Fig. 2.3 Change of center of buoyancy metacenter during submergence. 



tion of a vertical line through the center of 

 buoyancy of a body floating upright and a 

 vertical line through the new center of buoy- 

 ancy when it is inclined a small amount as 

 indicated by the letter M in Figure 2.3b. 



When a surfaced submersible is tipped as 

 shown in Figure 2.3b, the center of buoyancy 

 moves from B to Bl because the volume of 

 displaced water at the left of G has been 

 decreased while the volume of displaced 

 water to the right is increased. The center of 

 buoyancy, being at the center of gravity of 

 the displaced water, moves to point Bl and a 

 vertical line through this point passes G and 

 intersects the original vertical at M. The 

 distance GM is known as the metacentric 

 height. This illustrates a fundamental law of 

 stability. When M is above G, the metacen- 

 tric height is positive and the vessel is stable 

 because a moment arm, GZ, has been set up 

 which tends to return the vessel to its origi- 

 nal position. It is obvious that if M is located 

 below G, the moment arm would tend to 

 increase the inclination. In this case, the 

 metacentric height is negative and the ves- 

 sel is unstable. 



When on the surface, a submarine presents 

 much the same problem in stability as a 

 surface ship. However, differences are appar- 

 ent as may be seen in the diagrams in Figure 

 2.3c, where the three points B, G, and M, 

 though in the same relative positions, are 

 much closer together than is the case with 

 surface ships. 



As noted above, when a ship on the surface 

 heels over, there is a shift in the position of 

 the buoyancy center because of the volume 

 shape change below the waterline. In the 

 case of a submerged submarine, no such 

 change takes place because all the volume of 

 the submarine is below the surface of the 

 water. Thus, for submerged stability, the 

 center of gravity must be below the center of 

 buoyancy. 



During the process of going from the sur- 

 faced condition to the submerged condition, 

 the center of gravity of the submarine, G, 

 remains fixed slightly below the centerline of 

 the boat while B and M approach each other. 

 At complete submergence, G is below B, and 

 M and B are at a common point. These 

 changes are shown diagrammatically in Fig- 

 ure 2.3c. 



As the ballast tanks fill, the displacement 

 becomes less with the consequent rising of B 

 and lowering of M. There is a point during 

 submergence when B coincides with G. Due 

 to the configuration of the upper part of the 

 hull, B would only move a short distance 

 from G if a list were taken at this point. In 

 this condition, the stability is least; and the 

 time spent at this low-righting stage must be 

 minimal. When the ballast tanks are fully 

 flooded, B rises to the normal center of buoy- 

 ancy of the pressure hull, and stability is 

 attained with G below B. 



To keep the center of gravity low, batteries 

 and other heavy items are carried as low as 

 possible where they have the greatest effects 

 on stability. Submersible transverse meta- 

 centric heights (submerged) are quite small 

 and range from 3 to 12 inches. 



Power 



Electric power is compatible with all pro- 

 pulsion, lighting, hotel, and virtually all in- 

 strument requirements and is the exclusive 

 ultimate power source in all deep submers- 

 ibles. Long duration power can be supplied 

 from the surface through a cable, but at the 

 expense of maneuverability; conversely, ma- 

 neuverability is retained using self-con- 

 tained batteries, with a corresponding limi- 

 tation in operating time. Two power options 

 predominate in shallow (less than 1,000-ft) 

 submersibles: Manual and electric. Transfer 

 of manual power through the pressure hull 



17 



