Many of the coral islands in the Pacific and Indian Oceans contain valuable deposits of phosphate. On Christmas Island, Nauru and Ocean Island engineers have built special plant which facilitates the speedy loading of ships in difficult conditions
CALM WEATHER AND LOW TIDE at Nauru. A steamer is being loaded with phosphate in her forward and after holds by the two pivoted cantilever arms in which belt conveyers are installed. On either side are the lattice towers to which the cantilever loading arms are firmly secured in a strong wind. At high tide the foreshore is covered by water.
FICTION, generally highly coloured, dealing with the islands of the Pacific, no doubt gives rise to visions of palm trees, beachcombers, hibiscus wreaths and ukuleles. No thought of the engineer and his work intrudes on these romantic dreams. In more than one of these islands, however, the engineer has taken great pains to make it possible to tap their amazing wealth, hidden for ages, so that it shall be available for countries less favoured by Nature.
Two such islands are to be found in the central Pacific, almost on the Equator. One, the island of Nauru, has an area of 5,400 acres and lies about 500 miles north-north-east of the Solomon Islands and more than 2,000 miles from Sydney. The other, Ocean Island, is situated about 160 miles east of Nauru and has a circumference of six miles. Both islands are low, the highest point of Nauru being only 250 feet above sea level and the highest point of Ocean Island about 300 feet above sea level.
The wealth they contain consists not of copra, beche-de-mer or pearls, but of phosphate - that necessity for the agriculturist in the less sunny regions of the earth. Plants require about thirteen elements for their growth, and of these, nitrogen, potassium and phosphorus are the most important.
This process produces acid calcium phosphate and calcium sulphate, and the mixture was called “superphosphate”, a name by which it is still known. Later it was discovered that certain rocks contained calcium phosphate and nowadays nearly all the superphosphate is manufactured from this. The mineral is mined chiefly in French North Africa and America, but the softer deposits discovered in the Pacific Islands are a much purer form.
Besides Nauru and Ocean Island in the Pacific, there is another island, rich in phosphate, in the Indian Ocean. This is Christmas Island, some 200 miles south of the west end of Java. Christmas Island is about twelve miles long and about nine miles wide. It should not be confused with the island of the same name discovered by Captain Cook in the Pacific. All three islands are of coral formation and belong or are mandated to the British Empire, Ocean Island and Christmas Island for a considerable time past, Nauru since November 1914.
Before that date Nauru belonged to Germany, but it was assigned under a mandate to Great Britain, Australia and New Zealand at the Peace Conference. The phosphate is not all exported to Great Britain. The Nauru Agreement Act of 1919 laid down that the phosphate was to be divided between Great Britain, Australia and New Zealand in the proportion 42, 42 and 16 respectively. These quantities were assigned on the understanding that the phosphate was for internal consumption only, that is, it was to be used solely for agricultural purposes by the participating country and none of it was to be exported from that country, or from the islands, to any other country.
The phosphate deposit of all three islands is rich, being probably better than most of the other deposits contributing to the world’s supply. The Christmas Island deposit contains 80 per cent of tricalcic phosphate, that of Nauru nearly 86 per cent and that of Ocean Island about 89 per cent. The phosphate fields are also extensive. In Nauru and Ocean Island there is estimated to be a total of 100,000,000 tons available.
Scientists have, up to the present, been unable to-agree as to the manner in which these rich and enormous deposits have been formed. The explanation most generally accepted is that the islands at some time in the remote past were for long the resort of myriads of birds which left guano behind. Rain washed the guano into the soft coral rock, and volcanic action in far-off ages appears to have completely submerged the islands on several occasions. On their last reappearance the islands were left with almost pure phosphate of lime, the impurities having been dissolved away.
One objection to this theory is that the islands are nowadays seldom, if ever, visited by birds, though their absence does not really disprove the theory. But the question of how the phosphate got there does not affect that of its removal, which falls into two divisions: first, how it is extracted; and second, how it is removed from the island.
Removal of the Overburden
Excavation is a simple matter. An area having been selected for working, the trees on it are first felled and the undergrowth piled up and left to wither for three or four days. These piles are then burned, bonfire fashion. The next step is stripping the overburden. This expression is used in all kinds of quarrying and mining operations in which the material to be extracted is covered with a layer of unrelated stuff. The overburden in this instance consists of a soil supporting coarse grass and changing gradually into the phosphate deposit as the depth increases. The lower part of the overburden is normally discoloured by the action of the weather on the grass. As a rule the overburden has to be removed to a depth of about one foot.
The stripped field is now ready for working, but the phosphate, though it averages 30 feet in depth, is not in a uniform layer. Instead, it is pierced by numerous pinnacles of hard coral. A worked-out field presents a curious appearance, as the pockets between the pinnacles are cleared out as far as economically worth while. The phosphate has occasionally to be loosened by blasting, but generally a hand pick is sufficient.
HEAVY SURF BREAKING OVER THE REEF almost continuously at Nauru made extremely difficult the building of the massive concrete piers for the cantilever arms of the loading plant. Each of the piers contains 335 tons of reinforced concrete; the piers are firmly attached to the coral rock by heavy steel grids embedded in the concrete and held down by steel bolts.
The loose stuff is filled into baskets, which are then emptied into skips running on light temporary rails. The quarrying is done by native labour, though in Nauru and Ocean Island the indigenous population is small and has to be reinforced by immigrants, normally Chinese coolies or natives from the Gilbert Islands. Supervision is effected by white men of various nationalities The phosphate rock is clean and thus in contrast to that found in other areas, does not require washing. It contains, however, a certain amount of moisture and, as it would be foolish to use ships to carry unnecessary water, this has to be got rid of by drying. The trains of skips on the fields are drawn by locomotives to the drying plant. Here the phosphate is first crushed to break up the large lumps, which are reduced to pieces about the size of a cricket ball. The greater part is already in a condition resembling gravel. The crushed phosphate is dried artificially so that it finally contains only 3 per cent to 4 per cent of moisture. In this condition it weighs about 95 lb. a cubic foot. Storage in large bins follows until an opportunity occurs for loading it into the transporting ships.
It was the loading part of the operations that presented great difficulties until the engineer took a hand. These islands, being largely of coral formation, lying in the ocean, are exposed. Nauru may be taken as an example. It rises steeply from the foreshore to a height of about 250 feet and is surrounded by a reef of an average width of 400 feet. Dry at low tide, this reef is covered at high water to a depth of about 6 feet.
At the sea edge the reef drops steeply into deep water of from 120 fathoms to 180 fathoms. It is believed that the reef overhangs, and that the island is thus roughly of the shape of a huge mushroom. There is a strong undertow, or backward flow under the breakers.
Frequent, Heavy Seas
In calm weather the conditions are not bad, but sudden and violent changes are liable to occur, and even a swell from a distant disturbance causes a heavy surf at the reef edge. During the bad weather period, from about the middle of November to about the middle of March, there are frequent heavy seas.
These conditions, coupled with the fact that there are no harbours or proper anchorages, make it easy to realize that that coast is looked upon with misgiving by shipmasters. The loading difficulties were formidable in the past.
Captain Joseph Clarke, who went to the islands in 1908 with electric generating sets driven by oil engines for working the crushing and other plant, states that, at that time, the shipping arrangements consisted of wooden jetties down which the phosphate was run in small hand-propelled trams and shot into small lighters holding about 2¼ tons each.
The jetties extended only to the edge of the reef, and the lighters had to hang on under the chutes by ropes, a highly dangerous proceeding in anything of a sea. Then the lighters had to be rowed out to the ship and the phosphate hoisted on board in baskets. The ship could not lie close to the reef but had to be moored by buoys held by ground tackle a good distance from the land. No ship was allowed to lie at the moorings unless she had steam up ready to proceed to sea directly she was signalled from the shore.
If bad weather were to occur, a ship might have to get out to sea only partly loaded and might have to hang about in this condition for a fortnight or more. This meant heavy demurrage (payment for delay), and there might be as many as five or six ships waiting to load, coming in every morning, asking whether they could work and being sent off to sea again.
After a number of improvements had been made, Captain Clarke drew up a scheme for a cantilever loader projecting 500 feet beyond the edge of the reef so that the phosphate could be discharged directly into the ship’s hold. At the same time the ship would be free to swing round her moorings and be well clear of the reef edge. This scheme, though not proceeded with at the time, may be said to have been the germ from which the present effective plant has been evolved.
THE HUGE STORAGE BIN in course of construction on Nauru. The bin holds 12,000 tons of phosphate. It is filled from a conveyer belt high up in the centre of the roof and is emptied through doors in the bottom, which discharge on to a conveyer belt running
underneath the bin.
In the new plant there are two cantilever arms, pivoted so that they can swing round in a horizontal plane. The phosphate is carried along these arms and dropped into the holds of the vessels through telescopic spouts. The ships, however, are not in a more secure position when loading up than they were formerly. They still have to keep steam up all the time and are tied to the buoys of the deep water moorings. Should a sudden squall arise, however, the spouts can be rapidly telescoped and the buoy hawsers disconnected, leaving the ship free to sail away.
The main improvement is that the vessels can now be loaded in all but the worst weather, and delivery can be made at the rate of 1,000 tons an hour when necessary. A ship can now haul in, tie up to the buoys, and be loaded in one day with a cargo of, say, 8,000 tons, compared with a possibility of several weeks in former conditions. The installation of the new plant not only greatly reduces the risk of heavy demurrage costs, but also simplifies working in other ways. The fleet of lighters is no longer required. These needed maintenance, and though they could be kept tied to buoys in calm weather, they had all to be hauled up on a slipway on shore if a gale threatened.
The principal aim in laying out the loading plant at Nauru was to get the pivots, round which the cantilever arms swing, as close to the seaward edge of the reef as possible. This meant the building, in difficult conditions, of two heavy piers of concrete for each arm. The reef was clear of water for short intervals at low tide, and then only when there was little swell. Much of the work had to be done when the reef was awash, and it was possible, in any event, at comparatively infrequent intervals only. Working in the water in the tropics does not sound trying but, as the sea was infested with small marine creatures, any slight scratch was a source of infection and in many instances the men suffered considerably. Some of them had to be sent away for a change until they recovered.
The upper part of the reef was of fairly solid coral rock which was at first levelled in way of the site selected for the piers. Each of these is about 40 feet long and 11 ft. 6 in. wide at the base. The tops are about 15 feet above water level. The piers are 28 feet apart from centre to centre, and are connected at the base by a reinforced concrete raft and at the top by steel girders 4 ft. 6 in. deep. Each pier contains 335 tons of reinforced concrete, and in addition to the reinforcement a heavy steel grid is embedded in the concrete near the base. These grids are held down by a number of steel bolts penetrating to a depth of 8 feet in the coral rock, which was drilled out to receive them. Upwards from the grids other steel bolts pass through the piers to hold down the top cross-connexion girders. To lessen wave action, the ends of the piers are shaped in the same way as the bows of a boat.
In addition to the cantilever piers at the edge of the reef, a number of smaller piers had to be built farther inshore to carry different parts of the structure. Four of these carry two lattice towers which appear to have no function. They are, on the contrary, of great importance in heavy weather. The cantilever arms present an immense area to the wind which, on occasion, may attain a velocity as high as sixty miles an hour. It is impossible then to leave them in the loading position as they might be blown round, to the ruin of the slewing machinery. On the approach of heavy weather, the cantilever arms are swung round shorewards until they touch the lattice towers, to which they are securely moored.
The cantilevers are deep-braced girders measuring 172 feet from the centre of the pivot to the end, but inside each is a conveyer boom from which the delivery spout is suspended. This boom can be pushed out for 30 feet when necessary so that the total outreach available is 202 feet. As there are two arms which can be slewed into any position and as the outreach of the boom can be varied, all the holds of a ship can be reached without the necessity of altering her position. This arrangement speeds up the loading operation. The delivery spouts being telescopic, their length can be adjusted to suit the differences in level caused by the state of the tide, the height of the load in the holds as they fill and the sinking of the ship as the load increases.
The cantilever arms are balanced, the girders being extended to the rear of the pivot and provided with a counterweight at this end. The weight of the whole mass, 560 tons, is carried on forty-eight cast steel rollers, each of 10-in. mean diameter and 18 in. long, running on a circular path 28 feet in diameter. Outside the roller track is a toothed rack of cast steel, with which mesh two pinions that are geared to the slewing motor.
TELESCOPIC DELIVERY SPOUTS lead from the conveyer belt on the extending booms of the cantilever loading arms at Nauru into the holds of the vessel being loaded. The ship in the picture is the Nauru Chief, a vessel of 2,934 tons gross, owned by the British
The rack is fixed to the massive foundation structure on top of the piers and the pinions are carried in the base of the cantilever arm. As they are turned by the motor they travel round the rack and so slew the arm into the required position. Slewing can be carried out at the rate of one complete revolution in twelve minutes, although the arms never make a complete revolution. This rate may seem slow, but it means that the outer end of the boom when fully extended can travel at the rate of about 53 feet a minute, which is quite fast enough for such operations as changing position to another hatch.
The slewing motor is of 30 horsepower. A complete duplicate set of driving gear is fitted as a standby, and brakes and electrical safety devices are provided to prevent overrunning of the arms. The driving gear is situated in a house inside the cantilever immediately over the pivot. The main controls, however, are situated in a small cabin at the seaward end of each arm, so that the operator has full view of the delivery spouts.
After having passed through the rotary dryers, which are situated in a house some distance inland from the loading plant, the phosphate is taken, at the rate of 120 tons an hour, on a travelling belt conveyer about 1,000 feet long to a hopper holding 80 tons. Here the phosphate is automatically weighed and the weight recorded. Another conveyer delivers the phosphate to the junction house and deposits it on to a third conveyer, which is 2,000 feet long and runs in timber and steel framed gantries to the top of a huge storage bin situated on the shore.
The bin is 240 feet long and 39 feet wide at the top of the sloping plates forming the bottom. It holds, when full, no less than 12,000 tons of phosphate. The bin is necessary to provide storage so that work in the fields is not held up should stormy weather prevent ships approaching the loading plant. The filling conveyer is situated high up in the roof and runs the full length of the bin. It has a capacity of 190 tons an hour. The phosphate can be thrown off the belt by a travelling carriage at any point desired.
In a tunnel running along the centre of the bin is a discharging conveyer. The narrow strip at the bottom where the slopes converge is perforated, having a number of openings normally closed by doors. When the phosphate is to be removed from the bin the doors are opened as necessary and the phosphate falls on the conveyers to be run up to the top of, and discharged into, a circular hopper.
This has a capacity of 250 tons and is known as a compensating hopper. Its function is to make the flow to the loading arms controllable. From the bottom of the hopper two diverging conveyers carry the phosphate up to a point above the pivots of the cantilever arms and there discharge it on to further belts which take it along the the cantilever arms and booms for delivery down the spouts to the vessel’s holds. Either set of conveyers can be used alone or both can be used together.
At the base of the diverging conveyer galleries are automatic weighing machines. A reinforced concrete gallery runs from near the storage bin to the base of the compensating hopper. On this a 2-feet gauge railway enables trucks capable of carrying a weight of 5 tons to be run, so that new belting and the like can be taken to the loading plant. Numerous motors are required to drive the different belts, and all, from the storage bins seaward, are under the control of the operators in the cabins at the ends of the arms. At the same time push buttons are provided at various points so that all the conveyers can be stopped instantly in an emergency, for if one belt stopped, say, through the blowing of a motor fuse, the phosphate would pile up on to it from the moving belt behind it.
AT CHRISTMAS ISLAND, in the Indian Ocean, phosphate is loaded into ships that lie in deep water close to the end of a pier which is 150 feet long and 24 feet wide. The phosphate is carried along the pier by a conveyer belt and discharged from a spout at the end of a swivelling and luffing boom. The vessel in the picture is a Japanese ship, the Karafuto Maru, of 5,447 tons gross.
The loading plant at Ocean Island is not nearly so large as that at Nauru and does not enable ships to be loaded directly. The phosphate is delivered into boats which have to be rowed out to the vessel lying at a safe distance from the edge of the reef, which is serrated and broken by deep channels.
The condition of the reef made a similar construction to that at Nauru impossible as it would have been so much more costly. The seaward edge of the reef shelves at an angle of forty-five degrees for a distance of about 100 feet and then drops sheer downwards. This is a contour conducive to the formation of heavy surf, and it is dangerous for ships to lie close into the reef in anything but calm weather. Several ships were wrecked in the early days, and on one occasion a 7,000-tons vessel was lifted bodily on to the reef.
Work was difficult on the foundations for the piers of the cantilever jetty which was erected. Even for the inshore foundations operations were possible only at low water and a cofferdam had to be built. This, however, afforded little protection. After every tide the excavation had to cleared of pebbles washed in by the continuous surf. The coral had to be blasted out to a depth of about 3 feet. This is not a deep excavation in ordinary circumstances, but in this instance, as only small charges of explosive could be used because of the danger of fracturing the reef, it proved a long and arduous task.
The building of the seaward piers on the edge of the reef was even more troublesome. The surf was so strong that even at low water it was often impossible for a man to stand unaided. There were two great fissures in the reef, one on either side of the foundation site. These were filled by dropping in 4-feet cubes of concrete. The spaces between were then packed with concrete in small linen bags bonded together by iron spikes.
Aid of Surf Boats
The blasting for the foundations had to be done before the fissures were filled in and the work was slow and dangerous. It was completed, however, without serious accident, until the surf took its toll at the end in a tragic fashion. The engineer-in-charge, having finished his work satisfactorily, was waiting to board the ship for England, when some runaway railway trucks knocked him and an employee of the British Phosphate Commissioners into the sea.
The erection of the steel work was fairly straightforward. The loading jetty is about 300 feet long. It resembles a girder bridge with a central pier and with the bank which should have supported one arm missing. This arm is, however, a stiff cantilever with its end projecting over the edge of the reef, which it does for about 120 feet. Along the deck of the jetty is a belt conveyer which runs at the rate of 350 feet a minute and deposits the phosphate into a hopper, from which it is delivered down a spout into baskets in the lighters hanging on below. Light railway lines run alongside the conveyer belt, which is housed in a covered gallery.
THROUGH A FOREST OF PALMS at Nauru an apparently interminable belt conveyer brings the phosphate from the drying plant to the storage bin. There the phosphate is stored until a ship comes in. Then phosphate is carried from the bin by further belt conveyers on to the cantilever loading arms.
The lighters are towed out to the ship by motor boats and the baskets hoisted on board and emptied into the holds. The installation has greatly improved the loading conditions at Ocean Island, and it is now possible to speed up the shipping with surf boats, so that frequently vessels carrying 8,500 tons are loaded in three or four days. The installations at Nauru and Ocean Island were carried out by a British firm, Henry Simon, Ltd., for the British Phosphate Commissioners.
The installation at Christmas Island in the Indian Ocean is of different construction from the others and replaces a jetty which was completely washed away in 1932. There were two of these jetties, and one remains at a distance of about 230 feet from the new one, so that both can be used simultaneously for loading. As at the Pacific islands, the vessels cannot be brought alongside the pier, though at Christmas Island they can lie about 20 feet away. The island is exposed to storms having the nature of a heavy swell rather than of a gale. In the storm which swept away the old jetty the wind velocity did not exceed twenty-five miles an hour, though the waves reached a height of 30 feet, a condition pointing to severe disturbance elsewhere.
The chief distinction between this plant and the other installations lies in the structure carrying the conveyer belt. At Christmas Island the reef dips more gradually into the sea and it was possible to erect a jetty of the type seen in the familiar seaside pier. The vertical members consist of tubular piles, of 10 in. diameter, which go down about 5 feet into the coral. At the head of the jetty the water is about 33 feet deep at low tide and, as the vessels lie another 20 feet seaward, there is plenty of clearance even when they are loaded. The vertical members are connected by diagonal tubular bracing of 8-in. diameter, and the jetty, which is 150 feet long and 24 feet wide, is finished with a strong deck at about 42 feet above low tide.
At the shore end of the jetty is a large storage bin, near which is the house containing the automatic weighing machine through which the conveyer belt passes. This belt goes under cover to the seaward end of the jetty and is 30 in. wide. It is supported at close intervals on what are called troughing idlers - that is, sets of five rollers mounted on ball bearings and arranged in crescent form so that the belt is turned up at the edges and the phosphate cannot spill over. The belt runs at the rate of 400 feet a minute, and at this speed will transport 300 tons of phosphate an hour.
The conveyer head pulley is situated in a steel tower at the end of the jetty, and the phosphate is discharged down a chute on to a conveyer belt carried in a movable boom, at the outer end of which is the delivery spout to the hold of the vessel. The boom is moved by wire ropes operated from a winch situated in the tower, in a manner somewhat similar to the jib of a crane. The boom is 55 feet long and can be slewed through an angle of about 100 degrees. This means that the spout can be moved laterally for a distance of about 87 feet. The boom can be luffed 10 degrees above and below its horizontal position so that the spout can be moved up or down through nearly 18 feet to suit the state of the tide, the degree of filling of the holds and the load line of the ship.
The boom winch is driven by a 20 horse-power motor and its conveyer by a 7½ horse-power motor. The operator is situated in a cabin at the top of the tower and has thus a good view of the ship’s holds. The remaining older jetty can also be used, so that a loading capacity totalling 600 tons an hour is available. The loading installation was designed by Sir Alexander Gibb for the Christmas Island Phosphate Company, Ltd., and British firms were again responsible for construction. Fraser and Chalmers Engineering Works supplied the machinery and Redpath Brown and Co., Ltd., the jetty material.
It may be that similar phosphate deposits are awaiting discovery in other lonely islands of the southern oceans. It must be a source of satisfaction to humane people to reflect that if this occurs the treasure can be recovered in enormous quantities without unceasing toil such as that which constituted the slave labour of the old days. The reflective man will also realize that it is modern engineering which has made possible enterprises such as these. The plant at Nauru, for instance, could scarcely be visualized as possible if steam-engines had been used to provide the power instead of the easily controlled electric motors. Apart from the great convenience of the motor, a steam drive would have involved the importation of large quantities of fuel. With the oil engine as the ally of the motor not so much fuel is required, and it is in a more easily handled form.
A comparison of the three methods of solving an almost identical problem shows what the engineer has to consider in planning a job. At Nauru a thorough scheme was possible at a reasonable outlay; but it was cost, and not technical difficulties, that limited the Ocean Island equipment. Again, as phosphate had been worked at Christmas Island, there was a considerable store of experience of local conditions to draw upon, absent in the other islands.