Enclosed excavations or basins, formed for the reception of shipping. There are two descriptions of docks, viz. wet docks, and graving or repairing docks. Wet docks are extensive basins formed adjacent to rivers and harbours, with which they are connected by means of a lock, furnished with gates at each end, so that vessels remain afloat at all times of the tide. They are usually surrounded with warehouses, for the purpose of loading or discharging vessels. The wet docks in this country are numerous and extensive, and have proved highly beneficial to its commercial interests; as in these ships lie in perfect security from storms and depredation, their cargoes are taken in and delivered with the utmost dispatch, and the navigation of the rivers is freer from obstruction. The town of Liverpool, which, from the badness of its harbour, resorted to the construction of wet docks in 1708, has at the present day a range of them in front of the town, and along the banks of the river Mersey, extending more than two miles in length, and which, from their concentration in one spot, form the most striking display of the kind that can any where be met with.

Hull, Bristol, and Leith, have successfully emulated this example.

Although London was without the conveniences of wet docks until the commencement of the present century, it can now boast of several, some of which exceed in magnitude any in other parts of the kingdom. The first of these undertakings was the West India Docks, for the accommodation of the West India trade, erected under an Act of Parliament passed in July, 1799. The great basin is 420 yards in length, and 230 yards in width, covering an area of twenty acres. A basin of nearly three acres connects it with the river. The warehouses are most noble buildings; the tobacco warehouse is the most spacious erection of the kind in the world, being capable of containing 25,000 hogsheads of that article, and the vaults underneath, as many pipes of wine. This single building under one roof is said to occupy upwards of four acres of ground. These docks were opened in 1805. The London Docks were begun in 1800, and completed in 1805. The principal basin is 420 yards in length, and 276 in width, giving an area of 25 acres. The principal range of warehouses occupies a superficies of 120,000 square yards. The first stone of the East India Docks was laid in March 1825, and the first vessel entered them in August 1826.

The dimensions of the dock for unloading inwards are 1410 feet in length, and 560 in width; the dock in which vessels load outwards is 780 feet long, and 520 feet wide; and the entrance basin, which connects them with the river by a lock, is 2 3/4 acres in extent. The lock is 210 feet in length, the width at the gates 48 feet in the clear, and the depth of water at ordinary spring tides 24 feet. The warehouses at these docks are of trifling extent, the principal part of the cargo of vessels unloading here being conveyed in vans direct from the ships to the East India Company's warehouses, situated in various parts of the city of London. Besides these principal docks just enumerated, there are various others in the port of London, which our limits will not allow us to notice.

Fig. 2.

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Graving or Repairing Docks are excavations sufficiently large to admit one or sometimes two vessels for the purpose of being repaired. At the entrance is a pair of gates, forming an angle outwards or towards the river. When it is required to dock a vessel, the water is admitted by means of sluices, and when it has attained the same level within the dock as without, the gates are opened, and the vessel hauled in over a range of blocks previously laid on the floor of the dock; the gates are then shut, and the vessel, being steadied by shores or props placed against the side of the dock, as the tide recedes, settles upon the blocks. At low water the sluices are shut, and the water (if any) remaining in the dock is pumped out, so as to leave it perfectly dry, and to allow any part of the vessel's bottom to be examined and repaired. When the soil is of an unfavourable nature for excavations, as also with a view to avoid the delay which often occurs from ships being able only to enter some repairing docks or to leave the same at the height of the springs, a contrivance, called a floating dock, has been proposed, in which vessels may receive the necessary repairs.

Various constructions have been offered for this purpose.

The engraving on the following page represents a design for a floating dock, by Mr. Edward Clark, of New York, civil engineer. This dock is proposed to be constructed by forming a float of timber to constitute the bottom of the structure, and which, by its buoyancy, shall support a vessel within the dock with its keel above the surface of the water. To attain this end the float is made in the form of a hollow box, composed of strong logs firmly jointed together and caulked, so as to render it water-tight. The capacity of the hollow part must be such that, when exhausted of water by means of pumps, it shall be sufficiently buoyant to sustain itself with its load, a represents the float; b b the piers, forming a recess to steady and secure the float; c c perpendicular supports and braces appended firmly to the piers; d d also supports appended firmly to the float, so as to allow by means of the rollers e e of the easy and steady ascent and descent of the float conformably to the motion of the tides and waves, and also of sinking and raising the float in the same place; f the stern of the vessel; g g bilge blockings; h h braces, all for supporting and steadying the vessel in an upright position; i timbers framed into the piers, forming a bed for the support of the float while sunk.

The float a is supplied with valves and pumps (not shown in the engraving); and if it be required to float the vessel f, nothing more is necessary than to open the valves, when the float, being previously ballasted, will fill with water and sink to its bed. The vessel f being now removed, and another made to occupy its place by means of guides, the valves are to be closed, and the pumps put in motion, and when a quantity of water has been displaced from the float equivalent to the weight, she will be elevated entirely above the water, and placed in a most favourable situation to undergo repairs. A float of this description, for use in sea water, would require to be coppered externally, and occasionally to be filled with some other saline fluid, or with fresh water, to preserve it from worms. The Committee of the Franklin Institution at Philadelphia, to whom this invention has been submitted by Mr. Clark, state, in their report thereon, that the main objection to docks of this description, made sufficiently capacious for vessels of large dimensions, and for the operations to be carried on in repairing them, is the unequal pressure to which their bottoms must be subjected by the weight of the vessel upon them, and the upward pressure of the water.

They are aware that, by judicious shoring, much of the weight of a vessel may be distributed over the bottom; this, however, although it would lessen the objection, would not remove it. Ships, although constructed in a shape and braced in a manner calculated to render them stable, undergo in nearly every instance a change of form after they are launched; to this change of form the float in question would be much more liable, inasmuch as its flat surfaces are less calculated to resist the effects of the pressure to which they are subjected.

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