256 NOTES ON DOCKS AND DOCK CONSTRUCTION. 



The upright angle-irons in the centre of the caisson are 

 4 inches by 4 inches by J inch riveted at the intersections 

 to the longitudinal angle-irons and the cross-beams. The 

 horizontal stringers in the lower compartment are 15 inches 

 in width and J inch in thickness, and are screwed in the same 

 manner. The two water-tight bulkheads are formed of plating 

 of the same thickness as the corresponding strakes of the skin 

 plating and stiffened by angle-irons, thus forming very efficient 

 cross-bracing. The roadway deck is of fir planking 3 inches 

 in thickness, caulked and made water-tight, and is 2 feet below 

 the top of the caisson, the sides of which form the handrails. 

 The meeting-face of the caisson is of 6-inch by ^-inch plate iron, 

 and abuts against the timber meeting-face of the dock. Ring- 

 bolts are fixed to the caisson for securing the tackle used in 

 hauling the caisson into and out of the berth. The ends 

 of the caisson are protected by fenders of teak which abut 

 against the skewbacks or abutments of the dock entrance. 



The caisson is provided with sinking valves, drainage cocks, 

 and sluices similar to those previously described ; and in 

 addition there are two sluices or mud ports at the level of the 

 dock sill for the escape of muddy water. Each sluice is 18 

 inches by 9 inches clear dimensions, formed of plate iron with 

 a cast-iron flap valve on the outer end worked by chains from 

 the deck. 



Barry Dock Caisson. 1 This caisson (Figs. 255, 256) is a 

 floating vessel of a somewhat unusual section, and is designed 

 to be used in several positions. 



The length is 85 feet, and the beam 'midships 24 feet. 

 The height at the ends is 42 feet, and at the centre 48 feet 9 

 inches. 



The keel is formed to a radius of 137 feet, to correspond 

 with the inverts, the meeting-faces being lined with greenheart 

 15 inches by 7 inches. The caisson is ship-shaped on one side, 

 and flat on the other, so as to enable it to fit against any of the 

 faces, and to be placed, when out of use, in a recess provided 

 for it in the wall, when it will not project beyond the lino 

 of the wall. It is divided vertically by two water-tight bulk- 

 heads, and horizontally by eight decks, two of which nn> 

 water-tight, forming air, and water-chambers. The lower parts 

 of the skin are of wrought-iron, and the upper 19 feet of steel. 

 1 M.P.I.C.E., vol. ci. p. 140. 



