A Treatise On The Principles And Practice Of Dock Engineering

DOCK GATES. 345 Figs. 297, 298, and 299 illustrate tlie outer lock gates of the Alexandra Dock at Hull.* Each leaf consists of three framed greenheart voussoirs, similar in design to the Liverpool gates. In all the preceding cases the wood panels are framed in between the ribs. In the diagrams of the gates at the North and South Looks, Buenos Ayres t (figs. 300 to 303), it will be observed that the sheeting is continuous throughout the height of the gates. The iron gates at Kidderpur Docks, Calcutta,f are shown in figs. 304 to 309. The heel and mitre-posts are of greenheart. A particular interest attaches to the pair of metal gates exhibited in figs. 310 to 312, as indicating an extremely ingenious device for overcoming a natural difiiculty. The gates close the entrance to a graving dock on the River Tyne.§ The longitudinal axes of dock and river meet at an acute angle (fig. 313). Had the gates been constructed in the ordinary manner, with symmetrical leaves, and the line through the heel-post centres perpen- dicular to the axis of the dock, a considerable length of one quay would have been excluded from the graving dock, which would have been much shorter in conséquence. By adopting the form of two unequal leaves, the designer, Mr. J. M. Moncrieff, has been enabled to utilise the axial length to its fullest extent. The dock entrance is 49 feet wide, and the lengths of the leaves are 41| and 22^ feet respectively, their chord forming an angle of about 12° 35' with the normal to the dock centre line. Under this arrangement the heel-post of the larger gate turns through a greater angle than is usually the case, and the hollow quoin has been purposely kept narrow to enable the end of the leaf to clear it. The inner and outer faces of the shorter leaf are concentric throughout, but the longer leaf needed the stiffening which could only be afforded by increasing the thickness or width at the centre, and accordingly a flatter curve has been adopted for the inner face. A pair of iron gates at Dunkirk]] (figs. 314 to 319) are included as an example of the type of vertical girders. They have flat, parallel faces, and bear against a pointed sill. The extreme length of each leaf is 3.8 feet 4 inches, and the entrance closed is 69 feet wide. The plating covers the whole of the outer and the lower half of the inner face, forming a watertight chamber there. In alater type of gate erected at the same port the arrange- ment of the watertight compartments is slightly modified, as shown in the line diagrams, figs. 320 and 321. * Hurtzig on “The Alexandra Dock, Hull,” Min. Proc. Inst. O.E., vol. xcii. 4 Dobson on “Buenos Ayres Harbour Works,” Min. Proc. Inst. C.E., vol. cxxxviii. $ Bruce on “The Kidderpur Docks, Calcutta,” Min. Proc. Inst. C.E., vol. cxxi. § Moncrieff on “Dock Gates of Iron and Steel,” Min. Proc. Inst. C.E., vol. cxvii. Il Vide Discussion on “ Dock Gates,” Min. Proc. Inst. C.E., vol. lix.