ON THE STRENGTH OF MATERIALS FOR IRON SHIPS. 



253 



A similar formula may be derived for beams with double flanges. 



From the experiments on the model Conway tube we find S x = 16-5 tons ; 

 hence we have 



wJ°p, 



(9) 



which is the formula usually employed for calculating the strength of these 

 beams ; where W is expressed in tons, a t being the area of the bottom plate 

 in inches, D the whole depth of the beam, and I the distance between the two 

 supports expressed in the same units as D. 



In cast-iron beams with double flanges, as derived from the experiments 

 of the late Mr. Hodgkinson, 



W _2KP 



(10) 



Strength of an Iron Ship. 

 21. To determine the strength, <fcc, of an iron ship, the transverse section 

 being represented in the annexed diagram, AB and EF the upper and lower 

 decks, AD and BD ; the sides down to the bilge, LR, US, SD, &c. a series 

 of plates, assumed to be straight, forming the bottom, and so on. 



Fig. 13. 



Or 



Ml 



Y G 3 



F 



O 



Having divided the section into a convenient number of parts, formulae (1) 

 and (2), art 18, give the most exact method of calculating the moment of 

 inertia of the whole section ; where the moment of inertia of each part about 

 its centre of gravity must be determined, and so on. But the following method 

 of calculation is more simple and sufficiently exact for all practical purposes. 



Put a, for the area of the material in the upper deck ; a 2 for that of the 

 lower deck ; a 3 for the lower hold stringers ; a 4 for the bilge keelsons ; a. for 

 the sister keelsons ; «„ for the middle keelson ; a 7 for the keel piece L ; a t 

 for the plates LB,, LR X ; a 3 for the plates RSjR^ ; a 10 for the plates SD, S 1 D 1 ; 



