The Evolution of Floating and Other Dry Docks. 6 5 



modern steamer, however, has been suggested which would 

 enable cleaning, painting, or temporary repairs to be effected, 

 where no dry dock or other conveniences were available. 



Slipways. 



The Slipway, generally called Patent Slip, is a more 

 mechanical contrivance for external repairs, and consists of a 

 cradle running on wheels along an inclined track. This cradle is 

 lowered sufficiently below the water level to allow the vessel to 

 be floated above it, then the cradle with the vessel is hauled 

 high and dry by powerful machinery. The process is very 

 quick, but risky, and many accidents have happened at the 

 operation. 



Slipways are hardly suitable for large steamers, but are con- 

 venient and much used. 



There was one in Belfast, but it was removed some years ago. 

 A small one may be seen at Carrickfergus. 



Screw Docks. 



The Screw Dock, as the name implies, is a platform on which 

 vessels may be placed and raised by means of screws. The first 

 sample was built in 1837 and was of American origin, in which 

 country there are still a number. In 1836 the screws of the 

 original dock were replaced by hydraulic lifts, which are more 

 effective and easy of manipulation. 



Lift Dock 



A slight modification of the previous dock was constructed in 

 the Victoria Docks, London, in 1857, and worked by Hydraulic 

 Jacks. These jacks carried Pontoons, or Saucers, as they were 

 called, which were lifted with the vessel. The pontoons, when 

 drained were made water-tight, the vessel was then hauled to a 

 gridiron and deposited thereon. 



This dock had a great capacity depending upon the gridiron 

 area at disposal, and was more adapted for ports where there 

 was little or no rise of the tide. 

 S 



