Ships and Shipping. 173 



ber of tons required to be placed on board of a vessel, 

 or to be taken out so as to cause an increase or decrease 

 of one inch in the mean draught. 



We will suppose a vessel to be floating at a draught the 

 tons per inch of which is 20, and that a portion of her cargo 

 has to be discharged. After putting out this cargo the 

 mean draught is found to have decreased 5 inches, the 

 weight of the cargo so put out is 



20 X 5 = 100 tons. 



Suppose again that a vessel is at her load line, and 



the tons per inch is 20 tons, to consume 125 tons of 



coal on her voyage, the decrease would be about 

 125 = 6'2 inches. 



20 



Dead weight is the difference between the displace- 

 ment at any draught, and the weight or displacement of 

 the ship when light. 



By the curve of stability the metacentric height and the 

 position of gravity is determined in any state of loading. 

 The word or term metacentre is derived from the Greek — 

 meta and centra — and is defined to mean a point or 

 limit in afloatingbody, on the position of which itsstability 

 depends, The position of the metacentre is obtained by 

 calculation from the drawings or diagrams of the naval 

 architect or shipbuilder. 



By the term stability, is understood the period of 

 force at which the ship when inclined out of the up- 

 right position, immediately endeavours to right her- 

 self. The stability of a ship is a good deal dependent 

 upon her design and loading ; it is also affe6led by the 

 strength and build, round of beam, sheer, and freeboard. 



Freeboard is assigned to a ship as an edge or border for 



