Dock
an inclosure for the accommodation of shipping. Docks may be divided into two principal classes, viz., wet docks and dry docks (or graving docks).
Wet docks are used almost exclusively for purposes of marine commerce. Where the range of tide is more than 10 to 12 feet, docked vessels are kept alongside of the quay or dock at as nearly a uniform elevation as practicable by means of inclosing requisite water areas and preventing by suitable means the outflow of water during ebb tides. Such docks are DOCK the side walls of the lock chamber, or under the floor of the latter, through which water may flow from the dock into the lock chamber till the elevation of water in the latter is the same as that in the dock. When the lock is filled with water the gates between it and the dock are opened. After the ships have been admitted the gates are closed and the water is allowed to flow from the lock through sluices like those already described leading into the lower water of the basin or outer harbor. When the lock water in which the ship is floating has fallen nearly to the level of the water of the tidal basin or harbor, the gates at the exit end of the lock are opened, enabling the ship or ships to pass freely outward. The simple reversal of the latter operation enables a ship to enter the wet dock at any CONCRETE DRY DOCK frequently approached through what is called a tidal basin, or sometimes a halftide basin, the latter expression indicating the fact that ships may freely enter or leave such basins during the upper half of the tidal range. stage of the tide. The comparatively small range of the tides on the coast of the United States makes it unnecessary to construct closed docks in American ports; hence American docks, which correspond to the wet docks in Great Britain or other foreign countries, are simply open oblong spaces of water beor masonry piers.
In order that ships may enter or leave wet docks at any stage of tide, it is necessary that the entrances between substantially constructed timber fitted with locks. A lock in a wet dock is a long narrow chamber with its sides constructed of masonry or timber, with what are called gates at each end. Each of these gates usually consists of two parts or leaves, each precisely like the other. These leaves or half gates swing about vertical axes, and then close against each other, forming an obtuse angle like the two sides of a short and broad letter "A," pointing inward to the dock where the highest water is to be found. Such gates are called miter gates; the pressure of water against them tends to hold them shut till the height of water is equalized on both sides. Sluices fitted with proper valves are made, either in the lock gates, in Tidal-basin or half-tide docks are inclosures between wet docks and the open harbor. The gates or lock through which vessels enter or leave them are kept open during the upper half of the tidal range, so that ships may freely enter or leave during that period of time. The gates are closed, however, when the tide has half ebbed; from that time to the next mid-tide ships must enter and leave the tidal basin, if at all, in precisely the same manner as that of entering or leaving the wet dock.
The tidal basins are useful for the purpose of receiving ships prior to entering the wet dock, or on coming from the latter, having received their cargo. DOCK Tidal docks are basins surrounded by quay walls, and having open entrances permitting the free flow and ebb of the tide; they have the advantage of requiring no opening or shutting of gates. With small tides they answer very well; they are sometimes made deep enough to keep vessels afloat at low water. They are much more liable to silt up than wet docks.
Dry docks are inclosures with one end movable. Like wet docks, they are built of both masonry and timber, the former material being the more substantial.
Dry docks of the floating type are built of both steel and timber, the former material being better adapted to structures of large capacity and now generally used.
The ordinary dry dock, whether built of timber or of masonry, is preferably located where a foundation of very firm DOCK enter it. At one end of this floor is placed a sill, against which and the corresponding surfaces on the two vertical sides of the entrance the caisson rests in order to make the closed chamber.
The sides and one end of the dry dock are formed of substantially built steps called altars, the approximate outline of which is more or less nearly parallel to the sides of the ships as they lie in the dock.
Floating dry docks are composed of one or more large pontoons, so constructed and arranged as to carry along each side pumps and other appliances on suitable stiff frames. When the pontoons are filled with water they sink, and when water is pumped out of them they rise to a height corresponding to the amount of water taken out.
In 1919 considerable progress was made in the construction of dry docks of FLOATING DRY DOCK material is available. The top surface is a few feet only above high water; the bottom is placed at such depths as will accommodate the ships of greatest draught which are to use them. The movable end of the dock, if small, may be formed of a pair of gates like those of wet docks; but for structures of the dimensions requisite to accommodate large ships it is usually formed by a caisson, i. e., a floating vessel usually of steel, and deep enough to close the opening to the dock, and wide and stiff enough to sustain the water pressure at its full height on the outside, with no water on the other or dock side.
The interior of the dry dock consists of a floor constructed with sufficiently strong foundations to sustain the weight of the heaviest ship which is to the navy and merchant marine. In Norfolk, a navy yard dry dock measuring 1,011 feet long, 144 feet wide, and 40 feet deep, built at a cost of $4,500,000, was opened April, 1919. There was at the same time under construction in Boston a dry dock, 1,106 feet long and 149 feet wide. This dock was purchased by the Government and was used to provide accommodations for the largest naval and commercial ships. A dock of practically the same size as the Norfolk dock was constructed at the Philadelphia Navy Yard, and in 1920 the construction of a similar dock at the Charleston Navy Yard was begun. A dock of over 1,000 feet long and 150 feet wide was also constructed in San Francisco.
In August, 1919, the great dry dock at DOCKET Pearl Harbor, in the Hawaiian Islands, was completed and flooded. This dock is 1,022 feet long, 138 feet wide, and 39½ feet in depth.