COST OF GATES AND CAISSONS. 369 



, I. el. 



Alexandra Dock, Hull. 1 Outer lock gates constructed entirely of green- 

 beart timber, 40 feet high by 50 feet wide, built in three panels 



per foot super 280 



Whitehaven Dock.* Gates constructed of pitch-pine, except the heel- and 



mitre-posts, which are of greenheart per foot super 212 1J 



Limerick Dock. 3 Cellular gates constructed of Siemens-Martin mild 

 steel, each leaf being 42 feet 7 inches long, by 25 feet 6 inches 

 high, and 3 feet thick at the centre, cost, including all accessories 



per foot super 154 



Or, per foot square of entrance ., 1 10 9 



West India Docks. 4 Cellular iron gates 32 feet high, exclusive of gang- 

 way constructed of iron, except the heel- and mitre-posts, which are 

 of greenheart per foot super 1 15 2 



Or, per square foot of entrance ... . c . ... 2 4 2 



Havre. 5 Trans-Atlantic lock gates, 57 feet 5 inches long, by 34 feet 

 9 inches high, cellular, constructed of iron, with vertical main 

 members, and all iron galvanized e per foot super 339 



Mr. Hayter, M.I.C.E., as the result of his experience, estimates 

 the cost of iron gates at from 1 10s. to 2 per foot super 

 of gate, or an average of 1 15s. per foot super. 6 



Mr. Hayter, M.I.C.E., expresses an opinion that by the 

 omission of the roller, the spindle, and adjusting apparatus, the 

 roller-path, etc., the saving in the cost of a pair of 60 feet gates 

 may be taken to represent from 400 to 500. 7 



*. d. 



Caissons Greenock. 8 Boiling caisson closing entrance of the Garvel 

 Dock, 58 feet wide, and 28 feet 6 inches depth to invert, including 

 the lowering bridge or roadway, 12 feet 10 inches wide, hauling-gear, 

 and cover or deck of caisson-chamber 



per square foot of entrance (about) 4 18 6 



Portsmouth. 9 Floating caisson closing east entrance of the north lock, 

 82 feet wide, and 39 feet depth to invert, width of roadway over 

 caisson, 17 feet ... approximate cost per square foot of entrance 329 



Portsmouth. 10 Sliding caisson closing the west entrance to north lock, 82 

 feet wide, and 47 feet 8 inches depth to invert, including lowering 

 bridge, with 15 feet width of roadway, caisson -chamber, deck, and 

 hauling-gear per square foot of entrance 5 13 9 



Malta. Sliding caisson closing entrance to Hamilton Dock, 94 feet wide 

 by 41 feet from coping to invert, with fixed roadway deck with lifting 

 ends, to form an approach to coping level, including the cover to 

 caisson-chamber, hauling-gear, and hydraulic-engines 



cost per square foot of entrance 4 27 



Cost of Dredging. Statements as to the cost of dredging 

 are, perhaps more than as regards any other engineering detail, 



1 M.P.I.C.E., vol. xcii. p. 176. * Ibid., vol. Iv. pp. 44, 97. 



8 Ibid., vol. xcvii. pp. 335, 340. 4 Mid., vol. xxxiv. p. 176. 



Ibid., vol. xcii. pp. 451, 452. ' Ibid., vol. Iv. pp. 72, 118. 



T Ibid., vol. lix. p. 5. Ibid., vol. Ixv. p. 346. 



Ibid., vol. Ixiv. pp. 236, 237. " Ibid. 



2B 



