242 NOTES ON DOCKS AND DOCK CONSTRUCTION. 



to avoid the necessity of making a water-tight joint at the 

 hollow quoins, the method described by Mr. Hayter 1 was 

 adopted, viz., by making the gate a little longer and forming 

 the joint on a plane surface. 



The strains were calculated and the thickness so adjusted 

 that the tension of wrought iron should not exceed 5 tons nor 

 the compression 4 tons per square inch. The pressure on the 

 brasses of the thrust-blocks, when the water is level with tho 

 top of the gates, is under 1 ton per square inch, and then the 

 pressure exerted on the brickwork by the cast-iron thrust-blocks 

 does not exceed 5 tons per square foot. The pressure when the 

 water is at its normal level is about 50 per cent. less. 



The details of construction can, perhaps, be described best by 

 giving the following particulars, taken from the specification : 



The actual length of each gate, exclusive of woodwork, is 

 35 feet 3 inches, and the width at centre 2 feet 9 inches, and at 

 ends 1 foot 9 inches. The inner face is straight, but the outer 

 is to a curve of about 154 feet radius, and all work is bent or 

 cut to this curve. 



The horizontal bottom and top plates of the tank are J inch 

 in thickness, each in three pieces, or plates, with f-inch butt 

 straps 12 inches in breadth, and treble riveted; the inter- 

 mediate plates are f inch thick, with J-inch butt straps. Man- 

 holes 18 inches by 14 inches are cut at the ends. The top plate 

 or deck is J inch in thickness, with manholes, welded rings, and 

 covers made water-tight. The vertical end plates are % inch in 

 thickness, each in one length of 20 feet 8 inches and 1 foot 

 9 inches in breadth. The vertical plates forming the inside of 

 the manhole trunks are in three lengths of about 3 feet 5f i} inclii-s 

 3 feet 5^g inches, and 11 feet 7 inches respectively, and J inch 

 in thickness. The plates of intermediate bulkheads or bracing 

 are f inch in thickness of similar lengths, and have holes cut to 

 lighten them. The skin plating of the inside face consists of 

 three strakes % inch in thickness, the four strakes above it be in if 

 j 7 ^ inch, f inch, fy inch, and fa inch in thickness respectively. 

 The skin plating of the outside face consists of three strnk-< 

 forming a tank of J inch in thickness, and with stiffening pi' 

 at the sluices. The strake forming the flange of the deck or i )> 

 girder is 12 inches in width and inch in thickness, in 

 ] -ngths, with 12-inch cover straps. 



ol. lv. .. 7::. 



