tsS TiMEHRI. 



is of little importance, as, for pra6lical purposes, the 

 fra6lion may be eliminated, and the divisor only made 

 use of. 



Some ship owners have the displacement of their 

 ships calculated to various draughts of v^^ater by means 

 of a very skilfully invented instrument called a plani- 

 meter, and either a tabfe or a scale of displacement made 

 by which is indicated how much weight their ships have 

 on board by observing the draught of water. An ap- 

 proximation of the displacement of a ship may be arrived 

 at in the follovving way : — Multiply the length on the load 

 water line by the extreme breadth, and this produft 

 by the draught of water amidships, less the hanging 

 keel. This latter measurement is the moulded draught. 

 Thus : 



Displacement = Length x Breadth x Draught. 



xc 



c. is a co-efficient representing the percentage of 

 the surrounding figure taken up by the volume or dimen- 

 sions of the ship. The value of the constant c has been 

 adapted to various classes of ships, for instance: 



Merchant (passenger) Steamers 55 to .60. 



Cargo-carrying Steamers of moderate speed ... .65 to .70. 



Cargo Steamers have of late years been built of fuller 

 form, and the co-efficient exceeds .70 to .75. I'resh and 

 river water, differ in weight from sea water : the 

 former is about 62 and a half pounds per cubic foot, while 

 the latter differs considerably in various parts of the 

 world, and varies in weight according to its position 

 relative to the mouths of rivers. A change of draught 

 in a ship is caused by a change of the density in the 

 water. When a ship goes from the sea to the river her 



