On Docks— Dry, Wet, and Floating. 207 



The simplest kind of floating dock is a large box capable 

 of containing the vessel requiring repair, with space sufficient 

 to allow the shipwrights to work : into this the ship is floated, 

 the gates are shut, and the water pumped out, — the whole 

 gradually rising till the weight of the dock and the vessel 

 in it is balanced. 



It is necessary in this case that the dock should not be 

 placed in deep water, and that it should have either a level 

 bottom or a soft mud to ground upon, as when the water is 

 admitted the whole will of course sink. 



The next kind is one in which, in addition to the simple 

 box, there are water-tight chambers sufficient to float the 

 dock itself when the water is allowed to enter it : by 

 admitting water into these chambers, or by pumping it out, 

 the dock may be sunk or raised to the proper draft of water 

 of any vessel which may require repair. 



The third class, or those which may be more properly 

 called lifting docks, will in principle include the hauling-up 

 slip, — a contrivance by which vessels, when floated into a 

 frame rolling upon trucks, are hauled up an inclined plane 

 till they are beyond the reach of high tides : but I shall not 

 enter into any of the details of this plan at present. Those 

 to which the term hfting docks is more especially applied 

 consist generally of a series of frames supported from piles, 

 or piers by chains, which chains may be acted upon by 

 various descriptions of mechanical force, — such as hydraulic 

 rams, or steam engines working wheels, round which the 

 chains are wound, &c. 



The objections to the floating docks are the difficulties 

 which are encountered in repairing them. Should any 

 accident happen to the floor, the only mode by which it can 

 be repaired is by hauling the dock upon ways laid on a 

 sloping beach till the shipwrights can get at the floor ; and 

 this would involve a large expenditure of labour and material. 



