Chinese engineers have adapted a principle for reducing the drag of high-speed underwater projectiles to improve the energy efficiency of merchant ships. A second-generation bladder lubrication system installed on a newly built 50,000 ton product and chemical tanker reportedly reduced net energy consumption by approximately 5% during a five-month operational trial.
The system, developed by the Shanghai Merchant Ship Design and Research Institute, injects compressed air under a ship’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 ship operators reduce fuel consumption without changing their vessels’ primary propulsion systems. Additionally, the institute estimates that a 5% reduction for a tanker of this size could save about a ton of fuel per day.
Bladder lubrication reduces friction under the hull
The technology is based on the broader principle of reducing contact between an object and the surrounding water. Supercavitating torpedoes, for example, move in a gas-filled cavity that significantly reduces their contact with water and allows them to reach extremely high underwater speeds.
The merchant shipping system uses a different implementation of the basic idea. Instead of creating a large void around a fast-moving projectile, it continuously injects compressed air under the ship’s hull, forming a layer of microbubbles between the hull and the seawater. the South China Morning Post reported.
This changes the water flow near the surface of the ship and creates a gas-liquid mixture that reduces frictional resistance. With less resistance to overcome, the ship may require less propulsion power to maintain its speed.
The overall efficiency gains depend on the balance between the energy saved through reduced hull friction and the power used by the compressors to supply air. The reported net energy saving of 5% explains this additional energy requirement, although the institute did not provide a detailed breakdown of the test results.
Automated controls improve the second generation system
The second generation bladder lubrication system builds on an earlier version tested aboard a 1,800 TEU feeder container ship in April 2022. Development of the updated system began the following month, with engineers attempting to address the previous design’s reliance on manual operation.
The new version includes an improved air supply structure designed to reduce compressor power consumption, as well as automated control and monitoring functions. Its intelligent control system adapts the amount of air supplied under the hull to the speed and draft of the ship.
A digital operational support system also monitors and analyzes energy efficiency in real time. These features are intended to make the technology easier to operate as sailing conditions change, while reducing the energy required to generate bubbles.
The system is designed for use with various 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 use on commercial vessels, although wider adoption will depend on performance in different hull designs, operating conditions and routes.
