DOCK GATES. 229 



through some mal-adjustment, the roller had never borne upon 

 the roller-path, but was about inch clear. No difficulty had, 

 however, been experienced in working the gate, and the fact 

 would not have been known had the gate not been removed. 

 The span of the entrance was about 40 feet, and the rise and fall 

 of tide 30 feet. This fact goes to support the view that rollers 

 under gates of moderate spans are unnecessary. 



Mr. Stoney is also of opinion l that, although the practice, 

 following precedent, has been to support large gates on rollers, 

 it is by no means desirable or necessary, for iron gates may 

 be supported on the pintles alone, and in support of this 

 opinion, alludes to the fact that when the roller and path 

 of one leaf of the gates of the Dublin Graving Dock got out 

 of order, instead of going to the expense of repairing the defects 

 under water, the expedient was tried of tying back the upper 

 pintle by strong wrought-iron bars with adjusting screws, 

 and lifting the roller so that the weight of the gate did not 

 bear on the roller-path. The result was that this leaf was far 

 easier to move than the other one, and gave no further trouble. 



On the other hand, Mr. Abernethy 2 strongly objects to the 

 abandonment of rollers, on account of the tendency of the 

 unsupported gate to drag forward, a condition which involves 

 a continuous strain on the masonry at the upper part of the 

 side walls. 



Sir W. Armstrong is of opinion 3 that it is not so much 

 a question of sufficient rigidity of gates to support their own 

 weight as there can be no difficulty in making them, whether 

 of wood or iron, of sufficient strength to carry their own over- 

 hanging weight as the wear and tear on the heel-post. Without 

 the support of a roller a thrusting force is brought against the 

 bottom of the hollow quoin and a pulling force upon the upper 

 holding or anchor-straps. As regards the top bearings there 

 is no great difficulty, as they can be made sufficiently strong 

 and efficiently anchored back, and can always be lubricated 

 and adjusted as wear takes place. As regards the heel-pivot, 

 however, the case is somewhat different ; there is a continual 

 grinding due to the weight of the gates, the effect of which 

 cannot be met by adjustment, and access is difficult; therefore, 

 in his opinion, it would be unwise to abandon rollers and roller- 

 paths in the case of heavy gates. 



1 M.P.I.C.E., vol. lv. p. 113. * Ibid., Yol. 1. p. 90. Ibid., p. 97. 



