DOCK GATES. 



235 



the quoin and the post, in which loose material may lodge and 

 prevent the gates closing with accuracy. 



Avonmouth Dock Gates. 1 These gates consist of oak heel- 

 and mitre-posts, except in the case of the outer pair of gates, 

 which are of greenheart, with ribs, intermediate posts, and 

 walings of pitch-pine and MemeL The thickness at the heel- 

 and mitre-posts is 2 feet 8 inches, and at the centre of the leaf 

 about 2 feet 11 inches, exclusive of the walings. The back when 

 closed forms, from one hollow quoin to the other, a continuous 

 arc of a circle, the radius of which is 50 feet. 



In the upper gates, the three layers of cross-pieces, of which 

 the thickness of the gate is made up, are all cut to the same 

 radius, and are divided into lengths or segments, the ends of 

 which overlap or break joint with each other, and meet in a 

 vertical post 12 inches square. 



The objection to this arrangement was that nearly all the 

 segments required an 18-inch baulk of timber to cut them to 

 the proper curvature, involving a waste of about 50 per cent. 

 To reduce this waste, and retain the same curvature and thick- 

 ness of gate, the arrangement as shown in Figs. 223, 224, 225, 

 was adopted for the middle and outer gates. In this design, 

 the back of the ribs is the only curved face that has to be cut, 

 all the other joints or faces being straight, involving scarcely 

 any waste of timber. The ends of the rib segments do not 

 break joint as in the upper gates, but meet in an intermediate 

 post composed of six vertical pieces strongly built together. 

 The whole of this system of ribs and posts is thoroughly braced 

 and tied together by wrought-iron straps and bolts and timber 

 walings. 



The timber work of the gates was prepared and fitted under 

 a gantry on the works. It was then taken to pieces, con- 

 veyed to the lock, and built in place with travelling-cranes and 

 hydraulic jacks. 



As the work approached completion, it was found, when 

 a gate was moved on its roller, that it did not stand plumb, 

 but hung forward to the extent of 14 inches. It would have 

 been impossible to have obtained a good mitre joint with so 

 much deviation from the perpendicular as 14 inches. To remedy 

 this defect, it was decided to fix a small roller under the mitre- 

 post, and to lay down an additional roller-path on the platform. 

 1 M.P.I. C.E., vol. lv. p. 11. 



