278 NOTES ON DOCKS AND DOCK CONSTRUCTION. 



cut across the full width of the channel, the ship was " fleeted " 

 down about 25 feet into position for a fresh cut. 



It was estimated that the stream immediately astern of the 

 ship had a velocity of from 12 to 14 miles per hour, and at one 

 quarter of a mile distance a speed of 3 to 5 miles, according to 

 whether the vessel was working with or against the tide. The 

 stream carried the bulk of the eroded material across the bar 

 into deep water, while a portion was thrown up as a bank on 

 the side of the channel towards which the propeller turned. 



The longitudinal section of the cut showed a series of trans- 

 verse waves; by using a drag or rake to break down these 

 ridges, a further depth of about 2 feet could have been obtained 

 at a very small additional cost. 



Honfleur-Sluicing Basin. 1 The sluicing-basin constructed for 

 the purpose of maintaining the entrance channel has an area of 

 143 acres, and was formed by enclosing a portion of the foreshore 

 (Fig. 282). The embankment enclosing the basin is 40 feet 

 wide at the top, and has a slope of 3 to 2 on the inside and 

 3 to 1 on the out or seaward side. The inner slope is covered 

 with a layer of stones 20 inches thick, on which is laid a course 

 of rubble stone of the same thickness, set in Portland cement. 

 A trench of compact earthwork puddle 3 feet 3 inches deep 

 was formed at the bottom of the inner slope, to protect the bank 

 against the infiltration through the silty foundation. The 

 outer face is pitched with large blocks of rubble stone, and the 

 foot protected by a deposit of rubble stone, extending to a depth 

 of 42 feet below the surface. 



The sluice has four openings, each 16 feet 6 inches wide, 

 separated by piers 6 feet 6 inches in width. Each opening is 

 closed by a sluice-gate, turning upon a nearly central vertical 

 axis. The panel on one side of the axis is made 2 inches wider 

 than the other panel, to facilitate the closing of the gate against 

 the outgoing current. The working of the sluice is easily effected 

 by opening a little valve in the wider panel of the gate, which 

 reduces the water pressure on that panel below the pressure on 

 the other panel, so that the gate revolves and places itself in a 

 line with the stream as soon as it is released by a turn of the 

 post at the side, which retains it in place. The gate is shut by 

 giving it a sideways push, after the latter has been closed, so as 

 to make the current act on the larger panel. The sill of the 

 1 M.P.I.C.E., vol. Ixvii. p. 464; and Le Gfnie Civil, vol. i. p. 554, 579. 



