How a Submarine Floats and Sinks

Submarine surfacing

The first submarine was invented and demonstrated in 1620. English inventor Cornelius von Drebbel is credited with building the first working submarine. He actually built three, which all functioned. The American Revolutionary War saw the appearance of the first combat submarine---a wooden shell that was powered by a single operator using hand-cranked propellers. The craft was a conglomeration of air vents and valves, which gave it limited mobility and submersion ability. Today's nuclear-powered subs can reach lengths of 560 feet and stay submerged for 120 days.

Motorized Submarines

The first motorized submarine was built by John Holland, and it became the U.S. Navy's first commissioned sub in 1900. Dubbed the USS Holland, it had two motors: a gasoline engine for surface movement and an electric one for submerged motion. The first nuclear-powered submarine, the Nautilus, was launched 50 years later in 1954. It later journeyed under the polar ice cap to the North Pole in August 1958, demonstrating the capability of submarine vessels.

How Submarines Maneuver

Submarines are propelled, on the surface and beneath, by propellers, or screws, at the rear of the vessel. Submerged maneuvering is accomplished by the use of finlike structures called hydroplanes. Much like a fish's fins, or the flaps on an airplane, the hydroplanes can be angled to propel the sub up or down or to make turns. The fins also stabilize the sub to prevent the entire vessel from spinning. These are not what allow subs to float or sink, however.

Structure of Submarines

Due to the immense pressure beneath the surface of the water, submarines hulls must be incredibly strong. As a matter of fact, submarines have two hulls: an outer hull that is waterproof and a stronger inner hull. It is the space between these hulls that allows the sub to float or sink.

Ballast Tanks

Located between the two hulls are the ballast tanks. These can be filled with either water or air depending on the desired reaction. At the front of the vessel are the trim tanks, which are filled first so the front of the craft rises or falls first. Some submarines have fuel ballast tanks which, when emptied of fuel, can be used as additional ballast tanks.

Diving and Surfacing

Manipulation of the ballast tanks causes the submarine to float or sink. When the tanks are full of air, the increased buoyancy of the craft causes it to rise to the surface. When water is let into the tanks, the buoyancy decreases and the craft will sink. Water is moved in and out of the tanks by a system of pumps or valves.

References

• ARCO Navy: History of the Submarine
• Explain That Stuff: Submarines