298 NOTES ON DOCKS AND DOCK CONSTRUCTION. 



into two parts, the upper serving as permanent air-chambers 

 into which no water is allowed to enter. 



The working of the dock is as follows : Supposing it to be 

 empty, and the floor well above the level of the water, the sluices 

 are gradually opened and the water allowed to flow into the 

 different compartments. The dock will then commence sinking, 

 care being taken by watching the gauges that the supply of 

 water is so regulated that it may sink uniformly and gradually. 

 When the dock is sufficiently deep to take in the vessel, the 

 sluices are closed, and the vessel hauled over the keel-blocks, 

 and the breast and other shores applied. The water is then 

 pumped out; thus, for every one ton of water pumped out one 



SCALE 



40 50 



.00 



FIG. 293. 



ton of ship and dock is lifted. This operation is continued until 

 the floor of the dock is well out of the water. 



This dock partakes of the character of a transporting dock, 

 inasmuch as it is used for removing vessels from the harbour to 

 the slips. 



When it is desired to land a vessel, the dock is hauled into 

 small basin sufficiently large only to contain it, and of a unifoi 

 depth of 16 feet 6 inches from the top of the quay. 



From the end of this basin there are three lines of horizont* 

 ways (Fig. 294) radiating from the centre from which the en< 

 of the basin is described. Each slip is provided with four liiu 

 of timber-ways, spaced about 10 feet apart, with keel-blocks 

 correspond with those on the floating dock. 



In transferring a vessel to the slip the dock is floated inl 



