The World's Biggest Dock.

Pukekohe & Waiuku Times, Volume 4, Issue 26, 1 April 1915, Page 4 (Supplement)

The World's Biggest Dock.

ENGINEERING WONDERS OF THE MODERN DRY DOCK. The recent berthing of Great Britain's biggest liner, the Cunard steamer Acquitania, in 'die new Gladstone Dock at Live! pool, calls attention to the engineering wonders of this remarkable hospital for ships---for it is nothing else —and which can claim the unique distinction of being t!;e largest and finestequipped dock in tie world. The fact is, one hears very little about the triumphs of the dock engineer, ior the simple reason that these great basins, specially designed for cleaning and repairing ship*, are invariably tucked away out of sight up some river, and, not being picturesque in themselves, little h is been said of their romance, the difficulties encountered in their erection, the enormous strength of their walls, their rapid growth in point of size, their powerful pumps capable of discharging millions of gallons of water in an hour or two, and their strong gates. Then no two are exactly alike. This is due to the conditions under which the rock-builder has to work. In the first place he is not at liberty, like the ordinary engineer, more or less to select a suitabl■..» site for the erection of his edifice, nor is he free to utilise the site imposed upon him strictly in accordance with the ideals of pure science. Often the most convenient spot for a dock is a swampy and marshy ground. Then, for the' convenience of shipping, the dock must be placed in a certain position, or at a given angle, while it must also In. easy of access to a railway or a main road/ Then tides, depth of water, currents, the presence of shifting sand and mud, and a host of other factors have to be taken into consideration, whi.-li means that no two dock problems are soluable in the same way. KEEPING PACE WITH THE LINERS.

The new Gladstone Dock, which represents the last word in construction, is the only one at present that could accommodate the Aquitania, or the still bigger Germaa boats Imperator and Vaterland. With the exception of a floatiiig dock at Stettin, in Germany, all vessels over ',IOO feet in length needing repairs could only be berthed at Liverpool. It is the rapid increase in the length of our liners; that has made such a huge dock necessary. We get an idea of its immense size when it is stated that it is 1,050 feet long, 100 feet wide on the water-line, with an entrance width of 120 feet. It is closed by a sliding gate, or caisson, which alone turns the scale at 1,200 tons. To fill this' great basin to a depth of 45 feet over 44,000,000 gallons of water are needed, and every drop of this huge quantity can be pumped out in two-and-a-half hours. Naturally, when a vessel enters a dock she displaces the water in that dock in proportion to her ; ze. When the Aquitania was berthed she displaced such a great quantity that the remainder was pumped out in lesv than forty minutes. It is only after an inspection of the dock and a chat with the men who built it that one begins to realise its engineering wonders. It took nearly three years to construct and cost £568, 000. The first thing the builders did was to erect a great bank on the foreshore over a mile in length to keep back the water. This was built of rubble and concrete blocks, and occupied three months.. Then work on the actual dock site was commenced. First the earth, rock, and sand had to be excavated, and here it should be remembered that the dimensions of a dock by no means fully represent the amount of material that has to he removed. DIFFICULTIES OF THE DOCK ENGINEER.

If you dig a deep hole in your back garden in normally wet weather you will probably find, on reaching a depth of a few feet, that water begins to ooze through. If, therefore, you require a water-tight pit ot given dimensions, it will be necessary i > clear out an extra foot in all directions to allow for a cement or brick lining on five faces. Should your object be a pit very deep and dry, your difficulties will be increased by the external pressure of the water which may be roughly calculated at one pound for every two feet of depth below the top level of the water-bearing stratum, a very considerable force at any depth. I'he dock engineer has to contend with the same difficulties in an aggravated form through the presence of water in ground neai the sea. Hence he must r»move sufficient material to allow of the erection of thick walls and floor in addition to the mere dimensions of the dock. Otherwise, the walls will he bulged in by the earth pressure, and the walls and floors penetrated by water. We get an idea of the severity of this pressure of earth and water upon tin- walls and floors of docks when it is stated that it cost €68,000 to repair the wall- of a large dock in the north of England. Although built of concrete and lined' with granite, they were so badly clacked that the dock was rendered unserviceable. An expenditure of £30,000 was necessary upon the bottom of a recently-completed dock on the Tciie through penetration by water. ALL TO DKi A HOLE. What the excavation work at Liverpool meant is evidenced when it is stated that 1,500,000 cubic yards of earth, rock, and sand were removed. If this material had been taken out of level ground it would have resulted in a canal 350 miles leng. Although the greater portion was removed by manual labour by a small army of navvies, the "-team navvy" was also employed. In ibis way a huge hole much larger than tlie present dock was excavated on the Mersev shore. Indeed, it went down to a depth of 30 feet beyond the bottom of the dock and stretched over 100 feet beyond the present walls. Then came the task of lining it to make it waterproof. Thou-amis and thousands of tons of concrete were utilised for this purpose, Lacked by tons of hard filling. The tioor is of solid concrete six feet in thickness, through which no water could ever penetrate. This floor rests on huge underground chambers, used for curving off the water. The walls are built of concrete. At the bottom they have a width of 14$ feet, gradually tapering towards the top, where they are 4J feet wide. Immediately behind this wall of ma'-onry is a bed of hard filling, earth and rock well rammed down, and behind this again more hard earth and rock that should prove capable of withstanding any pressure. \n interesting factor about this new recepSacle for ship- is that it can be used as a graving dock and also as a wet dock. The former is only resorted to in- ships for scraping and repairing purposes, and the latter for unloading or for effecting repairs above the waterline The ordinary graving dock is lifted with a series of steps, or altars, down the wall sides to give support to the 'bores which bold the ship firmly ill position. Tt means that the dock is much narrower at the bottom than at the top. and it would be impossible tor a vess'<l to lie (lush along the quay on account of the projecting steps In a wet dock there are no steps, and ships can lie dose against the wall.

A DOOR 25 I'EET THICK. ' The walk of the Gladstone Dock arc broken by 2 projecting shelves to serve as altar-courses for the shores. The width at the bottom is 141 feet, and at the top 100 feet Access to the bottom o fthc dock and also to the shelvesis not obtained by steps down the wall tides, but by staircases carried down through the body 0 r the wall. The entrance is closed by a sliding door or caisson 1.32 feet long, 50 feet high, and do teet thick. It is built of steel girders and plates. It is provided with green-heart timber runners, and slides to and fro in a groove of polished granite. It is operated by two electric motors, and, despit" its great weight—--1,200 tons—can be instantly closed or opened.

More wonderful still is the manner in which the water is removed once a vessel is inside and the gate closed. On the south side of the dock, near the en-

trance, is a well, an immense chamber 126 feet long by 26 feet wide and 25 feet high from floor to roof. The water is led into this receptacle, whence it flows' into the river, by a series of suction pipes through two culverts placed below the floor of the dock. These culverts are RJ feet wide by 124 feet high. Naturally, to pump the water through these culverts into the well powerful machinery is required, and this consists of /iv sets of centrifugal pumps driven by oil engines of 5,000 horse-power. Thes-3 pumps are powerful enough to empty the dock of its whole contents, 44,000,000 gallons, in two and a half hours, but naturally the amount of water to be removed would depend, as already explained, upon the displacement of the vessel inside. The floor of the dock slopes on each side from the centre to allow an? surplus water to run off. Down th-; centre, too, nine a row of keel blocks, about four fee*high, upon which the vessel rests wfcito the water is pumped out.

In equipment the Gladstone Dock is wonderfully complete. Running around its walls is a sot of rails upon which travels a steam crane of five tons lifting capacity. On the quays also are to he found two capstans of twenty tons hauling capacity operated by hydraulic power. For working at night time there are eleven electric flame arc lamps carried on steel lattice columns 90 feet

high. Then down one side of the basin is a shed or wharf 900 feet long and 100 feet wide. In conclusion, it may be stated that the dock is named Gladstone, not in memory of the politician who was born in Liverpool, but in recognition of the great services rendered to the commerce of Liverpool by Sir Robert Gladstone a former chairman of the Mersey Docks and Harbour Board, who own and control the dock.