Movement of the Submarine
Surfacing and Diving
Submarines are able to
move vertically by controlling their own buoyancy.
Where: ρ is density
of fluid
V is volume of fluid displaced
g is acceleration of gravity
When the submarine dives, it is supported with a force equal to the weight of the fluid displaced. This means that a larger submarine have greater buoyant forces acting on it because it displaces more water.
When the submarine is diving, weight, in the form of sea water, is added to the total weight of the boat. This works to counteract the buoyant force and the submarine dives. The sub can then surface by exchanging the sea water with compressed air, reducing its weight. The buoyant force will then push the submarine upward toward the surface.
The water and air used in surfacing and diving is stored in ballast tanks. Ballast tanks are generally located between the outer hull and the pressure hull. Typically submarines are equipped with multiple ballast tanks. The first is the main tank that is used for surfacing and diving. Other smaller tanks, called trimming tanks, are located in the rear and front of the submarine and are used to reorient the submarine underwater. Adjusting the level of the water in either of the trimming tanks can tip the ship slightly, or level it out.
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