Our Drive - Part I: Cargo Vessels

What Drives Us – Long-Distance Inland Shipping as the Bridge to the Coast

The shipping industry is undergoing a paradigm shift: To comply with the Paris Agreement and achieve the European Union’s ambitious climate goals, the sector must reduce the CO₂ emissions by 80% by 2040.

Newbuilds and retrofits entail significant investment costs but also present an opportunity to move away from fossil fuels. Route planning is becoming increasingly dependent on the availability of alternative fuels, which are the key to environmentally friendly shipping.

Whether inland, coastal, or ocean-going vessels – there is no “perfect fuel” for the future. The choice of energy source is determined by critical factors such as logistics and refueling infrastructure, operational profiles, the ship operator, and the vessel’s dimensions.

Long-distance travel on inland waterways can be achieved with minimal energy consumption when navigating canals, whereas navigating against fast-flowing rivers requires significantly more energy. In contrast, seagoing vessels typically operate over long distances with increased energy consumption and are exposed to considerably stronger weather and wave influences. In both cases, various innovative energy sources can be utilized at their optimal operating points and combined within a hybrid system.

Our design process takes these different challenges into account. For each vessel, precise route profiles and environmental conditions are carefully analyzed to determine the most efficient propulsion concept. The focus is on modular systems that will enable completely emission-free operation in the future. These propulsion systems can be integrated into newly built and existing ships.

We had the opportunity to implement the described operational profile for inland vessels on a cargo ship with an H2-battery-diesel hybrid propulsion system. The energy required for canal navigation is drawn entirely from the battery, which can be recharged on demand by hydrogen fuel cells. The diesel gensets are activated when full power is required. Currently, the practicality of this overall system is being tested in real-world operations, laying an important foundation for the use of hydrogen fuel cells in inland shipping.

Modularity is also ensured: new energy sources and consumers can be integrated at any time. This future-proof design enables the vessel to transition to fully emission-free propulsion.

A similar system could be implemented on a seagoing vessel after adapting it to the specific operational profile. Over long distances, batteries can be used to handle peak loads efficiently, while fuel cells recharge the batteries and support the main propulsion system. During open-sea passages, additional power is provided by diesel gensets. The charged batteries can then be used within the 12-mile zone or Emission Control Areas (ECAs) to enable emission-free ship operation.

The choice of fuel used for the fuel cell significantly determines the required fuel cell type. In the maritime sector, two fuel cell technologies have proven particularly suitable in recent years: the Proton Exchange Membrane Fuel Cell (PEMFC) and the Solid Oxide Fuel Cell (SOFC).

PEMFCs (Proton Exchange Membrane Fuel Cells) are low-temperature fuel cells that can be flexibly started and stopped. However, these systems can only process pure hydrogen directly. In commercial shipping, hydrogen is currently stored primarily in containerized solutions. This approach offers the advantage that refueling can take place in a dedicated facility without time constraints. In port, the containers can be quickly exchanged without the need to comply with on-site refueling safety measures.

The efficiency of PEMFCs ranges from approximately 40% to 60%, with an expected lifespan of around 5,000 to 10,000 hours. At the end of their expected service life, the system does not fail entirely but experiences a decline in performance due to the degradation of membranes within the so-called "stacks." This is accompanied by an increased cooling demand.

Fuel cells are typically designed so that the stacks can be removed and recoated. This imposes specific design requirements on the ship, ensuring adequate maintenance spaces, lifting equipment, and accessibility to the stacks.

In contrast, high-temperature SOFCs (Solid Oxide Fuel Cells) can process organic compounds such as natural gas and methane directly using a reformer. This makes fuel storage and handling significantly less complex compared to pure hydrogen. SOFCs achieve an efficiency of 60–70% and have a lifespan of approximately 20,000 to 30,000 hours.

One drawback of SOFCs is that they should operate continuously to prevent damage from thermal stresses. This means that uninterrupted operation must be ensured even during port layovers. Legislators have a responsibility to support this promising technology by adapting shore power regulations accordingly.

From our perspective, port charging infrastructure should not only supply energy but also have the capability to absorb surplus energy. This would significantly reduce the technological complexity on board and lower integration barriers, particularly for SOFC systems. To enable a sustainable energy supply for shipping, these networks will need to be expanded far beyond their current capacity.

Currently, 90% of the hydrogen in use is "gray H₂," derived from fossil sources. To achieve climate targets, it is essential to rapidly expand electrolyzer capacity to produce green hydrogen on an industrial scale. It is also expected that additional industries will become increasingly dependent on this critical resource, further driving up demand.

A major advantage lies in the use of ammonia, which is already available in large quantities as a byproduct of the chemical industry. Ammonia can serve as a fuel in a PEMFC after undergoing a cracking process or be used directly in an SOFC without conversion. Storing ammonia on board is relatively straightforward, as it is kept in refrigerated low-pressure tanks. Its minimum ignition energy is significantly lower than that of pure hydrogen. However, ammonia is a highly toxic cellular poison and remains harmful to organisms even when diluted in water.

Practical application scenarios arise where favorable conditions and a well-designed safety concept minimize potential risks. Key factors include secure environmental conditions, clearly defined operating areas, limited exposure, and comprehensive protection of both people and nature.

Since fuel cells are currently only used in small series on ships, safety scenarios must be examined in individual approvals. For the cargo ship mentioned above, we have developed this individual approval in the form of a HAZID study with a classification society. A uniform regulatory framework across Europe, allowing planning to be carried out in a targeted and standardized manner, is urgently needed. In 2007, we designed the world’s first hydrogen fuel cell passenger ship, which was successfully approved and commissioned in 2008. To advance development, particularly in the regulatory landscape, the project was supported with research funding. Furthermore, regulatory barriers should be reduced at this point. Unfortunately, it must be noted that the approval procedure for such systems has only minimally evolved since then, and their attractiveness remains limited due to the expensive individual approvals required.

In addition to fuel cells, other technologies are also on the rise: The product range of methanol engines is continuously being expanded by manufacturers. Provided sufficient green hydrogen is available for methanol production, a conventionally designed propulsion concept with an internal combustion engine can be realized, which is net CO2-neutral across the entire process chain. However, these systems are not considered climate-friendly under the EU's funding guidelines, meaning little progress is expected in this area. The EU currently only supports projects that can demonstrably show "zero emissions at the tailpipe" under active funding guidelines. This is not the case with methanol systems.

Developments in battery technology are also making a significant contribution to the transformation of propulsion systems. Modern systems are not only becoming more powerful but also more compact and lighter, which continuously increases their capacity while reducing costs.

Last year, we developed a bunker ship that takes advantage of these advancements. The ship is largely filled by the handling systems required for its cargo, leaving only limited space for energy carriers. The volumetric efficiency of the latest battery modules enabled us to equip the ship with a battery-electric propulsion solution. The ship's operating profile spans a distance of 50 km, which it can travel completely emission-free. Sufficiently long layover times and the good availability of charging infrastructure complement the ship's concept.

With the significantly larger dimensions of sea and coastal vessels, this could become a scalable solution, even for large capacity requirements. The ongoing reduction in weight and increase in capacity of the modules is making their impact on payload ever smaller. However, the energy required for propulsion on long sea routes makes a fully electric system with batteries unrealistic at present. Additionally, charging infrastructure with the required power is simply not available on the open sea. A hybrid propulsion system with fuel cells and batteries, however, is quite realistic.

Battery-electric systems are expected to be deployed on RoRo ferries between mainland Germany and Denmark as early as 2025.

Choosing the right energy carrier is difficult: Infrastructure development is stagnating due to a lack of a common direction, and because the infrastructure is missing, there is no common direction. 

This results in a more complex, time-consuming, and therefore more expensive design process for engineering firms. For shipping companies, this situation is challenging: The days of universally applicable propulsion solutions (diesel engines) are over, yet no unified solution has emerged for every application. For our designs, this situation is exciting and presents a profitable business opportunity due to the increased planning effort. However, shipping companies that urgently need new ships must take on significantly higher business and financial risks. As a result, they hesitate to procure new builds and are hoping for new technical and regulatory developments. For engineering firms, these circumstances are roughly balanced: The number of projects is decreasing, but the scope of each project is increasing.

Due to these circumstances, the retrofit of existing cargo ships in inland areas is receiving increasing attention. A proven method for integrating alternative propulsion systems is the replacement of the entire aft ship, which is previously manufactured and equipped separately. This method significantly reduces the downtime of the ship, as it only goes into dry dock for the section replacement. The new systems are made operational before the retrofit, so the process mainly involves welding the sections together and connecting a few piping systems.

We have been involved in this type of retrofit numerous times in recent years. Using 3D laser scanning, we capture the existing ship hulls and design a precisely fitting aft ship. In addition to equipment plans and steel drawings, we were also responsible for the entire mechanical design and pipe coordination. The CO2 emissions are significantly lower than those of a new build, while the lifespan of the existing hulls is fully utilized, saving resources and further reducing environmental impact.

Moreover, the retrofit opens up various opportunities for modernization and efficiency improvements. Hydrodynamic optimizations can significantly reduce resistance in the water. Flow simulations (CFD) determine optimized hull and propeller shapes that result in lower fuel consumption and improved maneuverability. This phase also allows for consideration of noise and vibration levels. The use of sound-absorbing materials, improved bearing technologies, and vibration-optimized components not only ensures a quieter and more pleasant operation but also reduces underwater noise.

Furthermore, the retrofit provides an opportunity to bring the ship up to the latest international standards and regulations. This includes, for example, the implementation of energy efficiency measures (EEXI). Thus, replacing the aft ship is not only a cost-efficient method to minimize downtime but also offers extensive opportunities for technological and operational improvements.

This modular renewal of ships holds enormous potential for the maritime industry to initiate the transition to new propulsion technologies. Given the size of the vessels, it could be sufficient to pre-fabricate sub-sections of the ship’s hull with complex systems to significantly reduce the time required to integrate new propulsion technologies and energy carriers into existing ships.