A transverse section of this dock would expose water-tight compartments, which were all completely under the command of the powerful centrifugal- steam-pumps, so that they could be separately filled or emptied in a very short time. The dock could be heeled over to one side, for the purpose of getting at the bottom for repairing or cleaning it. This tilting over could be accomplished by filling the upper compartment on one side, and emptying all the others. The water-tight compartments were divided in their longitudinal direction into five separate divisions, making in all 25 water-tight compartments, any one of which could be filled or emptied at pleasure; thus affording complete command over the dock, and admitting of its being put into any required level, notwithstanding any irregularity in the distribution of the weight resting on the dock.
The French government had to provide a dry-dock at Saigon, in Cochin-China, for the use of the large steamers which had been subsidized by it to run between France and China. The soft muddy character of the soil at Saigon rendered the construction of a stone graving-dock impracticable. The French admiral, commander-in-chief of Cochin China, hearing of the construction of the Sourabaya floating-dock, and having examined the plans of it, recommended his government to have a similar dock, on a much larger scale, constructed for Saigon.
The performances of the Saigon dock are in every way most satisfactory; it has lifted, high and dry out of the water, the 70-gun frigate Another great dock on Mr. Thomson's principle has been erected at Callao, and is likewise answering its purpose admirably. It has lifted out of the water many large vessels—among others, the U. S. man-of war Wateree, and the Peruvian iron-clad Independencia. The latter ship weighed 3,300 tons. As the Callao dock floats in an open roadstead, some apprehension was felt that the swell would cause too much movement to admit of ships being safely docked, but it has done its work in the most satisfactory way. None of
these iron docks have doors or gates for excluding the water. The bottom part is made of sufficient buoyancy to float the vessels clear out of the water, and the equilibrium, of time dock is maintained during the time it is under water, for the purpose of admitting a vessel, by the great displacement offered by the hollow sides.
One of the most remarkable of recently constructed floating-docks was that sent out to St. Thomas (West Indies) in 1807, and designed by Mr. Frederick J. Bramwell. It is 300 ft. long, 72 ft. wide clear between the sides, and has a double bottom 0 ft. 9 in. deep. The sides are open girders, not hollow boxes, as in the Sourabaya dock, and immense rectangular air-vessels called "floats," each about 47 ft. X 11 ft. x 5 ft., are placed between the side girders, and are capable of being moved up and down by screws in order to preserve the stability of the whole while it is being raised or lowered. By an accident which happened very soon after its arrival at St. Thomas, this clock was sunk, and a hurricane which followed close on its sinking, injured it still further. It remained under water for a long time, but was raised to the surface in Jan., 1871, after operations which lasted a year and a half, and were quite unique in their way. This dock, as originally constructed, could take in and lift a vessel not drawing more than 24 ft. and not weighing more than 4,000 tons. The weight of the dock itself, with the machinery all complete, is about 3,400 tons. The docks made by the Messrs. Bennie for Cartltagena and Ferrol are even larger than the St. Thomas dock. The former weighs about 4,400 tons, and has lifted the Spanish iron-clad Kanuln,cia, weighing 5,600 tons, and supported it for 80 days.