Ships and Shipping. 157 



Firstly, there is displacement tonnage, which is the 

 weight in tons of the ship, and what may be on board at 

 the ti-me. 



Secondly, there is dead weight tonnage which includes 

 cargo, coals and stores. 



According to one of the laws of hydrostatics, a floating 

 body displaces a quantity of the fluid in which it floats 

 equal to its own weight. The line in which the sur- 

 face of the water cuts the surface of the ship when 

 floating in any position is called the water line, the 

 area enclosed by this line, being the water plane area, is 

 called the light displacement. The line shown by 

 the ship when fully laden is termed the load water 

 line. The difference between the light and load dis- 

 placement gives the dead weight cargo capacity of the 

 ship when she is immersed to her load line, which includes 

 coals, stores, and cargo. If, when a ship is floating in 

 water, the water line is marked, and the cubic contents 

 ascertained of the space occupied by the ship below the 

 plane passing through the water line, and the cubic 

 contents in feet multiplied by the weight of a cubic foot 

 of water will give the total weight of the ship and what 

 is on board ; the displacement is calculated in tons, the 

 immersed portion is calculated in cubic feet, allowing 

 35 cubic feet of sea water to the ton; this divided by 

 35 will give the tonnage. 



The ton of displacement, as we shall see farther on, 

 does not always mean 35 cubic feet, as it depends on 

 the density of the water. Some water equals 1,025 

 ounces to the cubic foot. The divisor of 35 cubic feet 

 to the ton weight is taken as allowing that 1,024 ounces 

 are equivalent to one cubic foot ; the difference, however, 



