306 NOTES ON DOCKS AND DOCK CONSTRUCTION. 



The dock is divided longitudinally into eight water-tight 

 compartments on each side of the keel, and each of these is 

 again divided into three smaller compartments, not water-tight. 



Transversely it is divided into three compartments on each 

 side of the keel, termed respectively the load-chamber, the 

 balance-chamber, and the air-chamber, each being water-tight 

 and distinct from each other. 



The dock, when not in use, has its chambers empty with 

 the exception of the air-chamber, in which a quantity of water 

 is always kept for supplying the pumps for filling the load- 

 chambers when required. 



The process of docking is as follows : The load-chambers 

 are first filled (Fig. 303) by the pumps driven by engines fitted 

 on the top of the dock sides, the water being taken from the 

 air-chambers. After this has been done, valves fitted in the 

 lower part of the balance-chamber, and communicating with 

 the sea, are opened and the chambers filled (Fig. 303) ; this 

 operation sinking the dock to such a depth that, by opening 

 valves fitted in the caisson, water can be run into the dock in 

 order to bring the water inside up to the level of the outside 

 water, when the caissons can be taken out, there being then a 

 depth of 27 feet of water on the blocks. 



The ship having been brought over the blocks, the water 

 in the load-chambers is allowed to run out, and the balance- 

 chambers partly emptied, if required, as shown by Fig. 304. 

 The ship is then breast shored, and the caissons put in place, 

 after which the water remaining in the dock is run into the 

 air-chambers, as shown by Fig. 305, by means of valves fitted 

 in the floor. In this state the dock remains until the vessel is 

 ready for undo eking. 



Should the vessel not be exactly on the centre of the blocks, 

 the dock is brought to a perpendicular position by letting a 

 portion of the water out of the balance-chamber on one side or 

 the other as the case may require. 



To undock the vessel, water is run into the dock through 

 the valves in the caisson, and the balance-chambers filled up; 

 this brings the dock into the position shown by Fig. 306 with 

 the ship afloat ; the caissons are then removed, when the vessel 

 may be undocked. 



To render the dock again ready for use, the water in the 

 air-chambers is pumped into the load-chambers and run into 



