The Evolution of Floating and Other Dry Docks. 63 



The natural method to get at the bottoms of vessels is to haul 

 them up high and dry, and in tidal harbours, the one still 

 resorted to, is to select a suitable beach, and at spring tides 

 gently strand the vessel, and when the tide recedes heel her 

 over to one side or the other as required, and await the next 

 spring tide to float her off. 



It was and is a common thing to excavate round the vessel 

 and form a dam and so protect the workmen from any incursion 

 of the water. These operations had to be resorted to in order 

 to caulk and pay the bottom seams and butts of the planking ; 

 the process was generally known as " Graving," and no doubt 

 this was the origin of " Graving Dock," dock where " Graving " 

 or " Paying " could be performed with little risk or interruption. 

 It was only a step to select a tidal crtek, build a wall across 

 the entrance, and demolish the latter when work was rinished. 



The next development appears to have been to make this 

 enclosure more symmetrical, watertight, and secure from 

 flooding, by excavation and building side walls with a gate on 

 entrance, and so permit of work wi'.hin going on with regularity. 



The first of the modern Graving Docks appears to have been 

 constructed about the year 1623 at Deptford. In this dock the 

 water was allowed to flow in, at high water the vessel was 

 hauled in, berthed and shored, and when the tide receded leaving 

 the bottom of dock dry, the gates at the entrance were closed, 

 preventing the next tide from flooding the dock and floating 

 the vessel. 



In more recent years Graving Docks have been deepened and 

 artificial means adopted to accelerate the removal of the water, 

 so that the vessel's keel may be much below the level of the 

 water outside, at low water mark, thus admitting vessels of 

 greater draft than the difference in rise and fall of tide ; never- 

 theless I think they have hardly advanced with the times, as 

 will be explained later. 



We have a very good example of a modern Graving Dock in 

 Belfast, 880' + 83' 8" + 26' 6," which may be divided in three 

 sections ; a more recent one at Glasgow, and a still larger one 



