Methane Slip from LNG Dual-Fuel Engines

Background

Why methane slip matters

The marine LNG fuel uptake from approximately 2010 onwards was driven by a confluence of regulatory and commercial drivers: the IMO 2020 sulphur cap (LNG has near-zero sulphur emission), the NOx Tier III requirements in Emission Control Areas (LNG-fuelled engines can meet Tier III without an SCR system), the EEDI and subsequently EEXI credits for LNG-fuelled vessels, and the WtW CO2 advantage of LNG over HFO of approximately 25% (on a TtW-only basis). By end-2024 the world LNG-fuelled fleet exceeded 1,000 vessels in operation with a similar number on order, with MSC, CMA CGM, Maersk, NYK, MOL, K Line, Hapag-Lloyd, Cosco, OOCL and other major lines all operating significant LNG dual-fuel fleets.

The methane slip issue emerged as a significant climate-policy concern from approximately 2018 onwards, when in-service measurements began to reveal that the actual slip rate from operating LNG dual-fuel vessels was significantly higher than engine manufacturer bench-test claims, particularly for low-pressure spark-ignition (LPSI) four-stroke engines and at part-load operation. The ICCT (International Council on Clean Transportation) 2020 study “Methane slip from LNG-fuelled vessels” quantified the in-service slip rates and concluded that, with then-prevailing slip rates and methane GWP-100 of 28, LNG provides 0 to 23% net climate benefit over HFO depending on engine technology, significantly less than the headline 25% TtW CO2 saving and well within the range where methane upstream leakage rates could push LNG to a net climate negative.

The methane slip issue substantially shaped the design of the FuelEU Maritime Regulation (which uses WtW intensity as the metric and applies the AR5 GWP-100 = 28 for methane), the IMO Net-Zero Framework (which uses GFI = WtW intensity, similarly applying AR5 GWP-100), and the engine technology direction (with HPDF engines increasingly favoured over LPSI for new-build orders).

LNG combustion chemistry and the slip mechanism

LNG (essentially methane, CH4, with small fractions of ethane, propane and nitrogen depending on the source field) burns cleanly under ideal conditions:

$$ CH_4 + 2 O_2 \rightarrow CO_2 + 2 H_2 O $$

In a real internal combustion engine, the combustion is incomplete in the cycle of every cylinder: small fractions of fuel methane escape combustion and exit through the exhaust as unburned methane. The principal slip mechanisms are:

• Crevice slip: methane trapped in the small crevices around the piston rings, between the piston top and the cylinder liner, that escapes the main combustion event and exits with the exhaust on the next exhaust stroke. Largest contributor to slip in low-pressure engines.
• Wall quenching: methane near the cool cylinder wall that is quenched below the combustion temperature before reacting; exits unburned. Significant in low-load operation.
• Valve overlap slip: in two-stroke engines and in some four-stroke engines, methane mixed into the exhaust during the valve overlap period (when both intake and exhaust valves are partially open) escapes combustion. Significant contributor in low-pressure two-stroke designs.
• Knock-induced misfire: at high load and high LNG fuel fraction, autoignition (knock) can cause some cylinders to misfire, releasing unburned methane.
• Lean limit misfire: at very lean air-fuel ratios (typically used at part load to maintain combustion stability), some cylinders misfire intermittently, releasing unburned methane.
• Fuel injection timing slip: late-injected methane that does not have time to fully mix before combustion ends.

The relative importance of each mechanism depends on the engine architecture (high-pressure direct injection vs low-pressure premixed injection, two-stroke vs four-stroke, slow-speed vs medium-speed) and on the operating point (load, ambient conditions, fuel fraction).

Engine architecture taxonomy

LNG dual-fuel marine engines are classified into four principal architectures:

• High-pressure dual-fuel (HPDF) two-stroke: methane injected at high pressure (approximately 300 bar) directly into the cylinder near top dead centre, after pilot diesel ignition. The high-pressure direct injection limits crevice slip and wall quenching. Examples: MAN ME-GI (in service from 2014), Win GD X-DF in HPDF mode (in service from 2018). Slip typically 0.2 to 0.5% of fuel.
• Low-pressure dual-fuel slow-speed (LBSI) two-stroke: methane premixed with combustion air at low pressure (5 to 10 bar) at the intake, ignited by pilot diesel. Crevice slip and valve overlap slip are larger than HPDF. Examples: Win GD RT-flex DF (in service from 2010, predecessor to X-DF), MAN ME-LGI (low-pressure variant). Slip typically 1.0 to 2.5% of fuel.
• Low-pressure dual-fuel medium-speed (LBDF) four-stroke: similar architecture to LBSI but with four-stroke configuration. Examples: Wartsila 31DF (medium-speed), Wartsila 34DF, MAN 32/40 DF. Slip typically 1.5 to 3.0% of fuel.
• Low-pressure spark-ignition (LPSI) four-stroke: methane premixed with combustion air at very low pressure, spark-ignited (no pilot diesel). Highest slip due to crevice and quenching mechanisms. Examples: Wartsila 50DF generation 1 (in service from approximately 2003), Caterpillar 3600 series. Slip typically 2.5 to 5.0% of fuel.

The historical adoption sequence was: LPSI four-stroke (early) → LBSI two-stroke (mid) → HPDF two-stroke (late). Most current newbuild LNG dual-fuel orders are HPDF two-stroke, although LBSI remains common for some segments and LPSI four-stroke remains the standard for auxiliary engines and for some smaller LNG-fuelled vessels.

Slip rates by engine type and operating point

HPDF (high-pressure dual-fuel) two-stroke

Engine-bench tests of MAN ME-GI and Win GD X-DF in HPDF mode typically report:

• At 100% MCR: slip 0.15 to 0.25% of fuel input.
• At 75% MCR: slip 0.20 to 0.35%.
• At 50% MCR: slip 0.30 to 0.50%.
• At 25% MCR: slip 0.50 to 0.80% (low-load slip is higher due to colder cylinder walls and longer combustion duration).
• At idle (10 to 15% MCR): slip 0.80 to 1.50% (significant slip increase at very low load).

In-service measurement campaigns (notably the ICCT 2020 study, SEA-LNG 2022 study, DNV 2023 study) confirm bench-test values within approximately ± 20% for HPDF engines, indicating that the bench-test characterisation is representative of in-service operation.

LBSI (low-pressure dual-fuel slow-speed) two-stroke

Engine-bench tests of Win GD RT-flex DF and Win GD X-DF in LPDF mode typically report:

• At 100% MCR: slip 0.5 to 1.0%.
• At 75% MCR: slip 0.8 to 1.5%.
• At 50% MCR: slip 1.5 to 2.5%.
• At 25% MCR: slip 2.5 to 4.0%.
• At idle: slip 4.0 to 7.0%.

In-service measurements typically show slip rates 30 to 80% higher than bench-test values, particularly at part load and during transient operation. This discrepancy is principally attributed to the variable LNG composition (some bunkered LNG has higher inerts or higher heavies content than the bench-test fuel), to engine wear over time, and to operator practice (some operators run consistently at lower load than the optimum due to slow-steaming or dynamic-positioning constraints).

LBDF (low-pressure dual-fuel medium-speed) four-stroke

Engine-bench tests typically report:

• At 100%: slip 1.0 to 2.0%.
• At 75%: slip 1.5 to 2.5%.
• At 50%: slip 2.0 to 3.5%.
• At 25%: slip 3.5 to 5.5%.

In-service rates are typically 20 to 50% higher than bench tests for similar reasons as LBSI.

LPSI (low-pressure spark-ignition) four-stroke

Engine-bench tests typically report:

• At 100%: slip 2.0 to 3.5%.
• At 75%: slip 2.5 to 4.0%.
• At 50%: slip 3.5 to 5.0%.
• At 25%: slip 5.0 to 7.5%.

In-service rates can be significantly higher (sometimes 50 to 100% above bench tests), particularly on aging engines. Some early-generation LPSI engines in continuous low-load operation (e.g. cruise ship auxiliary engines at port) have measured slip rates exceeding 7%.

Climate impact analysis

GWP weighting

The climate impact of methane slip depends critically on the choice of GWP:

• GWP-100 = 28 (IPCC AR5 without climate-carbon feedback): the value adopted by FuelEU Maritime, IMO Net-Zero Framework, IMO LCA Guidelines.
• GWP-100 = 34 (with climate-carbon feedback): used in some voluntary frameworks.
• GWP-20 = 84 to 87 (IPCC AR5): used in some climate-impact analyses focused on near-term warming.
• GWP* (an alternative metric reflecting the temperature impact of short-lived gases): increasingly cited in academic literature.

Under GWP-100 = 28, a 3% methane slip rate translates to approximately:

• 3% of 50 g-CH4/MJ (the methane content of 1 MJ of LNG) = 1.5 g-CH4/MJ slip.
• 1.5 g-CH4 × 28 = 42 g-CO2eq/MJ from slip.
• Plus combustion CO2 of approximately 56 g-CO2/MJ (TtW) = 98 g-CO2eq/MJ TtW.
• Plus WtT of approximately 18 g-CO2eq/MJ = 116 g-CO2eq/MJ WtW.

This is approximately 25% higher than the WtW intensity of HFO (93 g-CO2eq/MJ), making LNG a net climate negative under these assumptions.

Under GWP-20 = 87, the same 3% slip rate translates to approximately 130 g-CO2eq/MJ from slip alone, pushing the WtW intensity to approximately 200 g-CO2eq/MJ, more than double HFO.

Net climate benefit by engine type

Combining the slip rates above with the GWP-100 weighting and a representative WtT intensity of 18 g-CO2eq/MJ (FuelEU Annex II default for LNG):

The “net benefit vs HFO” column expresses the WtW CO2eq increase (positive) or decrease (negative) versus a HFO baseline of 93 g-CO2eq/MJ. HPDF has a real climate benefit; LBSI is approximately break-even; LBDF and LPSI 1st gen are net climate negative.

Upstream methane leakage

The figures above account only for engine slip. Upstream methane leakage during LNG production, transport and bunkering adds additional methane emissions to the WtW intensity. Estimates of the upstream leakage rate vary widely:

• EU JRC default (FuelEU Annex II): approximately 0.5% of LNG production volume (corresponding to approximately 7 g-CO2eq/MJ at GWP-100).
• IPCC default: approximately 1.5%.
• EDF (Environmental Defense Fund) ground-based measurements (US, 2018): approximately 2.3% for US natural gas (substantially higher than the official EPA value of 1.4%).
• Field measurements in Permian Basin (US) and Vaca Muerta (Argentina) 2021 to 2023: approximately 4 to 9% in some specific producing regions.

Higher upstream leakage further degrades the LNG climate benefit. At 2.3% upstream leakage and 1.2% engine slip (LBSI), the WtW intensity is approximately 105 g-CO2eq/MJ, clearly worse than HFO. At 4% upstream leakage and 4% engine slip (LPSI 1st gen on Permian-sourced LNG), the WtW intensity is approximately 200 g-CO2eq/MJ, more than double HFO.

Regional variation

LNG produced in different regions has materially different upstream leakage profiles:

• Norway, North Sea (Equinor production): leakage approximately 0.1 to 0.3%, the lowest in the world due to extensive monitoring and capture infrastructure.
• Australia (NWS, Gorgon, Wheatstone): leakage approximately 0.5 to 1.0%.
• Qatar (RasGas, QatarGas): leakage approximately 0.3 to 0.6%.
• United States (Henry Hub LNG): leakage approximately 1.5 to 5.0% depending on production basin (Permian Basin and Eagle Ford have higher leakage than Marcellus or Haynesville).
• Russia (Yamal, Sakhalin): leakage approximately 1.5 to 3.0% (limited monitoring data).
• Algeria, Egypt, Nigeria: leakage approximately 2 to 5%.

The EU FuelEU Annex II uses a single default leakage value across all sources; the IMO LCA Guidelines (in adoption 2025) similarly use a single global default, although both frameworks allow producers to certify lower-than-default values for specific batches.

Mitigation technologies

Methane oxidation catalyst (MOC)

A methane oxidation catalyst is a catalytic converter installed in the exhaust system, downstream of any exhaust gas cleaning system (sulphur scrubber) and any SCR (Selective Catalytic Reduction) NOx system, that oxidises unburned methane to CO2 and H2O:

$$ CH_4 + 2 O_2 \rightarrow CO_2 + 2 H_2 O $$

The catalyst is typically a palladium-based or platinum-palladium-rhodium material on a ceramic or metal monolith substrate, similar in form factor to an automotive catalytic converter scaled to marine size.

Performance of MOCs:

• Typical methane conversion: 50 to 90% at full operating temperature (typically 350 to 550 °C).
• Light-off temperature: typically 350 °C; below this temperature the conversion is significantly reduced. Marine engines operating in part-load have lower exhaust temperatures and may not reach light-off.
• Sulphur poisoning: marine fuels with even trace sulphur (e.g. dual-fuel pilot diesel, shore-side LNG with trace H2S) progressively poison the catalyst. Sulphur-tolerant catalyst formulations are under development; current marine MOCs require very low pilot-fuel sulphur or periodic regeneration.
• Capital cost: USD 100,000 to USD 500,000 per installation depending on engine power.
• Operating cost: minimal (small pressure drop adds approximately 0.5% fuel consumption).

By end-2024 only a small number of LNG-fuelled vessels have MOC installed, principally as commercial pilots. MAN Energy Solutions, Wartsila, Yara Marine, Caterpillar and several other vendors have commercial MOC offerings; the technology is expected to become standard on LNG-fuelled newbuilds from approximately 2026 to 2028.

Engine combustion redesign

Engine manufacturers have pursued combustion-side redesign to reduce slip without aftertreatment:

• MAN ME-GA (announced 2022): a low-pressure variant with revised combustion chamber and injection timing to reduce slip; targets 1.0 to 1.5% slip at typical operating points, intermediate between HPDF and LBSI.
• Win GD X-DF2.1 (in service from 2023): improved version of X-DF with revised port timing and injection, targets 0.8 to 1.2% slip.
• Win GD X-DF2.2 (in development for 2026 to 2028 delivery): further refinement targeting under 0.5% slip across the full operating envelope.
• Wartsila 50DF Mk2 and Mk3: progressive refinement of the LPSI design, with Mk3 (current) targeting under 1.5% slip in steady-state operation.

The combustion-side path has the advantage of reducing slip at source (no aftertreatment cost or complexity) but requires fundamental engine redesign and replacement of existing engines.

HPDF retrofit

For owners of LBSI engines, HPDF retrofit is in principle possible but is engineering-intensive and economically marginal. The retrofit requires replacement of the cylinder cover and injection system, and may require gearbox or shafting modifications. Typical retrofit cost is USD 5 to USD 15 million per engine; payback against avoided FuelEU penalty is approximately 8 to 15 years, marginal.

For owners of LPSI four-stroke engines, retrofit to HPDF is generally not feasible (the engine architecture is too different) and would require full engine replacement.

Operational measures

Several operational measures reduce slip without hardware modification:

• Avoid low-load operation: slip increases significantly at part load. Operators can consolidate auxiliary loads onto fewer engines running at higher load, sacrificing some redundancy.
• Avoid rapid load transients: slip is higher during load transients than in steady state. Operators can plan voyages and dynamic-positioning operations to minimise transients.
• Maintain engine condition: worn engines have higher slip than new engines. Regular maintenance and timely overhaul reduce in-service slip.
• Use LNG with consistent composition: variable LNG composition (heavies content, inerts) increases slip. Bunker quality control helps.

These measures typically deliver 10 to 30% slip reduction; useful but not transformative.

E-LNG

The ultimate methane-slip mitigation pathway is to use e-LNG (synthetic methane produced from green hydrogen and captured CO2 via the Sabatier process), which is chemically identical to fossil LNG and is fully compatible with existing LNG dual-fuel engines. The methane slip from e-LNG combustion is the same in absolute terms as from fossil LNG, but the WtW intensity is dramatically lower because the upstream production is renewable (rather than fossil) and the captured CO2 in the Sabatier process is from biogenic, industrial or DAC sources.

Under e-LNG, a 3% engine slip rate produces approximately 42 g-CO2eq/MJ from slip (the same as fossil LNG), but the upstream WtT intensity is approximately 5 to 15 g-CO2eq/MJ (versus 18 g-CO2eq/MJ for fossil LNG), and the combustion CO2 is approximately 56 g-CO2/MJ from biogenic carbon (which is conventionally counted as having upstream offset of zero, i.e. the CO2 was previously captured from atmosphere). The net WtW intensity for e-LNG with 3% slip is therefore approximately 65 g-CO2eq/MJ, better than HFO (93) but still significantly worse than green ammonia or e-methanol with low slip.

The slip issue is therefore not fully resolved by switching to e-LNG; methane oxidation catalysts and combustion redesign remain important even for e-LNG operations.

Regulatory treatment

FuelEU Maritime

FuelEU Maritime applies the AR5 GWP-100 = 28 for methane in the WtW intensity calculation. The Annex II default values for LNG include explicit accounting for methane slip:

A vessel with HPDF engines achieves a WtW intensity of approximately 74.5 g-CO2eq/MJ, comfortably below the 2025 FuelEU maximum of 89.34 g-CO2eq/MJ, but rapidly approaching the 2030 maximum of 85.69, the 2035 maximum of 77.94, and the 2040 maximum of 62.90. A vessel with LPSI engines is already non-compliant under FuelEU 2025.

Owners can certify a vessel-specific WtW intensity (lower than the Annex II default) through certified continuous emission monitoring of methane slip; this requires Class-approved instrumentation and a Class-approved measurement protocol.

IMO Net-Zero Framework GFI

The IMO Net-Zero Framework similarly applies AR5 GWP-100 = 28 in the GFI calculation. The IMO LCA Guidelines (MEPC.391, in adoption 2025) provide default WtW values for LNG that are broadly aligned with FuelEU Annex II. The default values are reviewed periodically as in-service measurement data improves.

EU ETS

Methane slip is not directly captured in the EU ETS for shipping calculation, which is based on combustion CO2 only. However, the EU ETS extension to methane and N2O under the EU ETS Directive amendment of 2023 brings methane slip into ETS scope from 2026. This will add an additional EUR 7 to 30 per t CO2eq of slip-related cost on top of the FuelEU penalty.

Voluntary frameworks

The Poseidon Principles, Sea Cargo Charter and RightShip GHG Rating frameworks all apply methane slip in their respective WtW intensity scoring. Some signatories use AR5 GWP-100; others use higher values (GWP-20 in some Sea Cargo Charter formulations; GWP* in some forward-looking analysis). The differences in scoring methodology can materially affect the relative ranking of LNG-fuelled vessels in these frameworks.

In-service measurement methodology

Continuous emission monitoring

The most accurate methane slip measurement method is continuous emission monitoring (CEM) of the exhaust:

• Exhaust flow measurement: typically by hot-wire anemometer or by ultrasonic transit-time meter at the funnel.
• Methane concentration measurement: typically by Fourier-transform infrared (FTIR) spectroscopy or by laser-based methane detector (TDLAS, tunable diode laser absorption spectroscopy).
• CO2 concentration measurement: typically by NDIR (non-dispersive infrared) detector.
• N2O concentration measurement (for ammonia engines): typically by FTIR.
• Sampling location: downstream of any methane oxidation catalyst (to capture net slip after aftertreatment) but upstream of the funnel cap to avoid dilution by ambient air.

CEM systems are commercially available from several vendors (FCT, Sintrol, IRcon, MKS Instruments, Servomex). Marine adaptation requires class-approved enclosures, vibration-tolerant mounting and ATEX/IECEx certification for the LNG fuel area.

Periodic spot measurement

For owners not investing in continuous monitoring, periodic spot measurement (typically annual, by a third-party measurement contractor during a planned port call) is an alternative. Spot measurements are typically lower-cost (USD 20,000 to USD 50,000 per measurement campaign) but provide less granular data and may not capture the full range of operating conditions.

Engine-modelled estimation

The lowest-cost (but lowest-accuracy) approach is engine-modelled estimation, in which the slip rate is estimated from engine-bench-test data combined with vessel operating profile data (load, speed, transient frequency). The MAN, Wartsila and Win GD engine performance simulators all include slip estimation modules.

SEA-LNG measurement campaign (2021 to 2023)

The SEA-LNG industry coalition coordinated a multi-vessel methane slip measurement campaign over 2021 to 2023, covering approximately 30 LNG-fuelled vessels across HPDF, LBSI and LBDF engine architectures. The campaign’s published results (2023) showed:

• HPDF in-service slip rates approximately 0.3 to 0.5% (consistent with bench-test values).
• LBSI in-service slip rates approximately 1.0 to 2.0% (slightly higher than bench-test values).
• LBDF in-service slip rates approximately 1.5 to 3.0%.

The SEA-LNG campaign also identified a strong load dependence of slip across all engine types, with slip at idle approximately 2 to 3 times the slip at 75% MCR.

ICCT measurement campaign and policy implications

The ICCT 2020 study measured slip rates on a sample of LNG-fuelled vessels and reached conclusions broadly aligned with the SEA-LNG campaign for HPDF and LBSI engines, but reported significantly higher slip rates for LPSI engines (typically 4 to 6% at typical operating points). The ICCT findings were instrumental in the EU and IMO regulatory uptake of GWP-100 = 28 (rather than lower values previously suggested by the LNG industry).

Implications for owners, charterers and insurers

Owners

Owners of LBSI and LBDF LNG dual-fuel vessels face significant FuelEU Maritime exposure under the post-2030 reduction trajectory. Mitigation options (in order of cost-effectiveness):

1. Operational measures: avoid low-load operation, maintain engine condition, use consistent LNG composition. Cost: minimal. Slip reduction: 10 to 30%.
2. Combustion-side engine refinement: incremental upgrade to a Mk2 or Mk3 LPSI variant. Cost: USD 200,000 to USD 1 million per engine. Slip reduction: 30 to 50%.
3. Methane oxidation catalyst (MOC): retrofit aftertreatment. Cost: USD 200,000 to USD 500,000 per engine. Slip reduction: 50 to 90%.
4. HPDF retrofit: replace LBSI/LBDF with HPDF. Cost: USD 5 to USD 15 million per engine. Slip reduction: 70 to 90%.
5. E-LNG bunker: switch to renewable LNG bunker supply. Cost: USD 2 to USD 6 fuel premium per GJ. Slip rate unchanged but WtW intensity dramatically lower.
6. Engine replacement: replace LBSI/LBDF with HPDF newbuild engine. Cost: USD 15 to USD 30 million per engine. Slip reduction: 70 to 90%.

For LPSI four-stroke owners, the options are more limited (HPDF retrofit not feasible). The most cost-effective path is typically MOC retrofit + operational measures + e-LNG bunker.

Charterers

Long-term charterers require certified slip rates to project FuelEU exposure. The BIMCO FuelEU Maritime Clause (in development 2024) provides a framework for slip-rate certification and cost allocation between owner and charterer.

Insurers

Marine insurers are integrating methane slip into hull and P&I underwriting for Poseidon Principles signatories.

Banks and finance

Ship-finance banks signed up to the Poseidon Principles report annual portfolio WtW intensity that explicitly includes methane slip. LNG-fuelled vessels with high in-service slip rates contribute materially negatively to the bank’s portfolio score.

Future outlook

Methane slip standards

The IMO is developing methane slip emission standards for LNG dual-fuel engines, intended to come into effect from approximately 2028 to 2030. The standards are expected to set maximum slip rates by engine type and by year of certification, with progressive tightening over time. This will progressively eliminate the highest-slip designs from new-build orders.

MOC standardisation

Methane oxidation catalysts are expected to become standard equipment on LNG dual-fuel newbuilds from approximately 2026 to 2028, similar to the historical pattern of selective catalytic reduction (SCR) becoming standard for NOx Tier III compliance. The MOC supply chain is scaling to support this transition.

E-LNG scale-up

E-LNG production is at small pilot scale in 2024 but is expected to scale through the 2030s as the underlying green hydrogen infrastructure expands. The principal bottleneck is the cost of synthetic methane production relative to e-methanol or green ammonia.

Continued LNG competitiveness vs ammonia, methanol

The methane slip issue, combined with continued tightening of the FuelEU and IMO Net-Zero Framework reduction trajectories, is putting pressure on the long-term competitiveness of LNG dual-fuel relative to ammonia and methanol dual-fuel architectures. Most major lines (Maersk, Hapag-Lloyd, CMA CGM) are now ordering a mixed fleet of LNG, methanol and (forthcoming) ammonia dual-fuel vessels rather than concentrating on LNG alone, hedging against the methane slip risk.

See also

Marine fuels

• LNG as marine fuel
• LNG fuel system
• Methanol as marine fuel
• Ammonia as marine fuel
• Biofuels in shipping
• Heavy fuel oil
• Marine gas oil
• Well-to-wake intensity
• RFNBO under EU rules
• N2O emissions from marine engines
• Black carbon and Arctic shipping

Engines, exhaust and machinery

• Marine diesel engine
• Marine gas turbine
• Marine propeller
• Exhaust gas cleaning system
• Bow thruster and stern thruster

Regulatory and reporting frameworks

• MARPOL Annex VI
• IMO Net-Zero Framework
• IMO GHG Strategy
• EEXI, EPL and ShaPoLi
• SEEMP I, II, III
• CII corrective action plan
• EU MRV Regulation
• EU ETS for shipping
• FuelEU Maritime
• FuelEU penalties, pooling and multipliers
• UK ETS for shipping
• China DCS
• IMO DCS vs EU MRV
• CARB at-berth rule
• Emission control areas
• NOx Tier I, II, III
• IMO 2020 sulphur cap

Voluntary frameworks

• Poseidon Principles
• Sea Cargo Charter
• RightShip GHG Rating
• Green Shipping Corridors
• BIMCO CII clauses
• EUA market mechanics for shipping
• Voluntary carbon credits in shipping

Operational and technical efficiency

• Wind-assisted propulsion
• Air lubrication systems
• Just-in-time arrival
• Weather routing
• Trim optimisation
• Slow steaming
• Bulbous bow retrofits
• Energy-saving devices
• Battery-hybrid propulsion
• Onboard carbon capture
• Cold ironing / shore power

Hydrostatics, stability and ship types

• Hull form design
• Block coefficient
• Hydrostatics and Bonjean curves
• Trim and list
• Metacentric height
• Free surface effect
• Intact stability
• Damage stability
• Ship resistance and powering
• Bulk carrier
• Container ship
• Chemical tanker
• LNG carrier
• General cargo ship

Conventions, codes and class

• SOLAS Convention
• MARPOL Convention
• Ballast Water Management Convention
• Hong Kong Convention
• COLREGs Convention
• ISM Code
• ISPS Code
• Classification society

Calculators

• Methane slip GWP calculator
• LNG WtW intensity calculator
• Methane slip CII penalty calculator
• Methane slip FuelEU penalty calculator
• WtW intensity calculator
• GFI compliance calculator
• SEEMP Measures Combined calculator
• EEXI Required calculator
• CII Attained calculator
• Calculator catalogue

References

• ICCT. Methane slip from LNG-fuelled vessels. International Council on Clean Transportation, 2020.
• SEA-LNG. Methane slip in LNG-fuelled ships: A 2023 measurement update. SEA-LNG, 2023.
• DNV. LNG as marine fuel: Methane slip and the well-to-wake assessment. DNV Position Paper, 2023.
• EDF (Environmental Defense Fund). Pneumatic controllers and other US natural gas methane emissions. EDF Synthesis, 2018.
• IMO Resolution MEPC.391 (in adoption 2025): Life Cycle Assessment Guidelines for Marine Fuels. International Maritime Organization, 2025.
• IMO Resolution MEPC.328(76): 2021 Revised MARPOL Annex VI. International Maritime Organization, 2021.
• Regulation (EU) 2023/1805 of the European Parliament and of the Council of 13 September 2023 on the use of renewable and low-carbon fuels in maritime transport (FuelEU Maritime). Official Journal of the EU, 2023.
• Joint Research Centre (JRC). Well-to-Wheels Analysis of Future Automotive Fuels and Powertrains in the European Context (JEC WTW Report v5). European Commission JRC, 2020.
• IPCC. Fifth Assessment Report (AR5) Working Group I: Climate Change 2013. Intergovernmental Panel on Climate Change, 2013.
• DNV. Maritime Forecast to 2050. DNV Energy Transition Outlook, 2023.

Further reading

• IRENA. A pathway to decarbonise the shipping sector by 2050. International Renewable Energy Agency, 2021.
• ICS. Catalysing the Fourth Propulsion Revolution. International Chamber of Shipping, 2022.
• World Bank. The Role of LNG in the Transition Toward Low and Zero Carbon Shipping. World Bank Group, 2021.
• SEA-LNG. LNG as a Marine Fuel - The Investment Opportunity. SEA-LNG, 2023.
• Methanol Institute. Methanol as a Marine Fuel. Methanol Institute, 2023.

External links

• International Maritime Organization
• International Council on Clean Transportation
• SEA-LNG
• DNV Maritime
• Lloyd’s Register Marine
• Environmental Defense Fund
• European Commission Joint Research Centre
• IPCC
• MAN Energy Solutions
• Wartsila Marine Solutions
• Win GD
• Yara Marine Technologies