How does a submarine go up and down in water?
To go from the surface to submerged and back, the submarine floods water into, or blows water out of, tanks that surround the submarine – main ballast tanks. While submerged, the submarine is almost always moving, and it uses planes (fins) attached to the “sail” – the part that sticks out in the middle. The planes tilt upward or downward to make the submarine go shallower or deeper as it moves through the water. If the submarine ever stops, keeping depth is much tougher, because the planes no longer work – they need moving water to create the lifting or diving force. Then the submarine must hover by adding water (flooding a tank) or pumping water out of a tank. Hovering is tough, especially when you are sinking, because pumping is very slow. You can blow a tank with air if needed, but that is bad because 1)you can over shoot and pop to the surface – very very bad, and 2) you make a lot of noise, also bad for a submarine.
The ‘Ballast’ tanks are ‘flooded’ with either sea water, or ‘blown’ with compressed air, from reserve tanks. Once the submarine has achieved ‘neutral bouyancy’ (neither sinking nor rising) then the the forward motion of the sub forces water over the control surfaces (elavators to rise & fall) and rudder (Yaw). Thus the sub is ‘flown’ under water, in a similar fasion to an aircraft.
