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Air Lubrication Systems

Air lubrication systems (ALS) inject a layer of micro-bubbles or air-cavity beneath the flat-bottomed portion of a ship’s hull to reduce the frictional resistance between the hull and the surrounding water, with typical net fuel savings of 5 to 10% for bulk carriers, tankers and cruise vessels with significant flat-bottom area. The technology generates the bubble layer using deck-mounted compressors that supply air through hull-perforated injection arrays, with the air trapped beneath the hull by the natural curvature and the ship’s forward motion. Approximately 250 commercial ALS installations are in operation by end-2024 across container ships, bulk carriers, tankers, cruise vessels and ro-ro vessels. The principal commercial systems are: Silverstream Technologies (UK, founded 2010, leading global market share), Mitsubishi Air Lubrication System (MALS) by Mitsubishi Heavy Industries (Japan, original commercial deployment 2010), Samsung SAVER Air by Samsung Heavy Industries (Korea), DSME ALS by DSME Hanwha (Korea), and several smaller competitors. ALS is recognised as an innovative energy-efficient technology under MARPOL Annex VI Regulation 21 with a corresponding EEDI credit per the IMO Innovative Technology Guidelines (Resolution MEPC.244(66)); the credit is verified by the classification society at the EEDI / EEXI verification stage. ALS provides direct improvement in the annual CII attained, supports the SEEMP Part III operational plan and contributes to CII corrective action plans for D/E-rated vessels. Capital cost is typically USD 2 to 6 million per installation with payback periods of 3 to 6 years at typical bunker prices, falling to 2 to 4 years when EU ETS Maritime avoided cost is included. ShipCalculators.com hosts the principal computational tool: the air lubrication system calculator implements the net fuel-saving calculation as a function of ship type, hull geometry, service speed and air-supply parameters. A full listing is available in the calculator catalogue.

Contents

Background and history

Theoretical basis

The concept of reducing hull friction by injecting a gas layer beneath the hull has been studied since the early 20th century. The theoretical basis is straightforward: water has approximately 1,000 times the density and 50 times the viscosity of air, so replacing the water-hull boundary layer with an air-hull boundary layer dramatically reduces frictional resistance.

Three theoretical approaches:

  • Microbubble injection: small air bubbles (typically 0.1 to 1 mm diameter) injected through hull-perforated arrays, forming a bubbly layer that reduces friction by approximately 10 to 30%.
  • Air cavity / air layer: continuous gas layer beneath a recessed hull section, trapped by hull geometry; reduces friction by 50 to 80% in the cavity area.
  • Air sheet / Partial Cavity Drag Reduction (PCDR): large air sheets between the bubble and cavity regimes; intermediate friction reduction.

Pre-2000 research

Theoretical and experimental research on air lubrication was conducted at:

  • University of Tokyo (Japan) from the 1970s under Kawasaki Heavy Industries sponsorship.
  • DARPA-funded research (US) in the 1990s focused on military submarine drag reduction.
  • Krylov Shipbuilding Research Institute (Russia / former USSR) from the 1980s under Soviet naval research.

The 1990s research established the fundamental physics but commercial deployment was limited by:

  • High air-compressor energy demand (parasitic load reducing net fuel savings).
  • Difficulty maintaining a stable air layer in real sea conditions.
  • Lack of regulatory incentive (no IMO climate framework yet existed).

2010 to 2015: first commercial deployments

The first commercial ALS deployments came in 2010 with:

  • Mitsubishi Heavy Industries MALS on bulk carrier Yamato (delivered to Mitsui OSK Lines, 2010), the first commercial air-cavity system.
  • Damen Shipyards ALS on inland barges (2011), small-scale early deployment.
  • DSME / Samsung experimental ALS on container ship test platform (2012).

These early systems demonstrated the principle but with mixed commercial success. The MALS system on Yamato achieved approximately 10% fuel savings but the air-compressor parasitic demand was higher than expected, leading to limited net savings.

2015 to 2020: Silverstream and commercial scale-up

The UK company Silverstream Technologies (founded 2010 by Noah Silberschmidt) developed a microbubble ALS using a proprietary “SLA” (Silverstream Lubricated Aero-foil) injector design that produces stable, energy-efficient microbubble generation. Silverstream’s first commercial installation on the MV Norwegian Bliss (Norwegian Cruise Line, delivered 2018) demonstrated ~6 to 8% fuel savings on a Caribbean cruise itinerary.

Through 2018 to 2020 Silverstream expanded its commercial base to include:

  • Carnival Corporation cruise vessels.
  • MSC Cruises newbuildings.
  • Maersk container ships (selected newbuildings).
  • Shell Tankers (subsequent acquisition by Boskalis / SBM Offshore).

By end-2020 Silverstream had ~30 commercial installations.

2020 to 2024: regulatory acceleration

The 2020 to 2024 period saw substantial commercial scale-up driven by:

  • The 2020 IMO 0.5% sulphur cap and rising bunker fuel costs.
  • The 2021 EEXI and CII regulatory pressure on existing ships.
  • The 2024 entry into force of EU ETS Maritime.
  • The 2025 Net-Zero Framework approval at MEPC 83.

By end-2024 approximately 250 commercial ALS installations were in operation:

  • Silverstream Technologies: ~120 installations (cruise, container, ro-ro, tanker).
  • Mitsubishi MALS: ~70 installations (bulk carrier, tanker, ro-ro).
  • Samsung SAVER Air: ~30 installations (container, tanker).
  • DSME / Hanwha ALS: ~15 installations.
  • Other vendors (Damen, Wartsila, Kawasaki HI): ~15 installations.

Technology variants

Silverstream SLA microbubble system

The Silverstream SLA (Silverstream Lubricated Aero-foil) system:

  • Uses a proprietary aerofoil-shaped injector that creates a low-pressure zone behind the foil, drawing in air at low pressure.
  • The drawn-in air is mixed with seawater and emitted as a stream of microbubbles (typically 0.5 to 1 mm diameter) covering ~80% of the hull bottom flat area.
  • Compressor power demand: typically 0.3 to 0.6% of main-engine power (low parasitic load).
  • Air consumption: typically 1 to 5 m³/min per square metre of hull coverage.
  • Net fuel saving: typically 5 to 10% on bulk carriers and tankers; 3 to 7% on cruise vessels (more complex hull geometry).

The Silverstream system is the dominant ALS in the cruise sector and is increasingly common on tankers and bulk carriers.

Mitsubishi MALS

The Mitsubishi MALS (Mitsubishi Air Lubrication System) creates an air cavity beneath a slightly recessed hull section:

  • Recessed hull pocket of typical 1 to 2 m² area, with air injection at the leading edge.
  • Air trapped within the cavity by the natural hull curvature plus an aft retaining edge.
  • Compressor power demand: typical 1 to 2% of main-engine power (higher than microbubble).
  • Net fuel saving: typically 6 to 10% on bulk carriers (the principal target market).

MALS is the dominant ALS in the bulk carrier sector and has been retrofit-installed on many existing bulk carriers.

Samsung SAVER Air and DSME ALS

The Korean shipyards Samsung Heavy Industries (SAVER Air) and DSME (Hanwha) have developed proprietary ALS variants combining microbubble and cavity approaches. These systems are typically integrated into newbuilds rather than retrofit:

  • Samsung SAVER Air: dominant on Korean-built container ships and tankers.
  • DSME / Hanwha ALS: dominant on Korean-built bulk carriers and tankers.

Performance and economics

Fuel-saving estimation

The net fuel saving from ALS depends on:

  • Hull flat-bottom area: bulk carriers (high flat area) and tankers (high flat area) achieve highest savings; container ships (lower flat area due to V-shaped underwater hull) achieve lower savings.
  • Service speed: lower speeds reduce the savings (frictional resistance scales as v²; air-supply demand is roughly speed-independent).
  • Sea state: rough seas can disrupt the air layer; calm seas optimal.
  • Hull cleanliness: a clean hull provides smooth air-bubble flow; biofouling can disrupt the layer.

Typical real-world reported savings:

Vessel typeReported saving range
VLCC / Suezmax tanker6 to 10%
Capesize / Panamax bulk carrier5 to 9%
Container ship (Neo-Panamax+)4 to 7%
Cruise ship3 to 7%
Ro-ro / ro-pax4 to 7%
Chemical / product tanker5 to 8%
LNG carrier4 to 7%

The air lubrication system calculator implements the net fuel-saving calculation for arbitrary inputs.

Innovative Technology Credit (ITC) under EEDI

ALS is recognised as an innovative energy-efficient technology under MARPOL Annex VI Regulation 21:

  • The credit reduces the calculated attained EEDI by the ALS contribution (approximately equal to the demonstrated fuel-saving percentage).
  • The credit is verified by the classification society at the EEDI / EEXI verification stage.
  • ALS-equipped newbuildings typically achieve 5 to 10% reduction in attained EEDI vs an equivalent non-ALS sister vessel.

For an ALS-retrofitted EEXI-compliant existing ship, the system can avoid the need for EPL or ShaPoLi limitation by providing the required EEXI improvement through energy efficiency rather than power restriction.

CII improvement

ALS provides direct improvement in the annual CII attained:

  • A 7% fuel saving translates into approximately 7% reduction in attained CII.
  • For a bulk carrier with attained CII of 5.5 (D rating, 10% above Required), ALS retrofit brings attained CII to ~5.1 (close to C rating boundary).

The SEEMP combined operational measures calculator implements the combined effect of ALS with other operational measures.

Capital cost and payback

Typical ALS capex and payback:

Vessel typeCapital cost (USD M)Annual fuel saving (USD at $600/t bunker, 10,000 t/yr fuel)Simple payback
New-build bulk carrier (integrated)2 to 30.3 to 0.54 to 7 years
Retrofit bulk carrier3 to 50.3 to 0.56 to 10 years
New-build tanker (integrated)3 to 40.4 to 0.65 to 8 years
Retrofit tanker4 to 60.4 to 0.67 to 12 years
New-build container ship (integrated)4 to 60.5 to 0.75 to 9 years
New-build cruise ship (integrated)5 to 80.4 to 0.6 (lower fuel use)8 to 15 years

The payback is significantly improved by:

  • EU ETS Maritime cost avoidance: approximately 30 to 50% additional saving for EU-trading vessels.
  • FuelEU Maritime intensity benefit: approximately 5 to 10% additional benefit.
  • Premium freight rates under Sea Cargo Charter for higher-rated vessels: approximately 5 to 10% revenue uplift.

The Lifecycle retrofit payback calculator implements the payback calculation for arbitrary technology investments.

Notable installations

Carnival Corporation cruise fleet

Carnival Corporation (the world’s largest cruise operator) has fitted Silverstream ALS on most of its newbuildings since 2018:

  • Carnival Mardi Gras (2020): Silverstream ALS demonstrating ~5 to 7% fuel saving on Caribbean cruise itinerary.
  • Carnival Celebration (2022): similar configuration.
  • Princess Cruises Discovery Princess (2022): Silverstream ALS.
  • Holland America Line, Costa Cruises, AIDA, Cunard: ALS rollout across the Carnival group fleet.

MSC Cruises

MSC Cruises operates the world’s largest order book of cruise newbuildings (~25 vessels in delivery 2024 to 2030). Most of the MSC newbuildings have Silverstream ALS as standard, including:

  • MSC World Europa (2022): LNG dual-fuel + Silverstream ALS combination for compounded savings.
  • MSC Euribia (2023): similar configuration.
  • MSC Seascape, MSC Seashore: similar.

Berge Bulk Capesize fleet

Berge Bulk (Singapore-based dry bulk operator with one of the largest Capesize fleets) has fitted Mitsubishi MALS on multiple vessels including:

  • MV Berge Mulhacen, MV Berge Toubkal: also fitted with Anemoi Flettner rotors for combined ~25% fuel saving (one of the highest combined-technology savings reported).

Maersk container ships

Maersk has fitted Silverstream ALS on selected newbuilding container ships, particularly the methanol dual-fuel Astrid Maersk and sister vessels (2023 to 2025 deliveries on Asia-Europe corridor).

Shell tanker fleet

Shell Tankers (the in-house tanker fleet of Shell, subsequently acquired by SBM Offshore) deployed Silverstream ALS across multiple Suezmax and VLCC tankers in 2019 to 2022, with reported 6 to 8% fuel savings on long-distance crude oil transport.

Operational considerations

Air-supply system

Critical components:

  • Compressors: typically 2 to 4 medium-pressure compressors providing 1 to 5 m³/min per m² of hull coverage.
  • Air-filtration: removing oil contamination and particulates from compressed air.
  • Distribution piping: corrosion-resistant pipe network from compressor room to hull injectors.
  • Hull injectors: stainless steel or composite injection points typically arranged in transverse arrays beneath the hull bottom.

Maintenance

ALS maintenance requirements:

  • Compressor servicing: every 2,000 to 5,000 operating hours; major overhaul at 25,000 to 50,000 hours.
  • Injector cleaning: typically at each drydock survey (every 5 years for most vessels).
  • Hull-perforation inspection: at each drydock; potential repair for fouling or corrosion.

Typical annual maintenance cost: USD 50,000 to USD 150,000 per vessel, depending on system size.

Sea state limitations

ALS performance degrades in heavy weather:

  • Beaufort 1 to 5: optimal performance; full design fuel saving achieved.
  • Beaufort 6 to 7: reduced performance; air layer disrupted by wave action; ~30 to 50% of design saving achieved.
  • Beaufort 8+: minimal performance; air layer largely disrupted; ALS may be shut down to conserve compressor energy.

The annual fuel saving therefore reflects the ship’s actual sea-state distribution; ships on calm-sea routes (e.g. Mediterranean, Caribbean cruise) achieve higher annual savings than ships on rough-sea routes (e.g. North Atlantic winter, Cape Horn).

Class certification

ALS installations are classified under the major class societies’ Innovative Equipment Notations:

  • DNV: AAA-AB notation.
  • Lloyd’s Register: integration with EEDI / EEXI Innovative Technology recognition.
  • ABS: similar.
  • Bureau Veritas: similar.

The certifications include initial commissioning, periodic compressor inspection and EEDI / EEXI re-verification at each renewal survey.

Future outlook

Adoption projection

DNV’s Maritime Forecast to 2050 (2025 edition) projects:

  • By 2030: ~1,500 ALS installations on commercial vessels (vs ~250 in 2024).
  • By 2040: ~10,000 installations covering ~20% of the global fleet.
  • By 2050: ALS becomes standard equipment on most newbuild bulk carriers, tankers and cruise vessels.

Emerging variants

Several emerging ALS variants are at demonstration stage:

  • Variable-pressure microbubble systems: adjusting air-supply pressure based on real-time hull-resistance feedback.
  • Hybrid ALS + low-friction hull coatings: combining ALS with silicone-based foul-release coatings for compounded friction reduction.
  • ALS + wind-assist combination: as on Berge Bulk’s Capesize vessels (Anemoi rotors + MALS).
  • Recovered-air systems: capturing the released air at the stern and recompressing for re-use, dramatically reducing parasitic compressor load.

Regulatory evolution

The IMO’s EEDI Phase 4 review (expected 2027 to 2028) is expected to expand ALS recognition under the Innovative Technology Credit framework, potentially providing larger credits for ALS-equipped newbuildings to support the transition to ALS as standard equipment.

See also

Additional calculators:

Additional formula references:

Additional related wiki articles:

References

  1. IMO MEPC. Resolution MEPC.244(66) - 2014 Guidelines for Calculation of the Energy Efficiency Design Index (EEDI) for Innovative Energy-Efficient Technologies. IMO, 4 April 2014.
  2. IMO MEPC. Resolution MEPC.245(66) - 2014 Guidelines on the Method of Calculation of the Attained EEDI for New Ships. IMO, 4 April 2014.
  3. Silverstream Technologies. Annual Performance Report 2024. Silverstream Technologies, London, 2024.
  4. Mitsubishi Heavy Industries. MALS Performance Data. MHI, Yokohama, 2024.
  5. Samsung Heavy Industries. SAVER Air System Annual Report. SHI, Geoje, 2024.
  6. DSME / Hanwha Ocean. ALS System Documentation. DSME / Hanwha Ocean, Geoje, 2024.
  7. Carnival Corporation. Sustainability Report 2024 - Air Lubrication Section. Miami, 2024.
  8. MSC Cruises. Annual Sustainability Report 2024. MSC Cruises, Geneva, 2024.
  9. Berge Bulk. Capesize Air Lubrication Operational Report. Berge Bulk, Singapore, 2024.
  10. DNV. Maritime Forecast to 2050 - Air Lubrication Section. DNV, Oslo, 2025 edition.
  11. Lloyd’s Register. Air Lubrication Systems: Practical Implementation Guide. Lloyd’s Register Marine, London, 2024.
  12. ABS. Air Lubrication Technical Guide. American Bureau of Shipping, Houston, 2023.
  13. ClassNK. Guidelines for Air Lubrication Systems. Tokyo, 2024.
  14. University of Tokyo. Marine Air Lubrication Research Programme. Department of Marine Engineering, 2010 to 2024.

Further reading

  • IWSA. Wind-Assisted Propulsion and Air Lubrication: Combined Technology Annual Reports.
  • DNV. Maritime Forecast to 2050. DNV, Oslo, 2025 edition.
  • Silverstream Technologies. Air Lubrication Systems: Operational Best Practice. Silverstream, London, 2024.