OF SHIP CONSTRUCTION. 63 



position and the plane of bending is vertical, but it seems safe to conclude that 

 an approximately similar relation of strength would be shown to exist were we 

 to continue the analysis for various angles of inclination, and we may make the 

 general deduction that in longitudinal bending strength an Isherwood ship is ma- 

 terially superior to a transversely framed vessel of the same dimensions. 



VERTICAL SHEARING STRENGTH. 



A similar inference may be made for the vertical shearing strength. From 

 the stress diagram for the hogging condition it was figured that the maximum ver- 

 tical shearing stress is 466 tons, which is resisted by a cross-sectional area of 2,004.5 

 square inches for the transverse vessel and 2,252.7 square inches for the Isherwood 

 vessel, giving unit shearing stresses of 520 and 468 pounds per square inch, re- 

 spectively. While there is a material reduction in the unit stress in favor of the 

 longitudinally framed vessel, this can scarcely be credited as an advantage for the 

 Isherwood system inasmuch as the stress values are too low for consideration. 



LONGITUDINAL SHEARING STRENGTH. 



Longitudinal or horizontal shear is usually found by the formula : — 



Longitudinal shear = 



tl 



where V = vertical shear. 



Mb = the statical moment of the section (= area X distance) between the 

 plane at which it is desired to find the longitudinal shear and the ex- 

 treme fiber, on one side of the plane of shear. 

 t = thickness of web at plane of shear, 

 / = the moment of inertia of the section. 



In applying this formula to ordinary structural work, no consideration is given 

 to transverse stiff eners or brackets, and consequently no careful investigation seems 

 to have been made in this field. It is evident, however, that if the hull were to fail 

 because of longitudinal shearing stresses, say along an edge lap in the shell at or 

 near the neutral axis, the transverse framing would have to be sheared off along that 

 edge lap. In the transversely framed ship we have transverse channel frames 

 spaced 2 feet 2 inches, continuous from the bilge to the upper deck. These frames 

 have a sectional area of 8 square inches each, but because of the elasticity of the 

 riveting connecting the frames to the shell plating, it would probably be unsafe to 

 regard more than 50 per cent of this area as effective in longitudinal shear. 



At the edge lap between H and / strakes we have, then, per frame space, for 

 one side of the ship : — 



