280 NOTES ON DOCKS AND DOCK CONSTRUCTION. 



sluice is 11 feet 6 inches below the average bottom of the basin, 

 which is sloped down to the sluice. 



To protect the foundations of the sluice from all danger of 

 being undermined by the scouring action of the current, a solid 

 wall of masonry 16 feet 6 inches thick was carried right across 

 the outer face of the foundations of the sluice, so as to overlap 

 the abutments on each side for a length of 26 feet 3 inches, 

 and carried from the sill down to the clay, a depth of 

 54 feet. 



The size of the inlet opening is sufficiently large to enable the 

 basin to be completely filled during the two and a half hours of 

 nearly slack water that occurs at Honfleur directly after high 

 water. The water at this period is comparatively clear; by 

 this precaution, the rapid silting-up of the sluicing-basin is 

 avoided. 



The inlet opening is composed of ten bays separated by 

 masonry piers 6 feet 6 inches in width. Each bay is 32 feet 

 10 inches wide, and is closed by three gates opening inwards, and 

 turning upon a horizontal axis on the apron of the weir. Each 

 gate is 11 feet 1| inch wide, and 7 feet If inch high. These 

 gates are placed at such a level that when raised their top 

 reaches the level of the highest tides, and when lowered they are 

 2 feet below high-water level, so that they admit the clearest 

 upper layer of water only into the basin. Each gate is worked by 

 means of a chain, one end of which is fastened to the gate ; it 

 then passes in succession over two pulleys, the first having its 

 axis parallel to the gate, and the other at right angles to it. 

 By this means the direction of motion of the chain is converted, 

 on passing through the second pulley, into a horizontal motion 

 parallel to the line of the gates. Then, by using chains of equal 

 length, having their other ends fastened symmetrically along a 

 beam capable of moving backwards and forwards along a bri!p' 

 placed across the piers of the weir, the gates can be moved in 

 unison up or down by a movement imparted to the beam. Two 

 of these beams are used for working the thirty gates. Each beam 

 is connected with a pair of conjugate pistons, working in two 

 cylinders containing water, and communicating with hydraulic 

 machinery. The hydraulic power acts merely as a brake when 

 the gates are being lowered, and only imparts motion when the 

 gates are being raised. 



A volume of 054,000 cubic yards of water is dischai'ged 



