(www.MaritimeCyprus.com) This study presents a comprehensive assessment of Hull Air Lubrication Systems (ALS) for maritime shipping, focusing on their technological maturity, economic viability, regulatory context, and safety implications. The study presents ALS as an interesting yet still maturing technology. However, the Shipping Industry still needs to have a clear picture of how systems perform under service conditions. Continued research, full-scale trials, and collaborative efforts among shipbuilders, vendors, regulators, and classification societies are essential to fully exploit the potential of ALS in sustainable maritime operations.
Overview of ALS
ALS technologies aim to reduce a ship’s frictional resistance by injecting air into the turbulent water boundary layer beneath the hull, thereby reducing frictional drag and lowering the ship's power demand, fuel consumption, and, consequently, greenhouse gas (GHG) emissions.
ALS systems employ various design philosophies and technologies, and flow topologies such as air-layer, bubble, or cavity drag-reduction are employed. ALS can be active, using compressors, or passive, using venturi effects for injecting the air. Air injection can range from microbubble to air-water mixture injection systems, each one with its own advantages and limitations.
The study includes insights from interviews and workshops with these stakeholders, providing a comprehensive view of the technology's current state and market readiness.
Sustainability
ALS is an emerging technology for reducing hull resistance and improving fuel efficiency. By lowering fuel consumption, ALS directly reduces GHG-emissions and other pollutants, including NOₓ, SOₓ, and particulate matter. Case studies were conducted on selected vessels operating in both coastal and deep-sea conditions. The findings indicate potential fuel savings up to 4%, depending on key factors outlined in Section 2.3 Suitability. Beyond emissions reduction, ALS may also decrease underwater radiated noise, supporting marine ecosystem protection and broader sustainability goals.
Performance prediction remains complex for systems with two-phase flow (an air-water mixture next to the hull), as the two-phase flow dynamics cannot be predicted by traditional scaled model tests and are not yet practical with state-of-the-art computational fluid dynamics (CFD) methods, owing to the lack of reliable full-scale data for verification. It remains challenging to determine the realistic savings potential during actual vessel operations, which directly influences the estimated GHG reduction. To address this uncertainty, further investigation based on longterm in-service measurements across various weather conditions and ship types is necessary to establish credible and representative GHG reduction figures for each system.
Suitability
ALS reduce hull resistance through strategic air release, with key factors influencing their performance as follows:
■ Lubricated area: drag reduction is most effective when air is released in hydrodynamically favourable areas, particularly the flat bottom forward (FoB).
■ Operational drafts: ALS performance is sensitive to the draft. Calibration must be vessel-specific and account for expected operational drafts.
■ Utilization: the more frequently a vessel operates, the greater the potential cumulative fuel and emission savings achievable with ALS.
■ Compressor power for ALS: active ALS typically requires 3–5% of propulsion power, while passive systems eliminate this need. Integration strategies vary by propulsion type, and existing machinery can often support ALS with minimal modifications.
■ Weather Sensitivity: performance may decline in rough seas; adaptive control and real-time monitoring are being explored to maintain effectiveness.
For more interesting details, you can download the full report from EMSA by clicking below:
Source: EMSA
