Our Drive - Part III: Coastal Vessels

The Development of Coastal Shipping Now and in the Future – Passenger and Cargo Transport

Coastal shipping connects inland and coastal ports over medium distances, including international routes. The vessel types operating in these waters are diverse, making them particularly interesting in terms of climate neutrality. They face both the challenges and opportunities of inland and ocean shipping. Since the distances covered in coastal traffic are significantly shorter than in deep-sea shipping, there is a broad field for the deployment of alternative propulsion technologies.

In many sparsely populated coastal regions, the electrical grids are often not strong enough to support large-scale electrification of ships. Deploying alternative fuels requires the expansion of bunkering facilities. Building supply infrastructure at strategically advantageous points such as ports, berths, or offshore maintenance hubs is therefore a key task for future planning.

Classic ship design is increasingly extending to landside infrastructure.

Shipbuilders and shipping companies must work more closely than ever with port operators, energy suppliers, and transport planners to develop an integrated, functioning concept. This includes charging infrastructure, safety and environmental standards for alternative fuels, and the organization of logistical processes. Beyond the design of the ship and its onboard systems, we increasingly act as energy consultants for individual requirements and operating profiles. To integrate zero- or low-emission technologies, we plan long-term, coordinated strategies across both water and land.

The continuous expansion of Emission Control Areas (ECAs), which include large parts of European coastal waters, is prompting many shipowners to retrofit their fleets. In these strictly regulated areas, significantly reduced emission limits apply, requiring vessels to operate with low-emission or completely emission-free propulsion. This also puts pressure on regions whose existing infrastructure is not yet ready to supply zero-emission technologies on a wide scale.

Shallow-water capability is gaining importance in coastal shipping.

In a past project, we developed a tugboat for a client operating in such an ECA. Alongside designing a low-emission propulsion system, particular attention was paid to the vessel’s shallow draft.

Climate-driven weather extremes are increasingly leading to stronger storm surges, which intensify sediment deposits in tidal waters and river mouths. This development affects not only coastal shipping but also ferry services in adjacent areas.

A solution based solely on shallow drafts is often not sufficient. In a current project to renew a car ferry route, we designed a ferry whose propulsion system actively flushes the fairway during operation. Using the flushing effect of two cycloidal propellers, accumulating sediment is efficiently displaced from the immediate navigation area, keeping the route navigable over the long term without external measures.

Battery technology will be a central element of coastal shipping.

On shorter routes and in scheduled passenger service, battery systems are highly attractive. The recent drop in cell-level prices for LFP chemistry makes large battery storage increasingly viable. However, for coastal vessels requiring short charging times, charging facilities capable of delivering megawatt-level power are necessary. In rural coastal areas, it is often difficult to provide such capacity.

A possible solution is the use of buffer batteries onshore, which can be charged continuously with the available electricity—even while the ship is at sea. Once the vessel docks, the stored energy can be transferred to the onboard battery in a short time at high power. Although the losses in such a system are not negligible compared to “classic” charging infrastructure, they can be offset economically. This solution can also be used in scheduled service to save weight onboard by storing part of the battery capacity ashore during charging. For one of our core competencies—the design of shallow-water vessels—this concept is particularly appealing.

Longer distances require additional energy carriers – hydrogen derivatives are on the rise.

Coastal vessels covering longer distances depend on additional fuels as energy carriers. Bringing alternative fuels onboard in an economically viable logistics chain remains an ongoing challenge that we must address in our design work. Due to the low energy density of these fuels, achieving the highest possible efficiency through hull geometry is becoming ever more important. Even in early concept phases, we use CFD simulations to make accurate energy consumption forecasts.

Vehicle ferries are a special case where energy carriers can be designed as Ro-Ro units that can be swapped within minutes. Loose tanks or battery modules can be put into service with minimal additional equipment onboard.

Among alternative fuels, hydrogen-based energy carriers are emerging as frontrunners. Liquid hydrogen derivatives such as ammonia and methanol are gaining traction, as they offer advantages in transport, storage, and onboard use.

Pure hydrogen is comparatively complex to handle on land and at sea, and bunkering is time-consuming. Even in specialized structural tanks, hydrogen—being the smallest atom—gradually diffuses into surrounding spaces, requiring strict safety and ventilation standards when stored below deck. For inland shipping, we have already implemented transport vessels powered by deck-mounted, containerized compressed hydrogen and fuel cells. Container exchange can be handled using standard container cranes, allowing rapid turnaround. We consider the technology transfer from inland to coastal shipping realistic and see this solution as suitable for feeders and coasters.

Not all vessels are suited to modular tanks—containerized solutions limit available space and layout options. Where these parameters are highly constrained, fixed tanks and hydrogen derivatives must be used. Since our first alternative propulsion system on a passenger ship in 2006, we have observed that the space required and the regulations governing onboard storage have grown steadily stricter. This can significantly reduce cargo capacity.

In ocean shipping, ammonia is currently emerging as the “fuel of the future.” Its advantages are numerous: it is widely available, produced as a byproduct of many chemical processes, and supported by scalable supply chains for large vessels. However, handling ammonia onboard requires stringent safety measures. In emergencies, it must be vented into the atmosphere through tall exhaust masts. While regulations mainly focus on crew safety, its impact on the immediate coastal environment must also be considered.

Methanol is one of the most promising energy carriers for longer coastal routes. Although it tends to create explosive atmospheres, the risks can be technically mitigated. Since methanol is less toxic than ammonia, its use as a fuel is subject to less stringent regulations. Furthermore, local particulate emissions during combustion are lower—an important factor in coastal ECAs.

Methanol can be used in combustion engines or in fuel cells (after a reforming process). This flexibility allows us to select the best energy concept and retrofit strategy for modern vessels. In hybrid applications with batteries, engines or future fuel cells can operate at an efficient load point.

Sail and wind technologies reduce the fuel consumption of modern coastal ships.

Various approaches aim to revive the use of wind power in commercial shipping. Due to weather dependence, wind alone is unrealistic for tightly scheduled logistics or passenger services. On certain routes, however, supplementary wind propulsion can support the vessel’s movement. These range from rotor sails (Flettner rotors) to foldable and retractable sails and large kites.

The use of a single rotor sail has been proven to save up to 5% in fuel when winds strike from the side. Provided vessel stability is sufficient, rotor sails can be integrated into operations without complex preparations. For areas with restricted clearance, collapsible rotor sails are now available.

Low-emission coastal vessels are key to environmentally friendly trimodal transport.

To reduce emissions, inland shipping uses the “Energy Efficiency Operational Indicator” (EEOI) as a basis for grants to retrofit existing vessels. To qualify, a vessel’s EEOI after conversion must be half the reference value of a truck. This can be achieved even without alternative fuels, demonstrating the importance of leveraging the strengths of each transport mode in trimodal logistics: inland and coastal vessels offer high capacity, rail transport provides speed, and trucks ensure flexible last-mile delivery.

A study by the German Federal Ministry for Digital and Transport (BMDV) shows that rail network utilization will remain high in many areas, even in the 2030 target network. Shifting goods from road to rail will quickly lead to rail congestion. It therefore makes sense to transfer large rail freight volumes directly to ships to relieve the network, enabling low-fuel transport per ton. With alternative propulsion systems or fuels, the EEOI or the EEDI (already established for coastal and ocean-going vessels and in development for inland newbuilds) shifts further in favor of shipping as the most environmentally friendly mode. To enable low-emission transport between inland and coastal regions, continuous availability of the required fuels must be ensured.

CO₂ carriers: New coastal ships to meet climate targets.

For heavy industry, where significant emissions occur at single points, CO₂ transport ships have evolved in the past five years from a niche application to a strategic link in modern “carbon capture and storage” logistics chains.

Where once only small pressure tankers served the food and chemical industries, today coastal and deep-sea vessels with capacities of 7,500–50,000 m³ are being built for transporting liquefied CO₂ at around –50 °C and 6–7 bar. These ships connect capture facilities at industrial emission sources with central export terminals, offshore storage sites, or CO₂ processing plants. In this way, millions of tons of CO₂ can be removed from the atmosphere annually, making a measurable contribution to achieving climate goals.

To maximize flexibility in future transport, inland waterways should also be accessible to vessels operating in coastal areas. This requires removing organizational barriers, such as the need for separate licenses for inland and sea zones and their division along historical but now outdated boundaries. It also calls for the development of new coastal motor vessels with shallow drafts to maintain freight transport even during low water levels in rivers.

Compared to pure inland vessels, the structural strength and propulsion power requirements increase because coastal motor vessels must also operate under wave impact. By applying direct calculation methods for steel design, we can optimize the ratio between lightship weight and payload, making an important contribution to the modernization of the coastal fleet to meet demand.

Developing a future-ready vessel requires moving away from isolated solutions—a cross-industry decision for a shared energy carrier enables reliable infrastructure growth. This allows shipping to realize its full potential in a trimodal transport model and significantly contribute to climate protection goals. If the specific requirements of the coastal and inland markets are united, the vision of integrated and environmentally friendly transport can become reality.