389 Inventions for the Improvement of 



is renticrerl nearly bunyant, being surmnnded by an air re- 

 ceptacle capable of suspending the wboie weight with great 

 exactness, which is riveted lo it in such a manner as also 

 to strcngthca the caisson, and support the principal shores 

 from the sliip. 



" This caisson draws nine feet water. When taken to 

 the ship intended to be docked, the water is to he let into 

 it at an opening or plug-hole at the bottom, and it is to be 

 suffered to sink until the upper part is even with the surface 

 of the water, the air receptacle still keeping it buoyant. 

 A small quantity of air is then to be discharged by opening 

 a plug-hole in the air receptacle, until a quantity of water is 

 let in just sufficient to sink .he caisson, which is to be then 

 drawn under 'he ship's bottom. This being effected, the 

 caisson (nearly buoyant) is then to be raised to the surface 

 of the water by ropes made fast from the caisson to each 

 quarter of the ship. A ptimp placed within the caisson, and 

 worked by a steam engine of 12-horse power, placed in a 

 barge alongside, will empty it in three hours, and reduce 

 the ship's draught of water eight feet j that is, from 26 to 

 18 feet ; when she may be carried up into shoal water, the 

 caisson floating with a draftof only 18 feet of water, while 

 the ship she carries would have required 26 feet. She may 

 then be carried into shoal water, if required, or alongside 

 \v4iarfs, or jetty-heads of the dock-yards. 



'' The ship's sides and bottom tending to fall outwards, 

 by its own weight, and the sides and bottom of the caisson 

 tending to be forced inwards, bv the external pressure of 

 the water, it is obvious that by placing props or shores, be- 

 tween, both will be supported, while the ship will ride with 

 all her stores on board and masts standing, nearly as easy 

 as when floating in the water. 



" Should inconvenience be apprehended at any time from 

 blowing weather, the caisson may be cast off, and let fall 

 to the bottom, where it cannot be injured, and from whence 

 it mav be raised to the ship's bottom again at pleasure, with 

 as little labour as weiijhing an anchor. 



" The upper part of this dock will be 12 feet above water 

 when there is a first-rate ship in it; this is a sufficient 

 heisrht to prevent the sea breaking over. 



" By this means a ship may have her bottom examined, 

 and be out again in six hours, without coming above the 

 Nore, and without undergoing the tedious process of un- 

 shipping and re-shipping her stores, or wailing for spring- 

 tides, or fair wind, to enable her to reach to^ or return 



