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The ship will be exposed to a lot of air bubbles in the sea, and now these bubbles have become a good helper to help the ship save fuel. Recently, bubble expert Steven Seschel of the School of Mechanical Engineering at the University of Michigan in the United States claimed that using a method called "air lubrication system" can help ships achieve 5% to 10% fuel savings.
According to Dr. Sesell, the specific method is to quickly pump air out of the small hole in the outer shell of the ship. At this time, the honeycomb-like bubbles will quickly join together and form a 1 cm to 2 cm thick one outside the ship. Layer of air. Since the resistance of the air is much smaller than that of water, this can reduce the resistance of the ship during navigation. As the ship moves forward, the layer of air attached to the hull slides back and eventually moves away from the surface at the bottom of the hull. Since there is not much energy required to replenish new bubbles, this method can save about 5% to 10% of fuel.
Dr. Seschel has been working on the air lubrication system for the US Navy. Military warships are conducive to rapid travel, generally using a V-shaped hull, which is not conducive to the accumulation of bubbles on the surface. In contrast, almost all cargo ships are flat in order to keep the hull larger and lighter. In this kind of punt, the push of bubbles will work better. And given that fuel costs often account for half or more of the entire cargo ship's operating costs, the savings potential of this bubble-based approach is undoubtedly huge.
It is understood that the air bubbles are usually slid in the flat ship's outer shell, but it has been tested by new naval testing techniques that it can be fixed somewhere in some way. One trick is to capture the air in the gap between the protruding points a few centimeters below the hull of the hull; another way is to modify the stern to prevent air from being drawn into the propeller, thereby preventing air from absorbing the propeller against the water. Control and reduce the driving force; you can even design a hull with an air valve that is recessed into a few meters deep.
This method of using air bubbles to save fuel has begun to be put into practical use. The Dutch company Damen Shipbuilding Group conducted tests on a 60-meter-long river cargo ship and found that the ship can reduce fuel consumption by about 15% after using this air cavity technology. A Dutch Naval Engineering Institute (MARIN) believes that this air cavity can reduce the fuel cost of large vessels by about 20%. The Damen Group also estimates that for a cargo ship with a water capacity of 110 meters, the air lubrication system may only increase construction costs by about 5%. The group expects production to begin at the beginning of next year and plans to authorize other shipyards to manufacture soon.
However, although the above test results are very optimistic, so far, few shipbuilding companies have adopted this air lubrication system. Part of the reason is that with the massive reduction in global trade, the business of the traditional shipbuilding industry has also decreased significantly. The design and construction of new ships will take many years, so investing in such an unstable market can be risky. However, Cartier-Kadans, the owner of the DK Group of the Nat Engineering Company in Rotterdam, calculated that it would be much cheaper to retrofit existing ships and install air-lubrication systems than to build new ones. The group's retrofit product Air Chamber System (ACS) has been on sale this year. It is understood that it can be installed at the bottom of the container ship and the installation can be completed within two weeks of regular maintenance of the ship at the dock. Tests have shown that ships equipped with ACS can save approximately 15% of fuel. According to Cardans, according to the conservative estimate of the DK Group, the investment return of ACS equipment may reach 7%-10% in the next one and a half to two and a half years.
Another reason for the lack of an air-lubrication system at present is that the navigation environment on the ocean is very harsh, and this air-lubrication system needs to wrap at least two-thirds of the hull, so there are concerns that it may affect the control of the vessel.
In fact, from some perspectives, the air lubrication system is beneficial to the control of the hull. The air chamber acts as a shock absorber that reduces bumps and rolling.
However, the problem with air-lubrication systems is that during maritime navigation, if a turbulent stream of water rushes out of the air in the air chamber, the ship becomes "caught" by the water, rather than sliding in it. This can cause severe vibrations in the hull.
The solution to this problem is to use radar and laser sensors to predict when and where the water flow will create a huge impact force, so that a large amount of air can be pumped into the air chamber at the right time to drain the water and mitigate the risk.