Is there no such thing as a zero-emission vessel?

Written by Nick Blenkey
No such g thing as a zero-emission

In a whole of life analysis, there's no such thing as a zero-emission vessel says OSK ShipTech [Image copyright OSK ShipTech]

Danish naval architectural consultancy OSK-ShipTech says, that in a cradle-to-grave life cycle analysis over a 20-year life cycle , there’s actually no such thing as a zero-emission vessel.

OSK-ShipTech has been involved in the designs of many recent high-profile RoPax ferries, a sector that has been leading the way when it comes to implementing alternative fuels and a transition to battery propulsion.

It is generally understood, says the firm, that the smaller the “direct” emissions footprint from ship propulsion, the bigger the “indirect” emissions footprint from the construction of the ship.

Anders Ørgård, Chief Commercial Officer of OSK-ShipTech, says that, while reducing direct CO2 emissions should remain a priority, shipowners cannot turn a blind eye on the indirect contributors of CO2 emissions: notably the manufacturing process of a ship and all the components it is made of.

A recent study conducted by the consultancy revealed that, for a fully-electric RoPax ferry, powered by climate-friendly electricity, non-operation-related CO2 emissions could reach well in the excess of 55 per cent of the total CO2 emissions produced during the ship’s 20-year life cycle. This study provides food for thought for responsible shipowners and illustrates that a holistic life cycle approach is paramount when considering a newbuild.

“Rather than exclusively focusing on the emissions from operations, shipowners should make a cradle-to-grave life cycle analysis,” says Ørgård. “A life cycle analysis offers the opportunity to develop a build strategy, reducing the emissions during both construction and operation, thus further optimizing the ship’s operational life.”

The study comes on the back of a controversy surrounding the idea of sustainability and new guidelines from the Danish consumer ombudsman that were released in December 2021. These emphasize that statements like “emission-free” and “climate-neutral” for example are to be fully documented through the product’s entire life cycle by use of life cycle analyses and to be verified by experts. .


OSK-ShipTech’s study included a life cycle assessment of Fanølinjen’s 2021-built, full-electric ferry Grotte; a 50-meter-long double-ended RoPax vessel operating the 12-minute Esbjerg-Nordby shuttle service. Notwithstanding the short distance it covers, Grotte effectively sails 12 hours per day. The study is therefore representative of a large ro-pax ferry with an equivalent daily operating time of at least 12 hours.

The assessment, which covered the six stages in a ship’s life, all the way from mining of the resources and processing of the steel to the recycling of the ship, was executed in line with ISO 14040 and ISO 14044 standards.

For redundancy’s sake, and to make long positioning trips possible, most electric ferries are still equipped with diesel engines. Experience from operating full-electric ferries has taught that they operate for approximately 90-95 per cent of the time on electricity. For this reason, they also need backup power from other energy sources. According to publicly available data, the climate-friendly electricity used to power Grotte has an emissions intensity of 0.0187kg CO2/kWh, compared to the 0.297kg CO2/kWh of the electricity generated from a typical mix of renewable and conventional energy sources (such as coal, wood chips, and natural gas) available on the grid.

OSK-ShipTech has calculated that during its entire lifespan, from cradle to grave, Grotte will produce 2,508 tonnes CO2-eq from the ship’s operation with 1,833 tonnes CO2-eq attributable to the manufacturing of the vessel. As the ship and its materials will be recycled upon demolition, scrapping of the vessel will have a positive CO2-eq footprint of 1,124.54 tonnes.

The tonne CO2-eq from Grotte’s operation still surpasses the tonne CO2-eq from the ship’s construction by a good margin, according to Ørgård.

“Our analysis clearly illustrates that a zero-emission ship doesn’t exist at all,” he says. “To put it simply, one can no longer ignore the CO2 emissions generated from manufacturing, which can be more than 50% of the cradle-to-grave CO2 footprint in some cases.”

Following this in-depth life cycle assessment, OSK-ShipTech is ready to apply the knowledge gained in future newbuilding projects, helping shipowners to develop a build strategy to drastically reduce CO2 emissions during the construction processes.

“A life cycle analysis already starts in the ship’s concept stage,” says Ørgård, “thus allowing us to develop a build strategy, which we can take into account, when we calculate the total cost of ownership and the total cradle-to-grave CO2 burden.”

As the steel structure accounts for nearly 40 per cent of the CO2 footprint in a ship’s construction, a strategy should be developed to focus on the hull and steel structure already in the design stage.

“One should also consider the country of build,” says Ørgård. “In many countries, steel production is coal-fired. As part of their build strategy, shipowners should equally consider where to build their ships and where to purchase the steel.”

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