On October 24, 2021, the Indian-awaited "Made in India" aircraft carrier Vikrant finally conducted a second sea test in the eastern Arabian seas, which is said to have been a "complete success". However, a video of helicopter tracking shows an interesting phenomenon: this medium-sized aircraft carrier with a standard displacement of 40,000 tons is running upside down at sea, as if it is "prostrating" all the way!
A volley occurred during the sea trials of the Vikrant
Like other countries, the Indian aircraft carrier chose a calm day to conduct the second sea test, the purpose is to test the reliability of the ship's power system and high-speed navigation capabilities, from the video footage to see the sea surface is relatively calm, the wave height is below 1 meter, occasionally white waves, belonging to the second level sea conditions.
For an aircraft carrier with a total length of 262 meters, the natural conditions are perfect enough, why does the warship sail and stir up a series of waves?
The carrier sways in regular waves
The direct cause of this phenomenon is the longitudinal shaking of the aircraft carrier during the voyage, referred to as vertical shaking.
When the sea conditions are bad, the ship will swing at sea, or swing sharply from side to side, or wave back and forth, even if it is a large drive of 10,000 tons, it is inevitable to be thrown up and down between the peaks and valleys of the waves, and the danger is fraught with danger.
Destroyers sail between peaks and valleys
When the UNITED States nuclear-powered aircraft carrier sails under high sea conditions, all carrier-based aircraft must be fixed, the deck cannot stand people, and the take-off and landing activities of aircraft are stopped. That's because sharp undulations and longitudinal rocking not only pose a risk to flight, but can also involve crew members falling into the sea.
U.S. aircraft carriers sail in high sea conditions
However, the vikrant encountered far more trouble than that, and an aircraft carrier still prostrated itself step by step in the second class sea conditions, which meant that even if the wind and waves were calm, the Pilot of the Indian carrier could be shot dead on the deck when landing.
What's the problem? Let's try to find out why the Vikrant was designed and built.
In the long manufacturing process of India's domestic aircraft carrier, careful Indian netizens found a very special detail: this aircraft carrier did not have a ball nose below the bow line!
The bow of the Viclant resembles a knife
Unlike the huge ball on the front of the American aircraft carrier, the bow of the Ussan Vikrant extends like a blade to the bottom of the ship. Some friends say that doing so has the least resistance when sailing, and some people say that it is conducive to breaking through the thick layer of ice.
There are no icebergs in the Indian Ocean, and the main task of the Vikrant is to take care of the homes and turn the Indian Ocean into the "Ocean of India", it does not have the ability to run to the North Pole, and there is no need to go to the South Pole to show off its might, so the theory of "ice-breaking" is basically not established. So, can it really be faster without a bulb?
The huge bulbous bow of the USS Ford aircraft carrier
The speed of the ship sailing on the water is related to the size of the power, but also the degree of resistance to the water. The greater the resistance, the slower the speed. The resistance of water is roughly divided into anti-wave resistance and water friction resistance, and anti-wave resistance includes wave breaking resistance and xingbo resistance. Small boats can reduce drag by minimizing the contact surface with water; however, large boats can only reduce drag by changing the streamlined shape of the bottom of the boat.
The speedboat jumped on the surface of the sea due to the resistance of the waves
When the ship is sailing at high speed, the bow cuts the current and squeezes the water around, then a bow wave will be generated on the side of the ship, and the vortex generated by the bow wave will act on the hull in turn, on the one hand, the bow will be pushed upwards, and the side of the ship will be squeezed, resulting in larger and larger waves.
By adding a bulbous bow to change the pressure distribution along the hull, the protruding orb will produce a water wave before the hull, and the trough of this wave is just in reverse with the peak generated by the hull, so the two waves cancel each other out, which can maximize the overcoming of the wave resistance, thereby increasing the ship's sailing speed, or saving fuel when sailing at the same high speed.
The bulbous bow eliminates the shock wave by producing an inverted phase wave
It should be noted that the use of bulbous bow waves to counteract bow waves is only useful for large ships sailing at high speeds. If the length of the ship's waterline is less than 15 meters, or the boat's speed is not fast, only a few or a dozen knots, the bulbous bow not only can not reduce the drag, but also because of the increase in wave resistance and the area of the infiltration area and drag the voyage.
There have been many very large container ships, bulk carriers and tankers that have also used huge bulbous bows in design, but the latest cargo ships have gradually eliminated the bulbous bow and replaced it with a traditional blade-shaped bow, which also shows that the bulb has a limited role in low-speed ships.
Some low-velocity merchant ships are canceling bulbous bows
The other two reasons for the cancellation of the bulb bow of commercial large ships are: the bulbous bow is more complex and much more expensive in terms of design and construction, after all, reducing the cost is equivalent to making more money; the steering of the ship with the bulb is not so flexible, most of the ball noses under the water line are damaged when colliding, and the ship is often hindered when it anchors, in order not to let the heavy large iron anchor hit the hull, the windlass equipment needs to be rearranged, and the anchor lip of the hull should be designed to highlight the hull.
Military ships are different, the speed of aircraft carriers is often around 30 knots, some ships are even higher than 30 knots, when the ship is sailing at such a high speed in the water, the Xingbo resistance will account for 40 to 50% of the total resistance of the ship, which is a factor that must be considered.
Another important role of the bulbous bow is to increase the longitudinal rock damping, which reduces the longitudinal swing of the ship.
Ship sloping
The ship's voyage occurs vertically, on the one hand, the front and lower wave resistance lifts the bow upwards, and another reason is that the center of gravity of the ship is not on the same plumb line as the drifting center.
The waterline profiles of military ships are often narrow and bullet-shaped, and ship designers and manufacturers need to take extra care to counterweight the ship so that its center of gravity coincides with the drift center. If the two are not in the same plumb line, then as long as there are undulations on the surface of the water, the boat will inevitably shake. This should be the case with the Vikrant.
The Vikrant center of gravity does not coincide with the drifting heart
Some destroyers or frigates will reduce the swing amplitude by setting automatically controlled fins on the outside of the hull, but aircraft carriers are too large to be equipped with anti-shake fins, nor can they control the attitude through the ballast water tank inside the ship. The construction of modern aircraft carriers not only tests the design capabilities of a country, but also requires the entire industrial system.
Aircraft carriers are not built in swimming pools, you have to let it go to the sea to dominate, to let the carrier-based aircraft take off and land from above. If an aircraft carrier is wobbly in secondary sea conditions, who can expect it to fight at higher sea conditions?
The high-speed navigation of warships requires a bulbous bow to increase speed and maintain stability, which is a common-sense problem that all ship designers understand. As the design leader of the Viclant, the Indian Naval Design Bureau certainly understood the importance of the bulbous bow. However, the aircraft carrier ball nose bow is not just a matter of casually topped a ball in front of it, which involves complex fluid mechanics and needs to be determined through scientific calculations and repeated experimental verification.
Soviet aircraft carriers also have domes
The real reason why the Vikrant does not have a bulbous nose bow in its manufacturer, due to the extreme complexity of the manufacture of the bulb, you need to bend a few centimeters of thick high-strength steel plate into the required three-dimensional surface and then weld it into a sphere, the whole process can not appear the slightest mistake, otherwise it will cause serious consequences. The Cochin Shipyard lacks the necessary manufacturing equipment and technicians, and the designers are happy to save trouble, after all, the blade-shaped bow is a steel plate welded to the end, which saves money and less trouble.
However, in the future, the Indian Navy pilots will fly carrier-based aircraft on this aircraft carrier that is constantly "prostrating", which is a test of technology and luck, if there is an accident, the light landing gear will be broken, and the heavy aircraft will be destroyed. This is no joke!
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