History of the Atlantic Cable & Undersea Communications
|Manufacture of Submarine Cable at Ocean Works, Erith|
Manufacture of Submarine Cable at Ocean Works, Erith
The greater part of the submarine cable for the transatlantic telephone cable project was manufactured at a new cable factory, Ocean Works, at Erith, Kent. This article describes the construction of Ocean Works, the manufacture of the cable and the special testing arrangements necessary during manufacture. The splicing into the cable of flexible repeaters, made in U.S.A. and flown to England, is also described together with the special arrangements necessary at Ocean Works for storage of the cable and repeaters and for loading the repeatered cable into H.M.T.S. “Monarch.”
WHEN the decision to proceed with the transatlantic telephone cable project was taken in 1952, many shorter submarine telephone cables had been manufactured, but it was quickly realized that manufacture of submarine cable in the quantity and with the precision required for the transatlantic project would necessitate the building of a new factory. Thus, when the contract for the greater part (92 per cent) of the transatlantic cable was entrusted to Submarine Cables, Ltd. (owned jointly by Siemens Brothers & Co., Ltd., and The Telegraph Construction & Maintenance Co., Ltd.), the Company had already acquired a site on the River Thames at Erith; Kent, and begun to lay out a completely new plant on the most up-to-date lines. The building of this new factory, “Ocean Works,” entailed a vast amount of engineering design, construction and installation work in a very short space of time. The first machine was ready for installation in March, 1954, and by November of- that year the factory was sufficiently far advanced for the manufacture of a short length of transatlantic telephone type cable to be demonstrated on 26th November, 1954, the occasion of the official opening by the Postmaster-General—the Earl de la Warr.
Full-scale production commenced in February, 1955. From then onwards work went on by day and by night, Saturdays, Sundays and public holidays included, until some 1,287 nautical miles (n.m.) had been produced. This was the length required to enable H.M.T.S. Monarch to sail for Clarenville on 30th July, 1955, nine days ahead of schedule, to begin the first of the deep-sea lays from the edge of the American continental shelf eastwards to Rockall.
In all some 1,728 n.m. of deep-sea and shore-end cable were produced in time for the 1955 summer shipments.
With scarcely a break in production save that necessary for the overhaul and maintenance of essential machinery, cable manufacture was continued at almost the same rate during the autumn of 1955 and spring of 1956, in order that the second cable would be ready for the Monarch’s laying programme during the summer.
In addition to the engineering difficulties which had to be surmounted, there were many problems in connexion with the supply of materials. The extremely exacting specifications demanded a hitherto undreamed of precision in the production of copper wire and tapes—to mention only one commodity. It was necessary to make inquiries all over the world to find a suitable source of supply, but after several had been examined and rejected it was decided that the only way to ensure satisfactory supplies was for the Telegraph Construction & Maintenance Co., one of the parent companies of Submarine Cables, Ltd., to install their own rolling plant and develop their own technique. With the help of Richard Johnson & Nephew, Ltd., of Manchester, who also re-equipped their factory similarly, supplies of wire and tape were maintained and the specification requirements were satisfactorily met.
The factory site at Erith has a river frontage to the Thames of 300 ft. It comprises buildings of an area of rather more than 100,000 ft2 divided into 10 bays 35 ft wide by 250 to 300 ft long.
The design of much of the machinery was based on existing machinery which the Company already possessed, with suitable, and often extensive, modifications to meet the exacting requirements of the cable specification.
Twelve cable-storage tanks, each of welded steel construction, 30 ft in diameter and 25 ft high, provide storage for 2,400 n.m. of finished cable. Storage capacity and handling equipment were also provided for 66 repeaters, and in order to obtain accurate test results the temperature of the cable and repeaters had to be maintained within ± 1°F. This was achieved by a water-circulating system and by housing the tanks in a building 80 ft wide and 200 ft long. The planning and construction of this last project was not helped by the fact that the tank house had to be sited on soft mud 48 ft deep (Fig. 1); to support the tanks and the building (Fig. 2), 480 piles had to be driven and capped with a reinforced concrete slab. However, by running the planning, design, construction and erection concurrently, tanks were made available to store cable only eight months after the land was occupied.
FIG. 2.—THE TANK HOUSE UNDER CONSTRUCTION.
A berth had to be provided to accommodate H.M.T.S. Monarch; it had to be accessible from the main navigable channel of the River Thames and was built some 400 ft off shore. About 250,000 tons of mud and ballast were dredged in four months to form a basin 29 ft below mean low-water spring tides. Three steel-piled flexible breasting dolphins, 120 ft apart, were constructed to absorb the berthing energy of the ship and provide a firm breast while the ship is moored. These dolphins were constructed from 180 tons of specially rolled high-tensile steel sections 90 ft long, driven 35 ft into the river bed. Access to the shore was provided at all stages of the tide by a causeway extending 270 ft riverwards from the wharf.
One of the most outstanding features of the factory is the method of transferring the completed cable from the armouring machines to storage tanks and thence to the cable-laying vessel. Between the armouring machines and the tank house a lattice girder bridge, 50 ft high, was constructed leading on to bridges above the two lines of tanks.
Three cables with repeaters can be transported simultaneously on routes extending 1,000 ft from the land end of the tank house to any point on the ship between the breasting dolphins, at all states of the tide and ship lading. This was made possible by the erection of two towers, shown in Fig. 3, one on the wharf edge and one 260 ft off shore. The cable at all times had to be 42 ft above mean high water at spring tides and it was carried by suspended wire rope spines (two of which were used for loading the cable into Monarch, and are shown in use in Fig. 3) from the wharf to the midstream tower and from there to the loading point on the ship. The wharf-edge tower also supports a 200-ft span bridge from the tank house passing over a public footpath, the river flood-defence wall, wharf, foreshore and factory buildings. In the tower itself there is a triple-sheave cable-hauling unit and the tower is supported on 18 steel piles with a reinforced concrete head weighing 250 tons, which was laid in only 48 hours.
FIG. 3.—CABLE TOWERS, USED FOR LOADING CABLE INTO THE SHIP
The mid-stream tower is 75 ft high and at the top carries anchor points for the six spans and a working platform with handling equipment to transfer cable and repeaters from the inner to the outer spans. The whole tower rests on a 175-ton reinforced concrete head standing on 104-ft steel piles.
The whole of this engineering work was completed in five months and ahead of schedule in spite of all difficulties. The structures were designed, fabricated and erected in three months, actual erection taking 70 days, and the 200-ft span wharf bridge, weighing 130 tons, was in full operational use 14 days after the start of its erection.
MAKING THE CABLE
The cable consists of a polythene-insulated inner copper conductor surrounded by copper tapes forming the outer conductor of the coaxial pair. This core is provided with protective coverings in the form of a layer of jute, acting as a bedding for the steel armour wires, which are helically applied and, finally, an overall serving of tarred jute.
The dimensions of the cables and their components are given in the appendix.
The very exacting specification provided by the Bell Telephone Laboratories, made necessary by the extreme uniformity of electrical characteristics required in the finished cable, necessitated the imposition of very close tolerances on the dimensions of all component parts at all stages of manufacture. The maintenance of this high standard of precision in manufacture was made possible by close supervision throughout and by a comprehensive system of inspection both by the Company’s own inspectorate and by teams of Post Office and Bell Telephone Laboratories’ engineers working in collaboration.
The Central Conductor.
The central conductor was manufactured almost entirely from copper wire and tape produced in the Greenwich factory of the Telegraph Construction & Maintenance Co., Ltd., with a precision never before attempted in the history of copper wire drawing and rolling.
The twisting of the three copper tapes around the central copper wire was carried out in a specially designed and constructed shop*, totally enclosed and fed with filtered and conditioned air from a small Plenum plant. Each operative was provided with white overalls and gloves so that the conductor was never touched by bare hands. These extreme precautions to eliminate any form of contamination were rendered necessary by the requirements of the extrusion process which followed.
*A photograph of the shop is given in Fig. 3 of the paper “Cable Design and Manufacture for the Transatlantic Submarine Cable System” in this issue of the Journal.
Insulation of the Central Conductor.
The polythene compound was also prepared in an enclosed, air-conditioned room (Fig. 4) . Weighed quantities of the components were introduced into the mixer and the plastic compound extruded hot, in strips 8 in. x 0.125 in. which were subsequently cooled and cut into 1/8in. cubes. These cubes of compound were conveyed into storage and mixing silos by means of an air blast. Before introduction into the extrusion machine the compound was cold blended, or homogenized. A quantity of about 5 tons was circulated continuously from one silo to another, the amount required to feed the extrusion machines being withdrawn and replaced by an equivalent amount from the storage silos. In this way any slight variation in characteristics that might have been present in the different batches from the mixer were minimized. Finally, the compound passed through a separator which automatically rejected any material contaminated with metal.
FIG. 4.—POLYTHENE MIXING PLANT.
The extrusion machine (Fig. 5) was automatically controlled by a series of monitoring devices that recorded and maintained, within the prescribed limits, the diameter of the extruded core, and also ensured that the resultant electrical characteristics of the core were uniform throughout each drum length and from length to length.
A device was also included that indicated and recorded graphically the concentricity of the conductor. Continuous records were maintained of the temperature at various points in the extruder, the tension in the conductor, and the core diameter at three different positions along the length of the machine, all of which enabled the operator to pin-point any irregularity or abnormal behaviour in any part of the machine.
FIG. 5.—EXTRUSION MACHINE.
A feature of the core extrusion which had not hitherto been experienced on large-scale production such as this was the hard grade of polythene specified. In the early stages a considerable amount of experimental and research work was necessary before the conditions of extrusion suitable for the production of core to specification requirements were determined.
One of the most important features in the production of a cable such as this is the examination, testing and jointing of the insulated core. Immediately after extrusion of the insulant, every inch of the core was therefore examined by hand so that any visible or otherwise detectable foreign matter or defect of any kind could be observed and remedial action taken. The dimensions of the core were carefully checked by means of a ring gauge and micrometer measurements were taken at frequent intervals.
After examination the core was coiled into shallow pans which were subsequently filled with de-aerated water, kept at a constant temperature, for electrical testing. In order to reveal any hidden defect which might otherwise escape detection, the insulation was subjected to a d.c. potential of 90 kV for 1 min.
Jointing the Core.
The lengths of core that successfully passed examination and electrical testing were joined together to form a repeater section length of approximately 37.5 n.m.
Jointing of the core was carried out by means of a small injection moulding machine. The two ends of the conductor were brazed together and then the insulation was restored to its normal diameter, by injecting hot polythene compound around the jointed conductor. The completed joint was then examined visually for defects of any kind, its dimensions were accurately checked, and it was photographed in three directions by means of X-rays. Finally the joint was subjected to a d.c. potential of 120 kV for 5 min.
The training of suitable operatives for this exacting work of core jointing in the short time available was a task of some magnitude and considerable selection was necessary before a suitable team could be brought together.
Before a trainee was permitted to make a joint in actual core he had to qualify by making 10 consecutive joints, each of which had to satisfy all the requirements of the specification. After qualification he had to make one satisfactory control joint on each shift before commencing work. If at any time he made two consecutive joints which failed to pass any of the specification requirements he was considered disqualified and was required to make a further 10 consecutive joints before requalification. A similar system was adopted for the brazing of all copper elements, i.e. wire and tapes, and for the welding of steel armouring wires.
The Outer Conductor and Armouring.
The 37.5 n.m. lengths of core were copper taped (Fig. 6) in continuous lengths and served with jute and then coiled in cylindrical tanks (Fig. 7) which were flooded with water for further electrical testing prior to armouring. After this test, the served core, still in 37.5-n.m. lengths, was armoured with the number of steel wires appropriate to the type of cable required. Finally, the armoured cable was coiled down into the storage tanks, each of which can hold some 200 n.m. of deep-sea cable.
FIG. 6.—COPPER TAPING MACHINE BEING PREPARED FOR USE.
FIG. 7.—MACHINES FOR APPLYING THE COPPER RETURN TAPES AND JUTE BEDDING FOR THE ARMOURING WIRES
Insertion of Flexible Repeaters in the Cable.
It was at this stage that the flexible repeaters were spliced into the cable. The repeaters, having been carefully unloaded from a special delivery vehicle (a modified ex-R.A.F. trailer), were uncrated and stored in shallow water-filled troughs (Fig. 8) located between the cable tanks. They were then spliced into the cable between each 37.5-n.m. section length so that continuous lengths of cable were built up into “Ocean Blocks” consisting of five repeater sections. The work of splicing in the repeaters is described in detail later. In these lengths the cable was loaded on board ship.
FIG. 8.—CABLE STORAGE TANKS AND THE TROUGHS CONTAINING THE FLEXIBLE REPEATERS.
Tests on Raw Materials.
Copper.—All copper wire and tape used in the cable was tested for resistance per unit length; the information obtained being given to the customer, the Company’s inspection team and to the production department concerned. It was found in certain cases that even the stringent tolerances required by the customer were inadequate to keep within established control limits, and that internal specifications had to be drawn up to even tighter limits.
An indication of the detail required was the specification of resistance measurements on the tinned copper binding wire used in making the safety spiral at joints.
Polythene and Polythene Compound.—Both the polythene resin and polythene compound, when ready for use, were tested for permittivity and power factor.
The measurements were normally made using the Hartshorn and Ward dielectric testing apparatus and for this purpose large numbers of moulded disks were required. Improved equipment was later brought into use but it is too early to state what effect this will have on the control of future production.
Tests of the Central Conductor.
Samples of completed central conductor were taken from each stranding machine at the beginning and end of each nm. Before the samples were cut it was necessary to solder the surrounding tapes to the central wire at the ends of the sample. These samples were tested for resistance, weight and dimensions, both of complete conductor and component parts. From an analysis of the results, it was possible to ascertain the behaviour of the forming dies and to predict when a die change would be necessary. The resistivity was calculated from the measurements to check that no measurable work-hardening of the copper had occurred.
Tests on the Core (Insulated Conductor).
For these tests the pans of core were flooded with water and measurements made of conductor resistance, capacitance and insulation resistance, after which a high-voltage test was made.
The acceptance limits for resistance and capacitance were ± 1.0 per cent and ± 0.4 per cent, respectively, but a closer capacitance tolerance was required, for matching purposes, when allocating lengths of core to a repeater section. The specification required the outputs of different extruders to be segregated into different groups, but it was found that the required degree of uniformity could be reached without the need for this grouping. The information obtained from these tests was used to help control all earlier stages of production and also in predicting the precise lengths of individual repeater sections.
Tests on Joints.
All joints in the cable were subjected to a high-voltage test of 120 kV, d.c., for 5 min. The operatives’ control and qualification joints were all similarly tested, but at 200 kV, and a selected number only at 500 kV. Practically all joints withstood this last figure, which is some 200 times greater than the maximum operating stress.
Tests on the Coaxial Pair.
When the outer conductor had been applied to the core the first transmission measurements could be made.
Measurements of insertion loss were made over the frequency range 6-200 kc/s, and the results indicated whether the section length prediction had been made accurately. The results were adjusted to sea-bottom temperature and compared with the design characteristics for purposes of quality control.
The pulse echo response was measured and photographed to provide a permanent record. The position and magnitude of the worst echoes were examined and compared with the records covering the assembly of core into the section.
Finally, a complete series of direct-current tests was made, finishing with a high-voltage test on the complete section, and then, subject to satisfactory results, the section was released for armouring.
Tests on the Armoured Cable.
After armouring, the tests made on the coaxial pair were repeated to test the cable’s stability with time, and additional transmission tests were made to assess the temperature coefficient of attenuation.
Some measurements of input impedance were made on selected sections up to frequencies well beyond the transmission range used in the transatlantic system, to provide data for future cables.
Tests on Repeaters and Ocean Blocks.
The repeaters were not in this instance the responsibility of the Company, but all repeaters received at the works were energized and tested at the works by the customer, the Company providing the special test leads needed and assisting in the tests where required.
After the repeaters and cable had been spliced to form ocean blocks, transmission measurements were made. The equipment used to feed power into the cable was actually one of the spare units that was eventually installed at the Oban terminal; a special test room was allocated for this equipment.
Tests While Loading Cable into “Monarch.”
While coiling the cable into the tanks on Monarch a continuous test voltage was applied to the cable so that if a fault of any kind had developed in any stage of the process it could have been detected and loading stopped immediately. The repeaters were energized and transmission signals fed over the cable so that the ship was in constant communication with the shore station at all times.
SPECIAL TESTING ARRANGEMENTS AND PLANT
The high order of accuracy required meant that special attention to the electrical testing arrangements was necessary. Most requirements were met by using existing methods with extensive refinement of detail but for other tests considerable elaboration of plant was needed.
Tests on Samples of Copper and Central Conductor.
The sample to be tested was tensioned between quick-release clamps, which served as current terminals, several pairs of differently shaped clamps being provided to cater for the various sizes of wire and tape. Two hardened-steel knife-edges were mounted on a base having a small coefficient of thermal expansion. The testing voltage was applied through the knife-edges, which made contact with the sample at points spaced exactly 3 ft apart. The sample was covered with a lid which, when closed, brought an open-scale thermometer in close proximity to the sample; this scale was viewed through a window provided for that purpose.
The tests were made on a precision Kelvin bridge, and a set of 4-terminal standard resistors with National Physical Laboratory calibration and covering the range of resistances measured were kept for checking purposes. Upwards of 100 samples per day have been tested on this apparatus.
The core under test was coiled in pans through which was circulated de-aerated salt water at constant temperature; the temperature of the water in the pans being measured by resistance thermometers embedded in the stack of core. For many years it had been known that air bubbles clinging to the core caused inconsistent test results and it had been the practice to treat the core with a wetting agent to assist in reducing the effect. More than two years before the contract for the transatlantic telephone cable was signed experiments were undertaken to find more efficient ways of eliminating the air. Mechanical vibration of the container was tried as well as ultrasonic vibration of the water, with only partial success. Finally the method of de-aeration now in use was recommended, although it could not be tried out until production at the new works had begun. In operation, water from a storage tank is fed to a column where it is subjected to low-temperature boiling and condensation before being fed to the pans of core. A complex heat-exchange system ensures constancy of temperature of the outgoing water and provides high thermal efficiency. The conductivity of the water is increased by adding sodium chloride until the specific gravity is approximately 1.01.
The conductor resistance was measured on a 5-dial Wheatstone bridge. To obtain the utmost accuracy possible, the bridge was checked at intervals of approximately one week against a 5-dial precision resistance-box. Both the bridge and the resistance-box have National Physical Laboratory calibrations. During the period of nearly two years that these checks were made, no significant changes in the bridge were measured.
The capacitance of the core was measured on a substitution bridge using a frequency of 21 c/s. The reason for the choice of this frequency is that a low frequency is needed to eliminate propagation effects (that is, the input admittance should not be modified by series impedance) and it was thought desirable to avoid frequencies that were submultiples of power mains frequencies in either the United Kingdom or North America (i.e. 15, 20, 25, 30 c/s, etc.). The choice of 21 c/s appears to be satisfactory although it was realized that at 21 c/s the mica capacitance standards would exhibit significant dielectric absorption and that it was thus necessary to obtain instruments especially calibrated at this frequency. A system of checking similar to that employed for resistance was used and, in addition, a standard capacitor was sent over from the Bell Telephone Laboratories as a cross-check.
During production of an earlier cable (the Aberdeen–Bergen cable) at Greenwich it had been found that the longer lengths of core appeared to be systematically higher in capacitance than shorter lengths. Calculations were made to show that this was not due to the normal propagation effects and it was found that it was due to insufficient conductivity of the water return path, permitting turn-to-turn inductance to appear. This can be demonstrated readily by testing two parts of a coil so that the inductance terms firstly aid and secondly oppose each other. The magnitude of the effect is such that the capacitance of a 6 n.m. length is measured approximately 0.2 per cent higher than its true value. It is interesting to note that this turn-to-turn inductance, which has been termed “coil inductance” to distinguish it from the normal coaxial core inductance, is shunted by the water return path. Water has a relatively high permittivity and it is thus advantageous to increase the testing frequency in order to reduce this “length” effect. Too great an increase cannot be tolerated for the reasons stated previously and it appears that a testing frequency of about 100 c/s would be the optimum.
For the high-voltage tests made at every stage of manufacture after that of extrusion, four separate sets of apparatus provided the necessary facilities.
200-kV set.—The 200-kV supply was provided by a voltage-doubling rectifier set capable of producing continuously up to 200 kV of either polarity at a current of 10 mA. It was used for testing core in pans, testing joints and testing completed coaxial pair sections. It was necessary to enclose four areas in the factory with safety fences; all the entrances to these areas were brought into a complex interlocking system so that any one area could be isolated as required. High-voltage test leads ran from the set to each area, and a swinging insulated arm, about 8 ft long, selected the test lead and connected the required set of interlocks into circuit while excluding those of other areas. An elevated control platform provided the operator with a view of the area under test.
600-kV set.—The 600-kV set was a rectifying set using a Cockroft-Walton ladder network capable of giving over 600 kV continuously. It was used solely for testing control joints and therefore was situated in an area not interconnected with the factory.
55-kV sets.—Two 55-kV sets were available, one being normally in use in the tank house for testing completed sections of armoured cable. The second was used as a standby and also on board ship when required.
Transmission Testing Equipment.
The attenuation and pulse echo testing apparatus was supplied by the Bell Telephone Laboratories and the Post Office, and the transmission tests are dealt with elsewhere*.
*1.LEBERT, A. W., FISCHER, H. B., and BISKEBORN, M. C. Cable Design and Manufacture for the Transatlantic Submarine Cable System. (In this issue of the P.O.E.E.J.)
The Tank House.
The special features of the cable-storage-tank house are the totally enclosed building and the water-circulating system. The extent of the system is indicated by the fact that each tank has 60 inlets of 3 in. diameter, spaced over the whole of the tank wall, through which water was pumped continuously when testing was in progress.
Resistance thermometers were buried between flakes of cable and wired in groups of 30 to the measuring positions. Just before shipping the main lay of cable, over 200 thermometers were in use. It was possible with this installation to determine cable temperature to 0.5°F or better.
Measurement of Cable Length.
Most of the electrical measurements made were converted to a standard length for quality control purposes and a stringent requirement was made on the accuracy of measurement of length. Units were available that gave the required accuracy provided they were maintained and adjusted. All units were therefore checked at intervals of approximately one month against a length of core reserved for this purpose. At each test the standard length of core was compared with an Invar tape standard.
Before production was commenced, measurements were made of the temperature coefficient of extension of the core and of its load-elongation characteristics. Provided that the temperature was kept within reasonable limits it was not necessary to apply a correction to the length. Care was taken to ensure that the tension in the core was sufficiently small to prevent length correction on this account becoming necessary.
HANDLING AND SPLICING THE FLEXIBLE REPEATERS
Transport and Storage.
The flexible repeaters for use in the main cable were produced in a specially designed and equipped factory in New Jersey, U.S.A., under conditions of the most extreme cleanliness and rigid inspection. The repeaters, together with the tail cables at each end, had an overall length of about 150 ft. They were packed in elaborately designed containers and flown from Newark, New Jersey, to London in specially converted aircraft.
Because of their sensitivity to damage by mechanical shock each repeater casing carried a recording impactograph. This was read and reset at each stage of the journey from New Jersey, U.S.A., to Ocean Works at Erith, so that a detailed record was obtained of all movements during transit. Subsequently, after removal of the repeater from its case, the strictest possible control of all movement was maintained at all times.
It was specified that, up to the time of storage in the ship’s cable tanks, the repeater with its tails must at no time be bent to a curvature exceeding that corresponding to a radius of 100 ft, over a length of 14½ ft on each side of the central point. This meant that a length of 29 ft had to be kept rigid within ± 1 ft, which necessitated the use of a securely lashed splint over this whole length.
Repeaters had to be protected against variation in ambient temperature outside the range + 20°F to 120°F and the central section of an energized repeater could not be allowed to exceed a temperature of 85°F. These temperatures were controlled by circulating water through the troughs in which the repeaters were stored before and after splicing into the cable.
The Company’s responsibility for handling the repeaters commenced the moment they arrived at the works from London Airport in the specially converted covered trailer.
The cases were carefully unloaded on to rubber-tyred trucks and wheeled into the tank house. Here the repeaters were uncrated and lifted by means of a spreader bar and a small overhead crane on to specially constructed stands where the splints were attached. Identification checks had to be made on either end of each repeater to ensure that the input and output ends were correctly orientated before lifting it into its resting place in the temperature-controlled troughs (Fig. 8).
Jointing and Splicing the Repeaters into the Cable.
The jointing and splicing of a cable section end to a repeater tail called for as much care and almost as much precision in the preparatory stages as during the actual operation.
The required repeater, still securely lashed to its splint, was lifted from its trough, gently lowered to ground level and brought to rest in wooden stands with its cable tail exposed ready to receive the end of the cable section.
In the case of the deep-sea (type D) cable, the 24 impregnated-cotton-taped 0.086-in. diameter high-tensile galvanized steel armouring wires and the 28 similar wires on the repeater tail were unlaid for distances of 10 ft and 45 ft, respectively. During this operation the original lay and sequence of the armouring wires was retained by means of a series of lay plates, two of which can be seen in Fig. 9.
A 4-ft length of the exposed copper-taped core was cut from the cable end and a 40 ft length similarly cut from the repeater tail, leaving the unlaid armour wires in each case uncut.
The unwinding of the jute bedding from the cable end and the five layers of glass-fibre tape from the repeater tail exposed in both cases the compounded-fabric tape which covers the copper barrier tape. Both these tapes were removed from their respective ends, the barrier tape being cut off but the fabric tape coiled back for re-use later.
The next operation, the unlaying of the six copper outer-conductor tapes, necessitated much care and skilful handling to ensure that the lay and form were retained with such a soft and malleable material.
Special retaining clamps were applied over the copper tapes at the positions where the unlaying terminated in order to prevent the possibility of any slackening in those portions still remaining intact on the insulated core.
The core jointing was then carried out exactly as described in the section on cable manufacture; the inner conductor ends being brazed and the insulation restored by injection moulding.
The copper outer-conductor tapes were restored to the original form and position which they occupied on the core as manufactured, and each tape was cut to a length which allowed a slight overlap but ensured that, when brazed to its partner, no undue difference in tension would exist between any of the six tapes. A bight was then made in the jointed insulated core and each corresponding pair of tapes brazed together. The six tapes were then carefully worked back into position on the core and formed down to a snug fit.
A new length of copper barrier tape was then applied, the impregnated-fabric tape restored, and the jute yarns and glass-fibre tape replaced, thus reforming the bedding for the armouring wires.
A carefully controlled tension was applied to the joint during the re-armouring and splicing operations. The 24 unlaid armouring wires of the cable end were then laid back over the jute-served coaxial core, with their original lay and sequence, by the skilful manipulation of lay plates (Fig. 9). The wires were then “chased” down on to the bedding so that the diameter was reduced as nearly as possible to its original size, temporary bindings of spun yarn being applied to retain the wires in position. Protective lappings were then applied to the exposed portion of the repeater tail and the 28 armouring wires similarly restored to their original positions and continued to overlay those of the cable end, thus effecting an overlap of something like 40 ft in length. A gradual reduction in the diameter over the armouring wires from the repeater to the cable proper was then brought about by “building up” with special impregnated tape over which a closely laid spun yarn was applied and the splice was finished with several coats of asphaltic “slushing compound.”
FIG. 9.—THE USE OF LAY PLATES FOR REPLACING ARMOURING WIRES AFTER JOINTING.
The splicing of repeaters into types “A” and “B” cable called for some difference in procedure and technique from that described above for type “D” cable. For example, when splicing type “A” cable, the heavier armouring wires, 0.300 in. in diameter, were arranged to overlap those of the repeater tail. This involved the difficult task of unlaying these heavier wires for a length of over 50 ft whilst preserving their original lay. Any distortion of these wires would have resulted in undue and inconsistent gaps between the wires after restoration, thus complicating the introduction of the “filler” wires. These “filler” wires were incorporated in the original armouring in order to build up the diameter of the cable and thus produce the gradual taper required.
Much could be written about the care and skill required to comply with the Bell Telephone Laboratories’ exacting specification for this work; happily, however, the jointing and splicing teams of Submarine Cables, Ltd., were equal to the task and achieved results to the complete satisfaction of the Company’s own and the customer’s inspectorate. Breaking-strain tests carried out on specimen splices of the three different types have shown that the spliced portion is in all cases at least as strong as the original cable.
Shipping the Cable and Repeaters.
Shipping the cable with the repeaters inserted at positions approximately 37.5 n.m. apart presented a completely new set of problems.
The comparatively short length of each section of cable not only greatly increased the number of cable ends to be accommodated during storage, but each end, after splicing to the repeater, became a long bight containing the repeater splice, which proved difficult to stow in its correct position for shipping.
Sufficient was known at an early date to design a tank house to meet all requirements and it was with considerable interest that the Company received a dummy repeater for trials. With this repeater it was possible to prove the shipping and handling technique and train personnel in all operations.
The first real repeater was received in May, 1955, and the job of splicing this into its position in the cable was tackled with a considerable degree of confidence, although at the time some 40 to 50 cable ends were arrayed in the tank house, as cable manufacture had progressed in advance of repeater deliveries.
Owing to the requirements for transmission tests on each repeater section, alternate section lengths of cable were coiled into a pair of tanks. This meant that alternate repeaters faced the wrong direction for direct shipping, and, therefore, during the course of paying out through the shipping spans via the mid-stream tower to the ship, every other repeater had to be turned through 180°.
Communication between the ship and shore was very critical owing to the tank changes and re-orientation of repeaters for shipping, but, by using throat microphones, communication from winchmen on board ship to the tank house was possible and movement was kept under complete control. Emergency switches were at hand if at any time the microphones failed to function.
When a 37.5-n.m. section of cable had been loaded into the 41-ft diameter tanks on the cable ship, the splinted repeater was lowered into the tank using a specially designed shute which enabled the repeater to be kept as rigid as possible during the whole operation. The splints were then removed from the repeater and the repeater positioned against the inside wall of the tank, shoring being used to keep the central portion straight. Shipment was then continued until the next repeater reached the ship, when the repeater storage operation was repeated.
Now that the cables—the longest submarine telephone cables in history—have been successfully laid and the first transatlantic telephone cable system has been inaugurated, Submarine Cables, Ltd., can look back upon the events of the past 2½ years with infinite satisfaction. The momentous decision to acquire the derelict factory site at Erith, the planning and erection of new buildings, the provision and installation of plant and machinery costing over 1,000,000, the training of personnel, the production of 4,200 n.m. of repeatered telephone cable to a specification of Draconian severity and the shipment of that cable on board H.M.T.S. Monarch in so short a period of time, seem almost unbelievable. But it is now an historic fact that, in spite of many difficulties and setbacks, this triumph of engineering skill was achieved just within the time limit laid down in the contract. It indeed reflects great credit on all concerned at Ocean Works where team work and long hours of hard labour have brought their just rewards. Without this sustained effort, the cable could not have been completed on schedule.
The author wishes to acknowledge with thanks the permission of Submarine Cables, Ltd., to publish this article and also to express his sincere thanks for all the assistance received from colleagues within the Company in the preparation and compilation of this article.
Conductor.—Centre copper wire 0.1318 in. ± 0.0002 in. diameter surrounded by three copper tapes 0.148 in. ± 0.001 X 0.015 in. + 0.0007 in. helically applied with a lay of 2.5 in.
Insulant.—Polythene compound containing 5 per cent butyl rubber extruded to 0.621 in. ± 0.003 in. diameter.
Return Conductor.—Six copper tapes 0.320 in. ± 0.002 in. X 0.016 in. ± 0.0005 in. helically applied with a lay of 11.75 in.
Binder and Barrier tapes.—Copper tape 1.75 in. x 0.003 in. applied with overlap. Compounded fabric tape 1.375 in. X 0.010 in. applied with small gap.
For Type D (deep sea) Cable.
Inner serving.—Single layer of jute rove impregnated with cutch preservative.
Armour.—24/0•086-in. high-tensile galvanized steel wires. (Each wire lapped with impregnated cotton tape.)
Outer serving.—Two layers of tarred jute yarn fully impregnated with compound under, between and over each layer. Overall diameter 1.21 in.
For Type B (intermediate) Cable.
Inner serving.—Layers of jute rove impregnated with cutch preservative.
Armour.—18/0.165-in. galvanized mild steel wire.
Outer serving.—Two layers of tarred jute yarn fully impregnated with compound under, between and over each layer. Overall diameter 1.40 in.
For Type A (shore end) Cable.
Inner serving.—Two layers of jute rove impregnated with cutch preservative.
Armour.—12/0.300-in. galvanized mild steel wire.
Outer serving.—Two layers of -tarred jute yarn fully impregnated with compound under, between and over each layer. Overall diameter 1.84 in.
The following photographs of TAT-1 cable sections and a repeater vacuum tube are courtesy of and copyright © 2016 Bell Canada Historical Collection. The cable sections are Type D deep sea - see specification above.
Last revised: 24 December, 2019