224 NOTES ON DOCKS AND DOCK CONSTRUCTION. 



too long, in which case they will nip on the outer edge of the 

 meeting faces. 'By wear, they may become a little too short, 

 causing them to nip on the inner or dock side, or foreign 

 substances may lodge between the heel-post or the sill and 

 the stonework. 1 In practice, this difficulty is met by slightly 

 rounding the meeting faces, or by chamfering the edges so as 

 to bring the line of pressure more to the centre of the mitre- 

 posts. 



Staunchness, In order to ensure the staunchness or water- 

 tightness of the gates at the centre, it is sometimes the practice 

 to arrange that they first close at the bottom of the mitre-posts, 

 leaving them a little apart at the top, so that the gates, touching 

 the sill at the bottom, gradually close by a slight twist, as the 

 pressure increases. 



Opening and closing Gates. The usual method of opening 

 and closing large gates is by an arrangement of chains. Each 

 gate-leaf is provided with two chains, one for opening, and the 

 other for closing ; one being attached to the front and the other 

 to the back of the gate, as low down as possible, and as near 

 to the rollers and mitre-posts as can be conveniently arranged. 



The opening chain passes from the back of the gate through 

 a culvert in the wall of the gate recess, up to the hauling 

 machinery, situated on or below the quay level. 



The closing chain is attached to the front of the gate; it 

 crosses the passage and passes through a culvert in the opposite 

 side wall, at a convenient distance outside the hollow quoin, to 

 the hauling machinery. 



Formerly the hauling gear consisted of ordinary crab-winches 

 or capstans, worked by manual labour. Now, however, hydraulic 

 power is almost universally adopted; applied to pressure-rain 

 fitted with multiplying speed-gear for hauling on the chains; 

 by small engines working crabs placed underground and attached 

 to the usual arrangement of chains ; or by rams acting directly 

 on the gates without the intervention of hauling chains. 



The method adopted at the Victoria Dock Extension, 

 London, 2 is shown by Fig. 210. The arrangement consists of 

 two hydraulic rams of 1G inches diameter to each gate, one of 

 12-feet stroke, and the other of 8-feet stroke. The chains are 

 attached to the gates in the ordinary way, and arc guided to 

 the rams by vertical and horizontal rollers built into the walls. 

 M.r.I.C.E., vol. Iviii. p. 159. * JWd., vol. lix. p. 20. 



