by this small sea-worm, the cores of the cables were wrapped round and round with brass ribbon, and this device completely baffled the teredo." Heavy weather renders cable repairing impossible, for movements of the ship in a rough seii would soon break the cable and undo the work previously done in calm water. Much delay results from bad weather. The work at times is as exciting as it is interesting, but the deep and its wonders and moods are incidents of trivial importance to the men who lay and i

repair cables and maintain connection by sea and under it between countries thousands of miles apart. Would "wireless" replace the marine cable? The authority interiJiewed thought not. Both systems could Ibe, as they had been, especially in the case of the wreck of the White Star liner Republic, worked to mutual advantage, and to the advantage also of the corresponding public, and particularly so for strategic purposes.