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This is how emissions from express ferries can be halved in just five years
High-speed passenger vessels with diesel engines are currently the least environmentally friendly form of passenger transport. It does not have to be that way.
The shipping industry has to cut its climate emissions. Express ferries are among the most polluting forms of passenger transport per kilometre.
For years, the Norwegian government has said it will introduce requirements for zero emissions in new tenders for express ferry services. The requirements have been postponed because the technology is not yet fully developed, according to the government.
A new solution shows that this is not true. By combining batteries and fuel cells, it is entirely possible to reduce emissions.
Researchers at NTNU can now calculate which ferry routes can be operated with zero-emission express ferries.
Emissions must be halved within five years
Express boats are vessels travelling above 20 knots.
They play an important role in passenger transport. Around 200 high-speed passenger vessels operate along Norway’s approximately 20,000-kilometre coastline.
There are large distances and challenging conditions on many of the hundred routes. This makes it difficult to make transport emission-free with current battery technology.
Only ten routes can be operated by express boats that can be charged or have their batteries swapped out along the route.
The remaining routes must use other technologies, or a combination of technologies.
Researchers can determine which solutions are suitable using the new method. It was developed by researcher Samieh Najjaran during her doctoral work at NTNU.
Took the toughest route
“Express boats are difficult to electrify. Batteries and hydrogen solutions are also significantly heavier than traditional diesel engines. More weight increases resistance, which in turn requires more energy. It's a classic vicious circle,” says Najjaran.
While developing the model, she used the Bodø–Sandnessjøen ferry route along the Helgeland coast as a guinea pig.
The route is approximately 220 kilometres long and is considered one of the most challenging in Norway.
“If we can make this stretch a zero-emission route, it basically means that all the other routes have the same potential. This is one of the most challenging routes, with many ports of call and limited time for charging,” Najjaran says.
The Nordland Express was examined
The Nordland Express route relies on two virtually identical high-speed passenger ferries.
One of them is the catamaran MS Elsa Laula Renberg. This vessel is built from carbon fibre and has space for 220 passengers. Four diesel engines provide a cruising speed of 33 knots.
“We have calculated the vessel’s operational profile based on detailed information from the automatic identification system over an entire year. This enables us to account for almost all weather scenarios and variations in wind, currents, and wave conditions across all four seasons,” says Najjaran.
This information has been incorporated into a model for calculating resistance and energy consumption for a typical high-speed passenger catamaran of the same size. The model was developed during John Martin Kleven Godø’s doctoral work at NTNU.
The results were integrated into a model for optimising energy management in the vessel’s electric power system. In this setup, batteries and fuel cells share the load.
The new model is scalable
The model is general enough so that different parameters can be scaled and adjusted.
“This means it can be used on all similar vessels and routes,” says Najjaran.
The researchers studied three possible alternatives:
- Battery-only operation – with charging or swapping batteries at selected ports.
- Hybrid solution with fuel cells and batteries – no charging at ports, powered solely by fuel cells.
- Plug-in hybrid solution with fuel cells and batteries – with battery charging at selected ports.
In the study, the researchers only looked at an existing vessel. They did not investigate what would happen if the vessel itself was modified, for example by making it longer.
“The biggest challenge is the increase in weight and thus increased resistance and energy requirements. The use of batteries alone on the existing Nordland Express vessel is not feasible,” says Najjaran.
Combinations are necessary to reach the goal
Najjaran believes that different technologies must be combined to achieve the target.
“For example, fuel cells powered by hydrogen, combined with rechargeable or replaceable batteries are a good way to make zero-emission express boats. However, the vessels’ design must be optimised, both in terms of hull length and hydrodynamic resistance,” she says.
This is where the model becomes useful. It combines three elements.
Najjaran says smart energy management is absolutely crucial. Hydrogen is an expensive fuel, while batteries are heavy.
Making this work will require finding the optimum balance between hydrogen consumption and battery use. This is important both when sizing the power system and when operating the vessel afterwards.
Hydrogen storage capacity will also have to be expanded at several ports.
“The energy must be distributed between the batteries and the fuel cells. Fuel cells operate most efficiently when running steadily, close to their optimal operating point, while batteries are able to handle rapid fluctuations in power demand more effectively,” Najjaran explains.
Batteries and fuel cells have complementary properties that enable them to work well together.
The researcher has not looked at the costs
When planning new routes or upgrading vessels, operators can use data from vessels already operating on those routes.
Using the model, they can determine the best energy distribution and what type of power system is required.
They can then adjust the vessel’s size and design and run new calculations until they find the best solution.
Najjaran has not investigated the financial cost of the various options, as this was not part of her research.
“That's something the county authorities and shipping companies need to consider for the specific routes,” she says.
Reference:
Najjaran et al. Feasibility assessment of zero-emission high-speed passenger vessels using optimal energy scheduling and power allocation, Ocean Engineering, 2026. DOI: 10.1016/j.oceaneng.2026.124430
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Read the Norwegian version of this article on forskning.no
