1868.] 



and Weight o f Iron-clad Ships. 



307 



In order to indicate clearly, but approximately] only, the purpose in 

 view, the author first considers the hypothetical cases of a long and a 

 shorter ship, both of which are prismatic in a vertical sense. The length 

 of the long ship is seven times its breadth, and its horizontal sections con- 

 sist of two triangles set base to base ; the length of the short ship is five 

 times its breath, the middle portion being parallel for two-fifths of the 

 length, and the ends being wedge-shaped. It is assumed also that at a 

 speed of 14 knots the long ship will give a constant of 600, and the short 

 ship a constant of 500 in the Admiralty formula, 

 speed mid. section 

 indicated horse-power" 



The draught of water is in each case 25 feet, and the total depth 

 50 feet. 



It is taken for granted that the form of the long ship has been found 

 satisfactory for a ship of such scantlings that we may consider her built 

 of iron of a uniform thickness of 6 inches, the top and bottom being 

 weightless. 



Now, let it be required to design a ship of equal speed, draught of water, 

 and depth, but of such increased scantlings (whether of hull proper or of 

 armour) that the weight shall be equivalent to a uniform thickness of 

 12 inches of iron, the top and bottom being weightless as before. First, 

 the new ship has the proportions of the long ship given to her; and 

 secondly, those of the shorter ship. In each case the engines are supposed 

 to develope seven times their nominal horse-power, and to weigh (with 

 boilers, water, &c.) 1 ton per nominal H.P. The coal-supply in each case 

 equals the weight of the engines, so that both ships will steam the same 

 distance at the same speed. But as the equipment of the smaller ship will 

 be less weighty than that of the larger ship, we will require the larger ship 

 to carry 2000 tons, and the smaller 1500 tons additional weights. 



Assuming the breadth extreme in each case to be the unknown, we can, 

 from the Admiralty formula given above, deduce an expression for the 

 Indicated Horse-Power ; thence, under the assumed conditions, the weights 

 of engines and coals can be found ; and these being added to the weights 

 of hull (calculated on the assumption that the sides are of 12-inch iron), 

 and to the weights carried, give an expression for the total displacement, 

 in tons, of each ship. Another expression is found for this displacement 

 by finding the weight of water displaced. The two expressions are equated, 

 and a quadratic equation is formed, from which the breadth extreme is 

 determined ; and from it all the other values can be found. 



The accompanying Table shows the results obtained by this method for 

 the two classes of ships : — 



