64 The Evolution of Floating and Other Dry Docks. 



in Liverpool is now under construction, to eclipse all other 

 dry docks, 920' long + 94' width of entrance, and 23' to 34' over 

 sill at high water. 



In Britain the most modern docks are constructed of concrete 

 with granite copings; others are hewn out of the solid rock ; 

 others constructed of hard or soft stone ; and a few of wood. 

 In America a great number are constructed of wood, and I 

 know of a few improvised iron dry docks. It is all a matter of 

 locality, material at disposal, and money. 



Gridirons. 



A gridiron consists of transverse timbers, on blocks fastened 

 to piles, or resting on and attached to the rock. 



The older kinds are only of use where there is a convenient 

 rise and fall of tide. The vessel is hauled over the structure at 

 high water and listed shorewards, and on the falling of the 

 tide the bottom is accessible. A modern adaptation of grid- 

 irons will be referred to. 



The principal objection to gridirons is that only a short time 

 between tides is available for work, and they are therefore 

 unsuitable for substantial repairs. They are, however, very 

 useful for minor examinations and repairs, and being cheap to 

 construct are to be found all round the coast. 



In passing I may mention a process to avoid the use of a 

 dry dock, which is termed " Careening" or " Heaving Down." 

 It is often resorted to for examination of a vessel's bottom, 

 especially in sheltered ports that have no rise and fall of tide, 

 nor Graving Docks. It is attended with some risk, especially 

 when the range of stability of the ship is unknown. The loss 

 of H. M.S. " Royal George," was the result of ignorant careening. 

 It is, however, often resorted to, and it was performed at my 

 request last year on a vessel in Holland ; the photo shows the 

 keel of vessel above water level. In this case it was done to 

 examine and temporarily repair the damage to bottom plating. 



Large vessels were often strained by careening, and the 

 practice no doubt will soon cease. A design for a self-careening 



