British]
DOCKYARDS
(b) Adapting Naval Ports to the Present Needs of the Fleet. Gibraltar.—The history of British naval dockyards is in general one of continuous development, extending over considerable periods of time, and reflecting in the various stages of that history the naval requirements, the engineering skill, and the mechanical resources and appliances of the day. As these have developed and increased, so the older and more obsolete portions and appliances of the yards have been from time to time renewed and readapted to meet modern exigencies; and the result exhibits the constantly increasing effort to meet the demands which modern naval architecture and strategy are as constantly renewing. In the case, however, of the great works at Gibraltar we have the somewhat unique example of the creation of a modern dockyard of the first class, as it were, at a stroke, as the small existing yard will have become entirely absorbed in the new extension works. The absence of any dry dock at Gibraltar had been for some time the occasion of considerable public discussion, and a commission was appointed in 1890 to consider the question. But the recommendations of this commission became greatly amplified in the scheme finally approved by the Admiralty, for which funds were provided in the Naval Works Loan Act of 1895 and subsequent years. This scheme may be said to consist of two principal parts: the construction of a dockyard with ample dry dock accommodation, with the necessary workshops, stores, and offices; and the construction of a great defensive harbour of sufficient extent to shelter a powerful fleet, and yielding largely increased coaling and wharfage accommodation. Combined with the defensive harbour, and forming an integral part thereof, is the new commercial mole, a portion of the cost of which is borne by the colony (Fig. 3). The necessary space for dockyard purposes is exceedingly limited at the Rock of Gibraltar, and thus, with the exception of the small area of the old yard, the area required has been obtained by artificially reclaiming the land over a considerable sea-space, of which the soundings range from low-water mark to 40 feet in depth. The total area thus created for dockyard purposes is about 64 acres. The material required for this reclamation is obtained chiefly from quarries on the eastern side of the Rock by means of a tunnel pierced for that purpose. The graving docks are three in number, alike in cross section and in depth over the sill, but of unequal lengths, to accommodate battleships and cruisers. Dock No. 1 is 850 feet in length, 95 feet in width at entrance, and has a depth of 35J feet over the sill at low-water springs. It is divided into two portions by an intermediate sliding caisson, and is capable of docking two ships simultaneously. Dock No. 2 is 550 feet, and Dock No. 3, 450 feet in length, and of similar dimensions in width of entrance and depth over sill. All the docks will have their entrances closed by steel sliding caissons, and are lined throughout with granite and limestone. The most important dockyard buildings are the pumpingengine house, the workshops of the chief constructor’s and chief engineer’s departments, the naval stores and offices. The pumping - engine house will contain the steam machinery for the emptying of the dry docks, which will be capable of pumping out the contents of the largest dock, amounting at high water to 105,000 tons, and discharging into the sea in five hours. The workshop for the chief constructor’s department is an extensive building, 407 feet in length and 322 feet in width. The shops of the chief engineer’s department are comprised within a building of similar dimensions. The staff captain’s department and other stores are comprised within buildings having a total floor-space of about 300,000 superficial feet. At the northern end of the yard are the administrative offices and a series of slipways for hauling up destroyers, together with a slip for small craft, a wharf for ordnance purposes, and an auxiliary boat camber. The reclaimed area of the dockyard is faced seawards by a wharf wall constructed of interlocked concrete blocks, upon a new system, built in the sea without the aid of a dam, and having an unbroken line for wharfage purposes of about 1600 feet lineal, with a depth of water alongside of 33 feet at low water. Upon this wharf are erected powerful shears and cranes for the use of vessels alongside. The older appellation of “harbour of refuge” has, from the point of view of the naval strategist, acquired a new and extended
493 meaning, and while the modern defensive harbour may still serve as shelter from bad weather, it further fulfils the not less important function of protection from torpedo attack. The defensive harbour now in course of construction at Gibraltar is formed by the enclosure of a water area of about 440 acres, of which some 250 acres will have a minimum depth of 30 feet at low water. This enclosure is formed by three several works of considerable magnitude: the New Mole Extension forming the southerly boundary, the Commercial Mole on the north side, and the Detached Mole forming the westerly boundary, while two entrances, each 200 yards wide, form the approaches to the harbour from the sea. The New Mole, so called in distinction from the Old Mole or Devil’s Tongue at the northern end of the town, is supposed to have been commenced during the Spanish occupation in the year 1620. Both New and Old Moles are frequently referred to in Drinkwater’s History of the Siege of Gibraltar, and the successful assault upon the former by the officers and men of the British fleet forms a leading incident in the capture of Gibraltar by Admiral Sir George Rooke in 1704. Additions to the length of this mole were made at various times, and in 1895 the total length of the artificial mound was about 1400 feet. The extension now in progress will add 2700 feet to this length. This mole is formed of a rubble mound, with a top width of 102 feet, the stone being obtained from adjacent quarries and deposited in the sea by barges. The harbour side is faced by a continuous wharf wall, having 30 to 35 feet depth of water alongside, and the total length of wharfage available for ships of war for coaling or other purposes will be 3500 feet. The Detached Mole, forming the westerly boundary of the harbour, is of a different type of construction. It is a vertical wall formed of massive concrete blocks, the greater number of which are of 32 tons in weight, arranged upon what is known as the sloping block system, and founded upon a rubble mound of stone deposited from barges and levelled for the reception of the blocks by divers. As this breakwater stands isolated, some half a mile from the nearest point on shore, in from 45 to 65 feet depth of water, and has at no time during its construction been connected with the land by any temporary staging, a brief description of the method employed for commencing its constuction will not bo without interest. A box-shaped steel caisson, 33 feet wide, 74 feet in length on the top, 101 feet in length at the bottom, and 48J feet high, fitted with compartments and with ends sloped to the angle of the blockwork, was constructed in this country, shipped to Gibraltar, re-erected, launched, towed to its correct position, and sunk, by the admission of water, on the rubble mound before mentioned. Concrete was then filled in as rapidly as possible until the entire mass, weighing about 9000 tons, had formed, so to speak, an artificial rock or island in the sea, being, in fact, a completed section of the breakwater itself. Upon this foundation were erected two block-setting Titans (see Titax Cranes), capable of setting 36-ton blocks at a radius of 75 feet, by which means this mole has been rapidly extended north and south to its full length of 2720 feet. The blocks, having been transported from the block-yard by rail and then shipped in bai’ges to the site of the mole, are laid in their sloping position by means of special apparatus designed and patented by the writer. The Commercial Mole, forming the northerly boundary of the harbour, is intended to serve the commercial requirements of the colony, while at the same time it forms an integral portion of the defensive scheme. This mole starts from the neighbourhood of the Waterport wharf, alongside the Old Mole or “Devil’s Tongue,” an appellation given to this portion of the defences of the fortress during the siege of Gibraltar in 1779-83, on account of the annoyance to the besiegers caused by its flanking fire. The mole consists of a rubble mound projecting in a westerly direction, furnished with five jetties, lying north and south, and terminating in a western arm lying parallel to the jetties. Each jetty and the western arm is faced with a concrete wharf wall, and the total length of wharfage available for mercantile coaling or other purposes amounts to 7000 feet lineal, with a depth of water alongside ranging from 20 to 30 feet. Extensive coal and bonded stores are provided, and an open viaduct is constructed in the connecting arm, leaving a waterway for the purpose of giving circulation to the enclosed waters of the harbour, which is being dredged to secure the depths already referred to. Devonport and Keyham.—Prior to the period dealt with in this article, the works at Keyham described in the ninth edition article on Dockyards had been completed; railway communication with the Cornwall line was established, and a tunnel formed a connexion between the two yards. Keyham yard in 1880 consisted substantially of two basins, the north basin of 9 acres and the south basin of 7 acres in extent; three docks, having floor-lengths of
