294 NOTES ON DOCKS AND DOCK CONSTRUCTION. 



FIG. 287. 



" The water should have only a limited cross range in thu 



tanks. 



" If the dock is emptied by pumps, they should be close 



to the bottom of the dock, so that the water may as far 



as possible run into the pumps without having to be drawn in." 

 The lifting power of various docks may be taken to vary 



roughly as the under-deck displacement. 1 



Sir F. Bramwoll has pointed out 2 that the stability varies 



as the square of the 

 number of tanks in 

 the cross-section of the 

 dock ; therefore, all 

 floating docks should 

 be built with numerous 

 water-tight longitudi- 

 nal bulkheads, so that 

 the water may have 

 comparatively little 

 transverse motion. 



The following dia- 

 grams illustrate this. 3 

 Fig. 287 shows a dock 

 and ship listed to 5 

 degrees. The water is 

 allowed to travel freely 

 from side to side. The 

 position of the centre 

 of gravity and the 

 centre of buoyancy 

 shows that it would 

 go further over before 

 coming to rest. 



The same applies 

 to Fig. 288, only in a 

 less degree, as by the 

 introduction of one 



bulkhead, dividing the space into two compartments, the water 



can only travel between the centre and the sides. 



1 Enyinccriny, vol. xlvi. p. 136. 



* Transactions of the Inttitute of Mechanical Engineers, 1863. 

 ' Engineering, vol. xlvi. p. 136 ; and Transactions of the North-East Coast Institute 

 of Engineer it and Shipbuilder*. 



FIG. 289. 



