Engineering Wonders of the World
Volume I

412 ENGINEERING WONDERS OF THE WORLD. steel composing the submerged portion of a dock. It is found that the internal parts and those portions of the structure between wind and water—that is, above the water when the dock is floating light and submerged when a ship is lifted—are the most liable to corrosion. As these parts are easy of access, due precau- tions can be taken to preserve them. A float- ing dock so constructed that all parts of the bottom can be reached possesses, however, an important advantage over the box dock, particularly when it is destined for service in foreign waters. The first Bermuda dock, built for the British Government in 1869, was in section almost like the letter U, the aim of the designers being that, by filling with water certain chambers in the side walls, the dock could be careened and the under-water end elevation resembles the letter L. The necessary stability to enable the pontoon to be lowered and raised is obtained by means of an out- Depositing rigger connected to the wall by parallel booms hinged at each end. The dock is built in two equal lengths, so that they can be disconnected, and the one raised on the other for cleaning and painting. The most striking feature of this type of dock, however, is the peculiar construction of the pontoons forming the bottom, by means of which the dock, after lifting a ship, is able to transport and deposit her on a grid formed of groups of piles (Fig. 4). Consequently, the number of vessels that can be raised out of the water at one time is only limited by the number of grids provided. The largest and Fig. 4.—DIAGRAM TO SHOW PRINCIPLE OF THE DEPOSITING DOCK. The dock pontoons, carrying a ship, are brought into position between the members of the grid, supported on piles. The dock is then submerged and drawn away, leaving the ship on the grid. portions reached. Unfortunately, this opera- tion proved so dangerous when attempted that it was never repeated. Most of the large modern floating docks have been built in separate sections, so that one part can be lifted out of the water for cleaning, etc., and supported on the other portion ; hence the “ self-docking ” floating dock. During the last thirty years several types of self-docking docks have been designed and built, and of these we propose to deal very briefly with the “ depositing,” “ off-shore,” “ sectional pon- toon,” “ Havana,” “ Hansson,” and “ bolted sectional ” types. The earliest example of the depositing dock was designed and built in 1877 for the Russian Government. This type has only one side wall (Figs. 2 and 3), so that its Off-shore Docks. most recent dock to be constructed on this principle is that stationed at Barcelona, with a lifting capacity of 6,000 tons. The off-shore dock, like the depositing type, has only one side wall, and is thus L-shaped, but it is not arranged for depositing ships after lifting (Fig. 5). The single wall is attached to a series of shore girders by means of parallel booms hinged at each extremity. Docks built on this principle are found very convenient in working, the ship entering the dock at either end, or, as is more frequently the case, being warped on broadside. The sectional pontoon dock is made up of a number of separate pontoons held together by two side walls, which are continuous and bolted on top of the pontoons. This type of