in Naval Archileciitre. 2S1 



is of course different in different ships. 'Dr. Young has investi- 

 g-ated this subject, the detail of which will be found in a very 

 interesting paper published in the Philosophical Transactions, 

 Part II. 1814. The result of his calculations applving to a 74 

 gun ship is as follows : 



"Let AB repre- r ? ' 'L-L^ f '■ \ 



sent the line of keel ^^^"'|_^J-— ^ — ■'-^'""^—^—-LZ^^^^Mad 

 of a vessel which A B 



has hogged — imagine the line a i to be parallel to the horizon, 

 touching the curve in e, and let it be divided into eight equal 

 parts as in the figure. Then if we sujjpose the ship to be con- 

 structed of an uniformly flexible substance, the curvature will be 

 such, that the fall of the keel below tiie imaginary line at each 

 of the points a, /', c, &c. is proportional to the following num- 

 bers, viz. at a, 1/153; at b, 09421; at c, 03738; at d, 

 00809; at e, 00000; at f, 00854; at g, 03721; at h, 

 08041; and at i, 13525." 



The two causes above mentioned, by which the arching of 

 the ship is ])roduced, act permanently; but when a ship is riding 

 over the waves, she is occasionally borne up by the fluid in her 

 central part only, while tlie head and stern are forsaken. The 

 strain hence produced, together with the agitation by which it 

 is accompanied, far exceeds that arising iiom the mere inequa- 

 lity of tlic distribution of weight and pressure. Dr. Young esti- 

 mates it, in certain cases, at nearly three times as much ; and 

 notwithstanding the temporary action of this cause, he justly 

 considers it as the most destructive, because, when the fastenings 

 have been strained and loosened !>y the action of the waves, the 

 ship will more readily give way to the operation of the perma- 

 nent causes. 



A degree of curvature is also produced in a transverse di- 

 rection, that is, at right angles to the foregoing, by the weight 

 sustained by the sides being heavier than that in the middle, 

 while the vertical pressure of the water is 

 greatest in the neighbourhood of the keel. 

 Thence arises an alteration in the transverse j 

 section of the ship, which assumes a formj 

 approximating to that of the annexed fi- 

 gure. 



And lastly, there is also a tendency to a lateral curvature. 

 When a ship is " hove down" on her side, there is an obvious 

 strain tending to produce this effect ; and when a series of large 

 waves strikes a ship obliquely, they must often act in a similar 

 manner with immense force. 



The principal improvement which lias hitherto been macje 



with 



