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DOCKYARDS

[BRITISH

in its place across the entrance and the dock is dry, it has of 295, 347, and 413 feet respectively, and extensive dock- iscourse to sustain the maximum water pressure which can come yard buildings. The most important addition to Devon- upon it at the highest tides. Owing to the causes above menport yard at this period was the construction of Dock tioned, the caissons at Keyham are of exceptional dimensions, No. 3, having a floor-length of 415 feet, with 34 9 over and the mechanical problems to be dealt with in their design of no ordinary kind. They are, as a rule, sliding caissons, the sill at high-water springs, and this, with certain dock- are constructed of riveted mild steel, and capable of withstanding a yard buildings, constitute the principal features in the hydraulic pressure amounting in some cases to 3700 tons. development of Devonport yard up to the year 1901. Simons Bay {Cape of Good Hope).—The existing naval Seamen’s barracks of considerable architectural importance, with accommodation for 1000 men, together with officers’ yard at this station covers an area of about 13 acres, quarters, drill shed, commandant’s residence, &c., were exclusive of the victualling establishment and naval completed on a site to the north of Keyham yard and hospital, and is provided with a small camber, slipways overlooking the Hamoaze. Such in brief was the extent for torpedo-boats and small vessels, together with various to which H.M. dockyards at Devonport and Keyham had dockyard buildings, storehouses, coal stores, &c., but has been developed up to the time when the scheme sanctioned no dry dock or deep-water wharf. The new works proby Parliament under the Naval Works Loan Act of 1895 posed under the Naval Works Loan Act of 1899, at an was first commenced, and the mud flats to the northward estimated cost of two and a half millions sterling, are of Keyham yard, and immediately in front of the seamen’s situated near Blockhouse Point, to the east of the present barracks above referred to, became the active scene of the naval yard. These works consist of a tidal basin of 28 acres in extent, and with a depth of 30 feet at low-water new works. These works present three leading features : a tidal basin with spring tides, enclosed by a breakwater on the eastern and entrance from the Hamoaze ; a group of three graving docks and northern sides and a similar projecting arm or pier on entrance lock ; and a large enclosed basin, with a coaling depot the west. The entrance to the basin faces north-westerly, at the northern end. The tidal basin is in the immediate and is 300 feet in width. South of the basin is a large neighbourhood of the old Keyham north basin, and is 740 feet in reclaimed area forming the site of the new dockyard. length by 590 feet in mean width, with an area of 10 acres and a depth of 32 feet at low water of spring tides. This basin Opening from the basin is a dry dock, 750 feet in length affords access to two graving docks of large dimensions, each on blocks, with an entrance 95 feet wide and having 30 dock serving also (when not occupied) as a lock for entrance into feet over the sill at low-water spring tides. the closed basin. One of these docks has a length of 745 feet on This dock can be subdivided by an intermediate caisson floor, with 20^ feet over the sill at low-water springs. The other is 741 feet on floor, with 32 feet over the sill at low-water springs. in such a manner as to form two docks, respectively 400 Each of these docks can be subdivided by means of an inter- feet and 320 feet in length, or 470 feet and 250 feet in mediate caisson. A third dock, opening out of the closed basin, length on blocks, as may be required, or the full length is 480 feet in length, with 32^ feet over the sill at high water of of 750 feet can be made available when necessary. The neap tides, and provision is made for an increase of length when required. An entrance lock, 730 feet in length between caissons, dockyard buildings include extensive shops for the chief with 32 feet over the sill at low water of spring tides, gives engineer’s and chief constructor’s departments, the pumpdirect access from the Hamoaze to the closed basin, which is 1550 ing-engine house, working sheds, &c., while ample space feet in length, 1000 feet in width, and covers an area of 35^ reserved for additional docks and buildings. Berthing acres, with a depth of 32J feet at low-water springs. An addi- is tional entrance, closed by caissons, but without a lock, com- accommodation is provided in the basin alongside the municates with the Hamoaze. A wharf wall forming the eastern wharf walls which surround it. The walls available for boundary of the closed basin will afford a length oi wharfage of this purpose have a total length of 2585 feet lineal, are 800 yards, with 30 feet alongside at low-water springs. The site constructed of interlocked concrete block work, with an of these works is an expanse of mud overlying rock at varying available depth of water of 30 feet at low water, and are depths, which in some places reach 100 feet or more below the level of coping. As the walls of docks, lock, and basins are in furnished with powerful shear-legs and cranes for the use every case carried down to the rock, it follows that the process of of vessels alongside. Extensive sheds for the storage of constructing foundations at such great depths involves engineer- coal are provided. The whole of the dockyard area, ing operations of considerable magnitude and difficulty. The docks and basins above described are remarkable for the together with that of the enclosing breakwater and pier, depths at which their floors and entrances are laid, and this, will be formed by reclamation from the sea; and as the combined with the tidal rise of 15J feet, causes the problem of total space thus created amounts to 35 acres, the entire closing and opening the dock and lock entrances to be attended extent of the proposed works, including the tidal basin, with somewhat more than ordinary difficulty. It is - therefore will amount to 63 acres in area. The works thus briefly not out of place to describe very briefly the practice in this respect customary in H.M. dockyards. The ordinary lock gate described will, in combination with the existing yard, form, usually found in private docks (though some of the finest modern an important naval station for the requirements of the docks use caissons) is too familiar to need description, but this fleet in South African waters. form of closing an entrance does not afford facilities for carrying Hong-Kong.—The naval yard at this important station a railway line across the dock or lock, and where this is required a swing bridge must be constructed. In the case of H.M. dock- consisted of an area of some 4f acres in extent, but yards it frequently happens that railway lines cross the dock unprovided either with basins, dry docks, or any wharfage entrances, and the weight to be transported by their means, such suitable for large vessels. The widening range of political as heavy guns, boilers, machinery, and the like, would require a affairs in the East, and the increasing requirements of the swing bridge of great strength and considerable span. It has consequently been found convenient and economical to construct navy in Chinese waters, had, however, made it obvious that the apparatus for keeping the water out of the dry dock in such the existing resources of the naval yard were inadequate. a form as to combine the functions of a movable dam and a The result was an Admiralty scheme of enlargement. The swino- bridge, and this is done by the employment of so-called principal features of this scheme are as follows: A tidal “caissons.” The great majority of dock entrances in H.M. dockyards are closed by caissons, and these are, broadly, of two basin of 9| acres in extent is provided, having a depth of principal types — the floating or ship caisson and the sliding 30 feet at low-water springs, and enclosed by wharf walls, caisson. The former is sunk into its place in a groove prepared giving a total length of wharfage of 2900 feet lineal. A. in the dock walls for its reception by means of water supplied by dry dock, opening direct into the roadstead, 550 feet m hose into a ballast tank, and raised again by letting the water out. The latter type consists of a rectangular steel or iron box- length on blocks, 95 feet wide at entrance, and with 30 shaped dam, which is drawn across the entrance by machinery, feet over the sill at low-water springs, will accommodate or withdrawn into a recess provided in the side of the dock the largest vessel in H.M. navy. Extensive workshops entrance when access is required into the dock. Both types can for the chief constructor’s and chief engineer’s departments, be designed to carry a railway across their upper deck capable shears, cranes, pumping - engine house, and slipway for of sustaining the heaviest loads ever required. When the caisson