Why Don’t Aircraft Carriers Tip Over?
It’s a delicate question, to say the least: could a $13 billion dollar aircraft carrier that took five years to build, now home to 5,000 people, just suddenly tip over?
I decided to broach the subject after seeing a post on Reddit’s r/Damnthatsinteresting subreddit, which pointed out something not everyone notices: aircraft carriers are “insanely curved,” which makes them look like they’re ready to topple over at any moment. The post tells a story in two pictures: the first shows a sharply curved aircraft carrier prow that narrows to a knifelike point, which to some implies the entire bottom of the ship is knifelike. The second picture shows what a carrier-like ship (here, a U.S. Navy amphibious assault ship) looks like below the waterline.
Tapered hulls may make carriers look unsteady, but there’s more than meets the eye here.
Buoyancy
According to the Greek mathematician and inventor Archimedes, any object resting on the surface of water is acted upon by a buoyancy force. The buoyancy force pushes upward, while gravity (which Archimedes did not know about) pushes downward. As a result, if the object is less dense than the liquid it displaces, it will float.
That’s essentially how ships stay afloat. Aircraft carriers, and most other ships, also have sharp prows, the front part of a ship above the waterline. (The front end of ships, in general, is known as the “bow.”) The flat nature of the flight deck, which gives aircraft carriers the nickname “flat tops,” accentuates the sharpness of the prow, making the ship look unstable.
The problem is that you miss quite a lot simply looking at a carrier floating in the water. It may have a knifelike bow, which helps reduce wind resistance and aerodynamic drag, but below the water line, the hull spreads out and is actually quite wide. A Nimitz-class aircraft carrier, for example, is 134 feet wide at its widest at the waterline; this prevents the buoyancy force from pushing on one side or the other from below and flipping the ship over.
Fast and Bulbous
Another part of the post shows what is known in naval architecture as the bulbous bow. Traditionally, ship designers assumed that a knife-like bow below the waterline reduced drag, allowing ships to effectively cut through water. This, in turn, made for faster ships and greater fuel savings.
In the early 20th century, ship designers began experimenting with a so-called “bulbous bow” concept. An object moving on the surface of the water produces a wave at its bow that increases drag. While the bulb looked like it would make ships slower, increasing drag as it plowed through the nearby water, it actually reduced drag. A bulbous bow creates a second wave that effectively cancels out the first, making the bow even more hydrodynamically efficient.
Starting in the 1920s, shipyards built passenger ships with large, bulb-like protrusions below the waterline. One of the most famous ships with a bulbous bow was the Imperial Japanese Navy battleship Yamato, the largest battleship of all time. Yamato’s bulbous bow stuck out 10 feet, giving her an extraordinary top speed of 28 knots.
U.S. Navy aircraft carriers have been built with bulbous bows since the USS Ronald Reagan. Bulbous bows are standard on the latest Ford-class carriers, including USS Gerald R. Ford, and will be features of the future carriers John F. Kennedy, Enterprise, and Doris Miller. They are also standard on the Wasp and America-class amphibious assault ships, and the Arleigh Burke and Zumwalt-class destroyers.
The Takeaway
A tremendous amount of naval know-how goes into every aircraft carrier, and not all of it is visible when the ship is in the water. An aircraft carrier is probably the ship least likely in the fleet to flip over, or “turn turtle” as it’s known in the Navy. That is, until the shooting starts.
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