HYDRAULIC LIFTING-DOCK. 3" 



valveman throws the water into either group or to waste at 

 pleasure. 



"The pontoons are not essential for raising or docking a 

 single vessel, for it is evident that the lift as described is all 

 that is required for that purpose. The girders might be con- 

 nected together by other longitudinal girders, so as to form a 

 sufficiently rigid platform, or the whole might be formed into 

 a pontoon which would support a vessel after it was raised. 

 Such an arrangement would be more economical and convenient 

 than any ordinary dock, but it would accommodate only a single 

 vessel, whereas, by the use of separate pontoons, an indefinite 

 number of vessels may be placed afloat, whilst the most costly 

 part of the system remains constantly available. 



" The following is the arrangement adopted : An open 

 pontoon, proportioned to the size of the vessel to be docked 

 is selected. Keel-blocks and sliding bilge-blocks adapted to 

 her shape form part of the pontoon, which is placed on the 

 girders, and sunk with them to the bottom of the dock. The 

 vessel is brought between the columns, and moored securely 

 over the centre of the pontoon. By lifting the girders, the 

 keel-blocks are first brought to bear under the keel of the vessel, 

 the side blocks are then hauled in by chains laid for the purpose 

 on each side of the dock, and the gridiron and the pontoon, 

 with the vessel upon it, are then all raised by the presses clear 

 of the water. 



The pontoon is provided with valves in the bottom, and 

 thus empties itself of water. The valves are closed, and the 

 girders again lowered to the bottom, but the pontoon with the 

 vessel upon it remains afloat. 



The number of vessels that can be thus docked is limited 

 only by the number of pontoons, each pontoon constituting a 

 separate and independent dock. The pontoons, which are all 

 about 58 feet wide, vary in length and depth, according to the 

 class of vessel intended to be docked, and are rectangular in 

 form and open decked. The sides are vertical, and are 

 strengthened longitudinally and transversely by wrought- iron 

 girders, running from side to side and from end to end, and 

 thus forming a series of rectangular divisions. The pontoons 

 are divided into water-tight compartments, each provided with 

 a circular valve in the bottom closed by a screw shaft. 



