SUBMARINE CABLES

Te Awamutu Courier, Volume 53, Issue 3807, 11 September 1936, Page 5

SUBMARINE CABLES

YESTERDAY AND TO-DAY. (By G. B. FULLER.) In the Illustatred London News of August sth, 1865, appeared a woodcut illustration showing the cable ship “Caroline” laying the shore end of the first Atlantic cable off Valencia, Ireland. Those were the early days of undersea telegraphic communication, the pioneer days, the days when engineers were meeting more rebuffs than success; when they were grappling with a little-known development in the linking up of continents, and groping ofjten in the blackness of doubt and the dismal despair of failure. In 1863, two years previous to the laying of the first Atlantic cable, the Persian Gulf Cable was laid. This was the deep sea portion of the historic telegraph to India. It was 1,615 miles in length, and it takes pride of place as the first successful long-distance submarine cable. Its manufacture and laying rank as one of the outstanding achievements in the history of submarine cable history. A number of books have been written with submarine telegraphy as their subject. Invariably the names of William Thomas Henley, and of the company which to-day bears his name, have prominence in their pages. Mr - Henley made the shore ends of both the 1865 and 1866 Atlantic cables and he manufactured the Persian Gulf cable, which was laid by Sir Charles Bright. The manufacture of these famous cables was carried out at his North Woolwich works, on the site of which stands the present-day Henley factory. The cable ship “Caroline” was his. Of the thousands of miles of submarine cables manufactured by him, many were laid from his historical cable-ship fleet—- “ Caroline,” “La Plata,” “Africa,” “Uruguay,” “Investigator,” “Roddam” and “Westmeath.”

A pioneer in a pioneering age was William Thomas Henley; a man with unbounded confidence in himself; a man who worked hard and alwaysa man who taught himself as much as—if not more than—he ever learned from others. He began life as a poor boy. He finished schooling when he was eleven years of age. He went to London at the ago of sixteen and obtained a situation as light porter in Cheapside. Leaving this post, he worked as a labourer at St. Katherine’s Docks and earned half-a-crown a day, averaging about four days’ work a week. Aiming at self-im-provement, he taught himself turning both in wood and brass, and in three years had become adept in electricity and magnetism, optics, pneumatics, chemistry, mechanics and the laws of motion. He made electric machines, producing silk and cotton covering for electro-magnetic apparatus. He became an employer of labour, and he made a considerable quantity of electrical apparatus for Professor Wheatstone, for use in his early experiments. He commenced at his North Woolwich works in 1859, with a capital of about £8,(NO!

Without this necessary brief sketch of William Thomas Henley, these notes on submarine cable work woqld be incomplete. Long before the first successful Atlantic cable was laid, there was a demand for telegraphic communication across the seas. In 1850 a copper wire with a thick coat of gutta percha was laid across the Straits of Dover, connecting with Dover and Calais. Rapid developments were made between 1850 and 1875, but of the various dielectrics suggested and tried, only two survived —rubber and gutta percha. While the former has been used only to a comparatively small extent, rubber has never proved itself to be a permanent dielectric for submarine cables. In his paper, “Telegraph Gable Manufacture Rubber and Gutta Percha,” read at the Institution of the. Rubber Industry in 1923, Mr H. Savage, the late Works Manager of Henley’s North Wdolwich Works, said: “It was early recognised that pure rubber had a low specific electrostatic capacity, perhaps lower than gutta percha, but that the introduction of pigments caused an increase of the capacity. The usual form of vulcanised rubber containing pigments and having good mechanical properties had a relatively high capacity. This was objectionable as tending to retard the signals and cause inefficient transmission. Conductors were therefore coated with a thick coating of pure rubber. This, being soft, allowed the conductor to get out of centre and did not successfully resist absorption of water. It was subsequently enclosed in an outer covering of rubber containing a large proportion of sulphur to produce rapid vulcanisation and a tough covering. Between the thick pure rubber and the outer covering was a layer of rubber containing oxide of zinc. The object was to mak? a hard, but not brittle, tube that would have a high resistance to the penetration of moisture, and to retain the inner soft layer with its low capacity next to the conductor, an intermediate layer, known as the separator, being used to form a junction between the pure covering and the tough vulcanised jacket. Unfortunately, even under these circumstances, rubber is not so impervious to water as gutta percha.” Where the temperature is sufficiently high to produce deformation of gutta percha—in tropical waters—-

rubber is sometimes used; but rubber cables have, generally speaking, been replaced by gutta percha cables for some years. Some .rubber cables however, are still in use and giving satisfactory service.

Gutta percha was first introduced in 1847. It has mla.intained its pride of place in submarine telegraph cabh manufacture during the seventy odd years of submarine telegraphy. In its natural state, gutta percha is a gum extracted from certain trees. Its origin, characteristics, treatment and uses, formed the subject of Dr Obach’s three Cantor Lectures at the Society of Arts in 1897 -—• lectures which have become classics. Raw gutta has four prime constituents, gutta, resin, dirt and moisture. The proportions vary. It has to be cleaned and boiled, masticated and strained before use. It is impervious to moisture. The prepared gum is usually applied to the conductor in a forcing machine, several wires being covered a.t one operation. The material is first masticated to render it plastic. It is then extruded through dies, through which also pass the conductors. Gutta percha is adversely affected by exposure to air and sunlight, both of which conditions render it resinous and brittle; but immersion in water has the effect of retaining all the essential qualities indefinitely. Immediately following the extrusion process, therefore, the gutta percha covered cores are passed throughout long troughs of cold water. This process sets the gutta percha sufficiently hard to enable the core to be wound on to drums.

The conductor of submarine telegraph cables is always of pure copper, generally 7 similar wires stranded together. When a larger conductor is required, composite form, consisting of a large central wire surrounded by several smaller ones, is used. The conductors are tinned when the dielectric is rubber, but when gutta percha is used tinning is not necessary.

Deep sea cables are liable to attack by marine life in minute form. These tiny creatures bore holes or plough channels in the gutta percha. Although the borers have their existence in tropical seas more than in any others, a protective lapping of brass or Muntz metal is usually applied to all submarine cables which are to be laid in comparative shallow water. This protection is not necessary for cables to be laid in deep water, as the minute marauders do

not lie in water deeper than 300 or 400 fathoms. Two of these destructive sea animals are the Teredo Navalis, “a sort of soft-bodied snail but little bigger than a pin’s head,” and the crustacean, “about a quarter of an inch long.”

The bedding of the armouring is usually one or more layers of jute oi' hemp yarn, laid up spirally, and the armouring consists of iron or steel wire, the tensile strength of which may vary from 25 to 100 tons per square inch, according to the depth of water in which the cable is to he laid. Ordinary homogeneous wire is standard for shore ends or intermediate cables where ,a. high breaking strain is not necessary. Although rustless steel has been suggested for cable armouring, it has not yet been used for armouring since the failure in 1857-8 of tha composite flexible aqinoliring of bunches of fine wires first used for the armouring - of the Atlantic cable. The armouring wires used to-day are always galvanised and, in addition, are usually compounded. Occasionally, wires for deep water - (of small diameter and used to minimise the weight of the cable) a’]e separately lapped with an impregnated cotton tape to assist preserva tion. One or more servings of stranded yarn, with alternative coats of a bituminous compound, are applied over the armouring.

A rather queer idea was put forward in the early days of submarine cable manufacture. It was suggested that sharp grit incorporated in the compound would damage the teeth of marine borers. Coupled with this was another suggestion that a. poisonous element be incorporated in tha compound. The first idea was superseded by the metal tape already mentioned. The second, although being experimented with from time to time, was never adopted, one reason being that the use of the poison would endanger the life of the workmen. So much for the cable.