The following text may have been generated by Optical Character Recognition, with varying degrees of accuracy. Reader beware!

14 with the ebb of the tide. As it es- capes the vessel slowly settles until she reposes upon the keel blocks at the bottom of the dock, with her sides supported by timber struts and shores resting upon. steps. previously men- tioned. Should the dry dock be lo- cated on a nontidal body of water the dock is pumped out by means of large centrifugal pumps after the ship en- ters. When the two new docks projected for the great lakes are completed there will be upon the great lakes, 13 dry docks measuring over 500 ft. in length. - This is conclusive evidence of the high development of the ship building and marine industries of these inland seas when it is considered that on the Atlantic and Pacific coasts of the Uni- ted States and Canada combined, there are but ten docks of equal size. There are but five dry docks in the - world larger than the 750-ft. dock at diotain on Lake Erie. Of. these, the largest is at Liverpool and is 925 ft. in length, the one at Glasgow is Bey ft, that at Tilbury is 875 {t.; the one at Belfast is 800 ft. and the one at Newport News, Va., is 860 ft. in length. Largest Dry Dock in the World. The distinction of possessing the largest dry dock ever built, now held by Great Britain, will soon be wrested from her by the United States as there is in course of construction at San Francisco a concrete dock which will measure when completed, 1,05uU ft. in length, 144 ft. in width at the top and 40 ft. at the gate. This dock will be eclipsed in size, however, by the dock which will be constructed by our government at Pearl Harbor, Hawaii. Its length will be 1,195 ft. and by means of caissons it will be possible to divide it into. an inner and outer dock, an innovation so far as American docks are concerned. : Dry docks are very expensive struc- tures, but the cost of those built by private concerns for public use is quite .moderate when compared with that of government docks for navy pur- poses, The naval' dock at Boston which is only 253 ft. long and 86 ft. wide, completed in 1833 when labor and material were cheap, cost $700,- 000. The Brooklyn navy yard dock, finished in 1851 and the finest in the world at that time, cost complete with machinery $2,000,000. This dock is 307 ft. long by 98 ft. wide and has walls of solid masonry 36 ft. wide. The Mare Island Dock, near San Francisco, was under construction 12 years. and represents an expenditure of over $3,000,000, THE Marine REVIEW The rapid and constant increase in the size of vessels has compelled the building of dry docks of the immense sizes mentioned within a comparatively recent period. The huge ocean liners and mighty lake freighters of the pres- ent day could no more get into the docks of twenty-five years ago than a man could squeeze himself into the garments of his five-year-old son. Except upon the Great Lakes, how-. ever, the docking facilities have not kept pace with the demands of mod- ern shipping. This is due not only to the enormous expense of the land suf- ficient for dry dock purposes, of ex- cavating same, of building the walls and gates, of installing machinery and of the constant repairs necessary, but also to the oftentimes insurmountable engineering difficulties met with in a project of this kind. The location most available and convenient for a dry dock is often so low and marshy or sandy and porous as to entirely pre- vent its construction or at least at a prohibitive cost. Tke Floating Dry Dock. The efforts to overcome these diffi- culties have proved the truth of the old adage that, "necessity is the mother of invention." The invention in this case is that of the floating dry dock ana. of the hydrantic' lift. dock. ~ The latter is in use at present only on the sea coasts and is a modern develop- ment of the gridiron. submerged platform, over which ships are floated at high tide but differs from its ancient prototype in that in- stead of the ships settling on the plat- form as the tide recedes, the platform approaches the ships immediately, from below, and elevates them above the surface of the water without hav- ing to wait for the tide to ebb. The finest example of this variety of dock and one which has attracted world wide attention from engineering ex- perts as a triumph of their profession, both as to construction and the appli- cation of hydraulics, 1s that of the Union Iron Works at San Francisco, Cal. Owing to the fact that their plant is located on a mud flat, it was impos- sible to construct a dry dock and as it was absolutely necessary to have some means of docking vessels for exten- Sive repairs, their famous lift dock was designed. Piers were constructed consisting of twenty-two iron cylin- ders, thirty-six on each side, in which piles 100 ft. long were driven; the cylinders extending several feet below the bottom of the water. These were used: to prevent the destruction of the piles by the ship worm which, in San It consists of a Francisco harbor, is ruinous to vessels' hulls and other submerged Wooden structures. Each cylinder is crowned by a_ heavy iron cap, and two hea steel girders, extending the full length of the dock on either. side and rest. ing on the cylinders, complete the Piers. On each of the piers are eighteey hydraulic rams, 30 in. in diameter with a stroke of 16 ft, which are suspen. ded between the cylinders by immense castings attached to the pier girders On top of each ram is a heavy pulley, six feet in diameter, over which pass eight steel cables, each two inches jn diameter. One end of each cable js secured to the bed plates supporting the hydraulic rams, while the other js attached to the side girders of the lifting platforms which is thus sys. pended between the two sets of rams by 288 cables. Each cable has been tested with a load of 80 tons, so that the platform is therefore capable of lifting 21,000 tons. It is built of cross and longitudinal steel girders and js 62 ft. wide and 440 ft. long. The rams are operated by four im- mense steam. pumps and every opera- -- tion of the dock has been so _ scien- tifically arranged that for each one foot movement of the rams, the plat- form rises two feet, thus giving a to- tal rise of 32 ft. which elevates the platform 10 ft. above the water at high tide. Feature of Union Iron Works' Dock. A regulator attached to the pumps controls the throttle valve of the en- gine operating them, and as the ship leaving the water becomes heavier on the platform and a greater strain on: the rams and consequently on_ the pumps, this regulator causes the en- gine to speed up to meet the addi- tional requirements until the full pres- sure of 1,100 lbs. per square inch is attained. An automatic arrangement ling the movement of the rams, in- sures the raising of the platform on an even balance, as otherwise, an un- equal distribution of the load upon it would cause the rams carrying the portion bearing the least weight to rise more rapidly than the others with disastrous results. When the platform is elevated to the full stroke of the rams, a line of locks on top 'of the foundation git- ders on each side are shoved under the platform by automatic hydraulic ma- chinery and the platform lowered on- to them, thus relieving the rams and sheaves of their heavy burden until the work on the ship is completed, when the platform is again lifted, the control-