Largest Aircraft Carriers

The Nimitz-class supercarriers are a class of ten nuclear-powered aircraft carriers in service with the United States Navy. The lead ship of the class is named for World War II Pacific fleet commander Chester W. Nimitz, who was the Navy's last fleet admiral. With an overall length of 1,092 ft (333 m) and full-load displacements of over 100,000 long tons, they are the largest capital ships in the world. Instead of the gas turbines or diesel-electric systems used for propulsion on many modern warships, the carriers use two A4W pressurized water reactors which drive four propeller shafts and can produce a maximum speed of over 30 knots (56 km/h) and maximum power of around 260,000 shp (190 MW). As a result of the use of nuclear power, the ships are capable of operating for over 20 years without refueling and are predicted to have a service life of over 50 years. They are categorized as nuclear-powered aircraft carriers and are numbered with consecutive hull numbers between CVN-68 and CVN-77.

All ten carriers were constructed by Newport News Shipbuilding Company in Virginia. USS Nimitz, the lead ship of the class, was commissioned on 3 May 1975, and USS George H.W. Bush, the tenth and last of the class, was commissioned on 10 January 2009. An embarked carrier air wing consisting of up to around 90 aircraft is normally deployed on board. After the retirement of the F-14 Tomcat, the air wings' strike fighters are primarily F/A-18E/F Super Hornets and F/A-18C Hornets. 

Description

The Nimitz class carriers have an overall length of 1,092 ft (333 m) and a full-load displacement of about 100,000–104,000 long tons (102,000–106,000 metric tons). They have a beam at the waterline of 135 ft (41 m), and the maximum width of their flight decks is 251 ft 10 in to 257 ft 3 in (77.76 m to 78.41 m) (depending on the variant). The ships' companies can number up to 3,200, not including an air wing of 2,480.


 Design

The hangars on the ships are divided into three fire bays by thick steel doors that are designed to restrict the spread of fire. This addition has been present on U.S. aircraft carriers since World War II. Nimitz carriers were designed with larger stores of aviation fuel and larger magazines in relation to previous carriers, although this was partly as a result of increased space available by the new design of the ships' propulsion systems.

Because of a design flaw, ships of this class have inherent lists to starboard when under combat loads that exceed the capability of their list control systems. The problem appears to be especially prevalent on some of the more modern vessels. This problem has been previously rectified by using damage control voids for ballast, but a solution using solid ballast which does not affect the ship's survivability has been proposed.

Since USS Theodore Roosevelt, the carriers were manufactured in modular construction (USS George H.W. Bush was constructed from 161 'super-lift' modules). This means that whole sections could be welded together with plumbing and electrical equipment already fitted, improving efficiency. Using gantry cranes, the modules were lifted into the dry dock and welded. In the case of the bow section, these can weigh over 1,500,000 pounds (680 t). This method was originally developed by Ingalls Shipbuilding and increases the rate of work because much of the fitting out does not have to be carried out within the confines of the already finished hull. The total cost of construction for each ship was around $4.5 billion.

Propulsion

All ships of the class are powered by two A4W nuclear reactors, kept in separate compartments. They power four propeller shafts and can produce a maximum speed of over 30 knots (56 km/h) and maximum power of 260,000 bhp (190 MW). The reactors produce heat through nuclear fission which heats water. This is then passed through four turbines (manufactured by General Electric) which are shared by the two reactors. The turbines power the four bronze propellers, each with a diameter of 25 feet (7.6 m) and a weight of 66,000 pounds (30 t). Behind these are the two rudders which are 29 feet (8.8 m) high and 22 feet (6.7 m) long, and each weigh 110,000 pounds (50 t). As a result of the use of nuclear power, the ships are capable of operating continuously for over 20 years without refueling and are predicted to have a service life of over 50 years.

Nimitz class ships were designed to have a fifty-year service life. At the end of the service life, ships will be decommissioned. This process will first take place on Nimitz and is estimated to cost from US$750 to $900 million. This compares with an estimate of US$53 million for a conventionally powered carrier. Most of the difference in cost is attributed to the deactivation of the nuclear power plants and safe removal of radioactive material and other contaminated equipment.