Submarine technical question?

Question

Do modern submarines contain any metal exclusively for ballast, i.e. to make it easier for the submarine to dive, or is diving and surfacing controlled only by adding water or air to ballast tanks?

Answer 1

All surface ships, as well as surfaced submarines, are in positively buoyant condition, weighing less than the water of their volume would. To submerge hydrostatically, a ship must gain negative buoyancy, either increasing its own weight or decreasing displacement of the water. To control their weight, submarines are equipped with ballast tanks, which can be filled with either outside water or pressurized air.

For general submersion or surfacing, submarines use the forward and aft tanks, called Main Ballast Tanks or MBTs, which are opened and completely filled with water to submerge, or filled by pressurized air to surface. Under submerged conditions, MBTs generally always stay flooded, which simplifies their design, so on many submarines these tanks are simply a section of interhull space. For more precise and quick control of depth, submarines use smaller Depth Control Tanks or DCTs, also called hard tanks due to their ability to withstand higher pressure. The amount of water in depth control tanks can be controlled either to reflect changes in outside conditions or change submersion depth. Depth control tanks can be located either near the submarine's centre of gravity, or separated along the submarine body to prevent affecting trim.

When submerged, the water pressure on submarine's hull can reach 4 MPa for steel submarines and up to 10 MPa for titanium submarines like Komsomolets, while the pressure inside stays the same. This difference results in hull compression, which decreases displacement. Water density also increases, as the salinity and pressure are higher, but this does not compensate for hull compression, so buoyancy falls with depth. A submerged submarine is in an unstable equilibrium, having a tendency to either fall down to the ocean floor or float up to the surface. Keeping a constant depth requires continual operation of either the depth control tanks or control surfaces.

Submarines in a neutral buoyancy condition are not intrinsically stable in trim. To sustain desired trim, submarines use specialized forward and aft trim tanks. Pumps can move water between these tanks, changing the weight distribution and therefore creating a momentum to turn the sub upwards or downwards. A similar system is sometimes used to maintain stability.

The hydrostatic effect of variable ballast tanks is not the only way to control the submarine underwater. Hydrodynamic maneuvering is done by several surfaces, which can be turned to create corresponding hydrodynamic forces when a submarine moves at sufficient speed. The stern planes, located near the propeller and normally oriented horizontally, serve the same purpose as the trim tanks, controlling the trim, and are commonly used, while other control surfaces may not be present on many submarines. The fairwater planes on the sail and/or bow planes on the main body, both also horizontal, are located closer to the centre of gravity, and are used to control depth with less effect on the trim.

When a submarine performs an emergency surfacing, all depth and trim methods are used simultaneously, together with propelling the boat upwards. Such surfacing is very quick, so the sub may even partially jump out of the water, but it inflicts serious damage on some submarine systems, primarily pipes.

Modern submarines use an inertial guidance system for navigation while submerged, but drift error unavoidably builds up over time. To counter this, the Global Positioning System will occasionally be used to obtain an accurate position. The periscope - a retractable tube with prisms allowing a view to the surface - is only used occasionally in modern submarines, since the range of visibility is short. The Virginia-class submarines have "photonics masts" rather than hull-penetrating optical tube periscopes. These masts must still be hoisted above the surface, and employ electronic sensors for visible light, infrared, laser range-finding, and electromagnetic surveillance.
http://www.deepflight.com/subs/index.htm

Answer 2

Technically speaking, anything onboard a submarine is considered ballast. Food, fuel, repair parts, torpedos, missiles, people, etc, etc. When the Diving Officer is figuring out how much water to put into the various trim tanks he takes all of the above into consideration and more. But, not only is it to figure out how much water should be taken onboard to allow the submarine to submerge and achieve neutral bouyancy, but also to allow the sub to achieve a "zero" bubble in regards to both list and trim.

Main Ballast Tanks or MBT's as previously discussed are used exclusively for diving and surfacing the ship and they are external to the ship's pressure hull.

Internal tanks (of which there are many, but we will only concern ourselves with variable ballast tanks) are used to fine tune the diving condition off the boat. Water canm be moved forward and aft as well as side to side or athwartships by the Trim system. Water can be flooded into certain of these tanks or pumped overboard as the situation dictates. Depth Control Tanks are used for hovering (missile launches or diver lock in/lock out procedures) when the ship needs to be held almost perfectly still at a certain depth.

Depth control of a submarine depends on ballast and speed and the angle of the planes (stern and fairwater or bow). But also greatly depends on the salinity of the water and to a smaller degree the temperature. The more saline the water is (saltier) the more weight the water can support.

Answer 3

there is no metal ballast per se. The engines and batteries are used as ballast in the design the main ballast that is used for diving is water which is flooded in and out of tanks to make the sub go up or down. The other way is to move the sub and us the diving planes to push the sub up or down like the flaps on a planes wing.

Answer 4

Water and air control the ballast. If you used metal, the sub would weigh the same all the time which would not affect the ballast needed to submerge and emerge.

Answer 5

I don't know about this. I had a couple of submariner buddies that swore their Chief of the Boat told them that the Captain would order that they be shot out the tubes if he needed to lighten ship because of an emergency. He claimed they had more lead in their asses than two flooded ballast tanks.

Answer 6

I am not an expert with submarines, but I believe that extra metal for ballast would be designed into the structure of the hull in order to make it stronger and not just tossed it in or welded on for extra weight. It would have been poor engineering if they had to add metal for ballast. It just seems logical. can anyone back me up on this guess?

Answer 7

There are some doors on submarines and every other Naval vessel. A "hatch" refers to a watertight door. On a door, it's called a "door knob" and on a hatch it's called a "dog wheel" or "dog crank". I've even heard it refered to has a "hatch lever" since on modern submarines, it isn't a wheel anymore, it's just a lever. On modern US submarines, there is only one interior hatch not including torpedo/missle tubes or escape trunks and that is the hatch between the forward and aft compartments. It's supposed to be closed at all times when underway unless someone is going through it.

Answer 8

only by adding water or air to the ballast tanks.

Answer 9

The second part of your question is correct, they utilize air and water.