China’s new bubble-lubrication system could save large ships’ 1.1 tons of fuel daily

Chinese engineers have adapted a drag-reduction principle associated with high-speed underwater projectiles to improve the energy efficiency of commercial ships. A second-generation bubble-lubrication system installed on a newly built 50,000-tonne product and chemical tanker reportedly reduced net energy consumption by about 5% during a five-month operational trial.

Developed by the Shanghai Merchant Ship Design and Research Institute, the system injects compressed air beneath a vessel’s hull to create a layer of bubbles that reduces friction with the surrounding water.

The tanker has entered service, and the results suggest the technology could help shipping operators lower fuel consumption without changing their vessels’ primary propulsion systems. Furthermore, the institute estimates that a 5% reduction could save roughly one metric ton of fuel per day on a tanker of this size.

Bubble lubrication reduces friction beneath the hull

The technology draws on the broader principle of reducing contact between an object and surrounding water. Supercavitating torpedoes, for example, travel inside a gas-filled cavity that substantially reduces their contact with water, allowing them to reach extremely high underwater speeds.

The commercial shipping system uses a different implementation of the underlying idea. Rather than creating a large cavity around a fast-moving projectile, it continuously injects compressed air beneath the ship’s hull, forming a layer of microbubbles between the hull and seawater, the South China Morning Post reported.

This changes the flow of water close to the vessel’s surface, creating a gas-liquid mixture that reduces frictional resistance. With less resistance to overcome, the ship can require less propulsion power to maintain its speed.

The overall efficiency gains depend on the balance between the power saved through reduced hull friction and the electricity consumed by the compressors supplying the air. The reported 5% net energy saving accounts for that additional energy demand, although the institute has not provided a detailed breakdown of the trial results.

Automated controls improve the second-generation system

The second-generation Bubble Lubrication System builds on an earlier version tested aboard a 1,800-TEU feeder container ship in April 2022. Development of the upgraded system began the following month, with engineers seeking to address the earlier design’s reliance on manual operation.

The new version includes an improved air-supply structure intended to reduce compressor power consumption, alongside automated controls and monitoring capabilities. Its intelligent control system adjusts the volume of air supplied beneath the hull according to the vessel’s speed and draught.

A digital operational support system also monitors and analyses energy efficiency in real time. These functions are intended to make the technology easier to operate across changing sailing conditions, while reducing the energy required to generate the bubbles.

The system is designed to work with different commercial vessel types and propulsion technologies. According to the institute, it is compatible with ships powered by LNG, electricity, methanol and ammonia. The new developments provide an additional basis for its deployment on commercial vessels, although wider adoption will depend on performance across different hull designs, operating conditions and routes.

Source: https://interestingengineering.com/energy/china-bubble-lubrication-system-energy-use