How do the tanks of a submarine work? How does the craft resurface?

Answer 1

There are several different kinds of tanks that control the buoyancy of the sub. These are depth control tanks, trim tanks and main ballast tanks. The trim tanks are located inside of the pressure hull front and back and are used to adjust the attitude of the sub, nose up or nose down. The depth control tanks are located near the middle of the sub and used to make fine adjustments to the buoyancy of the sub, normally slight negative buoyancy is desired. The main ballast tanks are the ones used to submerge and surface the sub. They are kept completely full or empty, not partially filled.

When the sub leaves port and prepares to submerge, the trim and depth control tanks are adjusted to the level estimated to result in neutral buoyancy after filling the main ballast tanks. The ballast tanks vents are opened and seawater fills the tanks and the sub goes under. The trim is adjusted after submerging. The sub can not submerge if the depth control and trim tanks are empty, but will always surface if the ballast tanks are emptied.

To do a normal surface, the sub drives to the surface, and then uses a powerful blower to fill the ballast tanks with air and push the water out of the bottom grates. In an emergency, high pressure air can be used to empty the main ballast tanks and bring the sub to the surface quickly.

The outer hull on American nuclear subs is actually just a steel fairing on the front and aft ends of the pressure hull; this is where the ballast tanks are. The Trident missile subs also have a fairing called the turtle-back on the top to cover the missile section as the missiles are taller than the pressure hull. Calling the fairing a double or outer hull is not quite correct.

Ranb

Edited to add; Once underwater, the sub normally controls the sub's depth by using the diving planes. These are small wing-like control surfaces that operate like an airplanes elevator. As long as the sub is moving more than 2 mph, then it can easily control depth without adjusting the amount of water in the trim tanks.

Answer 2

Most of the answers are correct in how the ballast tanks of the sub work how the sub dives and resurface. However it is not true that by allowing a curtain volume of water into the tanks you can control the depth of the sub. For instance say you want to stay 10m below the surface the amount of water inside the tanks is not going to govern the depth. The reason for that is water is non-compressible and thus the density of the water stays the same 99.999% of the way down to the depths of the ocean the pressure increases but not the density. The only parameter you can control, by allowing water into the tanks, is the rate of descending. Hot air balloons can control their heights for air is compressible.

Answer 3

There are 2 hulls on a sub. The inner pressure vessel, and the outer shell. The space in between the inner vessel and the outer shell contains the ballast tanks. When the ballast tanks are flooded, the ship sinks. Highly compressed air is stored in large pressure tanks when the ship is on the surface.

When the sub is underwater and they want to go back to the surface, the pressurized air is let out into the ballast tanks. It pushes the water out and makes the sub float to the surface.

By varying the amount of air and water in the ballast tank the sub can stay level at any depth (down to the limit of the inner pressure vessel, anyway).

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Answer 4

Ballast tanks, that were filled with sea water in order to submerge are 'Blown' out again by compressed air from on-board cylinders, thus the submarine becomes less dense than the sea water. (The sub returns to normal buoyancy).

Answer 5

The tanks are allowed to fill with water and it lets the sub sink. When they want to surface, compressed air is used to force the water out of the tanks and let it regain positive buoyancy.

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Answer 6

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