50 



APPLICATION OF BUOYANCY BOXES TO THE STEAMSHIP 



STABILITY CONDITIONS OF S. S. LUCIA AFTER TORPEDOING. 



Transverse Stability. 



Before attack- 



After attack- 



o^/a// v/iL vfL. 



B/i.eeo v^.i.. 



Shaded areas indicate displacement. 



We see that the center of buoyancy moves up while the center of gravity remains 

 stationary. Stability will of course increase accordingly. 



The hasty calculation of the conditions of the Lucia will show that the upset- 

 ting moment is reduced approximately 50 per cent while the righting water-plane 

 moment is only reduced approximately 30 per cent. 



The ship in bilged condition is therefore much more stable than before. 



Longitudinal Stability. 



Professor Hovgaard, whose method is used by navy circles, employs the meta- 

 centric height method, while in these calculations the section modulus method is 

 used. In other words, the problem is here solved just as we are used to solve the 

 problem of the bending of a beam. 



5" X / = -^^ is the well-known bending formula. 



When used in stability problems, 5" denotes the section modulus of the water 

 plane, / denotes the weight of a column of water of unit section and with a height 

 equal to maximum immersion, M denotes the stability moment. 



The metacentric method is really the sequel of the section modulus method and 

 each is readily transferred into the other. 



In drydock work and also in ship work where static problems are considered, 

 the mathematical expressions will be vastly simplified by the use of the section 

 modulus method. 



