TABLE II.-FOREIGN TRADE OF PRINCIPAL FOREIGN AND COLONIAL PORTS. TONNAGE OF SAILING AND STEAM VESSELS ENTERED AND CLEARED WITH CARGOES AND IN BALLAST IN THE FOREIGN TRADE DURING the Years 1899-1901. Port. 1899. 1900. 1901. Antwerp, Buenos Ayres, Gibraltar, Hamburg, Hong-Kong, Entrances. Clearances. Entrances. Clearances. Entrances. Clearances. Tons. Tons. Tons. Tons. Tons. Tons. 6,837,801 6,735,656 6,696,370 6,669,712 7,466,463 7,518,292 3,302,145 2,969,196 2,789,581 2,505,323 returns not available. 3,990,306 3,679,973 4,313,604 4,119,372 4,503,895 4,309,075 4,328,859 4,299,678 4,455,083 4,414,654 4,171,350 4,159,272 7,037,294 7,157,576 7,322,476 7,404,112 7,623,098 7,671,938 6,720,769 6,716,378 7,021,982 7,000,185 7,383,683 7,340,586 4,695,168 4,933,946 4,629,599 4,933,945 4,936,095 5,286,640 7,707,477 7,496,279 8,176,761 | 7,843,529 8,679,273 | 8,118,427 5,956,437 5,828,331 5,970,395 5,762,967 5,950,446 5,733,763 4,416,260 4,409,913 4,836,048 4,833,989 5,456,032 5,453,999 19 CHAPTER II. DOCK DESIGN. NECESSITY FOR DOCKS-RELATIVE ADVANTAGES OF DOCKS AND BASINS-RESTRICTION Necessity for Docks. In the days before steamships were known, when In one respect naval architecture has degenerated since those times. Nowadays, the attenuated plating of an ocean steamer, coupled with its enormous length and weight, would inevitably suffer serious strain, if not collapse, under such drastic treatment. Indeed, to such an extent have strength and stiffness been sacrificed to speed, that the foundering of at least one modern craft * is attributed to the fact that the ends of her keel were lifted momentarily upon the crests of two waves, while the central portion spanned the trough between, and, being unsupported, was fractured by the mere weight of the vessel and its internal fittings. Except then for small fishing craft, deep water berths in the form of harbours, basins, or docks, capable of maintaining shipping continuously afloat, are necessary features of every modern port. River frontage quays may suffice in minor cases in sheltered situations, but, as a rule, the accommodation thus afforded is insufficient. The question whether open basins or closed docks are more suitable for * This was a torpedo boat destroyer, it is true-the ill-fated "Cobra"--but the vessel and the disaster are typical of modern tendencies and their results. adoption in a locality depends upon the range of tide and the meteorological conditions. In an inland sea, such as the Mediterranean, which is practically tideless, an open basin will serve all the requirements of commerce, in so far as the provision of quayage, for the reception of cargo, is concerned. Nor is there much inducement to construct closed docks when the range of tide is moderate, say not exceeding about 10 feet, instances of which occur, amongst other places, at Glasgow, Belfast, and Hamburg; but when the rise and fall of the water level is very great, as at Liverpool, Bristol, and elsewhere, where there is a difference in level of between 30 and 50 feet, the necessity for enclosed areas, in which the water may be impounded at a fairly constant depth, becomes evident and imperative. The advantages attaching to tidal basins, where practicable, are the speedy and unrestricted arrival and departure of vessels, and the absence of costly appliances for closing the entrances. On the other hand, the maintenance of an unchanging and uniform water level in tidal situations, is of undoubted benefit in facilitating the loading and discharging of cargoes, in avoiding the chafing of vessels against the quayside, and in obviating the necessity of constant attention to and alterations in the moorings. Apart from the tidal question, an enclosed and sheltered dock has the advantage of providing a quiescent area unaffected by external waves and storms. In a determination of the particular design suitable for a dock or basin, such great influence is exerted by considerations of a purely local nature, and there is so much scope for the exercise of individual judgment and opinion, that it is quite impossible to lay down any hard and fast rules to be observed universally, or even in a majority of cases. Very rarely does the Engineer find himself absolutely unfettered by restrictions arising from fixed conditions, such as those relating to site, expediency, and economy. Commerce is erratic to this extent that it does not necessarily favour ports possessing admirable natural facilities for the accommodation of shipping. A port is only one of several stages in the journey from the manufacturer to the consumer. Consequently, any particular merits it may possess as a harbour, are entirely subservient to its position in regard to the great trade routes. In the maintenance of wellestablished lines of communication much inconvenience has been endured from natural obstacles, and large sums have been expended upon their mitigation and removal; whereas other ports, more favourably endowed by nature, have languished in obscurity. Trade, therefore, cannot be created at will; but much may be done to induce and foster it, just as it may be injured by indifference and neglect. It is mainly, then, within areas already occupied and probably densely populated, that provision has to be made for the formation and extension of dock accommodation. In such cases the acquisition of adjoining property has to be kept within remunerative or, at any rate, strictly utilitarian limits, and very often the new boundaries are so irregular as to need the exercise of much thought and skill in order to utilise the enclosed space to its fullest extent. Many docks owe the complexity and apparent eccentricities of their outlines to such conditions of evolution. As, however, in a treatise of this kind we must have some basis upon which to found our observations, which are to be as complete and comprehensive as possible, there is no alternative but to assume a freedom of choice and design which will rarely, if ever, be realisable in practice. Upon such an assumption the following points claim foremost attention:The most convenient position, and The most suitable shape for a dock; The best ratio between quay space and water area; and That between periphery and surface. Position. In regard to this point certain obvious requirements immediately present themselves accessibility, shelter, accommodation. Accessibility will depend, in the first place, upon the depth of water in the approach channel. This, of course, is susceptible of improvement by artificial means, but a naturally deep fairway is a great saving in cost, both of construction and of maintenance. In the second place, accessibility will depend upon the absence of dangerous shore eddies and currents; in the third place, upon proximity to the open sea, and, lastly, upon the range and duration of the tide. The amount of shelter will be governed by the configuration of the coast line, by the vicinity or otherwise of promontories and headlands, and by local experience in the matter of storms and cyclones. The accommodation will depend upon the area available and its disposition. Apart from considerations of exposure, a position upon the seaboard is preferable to one some distance up a river, for large ocean-going steamers. The navigation of a river, often tortuous in course and crowded with craft of various sizes, is a slow and, in fogs and darkness, a hazardous proceeding, rarely attended by any compensating advantages. Such ports as Antwerp and Bremen are undoubtedly handicapped by their inland situations. The disadvantage has perhaps not been fully apparent in the past, but it is bound to make its influence felt in the future. Joined to the difficulty of manoeuvring mammoth vessels will be the attendant loss of time, which busy mercantile communities can ill afford to endure. No doubt engineering operations are quite capable of maintaining and improving the accessibility of these ports, but only at considerable outlay in initial and current expenditure. Ports like Marseilles and Havre, on the other hand, will always naturally enjoy the privilege of direct and unimpeded communication with the ocean. But it must not be overlooked that such ports are subject to the whole violence of the open sea in time of storm, and that the provision of shelter from such destructive agencies will often necessitate very expensive protective works. Taking all things into consideration, an estuarine situation is perhaps most to be recommended, combining, as it does, the advantages of both the previous cases without any of their drawbacks in an acute form. But, in order to fulfil the ideal conditions, the estuary must be broad and well sheltered, free from shoals and from a shallow bar. Shape. The outline of a dock or basin may be that of any geometrical figure, or of several figures in combination. Figures approaching the curvature of the circle, unless, indeed, the radius be extremely great, are obviously unsuitable for enclosures destined to accommodate long straight vessels in contact with their sides. Curves are undoubtedly employed to advantage in many cases, in connecting outlying arms and branches, and in training ships through changes of direction, but their effective use is limited and otherwise to be deprecated. The most suitable forms are rectilinear, and those generally available for the purpose are the triangular, the square, the rectangular, the diamond (or lozenge), the machicolated, and the digital. The triangular form is rarely used, not so much, perhaps, on the ground of any inherent defect, as that the quay arrangements are not always conformable to a plan of that character. It has possible advantages for an entrance basin acting as a vestibule to a group of docks, as exemplified in the basin leading to the Albion and Island Docks at Rotherhithe (fig. 18). This example, however, be it noted, is somewhat defective, though not radically so. Other triangular outlines, more or less complete, are to be found in the Prince of Wales Dock at Swansea (fig. 20), the Morpeth Branch Dock at Birkenhead (fig. 6), and the Manchester Dock at Liverpool (fig. 5). The square dock offers the advantage of plenty of space for the turning of the vessels it accommodates. In the majority of instances a vessel leaves, and should leave, a dock stem first. As she generally makes her entry in the same manner, it behoves that sufficient room be provided for turning her within the dock. This proviso is of most importance in exposed situations with narrow entrance channels. With a wide open fairway, sufficiently sheltered, it is a matter of indifference whether the turning takes place within or without the dock. Many ships will take advantage of an outer basin in order to make their entry stern first, so as to be ready for direct departure. The disadvantage attaching to the square dock is the excessive proportion of its water area to the amount of quayage, which renders it unsuitable for the accommodation of large vessels. It is doubtful whether any existing dock is absolutely square, but the Albert and Collingwood Docks, at Liverpool (fig. 5), are sufficiently close approximations for the purpose of illustration. The rectangular dock is a modification of the square dock, designed to overcome the defect just mentioned. By proper manipulation the length and breadth may be arranged so as to give the maximum amount of quay frontage consistent with the water space absolutely required for manoeuvring purposes. This ratio will be discussed later. The rectangular form is common. A few instances of its adoption may |