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locks removed and the platform with its load lowered into the water. The ingenious devices everywhere in operation about this dock, extend even to the bilge blocks which support the ship while out of the water, they being applied by a clever arrangement of pawls and ratchets, The hydraulic lift dock possesses, more nearly than any other style of dock, the advantages of dry docks on account of its proximity to the shore; repair material being readily trans- ferred to it without expense, loss of time or effort. It can be used, how- ever, only where dredging can be done and piers of reasonable Iength con- structed. Where conditions are not fa- vorable for its operation, the floating dry dock is the last resort. Advantage of Floating Dock, Roughly described, a floating dock is a steel structure consisting of a series of floating platforms, composed of large watertight tanks, attached to the base of high, hollow, floating walls on each side, there being no end walls. On top of the high, broad walls are power houses for operating the big centrifugal pumps which fill the pontoons and side walls with water, or temove it at a rate sufficient to raise a 12,000-ton battleship clear of the level of the ocean in less than two hours. They also produce elec- tric light and furnish power for the | hauling machinery and mighty cranes which run along each wail from end to end. When a ship is to be docked, water is admitted into the pontoons and the side walls until the entire structure is sunk to any desired depth. The vessel then rides through between the walls of the dock and over the submerged pontodns until in place, when the water is pumped out from the pon- toons and. the walls which rise from their natural buoyancy, bringing with them and elevating the vessel. The whole dock, both pontoon and walls, is divided into sections sep- arately connected with the pumps and water may be admitted or removed from the various sections with ease in maintaining an even keel for the vessel being raised. When there are two walls to a floating dock it resembles a dry dock in form and being U_ shaped is known by that name, but there is an- other style of this dock, known as the L or offshore dock, which has but one upright wall. This is attached to the shore by parallel booms, or in a similar manner to prevent it from listing or tilting over when the hori- TAE MarINE REVIEW zontal pontoons are supporting a load. The offshore dock is thus restricted, like the hydraulic lift dock, to some comparatively sheltered place, while the U dock, being independent, may be towed from place to place and used almost anywhere. This is its great advantage over the various styles of docks already men- tioned. Shipping business may de- cline at one port and. spring into life at another and when it so _ happens, the floating dry dock can transfer its usefulness to the new field of action, whereas, that of the other docks is ended until a return of prosperity. So, also, when a vessel is desperately wounded, either in peace or war, at some distant place and it is impos- sible to remove her in her. damaged condition, the floating dry dock can be rushed to the scene of the acci- dent as a marine ambulance and first aid to the injured be administered to the disabled vessel or it can convey her to a port where complete repairs may be made. _ The latter . proceeding is entirely practicable, so far as the stability of the floating dock is concerned, as tests have proved that it is over 20 times as stable as a ship. The naval authorities of the world seem to be almost alone at the pres- ent time in their appreciation of the true value of the floating dock. This: is. surprising when its many advantages for mercantile marine pur- poses are considered. It can be constructed more quickly . and at a much more accurately calcu- lated price than a dry dock. It can care for vessels longer than itself, owing to the fact that the heaviest portion of a vessel is in the center and the bow and stern of a vessel longer than a floating dock suf- fer no strain by projecting over the floor of the dock. The usefulness of a dry dock in this respect is limited to. its own length. Cost of Dock Service. The cost of .dock service can be more equitably adjusted by the use of the floating dock than by that of the dry dock, as the chief item of cost in dry dock operation is in pumping out the dock. It is as expensive to do this for a small boat as for a large one and therefore the small boat pays a proportionately higher rate than the larger one does. In the case of the floating dry dock this is changed by reason of the fact that the dock need only be sunk to the draught of the boat to be docked and consequently there is pumpage onfy in proportion to the size of the vessel served, which can be charged for accordingly. When the ship is elevated by the floating dock, the air getting free cir- culation around it, in a manner im- possible in the dry dock, more quickly dries the slime and marine accumu- _ lation on the hull and thereby pro- motes quicker dispatch in repair work. The workmen also work more com- fortably in the light and air afforded by the floating dock and in the winter their comfort is increased by steam pipes beneath the floor of the dock. The only point of superiority in the dry dock, as compared with the float- ing dock, as a usual thing, -are its durability and proximity to the shops and machinery necessary in ship build- ing and repairing The latter point is of importance in the saving of labor, time and expense in moving the heavy material and machinery which go into the vessel under repair. It would seem, however, that the lighterage and other charges incidental to trans- ferring repair material from the shore to a floating dock, are amply compensat- ed by the many advantages of this dock. Floating Dock of the Great Lakes Engineering Works. | The great lakes, ever abreast of the times in matters of shipbuilding, can 'boast of one of the largest and finest floating docks in existance devoted en- tirely to mercantile iwartne work. and which is approached in size by but one other in commission at the present time in the United States. It is owned by The Great Lakes Engineering Works, at Detroit, Mich., and is: 600. ft. long and. 105.14 be. tween the walls. It is not only long long enough to accommodate the largest vessels on the lakes, but also the larg; est flying the Amercan flag on either ocean, either® merchantman or _ battle- ship. In "this connection. 1t . may; be said that there are but two ocean go- ing United States vesseis longer than the largest Great Lakes vessels and but 16 of greater tonnage. The most powerful, although not the largest, floating dry dock in the world is the United States naval dock Dew- ey, stationed in the Philippines. | It is 500 ft. long, 100 ft. between walls and has a draught of 32 ft. Its lift- ing capacity is 16,000 tons and it cost $1,124,000, exclusive of the expense of towing it to the Philippines. This item of expense would have been: much greater, however, had not the govern- ment been compelled to do the towing itself. The largest towing firm in the world refused to undertake the gigantic task