ShipCalculators.com

Published · last updated

Hydrogen as Marine Fuel

Hydrogen (H2) is the lightest chemical element and the most energy-dense fuel per unit mass (LHV approximately 120 MJ/kg, approximately 2.7 times the energy of HFO) with near-zero tank-to-wake CO2 emissions when properly combusted. In marine applications hydrogen can be used in two principal configurations: (i) fuel cells, principally Polymer Electrolyte Membrane (PEM) for short-route applications and Solid Oxide Fuel Cells (SOFC) for higher-temperature operations, providing direct electrochemical conversion of hydrogen to electricity at typical efficiencies of 50 to 60% (PEM) or 55 to 65% (SOFC); and (ii) modified internal combustion engines (MAN ME-LH2 under development for delivery 2026 to 2028, Wartsila hydrogen engine, Win GD X-DF hydrogen variant), which provide higher power-density propulsion at typical efficiencies of 35 to 45% and which can be retrofitted from existing dual-fuel platforms. The principal commercial constraint is the very low volumetric energy density: liquid hydrogen at -253 °C has a volumetric energy density of approximately 8.5 MJ/litre (compared to approximately 35 MJ/litre for VLSFO) and compressed hydrogen at 700 bar approximately 4.5 MJ/litre. The storage volume requirement therefore restricts hydrogen propulsion to short-route ferries (under 200 nautical miles per leg) and harbour craft in 2024, with potential for medium-route vessels through the 2030s if storage and supply infrastructure scale. Approximately 15 to 25 hydrogen-fuelled commercial vessels are in operation or on commercial trial by end-2024 (notably the Norled MF Hydra in service April 2023 in Norway, the Topeka ro-ro under construction by Wilhelmsen for delivery 2025, and several harbour tugs and pilot boats). ShipCalculators.com hosts the principal computational tools: the hydrogen energy density comparison calculator, the hydrogen storage volume calculator, the PEM fuel cell efficiency calculator, the SOFC efficiency calculator, the hydrogen ICE NOx calculator, the WtW intensity calculator and the GFI compliance calculator. A full listing is available in the calculator catalogue.

Contents

Background

Why hydrogen matters for marine

Hydrogen is the simplest chemical fuel and the only one that can produce near-zero tank-to-wake CO2 emissions when properly combusted (the only TtW byproducts are water vapour and trace NOx from N2 oxidation in the engine air). Combined with an RFNBO-eligible green hydrogen production pathway, hydrogen offers the lowest theoretical WtW intensity of any marine fuel: approximately 5 to 10 g-CO2eq/MJ, lower than the corresponding values for green ammonia (which is produced from hydrogen and so cannot be lower than hydrogen) and lower than e-methanol (which is produced from hydrogen + captured CO2 with additional process emissions).

Hydrogen is therefore widely seen as the theoretical end-state for deep marine decarbonisation. The practical question is whether the storage and infrastructure constraints can be solved in a timeframe that allows hydrogen to play a meaningful role in the 2030 to 2050 decarbonisation, or whether ammonia and methanol (which are easier to store but ultimately less efficient than hydrogen) will dominate.

History

Hydrogen has been used as a propulsion fuel in niche applications since the 1960s (notably the rocket and space industries). Marine hydrogen propulsion has been studied since the 1990s but commercial deployment has lagged the land-based fuel cell vehicle and stationary fuel cell sectors due to the storage and supply chain constraints.

Key milestones in marine hydrogen propulsion:

  • 1990s to 2000s: laboratory and concept studies; minimal commercial deployment.
  • 2000: the MS Hydra, a Norwegian fjord ferry, was retrofitted with a small PEM fuel cell pilot; initial trials.
  • 2008 to 2012: the FellowSHIP project (a Norwegian-led consortium including DNV, Wartsila, Eidesvik and Hydro) deployed a 320 kW SOFC on the offshore vessel Viking Lady, the first commercial-scale marine SOFC.
  • 2014 to 2018: several hydrogen-electric concept ferries developed in Norway (Color Line, Norled, Bastø Fosen).
  • 2017 to 2019: the MF Hydra was ordered (Norled, Westcon Yards) as the world’s first commercial hydrogen-fuelled passenger ferry.
  • April 2023: the MF Hydra entered service on the Hjelmeland-Skipavik-Nesvik triangle in Norway, with two 200 kW PEM fuel cells, two 1,360 kWh battery packs, and 4,000 kg of liquid hydrogen storage.
  • 2024: several additional hydrogen vessels ordered or in commissioning (Topeka, Ulstein SX190, harbour tugs).

The MF Hydra is the principal demonstrator vessel; subsequent commercial deployment is following its lead.

Properties of hydrogen

Energy density

Hydrogen has the highest gravimetric energy density of any chemical fuel:

  • Lower heating value (LHV): 120 MJ/kg.
  • Higher heating value (HHV): 142 MJ/kg.

For comparison:

  • HFO LHV: approximately 40 to 42 MJ/kg.
  • LNG LHV: approximately 49 MJ/kg.
  • Methanol LHV: approximately 19.9 MJ/kg.
  • Ammonia LHV: approximately 18.6 MJ/kg.

However, hydrogen has very low volumetric energy density in any practical storage form:

  • Hydrogen gas at standard pressure (1 atm, 20 °C): 0.011 MJ/litre. (Useless for marine.)
  • Hydrogen compressed at 350 bar: approximately 2.7 MJ/litre.
  • Hydrogen compressed at 700 bar: approximately 4.5 MJ/litre.
  • Liquid hydrogen at -253 °C and 1 atm: approximately 8.5 MJ/litre.

For comparison:

  • HFO at ambient: approximately 36 MJ/litre.
  • VLSFO at ambient: approximately 35 MJ/litre.
  • LNG at -162 °C: approximately 22 MJ/litre.
  • Methanol at ambient: approximately 16 MJ/litre.
  • Ammonia liquid at -33 °C: approximately 13 MJ/litre.

The volumetric energy density gap (approximately 4 to 8 times less than diesel/HFO) is the defining technical challenge for marine hydrogen.

Storage forms

Three principal forms of marine hydrogen storage:

  • Compressed gaseous hydrogen (CGH2) at 350 bar: standard for hydrogen vehicles, less common in marine. Tank weight (typically 5 to 7 kg per kg-H2 stored) is significant. Most appropriate for very small vessels (harbour craft, pilot boats).
  • Compressed gaseous hydrogen at 700 bar: more common for vehicle applications. Higher tank weight ratio (typically 8 to 12 kg per kg-H2) but smaller volume. Limited marine deployment due to high pressure handling requirements.
  • Liquid hydrogen (LH2) at -253 °C and 1 to 4 bar: dominant for medium-to-large marine deployment. Tank weight ratio (typically 1.5 to 4 kg per kg-H2 including insulation) is significantly better than compressed. Requires cryogenic insulation and active boil-off management.

The MF Hydra uses LH2 storage at -253 °C; future commercial newbuilds (Topeka, Ulstein SX190) are also planned for LH2.

Boil-off

Liquid hydrogen has a very low boiling point (-252.9 °C); even very efficient cryogenic insulation cannot fully prevent boil-off (vapourisation of stored LH2 due to ambient heat ingress). Typical boil-off rates for marine LH2 storage:

  • Daily boil-off: 0.1 to 0.5% per day for well-designed cryogenic Type C tanks.
  • Boil-off management: the boiled-off gas is typically routed back to the fuel cell or engine for consumption (avoiding waste); for vessels in extended port stays, the boil-off may need to be vented to atmosphere or recovered to a shore facility.

The boil-off rate is critical to the economic viability of LH2 storage for medium-to-long voyages: at 0.5% per day, a vessel on a 30-day voyage loses 15% of its hydrogen inventory to boil-off, eroding the effective range.

Combustion and explosion characteristics

Hydrogen has a wide flammability range (4 to 75% in air, compared to 5 to 15% for methane) and a low minimum ignition energy (0.02 mJ, compared to 0.28 mJ for methane). The combination makes hydrogen leak detection critical and requires careful engineering of all hydrogen-handling components.

Hydrogen burns with a near-invisible flame (no soot for combustion contrast), making leak detection by sight impossible; thermal imaging or hydrogen-specific gas detectors are required.

The deflagration-to-detonation transition (DDT) for hydrogen is more easily triggered than for methane, increasing the explosion hazard in confined spaces. Marine hydrogen installations must therefore include extensive ventilation, leak detection, ignition source elimination and structural design for containment.

Fuel cell propulsion

PEM fuel cells

Polymer Electrolyte Membrane (PEM) fuel cells use a polymer electrolyte that conducts protons but not electrons; hydrogen is fed to the anode and oxygen (from air) to the cathode; the chemical reaction (2 H2 + O2 → 2 H2O + electricity + heat) produces direct electrical output.

Key characteristics:

  • Operating temperature: 60 to 80 °C (low temperature, allowing rapid start-up and shut-down).
  • Efficiency: 50 to 60% LHV at design point.
  • Power density: 1 to 3 kW/kg, approximately 1.5 kW/litre.
  • Hydrogen purity requirement: typically > 99.97% (PEM is sensitive to CO and S poisoning).
  • Membrane lifetime: typically 20,000 to 40,000 hours of operation.

PEM fuel cells dominate the small-vessel marine fuel cell market. The MF Hydra uses two 200 kW PEM modules (Ballard Power Systems, Canada). Other marine PEM suppliers include Plug Power (USA), Cummins (USA, formerly Hydrogenics), Toyota (Japan), Hyundai Mobis (Korea), Honda (Japan), Nuvera (USA), and several smaller Chinese and European specialists.

SOFC fuel cells

Solid Oxide Fuel Cells (SOFC) use a ceramic electrolyte that conducts oxygen ions at high temperature; the cell can operate on a wider range of fuels including hydrogen, natural gas, methanol and ammonia (with internal reforming).

Key characteristics:

  • Operating temperature: 600 to 1,000 °C (high temperature, slow start-up, well-suited to base-load operation).
  • Efficiency: 55 to 65% LHV at design point; up to 80% with combined heat and power.
  • Power density: 0.5 to 2 kW/kg, approximately 0.5 to 1.5 kW/litre.
  • Fuel flexibility: hydrogen, natural gas, methanol, ammonia (with reforming).
  • Stack lifetime: typically 30,000 to 50,000 hours.

SOFC is increasingly being deployed for larger marine applications and for non-hydrogen fuel use (notably ammonia and methanol). The principal marine SOFC suppliers are Bloom Energy (USA, large stationary applications), Mitsubishi Heavy Industries (Japan, MHIRJ developing marine variants), Topsoe (Denmark, with marine partnerships), Ceres Power (UK), and Sunfire (Germany).

Combined fuel cell + battery hybrid

For medium-route vessels (50 to 200 nm per leg), the typical configuration is fuel cell + battery hybrid: the fuel cell provides sustained energy from hydrogen storage; the battery provides peak power and load smoothing; the battery may also be charged from shore at ports. This configuration matches the battery-hybrid propulsion concept but with the combustion engine replaced by the fuel cell.

The MF Hydra uses this configuration: 2 × 200 kW PEM fuel cells + 2 × 1,360 kWh batteries.

Hydrogen internal combustion engines

Engine architectures

Hydrogen can also be used in modified internal combustion engines, providing a higher-power-density and lower-cost alternative to fuel cells for medium-to-large vessels. Several engine manufacturers are developing marine hydrogen ICE:

  • MAN ME-LH2: hydrogen variant of the MAN ME-LGI low-pressure dual-fuel engine; commercial pilot delivery 2026 to 2027.
  • MAN B&W type design: high-pressure direct-injection hydrogen variant; under development for delivery 2027 to 2028.
  • Wartsila hydrogen engine: under development based on the 31DF four-stroke platform; pilot delivery 2025 to 2026.
  • Win GD X-DF hydrogen variant: under development for delivery 2027 to 2028.
  • Cummins hydrogen ICE: smaller medium-speed engines for harbour craft and inland waterway, in commercial trial 2024.

Hydrogen ICE has key advantages over fuel cells for some applications:

  • Higher power density: typically 3 to 5 kW/kg engine, similar to conventional diesel.
  • Lower capital cost: typically USD 200 to USD 500 per kW (vs USD 1,500 to USD 3,500 per kW for marine fuel cells in 2024).
  • Lower hydrogen purity requirement: tolerates approximately 99.5% pure hydrogen versus the > 99.97% required by PEM.
  • Higher thermal robustness: tolerates wider temperature variation than PEM.
  • Existing engine infrastructure for installation, maintenance and crew training.

Disadvantages:

  • Lower efficiency: typically 35 to 45% versus 50 to 65% for fuel cells; consumes more hydrogen per unit energy delivered.
  • NOx emissions: hydrogen combustion produces NOx (from N2 in the combustion air); requires SCR aftertreatment for Tier III compliance.
  • Risk of flashback: hydrogen’s high flame speed can cause flashback (combustion propagating into the intake manifold) under some operating conditions; requires careful injection timing.
  • Trace methane content of pilot fuel: dual-fuel hydrogen ICE typically use a small pilot diesel for ignition; the pilot diesel adds a small WtW intensity and may produce trace methane slip (similar to LNG dual-fuel).

Configuration

Hydrogen ICE is typically configured as:

  • Dual-fuel (DF): hydrogen + pilot diesel (or pilot diesel and switching to MGO/HFO when hydrogen unavailable). Standard configuration for the upcoming commercial generation.
  • Spark-ignition (SI): pure hydrogen, spark-ignited. Used for some smaller engines (Cummins).
  • Compression-ignition (CI): hydrogen alone, compression-ignited. Difficult due to hydrogen’s high autoignition temperature; not in commercial development.

Notable deployments

MF Hydra (Norled, in service April 2023)

The MF Hydra is the world’s first commercial hydrogen-fuelled passenger ferry, operating on the Hjelmeland-Skipavik-Nesvik triangle in Sognefjord, Norway. Specifications:

  • Length: 82.4 m, Beam: 17.6 m.
  • Capacity: 300 passengers, 80 cars.
  • Power plant: 2 × 200 kW Ballard PEM fuel cells + 2 × 1,360 kWh Corvus battery packs + 1 × 440 kW backup diesel.
  • Hydrogen storage: 4,000 kg LH2 in two cryogenic tanks at -253 °C.
  • Range on hydrogen: approximately 7 days of normal service (one bunkering per week).
  • Hydrogen supply: trucked LH2 from Linde plant in Leuna, Germany.

The MF Hydra demonstrates the technical feasibility of hydrogen propulsion for short-route ferries; it is the principal real-world demonstrator for the upcoming wave of commercial hydrogen vessels.

Topeka (Wilhelmsen / Heeren Werft, delivery 2025)

The Topeka is a 75-passenger / car ro-ro vessel under construction by Wilhelmsen Wilh. Wilhelmsen for delivery 2025, operating between Halmstad (Sweden) and Holmestrand (Norway). Specifications:

  • Length: 117 m.
  • Power plant: 4 × 250 kW PEM fuel cells + battery + 2 × diesel auxiliary engines.
  • Hydrogen storage: 3,000 kg LH2.

Ulstein SX190 (Ulstein Group, ordered 2023)

The Ulstein SX190 is an offshore construction vessel designed by Ulstein for hydrogen-electric operation. The first orders are for the offshore wind installation market. The SX190 incorporates:

  • Power plant: 4 × SOFC modules + battery + emergency diesel.
  • Hydrogen storage: approximately 80 t LH2.
  • Operating range on hydrogen: 4 weeks at typical OCV operating profile.

Harbour tug deployments

Several harbour tug deployments are in commissioning or operation:

  • Eberswalde (Germany, 2023): 2 × 250 kW PEM fuel cells, harbour service.
  • Vard hydrogen tug (Norway, in delivery 2024 to 2025).
  • Damen RSD-E hydrogen tug (Netherlands, in delivery 2024).
  • Singapore harbour tug pilots (in development by Sembcorp Marine and PSA International).

LH2 carrier (Suiso Frontier, in service 2022)

The Suiso Frontier (Kawasaki Heavy Industries, in service January 2022) is the world’s first liquid hydrogen carrier, originally built for the Hydrogen Energy Supply Chain (HESC) Australia-to-Japan demonstration project. Specifications:

  • Length: 116 m, Beam: 19 m.
  • LH2 cargo capacity: 1,250 m3.
  • LH2 carrier propulsion: dual-fuel diesel (not hydrogen-fuelled itself; uses LH2 boil-off from cargo to supplement).

The Suiso Frontier is principally a cargo carrier (for hydrogen as a commodity, not as a fuel) but provides important operational experience with marine LH2 handling.

Hydrogen production and supply

Green hydrogen (RFNBO-eligible)

Green hydrogen is produced by water electrolysis using renewable electricity. The principal production technologies are:

  • Alkaline electrolysis (AEL): mature, low-cost, moderate efficiency (60 to 70% LHV).
  • Proton Exchange Membrane (PEM) electrolysis: faster ramp, more compact, higher cost.
  • Solid Oxide Electrolyser Cell (SOEC): highest efficiency (potentially 80 to 90%), commercial maturity still limited.
  • Anion Exchange Membrane (AEM) electrolysis: emerging, lower-cost than PEM.

Green hydrogen production cost in 2024 is approximately USD 4 to USD 8 per kg-H2, projected to fall to USD 2 to USD 4 per kg by 2030 as electrolyser costs decline and renewable electricity costs continue to fall.

Blue hydrogen

Blue hydrogen is produced by steam methane reforming (SMR) of natural gas with carbon capture and storage (CCS) of the resulting CO2. Production cost is approximately USD 1.5 to USD 3 per kg-H2 (depending on natural gas price and CCS cost), significantly cheaper than green hydrogen but with WtW intensity of approximately 30 to 50 g-CO2eq/MJ (depending on methane upstream leakage and CCS efficiency), not RFNBO-eligible.

Grey hydrogen

Grey hydrogen is produced by SMR without CCS. Production cost is approximately USD 1 to USD 2 per kg-H2 but with WtW intensity of approximately 100 to 130 g-CO2eq/MJ, comparable to or higher than HFO.

Hydrogen bunkering infrastructure

Marine hydrogen bunkering is currently very limited. The principal bunkering options are:

  • Trucked LH2: standard for small-scale supply (e.g. MF Hydra). Practical for vessels with daily LH2 demand of 1 to 10 t.
  • Bunker barge: under development for medium-scale supply. The first commercial LH2 bunker barges are expected from 2026 to 2028.
  • Pipeline hydrogen at port: under development, requiring shore-side liquefaction or compression infrastructure.
  • Onsite electrolysis: hydrogen produced at the port using local renewable electricity. Most attractive for ports with abundant renewable resources.

The Port of Rotterdam, Antwerp, Singapore, Yokohama, Busan, San Pedro Bay (LA/LB), Northern Lights / Bergen (Norway) and several other ports are developing hydrogen bunkering infrastructure for delivery 2025 to 2030.

Regulatory framework

IGF Code

Marine hydrogen is regulated under the IMO IGF Code (International Code of Safety for Ships using Gases or other Low-flashpoint Fuels). The IGF Code originally covered LNG-fuelled vessels; amendments to cover hydrogen are in development and are expected to enter force from approximately 2026.

In the interim, hydrogen-fuelled vessels typically receive alternative design approval from the flag administration and classification society, applying the IGF Code principles by analogy.

Class society notations

The principal classification societies have developed hydrogen-specific notations:

  • DNV: Hydrogen Fuel Ready (Hydrogen FR), Hydrogen Fuel notation.
  • Lloyd’s Register: ShipRight Procedure for Hydrogen.
  • ABS: Hydrogen Fuel Notation.
  • BV: Hydrogen Fuel notation.
  • NK: Hydrogen Fuel notation.
  • KR: Hydrogen Fuel notation.
  • RINA: Hydrogen Fuel notation.
  • CCS: Hydrogen Fuel notation.

FuelEU Maritime and IMO Net-Zero Framework

Hydrogen is included in FuelEU Maritime Annex II with default WtW intensity values for green, blue and grey hydrogen pathways. RFNBO-eligible green hydrogen receives the 2x multiplier under FuelEU.

The IMO Net-Zero Framework (from 2027) similarly includes hydrogen with default WtW intensity values from MEPC.391 (LCA Guidelines).

Polar Code and Arctic operations

For Arctic operations, hydrogen has the operational advantage of zero CO2 emissions and zero black carbon emissions, making it attractive for the Arctic where the climate impact per fuel burnt is amplified. However, the LH2 storage challenge in cold ambient temperatures is non-trivial. Conceptual studies suggest hydrogen-fuelled Arctic operations are feasible but commercial deployment is some years away.

Challenges and limitations

Storage volume

The volumetric energy density gap (4 to 8 times less than diesel) is the binding constraint on hydrogen for most marine applications. For long-distance vessels (transpacific, transatlantic), even with LH2 storage, the cargo space sacrifice is prohibitive.

Bunkering infrastructure

Marine hydrogen bunkering infrastructure is in its infancy. The infrastructure scale-up is the principal critical-path constraint on commercial hydrogen-fuelled vessel deployment.

Cost

Hydrogen production cost is significantly higher than fossil fuel cost on an energy-equivalent basis. Even with green hydrogen at USD 4/kg (LHV-equivalent of approximately USD 33 per GJ), the cost is approximately 4 to 8 times the cost of HFO at USD 600/t (USD 14 per GJ). The cost gap is expected to narrow but is unlikely to close completely by 2050.

Safety

Hydrogen safety hazards (wide flammability, low ignition energy, leak detection difficulty, explosion potential) require careful engineering and significant safety system investment. Crew training on hydrogen handling is more demanding than on conventional fuels.

Boil-off

Cryogenic boil-off limits the practical voyage range for LH2-fuelled vessels.

Future outlook

Short-route ferry rollout (2025 to 2030)

The MF Hydra and Topeka deployments will be followed by further short-route ferry orders through 2025 to 2030, principally in Norway, Sweden, Denmark, Netherlands and Iceland (where renewable electricity for hydrogen production is abundant and where short-route ferry geography is favourable).

Offshore vessel deployment (2026 to 2032)

The Ulstein SX190 and similar offshore designs will see commercial uptake from 2026 onwards, particularly in offshore wind installation and operations.

Medium-route potential (2030 onwards)

Conceptual studies suggest hydrogen-fuelled medium-route container ships (typically 1,000 to 8,000 TEU on intra-Asian or short Europe routes) could be technically feasible from 2030, contingent on:

  • Significant LH2 bunkering infrastructure expansion.
  • LH2 production cost reductions.
  • Engine and fuel cell technology maturity at larger scale.

Comparison with ammonia and methanol

For deep-sea marine applications, ammonia and methanol are likely to dominate over hydrogen due to their better volumetric energy density and existing infrastructure. Hydrogen is likely to occupy short-route and harbour craft niches, with potential for specific medium-route applications.

The choice between hydrogen, ammonia and methanol for any specific marine application is a function of: route distance, vessel size, hydrogen vs ammonia vs methanol production cost in the relevant region, and the local availability of bunkering infrastructure.

See also

Marine fuels

Engines, exhaust and machinery

Operational and technical efficiency

Regulatory and reporting frameworks

Voluntary frameworks

Conventions, codes and class

Hydrostatics, stability and ship types

Calculators

References

  • IMO Resolution MSC.391(95): International Code of Safety for Ships using Gases or other Low-flashpoint Fuels (IGF Code). International Maritime Organization, 2015 (with hydrogen amendments in development 2024 to 2026).
  • IMO Resolution MEPC.328(76): 2021 Revised MARPOL Annex VI. International Maritime Organization, 2021.
  • IMO Resolution adopted MEPC 83 (April 2025): IMO Net-Zero Framework. International Maritime Organization, 2025.
  • Regulation (EU) 2023/1805 of the European Parliament and of the Council of 13 September 2023 (FuelEU Maritime). Official Journal of the EU, 2023.
  • Directive (EU) 2023/2413 of the European Parliament and of the Council of 18 October 2023 (RED III). Official Journal of the EU, 2023.
  • DNV. Hydrogen as a marine fuel: Position Paper. DNV Maritime, 2023.
  • DNV. Maritime Forecast to 2050. DNV Energy Transition Outlook, 2023.
  • IRENA. Hydrogen: A renewable energy perspective. International Renewable Energy Agency, 2019.
  • ICCT. The role of hydrogen in shipping decarbonisation. International Council on Clean Transportation, 2024.
  • Norled. MF Hydra: First Year of Operation Performance Report. Norled AS, 2024.
  • Wilhelmsen. Topeka Project Technical Brief. Wilhelmsen Wilh. Wilhelmsen, 2024.
  • Kawasaki Heavy Industries. Suiso Frontier Operational Experience: Pilot Voyage Report. KHI, 2022.
  • HydrogenEurope. Marine hydrogen: A pathway analysis. Hydrogen Europe, 2024.

Further reading

  • IEA. The Future of Hydrogen. International Energy Agency, 2019 and updates.
  • Hydrogen Council. Hydrogen Insights 2023. Hydrogen Council, 2023.
  • ICS. Catalysing the Fourth Propulsion Revolution. International Chamber of Shipping, 2022.
  • IRENA. A pathway to decarbonise the shipping sector by 2050. International Renewable Energy Agency, 2021.