Bionic dolphin skin saves fuel for large crude carrier

BEIJING, July 16 (Xinhua) -- Docked at the Quanzhou port in east China's Fujian Province, after completing three oil delivery trips, is a very large crude carrier (VLCC) with a deadweight tonnage of 300,000 tonnes, equipped with a bionic skin propeller.

The bionic skin on the propeller saved about 2 percent of the crude carrier's fuel consumption, according to media reports. It was also estimated that 1.5 percent of energy would be saved on average within a 2.5-year maintenance cycle.

According to such energy consumption, a VLCC is estimated to save more than 300 tonnes of fuel each year, achieving direct economic benefits of over 1 million yuan (about 140,000 U.S. dollars) and reducing carbon dioxide emissions by more than 900 tonnes.

Sea transportation is crucial to the global economic activity, but it also consumes a large amount of energy and has become a significant source of greenhouse gas emissions. Thus, it is urgent to make breakthroughs in the key energy conservation and emission reduction technologies for large carriers as well as to push the green transformation of global marine transport industry.

Large crude carriers were primarily powered by the thrust generated by propellers, which overcomes the resistance between the ship's body and water to propel the ship forward.

Researchers from the Ningbo Institute of Materials Technology and Engineering under the Chinese Academy of Sciences collaborated with the COSCO SHIPPING Energy Transportation Co., Ltd. to carry out a research project on marine bionic skin development in order to save energy in marine transportation.

This study was inspired by the marine creatures such as dolphins and sharks, which encounter very little resistance when swimming in the sea, mainly due to their surface's micro-structure, flexibility and mucus secretion.

The dolphin skin forms a micro-structure in the water flow, generating micro-eddy currents that convert the sliding friction between the skin and the water flow into rolling friction. When combined with the lubrication of the epidermal mucus, the turbulent kinetic energy of the water flow is effectively minimized.

The bionic dolphin skin, similar to the dolphin skin, was developed by the artificial synthesis method. It was composed of liquid-like dynamic interfacial materials and flexible materials between 0.1 and 0.2 mm microstructure, said Zeng Zhixiang, a researcher at the institute.

"Different from bionic shark skin, the bionic dolphin skin has a comparatively simpler structure and is more cost-effective," said Zeng.

He estimated the cost of placing the bionic dolphin skin over a propeller would cost about 20,000 U.S. dollars.

The bionic skin, when placed on the propeller's surface, can reduce shear force with the water, counteract the work of the reverse thrust on the water, improve the propeller efficiency, and reduce energy consumption.

The bionic flexible drag reducing material used in the crude carrier complies with the International Convention for the Control of Harmful Anti-fouling Systems on Ships.

Meanwhile, for approximately 200 days, the bionic dolphin skin-equipped VLCC sailed over 35,000 nautical miles between Chinese coastal ports and major Middle Eastern ports.

COSCO SHIPPING Energy Transportation and Ningbo Institute of Materials Technology and Engineering intend to promote the application of such bionic skins in more than 100 crude carriers to provide significant economic benefits while also effectively reducing carbon dioxide emissions.