244 NOTES ON DOCKS AND DOCK CONSTRUCTION. 



ordinary dock gate. In construction it is similar to a gate with 

 the addition of a special pneumatic chamber or reservoir. To 

 open the dock, air is pumped into the pneumatic reservoir, which 

 causes the vessel to float off its bearings. To close the entrance, 



the air is allowed to escape from the 

 reservoir, and the vessel then sinks to 

 its place. 



The Bellot Lock gates or caissons 1 

 at the Port of Havre, designed by M. 

 Guillain, are on this principle, Figs. 23G, 

 237, 238. Each of the leaves is 54 feet 

 2 inches wide and 35 feet 11 inches 

 high. They are made with vertical 

 frames placed about 40 inches apart, 

 and two horizontal intermediate frames, 

 which with the top and bottom mem- 

 bers divide the leaf into three equal 

 parts. The space comprised between 

 the upper and first of the intermediate 

 frames is open, the remaining part of 

 the leaf is formed partly as an air- 

 chamber and partly as a ballast- 

 chamber into which water is admitted ; 

 by this arrangement the weight on the 

 turning-post is reduced from 155 tons 

 to 25 tons. Access to these chambers 

 is obtained from the upper part of the 

 gate ; and the water can be driven out 

 of the lower compartments by forci: 

 in compressed air, the pump employed 

 for this purpose being placed on a 

 travelling-carriage on the top of the gate. The operations of 

 opening and closing are effected by chains actuated by hydraulic 

 pistons. 



West-India Dock Gates. 2 These gates (Figs. 239 to 241) are 

 of iron with the exception of the heel-posts, meeting-posts, ninl 

 sill-pieces, which are of greenheart timber. The gates jin- 

 cellular, with two skins formed of iron plates separated by and 

 riveted to horizontal and vertical ribs. The gates are curved 

 outwards, but the sill-piece is straight to fit the sill. The 



1 Engineering, vol. xlviii. p. 620. * M.P.I.C.K, vol. xxxiv. p. lf>9. 



FIG. 23G. 



