A DRY DOCK is a masonry or timber -lined ba sin connecting: with the harbor water, and hav ing approximate ly the shape of a ship's hull. into which a vessel can be floated and which can then be closed and emptied so as to leave the bot tom of the vessel dry and available for cleaning and repairs. In Europe it is the almost Ind Versal practice to line dry docks with masonry. In the United States the prevailing practice has been to build timber dry docks. although there has recently been a reaction against timber docks. the present time a timber dock can he built for about 25 per cent. less money, but engineers are quite unanimous in opinion that the greater oust of masonry docks is compensated for by their lower cost for re pair, and their far greater durability, strength. and safety. The following figures show the leading dimensions of some of the more impor rant foreign and _linerican dry docks: London I:Iackwall, 471\ 63 X •:1 feet : Tilbury, s46 X 711,35 it (can be divided) ; Liverpool, NV %V «nada Graving Dock. 925 X 94 met. and 565 X 711 X 22.4 leo. and 71IS X 60 X 22.10 feet ; 750 X S.i X 26.7 feet SOO X no \ 23.s feet ; lna:gow, StiO X S3 X 26.1; feet : 660 X !II X 32.6 feet : Plymouth, 464 X SO X 22. feet ; 551) X 63 X 21.6 feet : Leith. 410 X 70 X 21 feet ; Barrow, 3)))) X 60 X 22 feet : New le, 530 X SI) X 26.8 feet ; 61S X 62 X 27 feet ; Newport, 520 X 65 X 32 feet; Barry, two docks, 747 X GO X 28 feet (divided). and (i10 X 63 X 29 feet, in construc tion; Antwerp, 45!) X 81 X 23 feet ; Bordeaux, 340 X 72 X 27 feet ; Dunkirk, 622 X IIS X 21i feet ; Genoa,. 622 X 68 X 26 feet ; Bremerhaven, 7011 X SO X 31 feet : Sydney, 640 X 66 X 20 feet, and 603 X S4 X 32 feet : Buenos Ayres. 5S7 X 65 X 26 feet ; 617 X 57 X 30 feet ; Po•ts mouth. N. IL, 350 X 10 X 2.1 feet : 110-ton, Ala,s., 3671.4 X GO X 23.8 feet ; Xew Vork. N. Y., 439.8 X S5 X feet. and 33Sli X 66 X 25ii feet, and 112(12 X 1 X 29 feet : League 1st and. Pa.. 139.S X S5 X feet ; Norfolk, Va., X 60 X 23 and X S3 X feet : Port Boyal. S. t59 X 97 X 26 feet ; Alare Island. Cal., 459 X X feet ; Puget Sound, Wash., X 92.6 X 30 feet. Di the eleven American 11:11111.11, three only are built of masonry.
In IS9S-99 authorized the eonstrue lion of four new t WO of ina-onry and two of timber, at the Government Navy Yards at Boston, Portsmouth. N. 11.. League
1-land, Philadelphia, Pa., and Island, San Franeiseo. Cal. The following are the dimem -.ion- adopted for these docks: OATi pia DOCKS hatebeen lit in eon .-iderable number, in both Europe and .\ineri•a, the majority of them being for of from 2000 to 4000 ton,. tine of the largest and most re( tilt of these i? that for the Cnited Natal Station at Algiers, La. The Algiers Dock has a lifting capacity of 15,000 ton, la hattle•ship of this is shown in the sectional drawing) and eonsi,ts of live separate pontoons or water-tight boxes. Three of these the bottom of the dock, while two form the side walls. These pontoons are divided by nicans of interior into forty water-tight compartments and each of these compartments an inlet for the ,ion of sea-water and an outlet commeted by piping with for expelling the or. The operation of raising a ves sel with the dock is sub stantially as follows: \Viten a II compart ments of the dock are emp ty it float, at.
a draught of four feet. To sink it, the valve, are opened. ad mitting water to the various e o iii I) a r t moats. It may he sunk to such a depth that it will take in a vessel of 30 feet draught. The vessel is (looted in and earefully centred over the la el-blocks. and the pumps are then set to work to remove the water from the compartments. In pumping out the water the chief care is to see that the dock keeps level. This is aecom 'dished by altering the of pumping front the I litterent compartments to suit the condi tion•. .\- the dock the vessel out of the water, shores are inserted between the hull and the side ;11111 the pumping is continued until the floor of the dock is raised above the water-level. The keel-blocks are high imough to raise the bottom of the vessel some four feet show the floor of the dock at the point next the keel, giving space enough to work underneath the vessel. Duly a few on dock eim•truelion are now available. Colson, A Wes On pork ronsfritrtion (London, 14941. and Steven...in. and COIISt of Ilarbor.e (Loudon. are standard treatises, but both are wanting in the dismission of reeent work. A recent book in l'reiteli ('ardniii•, lass porig mod. ra. s (Paris, 1900). By far the most fruit ful sources of information are the proceedings of the various engineering societies and the engineering journals.