How Does a Diesel Electric Submarine Work?
Submarines have undergone experimental designs and research since the first application of man-powered submersibles before the 1900s. The first practical diesel-electric submarine was pioneered by the German scientist Rudolf Diesel in 1909. Rudolf's design implemented the use of an internal combustion diesel engine that was run on the surface to charge large battery banks and power the electric motors that propelled the sub underwater. The diesel-electric submarine, although eventually phased out by the nuclear-powered variant, contained a number of systems that made it a popular choice for commercial usage, but especially for the military during WWII.
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Hull
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Submarines have thick interior pressure hulls, long and cylindrical and constructed of steel. The thick inner hull protects the occupants, machinery and systems from the high seawater pressure when the vessel submerges to great depths. An outer hull surrounds the inner hull and has a more aerodynamic design that allows it to pass through water with the least amount of friction. The outer hull, although much lighter than the inner, also serves as an impact safety device in case of breech or penetration. Submarine hulls are always water-tight. Different compartments within the hull are separated by water-tight bulkhead hatches or doors.
Ballast Tanks
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Submarines can change from positive buoyancy, which allows them to float upward, to negative buoyancy, which lets them sink, to neutral buoyancy, which keeps them stable in the water column. When water is pumped into the ballast tanks along the sides of the hull, the submarine sinks. To rise, large compressor motors force air into the ballast tanks, dispelling the water and giving the boat positive buoyancy. Neutral buoyancy is attained when the air and water inside the ballast tanks reaches the same density with the outside seawater.
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Diesel Engines
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Multiple diesel engines provide the voltage needed to charge the large electric motor batteries that are used for underwater propulsion. The engines power large electrical generators, which in turn charge the batteries. Diesel engines, which use an air-fuel mixture to run, need outside air introduced into the combustion chambers. Snorkels are used at periscope or snorkel depth to draw in fresh air when the submarine runs just under the surface. Diesel engines will not run underwater without a source of fresh air for combustion. Diesel fuel has a lower flash point and is much more economical to run in submarines than gasoline engines.
Planes and Rudders
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Submarines use dive planes -- large, horizontal fins -- to control up and down movement in the water. Stick your hand out of the window of a moving car, and tilt it up or down. Just like your hand, the submarine will rise or sink as the up or down angle of the diving planes changes. A greater angle produces a more rapid descent. Dive planes function when the submarine makes headway underwater and lose effectiveness when the speed is reduced or stopped. Rudders on the rear of submarine provide lateral movement, used in turning left or right. Rudders function just as on any boat, providing shallow or deep turning angles.
Electric Propulsion
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Submarines use powerful electric motors to turn multiple propeller shafts, or "screws." The electric motors can only function when the batteries have sufficient charge, which is provided by the generators run by the diesel engines. Total electric propulsion provides smooth, quiet and economical running time while the craft is submerged. Electrical motors give off no harmful fumes or emissions, and they can be run at various speeds. Propellers are attached to the main drive shafts through a series of gears, and they provide the thrust through the water, just like a boat propeller.
Combination Maneuvers
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Submarines can make many combination of maneuvers by use of their control surfaces and engine, since they occupy a three-dimensional environment. They can make a climbing turn to either side by blowing ballast, using the up function of the dive planes and applying rudder action. They can take on ballast, and use the dive planes and rudder to make a descending turn. Submarines can sit on the seafloor, with negative ballast, with engines and controls at full stop. Emergency surfacing is accomplished by blowing all ballast with dive planes fully "up" and full engine rpm.
Crew
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Submarines can not function without a crew to monitor and run the many systems on board. Diesel-electric submarines are self-sufficient, in that they carry food, water, hygiene provisions and other supplies. Scrubbers and ventilating systems remove carbon dioxide, and environmental control systems provide comfort. Submarines have a range that is dependent upon how much fuel they need to get from one point to another, and the amount of provisions needed to sustain a full crew. Most minor, and some difficult, maintenance chores are done by mechanics on board. Submarine crews drill constantly for any emergency at sea.
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References
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