300 NOTES ON DOCKS AND DOCK CONSTRUCTION. 



the basin and grounded. The timber-ways on the slip 

 then in exact line and level with those on the dock, the vessel 

 can be hauled on shore by hydraulic power. 



The entrance to the basin is closed when required by a 

 floating caisson, so that when pumped out it can be utilized as a 

 dry dock for effecting repairs to the floating dock. 



Off-shore Floating Dock. This type of dock (Fig. 295), used 

 for lifting purposes only, is suitable for any sheltered position. 



It is similar in all essential particulars, as regards construc- 

 tion, to the depositing dock, except that instead of being pro- 



FIG. 295. 



vided with a balancing or outrigger pontoon it is kept in a hori- 

 zontal position during the rise and fall of the water, and its 

 stability ensured during the operation of raising or lowering by 

 parallel-motion booms connected to the vertical side of the dock 

 and to vertical columns erected on shore. The arrangement of 

 these booms is shown by Fig. 295. 



Depositing Dock, This class of dock consists of a rectangular 

 box side, divided into separate water-tight compartments, to 

 which are attached a series of pontoons forming the bottom. 

 These pontoons are firmly connected at one end to the vertical 



