Following the Paris Agreement to limit global warming to 1.5°C compared to pre-industrial levels, the IMO introduced a Clean Energy Strategy for the marine sector to reduce carbon emissions to 40% by 2030 and 70% by 2050. Revised GHG limits were introduced this July, targeting 30% carbon reduction by 2030, 80% by 2040 and zero by 2050.

‘This puts pressure on the industry,’ says McMahon. ‘New ships need to have a design index and an efficiency plan and measurement plan, with a CO₂ intensity indicator and an operational carbon intensity plan which has to be certified by a surveyor and submitted to the IMO so ships get a rating next year.’ The rating will go from A to E, where A is the best and E is the worst. The measures will cover bulk ships, cruise ships, passenger ships and container ships of 5,000 gross tonnage and above for GHG emissions reduction (representing 85% of the total GHG emissions from international shipping).

Control measures cover heavy fuel oil (HFO) and scrubbers, low sulphur fuel, slow steaming, energy power limiting, exhaust gas recovery and energy saving technology. The International Energy Agency (IEA) notes that: ‘The first fuel is energy efficiency’ – or fuel that isn’t needed or burned – when it comes to limiting carbon emissions.

Electric propulsion  
Electric propulsion offers significant reduction in fuel consumption and hydrodynamic performance. Attachment of a high efficiency Azipod permanent magnetic motor to the hull of a cruise ship or ferry, for example, can reduce fuel consumption by 20%, with 360° steerable propulsion. The new P&O Pioneer roll on-roll off ferry (ro-ro; where vehicles can drive straight on and off) is Azipod propelled and uses 40% less fuel than the cross-Channel ferries it replaces, along with the world’s largest battery system fitted to a ship. A power management system and heat recovery system also help optimise fuel consumption.

Meanwhile, ports such as Dover, Rotterdam, Calais and many others are being equipped with green power and batteries to lower the carbon footprint when shore power is utilised.

Sail power returns  
Sails are very popular, particularly with the French. Ship operator CMA CGM is developing a green liquid hydrogen fuel cell-propelled cargo ship, Energy Observer II, which is also equipped with four propulsion sails to reduce energy consumption by 15–30% depending on the angle and force of the wind. In addition to the renewable energy mix, hydrodynamics, routing and logistics also improve energy efficiency.

Wind-assisted rotor sails can also play a significant role. Norsepower aims to decarbonise by harnessing wind power for large ships. Verified performance data by some of the world’s best known shipping companies and charterers shows fuel savings of 5–25% with rotor sails. What’s more, ‘crews love them, because they understand sails’, McMahon says. The top speed on rotor sails is 19.7 knots.

The Meltem container ship developed by Zéphyr and Borée of France has four pairs of sails with retractable wings and is estimated to reduce the carbon footprint by 80% on a transatlantic crossing. The sail assisted ro-ro cargo ship Navire Ariane 6 Canopée, launched in Poland in 2022 also has LNG propulsion.

Another popular efficiency measure is to install air bubble lubrication, where a microscopic layer of air bubbles is generated under the hull to reduce the energy required by the engines. According to DNV, an air lubrication system can save up to 10% fuel consumption.

‘The marine crews tend to like the sails but are not so keen on the new gases coming in,’ comments McMahon.

Stena Line was the first major operator to run a ship on methanol, since 2015 – the Stena Germanica was refuelled with recycled methanol from residual steel gas in June 2021
Photo: Stena Line

New gas options  
Ammonia is considered to be high risk at sea, as it is highly toxic. Understandably, this worries seafarers. ‘So, training in effective safety systems and practices is vital,’ says McMahon. The IEA predicts that ammonia will be the primary marine fuel, representing 75% of the market by 2050. Although ammonia needs a pilot fuel to get it started, it is safer than hydrogen, which is explosive at any temperature. 

However, ammonia’s GHG potential is 300 times that of CO₂. But marine engine builders are confident that the nitrogen dioxide (NO₂) exhaust issue will be solved by exhaust gas recirculation with catalysts to remove emissions.

Meanwhile, methanol is winning over hydrogen for now. Although it is relatively safe to ship, store, handle and bunker, methanol has a few problems due to its density and lower heating value. Methanol fuel tanks are about 2.5 times larger than oil tanks for the same energy content. Methanol is also toxic, flammable and can be explosive, so it must be handled carefully.

Nevertheless, marine experts suggest that eventually the biggest ships will be fully hydrogen powered with zero emissions.

‘The marine crews tend to like the sails but are not so keen on the new gases coming in.’  – Robert McMahon, marine engineer

Stena Line claims to be the first major operator to run a ship on methanol, the Baltic Stena Germany ro-pax ferry (a ship that combines the features of a cruise ship and night cabins with a ro-ro ferry), which uses methanol from recycled steel gases. The group also took a recognised fuel efficiency step by lengthening the ship about 30 metres to get more capacity, cargo and passengers using the same power.

Maersk has 24 green methanol-enabled ships on order – with its first ship in operation – and is aiming for 50% ship decarbonisation by 2030, with 25% of cargo carried using green fuel by this date and net zero emissions by 2050. Gas fuels occupy more space than diesel or heavy fuels – up to four times for hydrogen and 2.6 for methanol, ‘so that’s also a big issue’, explains McMahon.

Under Maersk’s fuel pathway, biodiesel is being used as a drop-in fuel in existing vessels. There are plans to use bio-methanol and e-methanol from biomass increasingly, and green ammonia when produced at scale, as well as harnessing new technology to achieve net zero.

Meanwhile, the design for an Australian compressed hydrogen gas carrier H2NEO has been approved by ABS Consulting. Operated by Provaris Energy, it will export 100,000 m³ of gas per annum from a hydrogen project at Tiwi Islands, Northern Territories, Australia, to the Asia-Pacific region. Construction begins this year, to be followed by a fleet of 120,000 m³ gas carriers with hybrid electric drive, to service the company’s Gascoyne Green hydrogen project in western Australia.

Seafarer concerns  
Seafarers fear they are being left behind. A survey was carried out by DNV 500 Charity in Singapore to ask if they would be happy to work on these modern ships. About 87% said they would need further or full training. Only 13% said they were happy to work on the new generation of ships.

‘That’s a huge problem. We have the technology coming but we haven’t got the people to run it,’ remarks McMahon.

Other technologies  
Different owners are looking at a range of technologies.

The Havila Capella won the Next Generation Ship Award for 2022. The vessel runs along the Norwegian coast and is prepared for hydrogen, which is seen as the ‘fuel of the future’ for short sea missions. The vessel can also maximise efficiency using battery packs to plug into green power from hydropower. An advanced data management system also helps to optimise operations and reduce emissions. Heat can be re-used using a huge thermal tank.

The Corona Utility is a coal carrier which runs from Newcastle, New South Wales, Australia, to Japan. It has the first marine carbon capture system with LNG and sea kite assist, aiming to achieve 50% CO₂ reduction by 2030, compared to the 40% IMO target.

The MOL Emerald Ace car carrier, which is a regular in Australian ports, uses 768 solar panels, 160 kW of electric power generation and 324,000 Li-ion batteries with a hybrid diesel and electric power fuel system. The first fully electric tug is the Sparky in Auckland, Australia. The operating cost of the electric motors is estimated to be one third those of a diesel tug and the ship has cloud-based fuel optimising systems. The famous Staten Island ferry is also going electric with Voith Schneider propulsion and azimuth thrusters aimed at low exhaust emissions by 2030, with plans to replace diesel power with green hydrogen eventually.

LNG power  
Hawaii’s first LNG powered containership, the George III, features a MAN B&W 30,000 kW dual fuel engine with three auxiliary MAN B&W 2,760 kW engines. The operator claims to have achieved zero emissions by buying carbon offsets for greening of forests in Hawaii.

In Australia, Incat Tasmania is building the world’s largest electric powered ferry for Buquebus, for operation between Buenos Aires, Montivideo and Colonia in 2025, designed for propulsion by LNG initially but scheduled for future revamp as battery electric by its Uruguay owners.

One of the first LNG ferries in North America is the Salish Heron ro-ro ferry, which has reduced CO₂ emissions by over 25% and sulphur oxides by over 85% in operations on the Salish coast of British Columbia, Canada.

Learning curve  
Reducing carbon emissions in the marine sector is a steep learning curve. A raft of efficiency measures are under consideration (so long as they’re cost effective), from sail assist and mechanical solutions to electric motors, hybrids, heat recovery and hydrogen. Generally, the battery size needed for large, long haul electric propelled container ships is too large.

Use of lower cost, green ammonia fuel is also planned. Mitsubishi Shipbuilding has completed a conceptual study with Inpex Corporation of an ammonia bunkering vessel to supply ammonia to ships. An ammonia dual-fuelled tanker, Kritti Future, was built by Mitsubishi in 2022, which handles conventional fuel and is ammonia ready.

The new fuels are coming. However, a major problem is the lack of infrastructure with bunkering facilities around the world for ammonia and hydrogen, says McMahon. ‘For the time being, companies like Maersk are focused on methanol, which is generally available. Others are likely to follow which will encourage the infrastructure to be built.’

So, what comes first – the market or the product? ‘It’s like the chicken and egg analogy,’ suggests McMahon.