Air Lubrication Systems

Background and history

Why frictional resistance is the target

A ship’s calm-water resistance splits into three parts: frictional resistance, form (viscous-pressure) resistance, and wave-making resistance. ABS quantifies the split: frictional resistance is about 40% of total resistance on higher-speed displacement vessels and can reach 85% on slow displacement vessels. Air lubrication attacks only the frictional component, because it changes the fluid in contact with the hull bottom, not the hull’s shape or the wave field. Form and wave resistance stay roughly fixed when air is injected, so the practical ceiling on what ALS can deliver is set by how large a share of total resistance is frictional, and that share is highest on full-form, slow vessels: the bulk carrier, the crude tanker, the LNG carrier.

The physical argument is short. Air has roughly one-thousandth the density and about one-fiftieth the viscosity of seawater. Put a film of air between the steel and the water, and the shear stress on the wetted plate falls. The catch is that the air has to be made, moved, and held in place against buoyancy, wave action, and the forward flow, and the energy to do that comes off the same fuel bill ALS is meant to cut. Net saving is gross frictional-drag reduction minus the compressor (or blower) penalty, and the whole engineering history of ALS is the chase to widen that gap.

Three drag-reduction regimes

Researchers and ABS group air lubrication into three regimes, distinguished by how much air is injected and the form the gas takes under the hull:

• Bubble Drag Reduction (BDR): small or micro-sized bubbles, generally under 0.1 mm at their most effective, modify momentum transport and lower the average density in the boundary layer. There is no single agreed mechanism; the candidates are an effective-density reduction that lowers the Reynolds stress, a turbulence-suppression effect in the boundary layer, and a drop in effective viscosity from the void fraction. McCormick and Bhattacharyya (1973) towed a fully submerged body skinned in electrolytic hydrogen bubbles and recorded skin-friction reduction rising toward 80%, but micro-bubbles are hard to generate at full scale and lose effectiveness at low speed as buoyancy pulls them off the surface.
• Air Layer Drag Reduction (ALDR): when enough air is injected into the near-wall region, the bubbles coalesce into a continuous or near-continuous air layer that separates the steel from the water over a larger wetted surface, giving a larger reduction than discrete bubbles. Jang et al. (2014) tested a flat plate and a 66,000 dwt wide-beam Supramax bulk carrier model in the Samsung Ship Model Basin and estimated net power saving from ALDR at roughly 5 to 6%.
• Partial Cavity Drag Reduction (PCDR): a recess or step in the hull bottom holds an inflated air cavity that persists aft, separating hull from water with a much thicker air film than BDR or ALDR can sustain, and at a far lower air-injection rate once the cavity is established. Slyozkin et al. (2014) reached a 26% drag reduction on a stepped flat plate and found the air-injection rate to maintain a cavity was about one-third of the rate to maintain an air layer.

Most commercial systems sit at the BDR or air-layer end, because cutting a deep cavity recess into a cargo ship’s bottom is a heavy structural change. The economic appeal of the cavity, much lower air demand, keeps it alive in coastal and inland designs.

Pre-2000 research

One of the earliest air-bubble applications was the Prairie/Masker system the US National Defense Research Committee developed in US Navy laboratories after World War II (Domenico, 1982). The Masker system emitted bubbles under the hull to mask engine-room noise; the Prairie system bubbled air around the propeller. Both were acoustic-stealth measures rather than drag-reduction devices, but they put air under steel and drew researchers toward the drag question.

Partial-cavity work has the longest pedigree. The Krylov Shipbuilding Research Institute began air-cavity studies in the early 1960s on river vessels and barges using linearized 2D cavitation-flow theory, then extended them through the 1980s and 1990s to fast displacement vessels, semi-planing catamarans, monohull fast ferries and ro-ro vessels, and into the 2000s to fast-containership models; Sverchkov (2010) explored hull profiles tuned to optimise cavity shape. The Dutch project “Project Energy-saving air-Lubrication Ships” (PELS), formed in 1999, studied all three techniques with numerical analysis verified against model tests and reported 3 to 10% average net energy saving in calm water. Two follow-on projects, PELS 2 and EU-SMOOTH, ran full-scale demonstrators on inland and coastal ships.

This research settled the physics. Commercial deployment stayed limited by three things: high air-supply energy demand that ate into net saving, difficulty holding a stable air film in a real seaway, and the absence of any regulatory incentive before the IMO climate framework 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).

2020 to 2025: regulatory acceleration

Commercial scale-up through this period was driven by regulation and fuel cost together. The 2020 IMO 0.50% sulphur cap raised compliant-fuel prices and made every percent of saved fuel worth more. The 2023 entry into force of EEXI and CII put existing ships under an efficiency standard for the first time, and the phase-in of EU ETS Maritime from 2024 put a price on the carbon a saved tonne of fuel would have emitted. Each of those shifts the payback on a fixed-cost efficiency device toward feasibility.

The order book reflects the shift. By 2025 the Silverstream System alone was operating on over 100 vessels and held over half of roughly 500 systems on order, spanning cruise ships, LNG carriers, container ships, ro-ros, PCTCs, bulk carriers and CO2 carriers, with more than a million in-service hours logged (Lloyd’s Register, 2025). MALS, SAVER Air and Foreship systems add to that total across the bulk, tanker, LNG and cruise sectors. The pattern across all vendors is the same: the systems land first and densest on the ship types with the largest flat bottoms and the highest frictional share, where the physics pays best.

Technology variants

Silverstream System

Silverstream Technologies traces its origins to the DK Group, which applied large air cavities to reduce frictional drag, then re-formed as Silverstream Technologies in 2014 around a patented design using smaller air chambers. The system comprises air compressors and air-balancing modules that release a carpet of microbubbles through air release units set in the ship’s hull bottom. The microbubble carpet covers the flat-bottom wetted area and rides aft on the forward flow.

The first installation was the 40,000 dwt products tanker MT Amalienborg, owned by Dannebrog Rederi and chartered by Shell, in 2014. Lloyd’s Register’s Ship Performance Team verified a net saving of about 4.3% at 14 knots; over a following 11-month operating period the net saving was reported at about 4% in the unfavourable fully laden deep-draught condition. Lloyd’s Register has provided research support and independent verification of system performance since the first installations and built a system of third-party oversight covering design, installation and operation. By 2025 the Silverstream System was operating on over 100 vessels across cruise ships, LNG carriers, container ships, ro-ros, pure car and truck carriers (PCTCs), bulk carriers and CO2 carriers, with more than a million hours of in-service monitoring logged and over half of the roughly 500 systems on order at that point. The system is fuel-agnostic: it cuts the energy a hull needs regardless of which fuel the engine burns.

Mitsubishi Air Lubrication System (MALS)

The Mitsubishi Air Lubrication System was one of the first commercial systems in the marine industry, developed by Mitsubishi Heavy Industries (MHI) from Japanese research running since the 1980s. MALS is a patented bubble-drag-reduction system, and MHI built its own turbo-blower, the Mitsubishi Turbo-blower, specifically for it. On the 2010 module carriers MV Yamato and MV Yamatai for the NYK-Hinode Line, MHI used a triple-outlet injection scheme: a centre injector at the front of the ship bottom and two side injectors placed symmetrically, fed by two sets of air blowers in the auxiliary engine room. MV Yamatai reportedly showed net energy savings near 10% in calm-water sea trials, and MV Yamato was still running without major failure four years into service (Kawakita et al., 2015). On the deep-draught coal carrier MV Soyo (NYK and Oshima Shipbuilding) the verified figures were lower, about 5% CO2 reduction in ballast and 3% in the loaded condition, a reminder that hull form and loading move the result.

Samsung SAVER Air and Foreship ALS

Samsung Heavy Industries (SHI) developed the SAVER system, which uses a series of air dispensers on the ship bottom to spray bubbles into an air carpet. On a retrofitted heavy cargo carrier, SHI’s full-scale performance test reported an average power saving of 8.8% on an actual voyage; on a 180,000 m3 LNG carrier in a joint project with BG Group (now Shell), ABS and GasLog, the net power saving was reported at about 4.5% from full-scale measurement. Foreship, a Finnish ship-design and engineering firm established in 2002, built an ALS with air dispensers in a box added to the underside of the hull, hydrodynamically shaped so it would not increase skin friction when the air is off. The Foreship system was fitted on the cruise ship Quantum of the Seas (2015). R&D Engineering’s Winged Air Induction Pipe (WAIP) system, developed in Japan by Yoshiaki Takahashi and Yuichi Murai from 1998, uses small air chambers fitted with a foil for ultra-fine micro-bubble generation.

Full-scale sea-trial record

The honest position on ALS performance is that the public record rests on a limited set of full-scale trials, many run on ships that were never subject to EEDI compliance and so did not collect data to the EEDI trial standard. ABS identified about 18 full-scale performance tests between 2002 and 2015, with net energy savings clustering between roughly 4 and 10%. The spread inside that band is large, and it tracks how well the system was matched to the hull.

The early trials show the learning curve. The Japanese training ferry Seiun-Maru (2002) returned a 2% net saving at an air-injection rate of 40 m3 per minute. The cement carrier Pacific Seagull first returned only 1% net at 50 m3 per minute because the bubbles did not cover the bottom sufficiently; after end plates were welded along each side of the bottom in 2008 to keep bubbles from escaping, the net saving rose to 10% in ballast and 5% at full load. The ferry MV Misaki (2004), with 14 WAIP devices, reported 6% net at 18 knots. These results frame the central design problem: holding the air under the bottom rather than letting it slide off the bilge.

Several later trials produced the figures the industry now cites. The Damen ACES air-cavity chambers on Till Deymann, under the EU-funded SMOOTH project, reportedly cut frictional resistance by some 10 to 20% at typical operating speeds, though an earlier model-and-trial round on the same vessel saw net saving sit at about -0.6% when bubbles failed to attach. The river barge Kraichgau I (PELS 2), after its bow was redesigned to stop the cavities raising resistance, reported about 15% net power saving in deep and shallow water. The post-Panamax bulk carrier MV Harvest Frost, delivered with MALS in 2014, obtained the world’s first EEDI certification including air-lubrication calculations from ClassNK in 2017. The container carrier MV Olivia Maersk (124 WAIP devices, 2009 to 2011) ran over a year on its Europe-to-South-America schedule but the collected data did not show conclusive performance gain, which is itself part of the record.

Performance and economics

The compressor penalty and net saving

The number that matters is net saving, not gross drag reduction. Air has to be compressed to overcome the static head at the injection depth plus line losses, and that work is parasitic. In symbols, the net saving fraction is

where $\Delta P_{friction}$ is the propulsion power saved by the reduced skin friction, $P_{air}$ is the shaft-equivalent power drawn by the compressors or blowers, and $P_{ME}$ is the main-engine power at the trial condition. A gross drag reduction that looks impressive on a model can collapse to a small or negative net once $P_{air}$ is charged against it. Till Deymann showed exactly this failure mode, with one trial round sitting near -0.6% net when the bubbles did not attach.

The air-injection rate sets $P_{air}$, and the three regimes differ sharply on it. Slyozkin et al. (2014) found that maintaining a partial air cavity took about one-third the air-injection rate of maintaining an air layer, which is the whole economic case for the cavity. Trial injection rates run from 40 m3 per minute on Seiun-Maru to 50 m3 per minute on Pacific Seagull. Once a cavity is established, raising the injection rate further does little: extra air does not buy much extra drag reduction. Bubble and air-layer systems, by contrast, keep paying for air continuously to hold coverage.

Two variables move net saving most: the share of total resistance that is frictional, and the loading condition. Frictional share rises on slow, full-form hulls, so bulk carriers, crude tankers and LNG carriers sit at the top of the band. Loading matters because draught changes the wetted flat area and the air-coverage geometry: MV Soyo verified about 5% in ballast against 3% loaded, and MT Amalienborg dropped from 4.3% at trial to about 4% in the deep fully laden case. Service speed enters through the resistance: frictional resistance grows with speed, so the absolute power saved grows with speed while the air demand is closer to speed-independent, which is why several WAIP trials reported saving rising toward 10% only in the high-speed range near 14 knots.

The reported full-scale savings, all net of the air-supply penalty and drawn from named trials:

The air lubrication system calculator implements the net-saving estimate for arbitrary ship type, geometry, speed and air-supply inputs.

EEDI treatment as a Category B-1 technology

The IMO Marine Environment Protection Committee agreed at its 65th session to circulate MEPC.1/Circ.815, the 2013 Guidance on Treatment of Innovative Energy Efficiency Technologies for Calculation and Verification of the Attained EEDI. The guidance is interim by its own terms, expected to evolve as experience accumulates, and it sorts innovative technologies into three categories by their effect on the EEDI formula:

• Category A: technologies whose beneficial effect has not yet been proven by a long track record of sea trials.
• Category B: technologies whose beneficial effect can be proven, split into B-1, which reduce propulsion power but do not generate electricity, and B-2, which reduce propulsion power by generating electricity.
• Category C: technologies whose effect is already in the EEDI baseline formula.

Air lubrication is classified as Category B-1: it reduces propulsion power, generates no electricity, and can run at any time during operation. In the attained-EEDI calculation the credit applies through the term that captures propulsion-power reduction in the numerator, so a verified ALS saving lowers the attained EEDI roughly in line with the demonstrated net power saving. ABS describes the effect as an adjustment to the propulsion-power-reduction term of the EEDI formula. MV Harvest Frost received the first EEDI certification including air-lubrication calculations from ClassNK in 2017, which set the precedent that a B-1 ALS credit can be carried into a delivered ship’s EEDI Technical File.

For an existing ship, the same physics feeds the EEXI. Because ALS lowers the power a hull needs at a given speed, it can deliver part of a required EEXI improvement through genuine efficiency rather than through an engine-power limit, so it is one of the few levers that improves EEXI without the speed penalty that EPL or ShaPoLi imposes.

EEDI verification at sea trial

The credit is not granted on a brochure figure. MEPC.1/Circ.815 routes ALS through a two-step verification: a preliminary stage at design, where the builder submits speed-power predictions for the EEDI loading conditions taking the ALS into account, and a final stage at sea trial, where the verifier attends and confirms the measurements. The survey procedure follows the 2014 IMO Guidelines on Survey and Certification of EEDI in MEPC.1/Circ.855 read with MEPC.1/Circ.815. For the trial to count toward the ALS credit, ABS lists the items the trial condition must capture: the area of ship surface covered with air, the thickness of the air layer, the reduction rate of frictional resistance from that coverage, the change in propulsion efficiency from bubble-propeller interaction (self-propulsion factors and propeller open-water characteristics), and any resistance change from additional devices.

The trial data themselves are collected and corrected to a recognised standard. ABS recommends following ITTC Recommended Procedure 7.5-04-01-01.1, “Preparation, Conduct and Analysis of Speed/Power Trials,” with ship speed measured per ITTC 7.5-04-01-01.1 or ISO 15016:2015, “Ship and marine technology, Guidelines for the assessment of speed and power performance by analysis of speed trial data.” Using a controlled speed-power trial standard is what lets a verifier separate the ALS effect from wind, current, and seabed-shallow-water effects that would otherwise swamp a few percent of power.

CII improvement

ALS feeds straight into the operational CII attained, because the attained CII is a ratio of CO2 emitted to transport work and ALS cuts the numerator at constant transport work. A net fuel saving of a given percentage at sea translates, to first order, into the same percentage cut in annual CO2 for the share of the year the system runs, so a vessel sitting just below a rating boundary can use ALS to move up a band without slowing down. The qualifier is the run-time: the saving only accrues while the system is on and holding coverage, so the annual figure tracks the ship’s sea-state and route profile, not the calm-water trial number. The SEEMP combined operational measures calculator handles ALS stacked with other operational measures, where the savings do not add linearly.

Capital cost and economics

Typical ALS capex and payback:

The capital is the air-supply train (compressors or blowers, air-balancing modules, filtration), the hull steelwork for the dispensers, and the integration of piping and control. A retrofit costs more than newbuild integration because the dispenser openings, the machinery space and the piping all have to be worked into an existing ship rather than designed in. The return scales with the absolute fuel burn the percentage saving acts on, so a large slow tanker or bulker that burns a lot at sea recovers the outlay faster than a smaller ship saving the same percentage of a smaller bill. The regulatory layer adds to it: under EU ETS Maritime every saved tonne of fuel also avoids the cost of surrendering allowances for its emissions, and a better CII rating carries commercial weight with charterers and lenders. The retrofit payback calculator and the alternative-fuel TCO calculator take site-specific cost and fuel inputs rather than relying on a generic table, because the payback is hull-specific and bunker-price-sensitive.

Notable installations

Combining ALS with other levers

Air lubrication is one measure in a stack, and operators pair it with wind-assist and hull-coating measures to compound the effect. Dry-bulk operators have fitted Capesize vessels with both an air lubrication system and Flettner rotors, on the logic that the two attack different parts of the resistance budget, friction and the wind-and-wave contribution, so they do not cannibalise each other the way two friction-reduction measures would. The savings still do not add linearly, and a combined figure has to be verified on the specific hull rather than summed from each maker’s number.

Cruise and tanker deployments

The cruise sector took ALS early because its large flat-bottomed hulls and calm-water itineraries suit the technology. ABS recorded that recently delivered ALS vessels through 2018 were mostly cruise ships, naming Quantum of the Seas (2015, Foreship), AIDAprima and AIDAperla (2016 and 2017, MHI), Norwegian Joy (2017, Silverstream) and Diamond Princess (2018, Silverstream). Sea-trial savings for those cruise hulls were not all published, which is part of why the verified-saving record leans on the tanker and bulk-carrier trials. The tanker case rests on MT Amalienborg, the first Silverstream vessel, whose Lloyd’s-Register-verified figures of 4.3% at trial and about 4% deep laden remain among the most-cited independently confirmed results.

Operational considerations

Air-supply system

An ALS is, mechanically, an air-supply plant feeding the hull bottom. ABS describes the package as piping, pneumatic and control systems, and air dispensers. The air source is either compressors or, on the MALS and several Japanese systems, purpose-built blowers, fed into the hull bottom through dispensers or release units. MHI built its own Mitsubishi Turbo-blower for the MALS and placed two sets of blowers in the auxiliary engine room of MV Yamato and MV Yamatai. The supply has to clear the static head at the injection depth plus line losses, which is why the compressor sizing, not the injector count, sets the parasitic load.

The injectors themselves are the design variable that separates a working system from a poor one. On Pacific Seagull the air injectors were placed on both sides near the bow and the bubbles did not cover the bottom, so the first trial returned only 1%; the fix was welded end plates to hold the air, after which ballast saving reached 10%. The MALS triple-outlet scheme on MV Yamato used a centre injector at the front of the bottom and two symmetric side injectors precisely to spread coverage across the flat.

Sea-state sensitivity

ALS gives back part of its calm-water figure in a seaway, because wave action breaks up the air film. The clearest sourced data point is MHI’s Naminoue, where the claimed propulsion-power reduction exceeding 5% was stated for waves of 2.5 to 3 m, a narrow window rather than an all-weather figure. The annual saving therefore reflects the ship’s actual sea-state and route distribution, which is one reason cruise ships on calm-water itineraries and tankers on steady ocean passages report different effective savings from the same hardware. In heavy weather the operator can shut the air supply off to stop paying the compressor penalty for a film that is no longer holding; Foreship designed its dispenser box specifically so it would not raise skin friction with the air off.

Class society support

The major class societies provide both classification and powering-performance advisory for ALS-fitted ships. ABS published its Guide on Air Lubrication System Installation in October 2018, setting installation requirements for ABS-classed vessels, and its Air Lubrication Technology advisory in April 2019 summarising the state of the technology and the EEDI treatment. Lloyd’s Register has run independent verification of system performance since the first installations and built third-party oversight of design, installation and operation; its Ship Performance Team verified the MT Amalienborg figures. ClassNK issued the first EEDI certification including air-lubrication calculations, on MV Harvest Frost in 2017. Across societies the workflow is the same: preliminary verification at design against submitted speed-power predictions, final verification at sea trial with the verifier in attendance per MEPC.1/Circ.855, then periodic survey of the machinery and re-verification at renewal.

Future outlook

Adoption trend

Order-book data points one way. The Silverstream System moved from a single tanker in 2014 to over 100 operating vessels and over half of roughly 500 systems on order by 2025 (Lloyd’s Register, 2025), and the other makers are growing alongside it. Uptake concentrates on the ship types where the frictional share is highest and the flat bottom is largest: bulk carriers, crude and product tankers, LNG carriers, and the large flat-bottomed cruise hulls. The combination of EEXI, CII and a carbon price under EU ETS Maritime is the demand driver, because each turns a fuel saving into a regulatory and financial saving at once. What the public trial record cannot yet support is a precise fleet-penetration forecast, because the verified-saving dataset is still small and hull-specific.

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 it for re-use, cutting the parasitic compressor load that limits net saving.

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.

Structural and stability integration

An ALS is not only a piping and machinery package; it cuts openings in the hull bottom and adds weight, so class society review reaches into structure and stability. ABS notes that air lubrication systems generally consist of piping, pneumatic and control systems, and air dispensers, and that installing dispensers on the hull introduces additional openings that can create local stress concentrations needing reassessment. Equipment, piping and ventilation around the compressor or blower room commonly have to be rearranged to fit the system, which on a retrofit competes with existing machinery space.

Weight and its longitudinal distribution drive the stability check. ABS sets two concrete triggers for a fresh stability calculation or stability test: a change in lightship displacement exceeding 2% of the most recent approved lightship displacement, or a change in lightship longitudinal centre of gravity exceeding 1.0% of the length between perpendiculars relative to the approved lightship data. On a large cargo ship the compressor sets, air-balancing modules and steel for the dispenser arrays can approach the displacement trigger, so the lightship survey after installation is not a formality.

The injectors sit in the most fouling-prone and impact-prone zone of the ship, the flat bottom, so the structural detail of the air release units matters for the life of the system. Coverage geometry is also a structural decision: Pacific Seagull needed end plates welded along the bottom to stop bubbles escaping at the bilge before its saving climbed from 1% to 10% in ballast, which shows that the steelwork that retains the air is as important as the air supply that makes it.

Limitations

The savings band is real but conditional, and several limits should temper any single headline figure. The public full-scale record is thin: about 18 trials between 2002 and 2015, many on ships outside EEDI compliance that did not collect data to the EEDI trial standard, so the often-quoted 4 to 10% net band carries real scatter and a few near-zero or negative results, such as the -0.6% round on Till Deymann before the bubbles attached. A number lifted from one trial does not transfer cleanly to a different hull, loading, or route.

Loading and hull form move the result more than marketing allows. MV Soyo verified about 5% in ballast against 3% loaded, and MT Amalienborg fell from 4.3% at trial to about 4% in the deep fully laden condition, because draught changes the wetted flat area and the air-coverage geometry. Container ships and other fine-form hulls, with a smaller frictional share and less flat bottom than a bulk carrier or tanker, sit at the bottom of the band by construction.

Sea state and the parasitic load are the two operational caps. Wave action disrupts the air film, so a system that delivers its design figure in calm water gives back part of it in a seaway; MHI’s Naminoue claim of propulsion-power reduction exceeding 5% was stated specifically for waves of 2.5 to 3 m, which is a narrow window. The compressor or blower draws shaft-equivalent power continuously for bubble and air-layer systems, and if coverage is poor the net result can go negative, as the early Pacific Seagull and Till Deymann trials showed. ALS also competes for space and capital with other levers: it is one measure in a stack that includes trim optimisation, hull coatings, and wind-assist propulsion, and the savings do not add linearly. Finally, MEPC.1/Circ.815 is interim guidance by its own terms; the EEDI credit a system can claim depends on what a verifier confirms at sea trial under MEPC.1/Circ.855, not on the maker’s figure.

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See also

• Wind-Assisted Propulsion - parallel technology often combined with ALS
• What is EEDI - design-phase index recognising ALS as innovative tech
• What is EEXI - existing-ship index also recognising ALS
• What is CII - operational index that ALS directly improves
• SEEMP I, II and III - operational plan documenting ALS
• EEXI EPL and ShaPoLi - alternative EEXI compliance levers
• CII Corrective Action Plan - corrective measures for D/E-rated ships
• Slow steaming and CII - operational lever combined with ALS
• MARPOL Annex VI - parent regulation
• IMO GHG Strategy - policy framework
• IMO Net-Zero Framework - GFI standard from 2027
• EU ETS for shipping - EU cap-and-trade
• FuelEU Maritime explained - parallel intensity regime
• FuelEU penalties, pooling and multipliers - FuelEU mechanics
• UK ETS for shipping - UK cap-and-trade
• EU MRV Regulation 2015/757 - reporting framework
• IMO DCS vs EU MRV - reporting comparison
• Poseidon Principles - bank-side framework
• Sea Cargo Charter - cargo-buyer-side framework
• RightShip GHG Rating - per-vessel rating
• Green Shipping Corridors - operational corridors
• EUA Market Mechanics for Shipping - allowance market
• Voluntary Carbon Credits in Shipping - parallel mechanism
• CARB At-Berth Regulation - California regional regime
• China DCS - China’s national reporting regime
• Cold ironing and shore power - in-port emission reduction
• Emission Control Areas - regional sulphur and NOx framework
• NOx Tier I, II and III - engine certification regime
• IMO 2020 sulphur cap - global sulphur cap
• Biofuels in shipping - low-carbon fuel pathway
• LNG as marine fuel - dual-fuel pathway often combined with ALS
• Methanol as marine fuel - alternative pathway
• Ammonia as marine fuel - zero-carbon pathway
• Heavy fuel oil - residual fuel
• Marine gas oil - distillate fuel
• Specific fuel oil consumption - engine efficiency metric
• Marine diesel engine - main propulsion benefiting from ALS
• LNG fuel system - dual-fuel ship handling
• Exhaust gas cleaning system - scrubber technology
• Selective catalytic reduction - SCR for Tier III NOx
• MARPOL Convention - parent IMO treaty
• SOLAS Convention - principal IMO safety treaty
• STCW Convention - training and watchkeeping standards
• COLREGs Convention - parallel IMO instrument
• Bulk carrier - principal vessel type for ALS
• Oil tanker - significant ALS deployments
• Container ship - growing ALS deployment
• Ro-ro vessel - some ALS deployments
• Chemical tanker - some ALS deployments
• LNG carrier - some ALS deployments
• Voyage charter party - typical contract type
• Time charter party - alternative contract type with BIMCO clauses
• Port state control - parallel federal enforcement framework
• Classification society - ALS installation certification
• Flag state and flag of convenience - flag-state role
• Air lubrication system calculator - net fuel-saving calculation
• Lifecycle retrofit payback calculator - investment payback
• Lifecycle alternative-fuel TCO calculator - alternative-fuel total cost of ownership
• Wind resistance ISO 15016 calculator - vessel wind resistance
• Wind-assist Flettner rotor calculator - parallel wind-assist technology
• Wind-assist wing sail / kite calculator - parallel wind-assist
• Battery hybrid SOC calculator - battery state of charge
• Cold ironing OPS offset calculator - per-visit emissions reduction
• JIT arrival calculator - just-in-time arrival savings
• JIT economic-speed calculator - economic speed for JIT
• Weather routing savings calculator - weather routing fuel savings
• Weather routing fuel savings calculator - alternative weather routing
• Trim optimisation calculator - trim optimisation
• PBCF energy-saving device calculator - propeller boss cap fin
• Mewis duct calculator - Mewis duct savings
• Pre-swirl stator calculator - pre-swirl stator savings
• Bulbous bow retrofit savings calculator - bulbous bow savings
• SEEMP combined operational measures calculator - non-overlapping savings stack
• SEEMP Part I calculator - Part I structure
• SEEMP Part III calculator - Part III CII operational plan
• CII attained calculator - operational AER calculation
• CII required calculator - regulation-driven Required CII
• CII rating calculator - A-to-E rating mapping
• CII corrective trajectory calculator - corrective plan forecast
• SFOC-to-CII converter - engine SFOC to ship CII rating
• EEDI attained calculator - design-phase index
• EEDI required calculator - Required EEDI
• EEDI innovative-tech credit calculator - the formal credit for ALS
• EEDI reference line calculator - 2008 baseline
• EEDI phase factor calculator - reduction factors
• EEXI attained calculator - EEXI as-built calculation
• EEXI required calculator - Required EEXI
• EPL required MCR reduction calculator - EEXI compliance limited MCR
• GFI attained calculator - WtW intensity from fuel mix
• GFI compliance calculator - Net-Zero Framework compliance position
• EU MRV emissions calculator - per-voyage emissions
• EU MRV to EU ETS allowance crosswalk calculator - bridges MRV data to ETS surrender
• MARPOL EU ETS cost calculator - EU ETS surrender cost
• MARPOL FuelEU penalty calculator - FuelEU non-compliance penalty
• CARB at-berth compliance calculator - California compliance check
• Methane slip calculator - LNG dual-fuel methane slip
• Methane slip CO2-equivalent calculator - GWP100 conversion
• LNG well-to-wake calculator - LNG WtW intensity
• Tier II NOx calculator - rated-speed-dependent Tier II
• Tier III NOx calculator - rated-speed-dependent Tier III
• NOx Tier compliance check calculator - integrated tier compliance check
• Norway NOx Fund calculator - national NOx levy
• ECA fuel-cost premium calculator - trade-route ECA economics
• ESI score calculator - Environmental Ship Index voluntary recognition
• Poseidon Principles alignment calculator - lender-side CAS
• RightShip GHG calculator - per-vessel rating
• Engine cube-law fuel calculator - speed-fuel relationship
• Brake thermal efficiency calculator - engine thermal efficiency
• Engine CO2 emission per kWh calculator - engine CO2 rate
• Survey calculator - Annex VI survey cycle
• IAPP certificate calculator - IAPP issue and endorsement
• IMO DCS report calculator - annual fuel-consumption report
• Reg 28 CII calculator - CII rating
• Wind-assist Flettner thrust calculator - parallel wind-assist tool
• Wind-assist Flettner power calculator - parallel wind-assist tool
• Wind-assist sail thrust calculator - parallel wind-assist tool
• Wind-assist kite force calculator - parallel wind-assist tool
• ShipCalculators.com calculator catalogue - full listing

Additional calculators:

• Hull Cleaning ROI

Additional formula references:

• Yard Samsung Heavy Industries
• System Control Air Compressor Screw
• System Starting Air Compressor Reciprocating

Additional related wiki articles:

• Energy-Saving Devices (ESDs)
• Waste heat recovery system

References

1. IMO MEPC. MEPC.1/Circ.815: 2013 Guidance on Treatment of Innovative Energy Efficiency Technologies for Calculation and Verification of the Attained EEDI. IMO, 17 June 2013.
2. IMO MEPC. MEPC.1/Circ.855: 2014 Guidelines on Survey and Certification of the Energy Efficiency Design Index (EEDI). IMO, 2014.
3. ABS. Air Lubrication Technology (advisory). American Bureau of Shipping, 1 April 2019.
4. ABS. Guide on Air Lubrication System Installation. American Bureau of Shipping, October 2018.
5. ITTC. Recommended Procedure 7.5-04-01-01.1, Preparation, Conduct and Analysis of Speed/Power Trials. International Towing Tank Conference, 2017.
6. ISO. ISO 15016:2015, Ship and marine technology, Guidelines for the assessment of speed and power performance by analysis of speed trial data. ISO, 2015.
7. Silberschmidt, N., Tasker, D., Pappas, T., & Johannesson, J. Silverstream System: Air Lubrication Performance Verification and Design Development. Shipping in Changing Climates Conference, 2016.
8. Lloyd’s Register. Charting Silverstream’s innovative journey as air lubrication comes of age. LR Horizons, July 2025.
9. Jang, J., Choi, S. H., Ahn, S. M., Kim, B., & Seo, J. S. Experimental investigation of frictional resistance reduction with air layer on the hull bottom of a ship. International Journal of Naval Architecture and Ocean Engineering, 6(2), 2014, 363 to 379.
10. Lee, J., Kim, J., Kim, B., Jang, J., Mcstay, P., Raptakis, G., & Fitzpatrick, P. Full Scale Applications of Air Lubrication for Reduction of Ship Frictional Resistance. 2016.
11. Hoang, C. L., Toda, Y., & Sanada, Y. Full scale experiment for frictional resistance reduction using air lubrication method. ISOPE, 2009.

Further reading

• Butterworth, J., Atlar, M., & Shi, W. Experimental analysis of an air cavity concept applied on a ship model on the hull resistance. Ocean Engineering, 110, 2015, 2 to 10.
• Perlin, M. & Ceccio, S. Mitigation of hydrodynamic resistance: Methods to reduce hydrodynamic drag. World Scientific, 2014.
• Foeth, E. J. The efficacy of air-bubble lubrication for decreasing friction resistance. The Naval Architect, April 2011, 44 to 46.