THE maritime industry has spent years debating which fuel will define its transition. LNG, methanol, ammonia, hydrogen and other alternatives have all been presented as possible answers, each with its own technical, regulatory and commercial logic. Yet, for shipowners preparing investment decisions today, the problem is that none of these paths has yet become the obvious long-term winner.

That uncertainty matters. A vessel ordered now will not be operating only in the regulatory and commercial conditions of the late 2020s. It is likely to remain in service into the 2040s and 2050s, crossing several phases of policy development, fuel infrastructure expansion, technology maturity and market expectation. In this context, the design decisions taken today may either protect future competitiveness or make a vessel harder and more expensive to adapt later.

This is why the discussion needs to move beyond the question of fuel choice alone. Fuel remains central, but it is only one part of a wider design challenge. Owners are no longer simply asking which energy source they should select. They are asking how to avoid locking themselves into assumptions that may no longer hold true in 10 or 20 years’ time.

Reduce investment risk

RINA’s Mermaid concept was developed from this starting point. Rather than promoting one specific fuel or propulsion route, it looks at how ship design can reduce long-term investment risk while delivering immediate operational benefits. Its underlying logic is simple: ships should be engineered to perform efficiently today, while remaining adaptable enough to respond to tomorrow’s fuel, technology and regulatory landscape.

At the heart of the concept is a different use of the vessel’s two-stroke main engine. Traditionally seen primarily as the source of propulsion, the main engine can also become the main provider of onboard electrical power. By integrating a shaft generator, propeller shaft clutch and battery energy storage, the engine can continue producing electricity when the propeller is disengaged, for example in port. The batteries can then supply onboard demand, allowing the engine to operate in a more efficient range and reducing reliance on auxiliary engines.

The benefit is not only lower fuel consumption. It is also a more flexible energy architecture. As vessels increasingly operate in conditions different from those assumed at the design stage, particularly with the spread of slow steaming, propulsion systems must be able to match real operating profiles more closely. A hybrid arrangement combining auxiliary engines and battery energy storage can help avoid excessive installed power while maintaining the ability to respond when higher power is needed.

Fuel agnostic

This is where technical design and commercial strategy meet. Mermaid is fuel agnostic, which means it does not require owners to make an early, irreversible bet on one decarbonisation pathway. RINA’s analysis indicates that, in certain applications, the concept can cut fuel consumption by more than 1,000 tonnes per year, while also helping to reduce exposure to future emissions-related compliance costs.

There is also a resilience argument. As ships become more electrified, the reliability of onboard power systems becomes increasingly important. Maintaining electrical availability in critical conditions is not simply an efficiency issue; it is a safety and operational continuity issue. In this sense, electrification should be seen not only as part of the decarbonisation agenda, but also as a way to improve the robustness of vessel operations.

The wider lesson is that the industry may be looking for certainty in a period that will not provide it. Waiting for a single answer on future fuels risks delaying action, while committing too narrowly risks creating stranded or less competitive assets. A more practical approach is to design vessels around flexibility, efficiency and resilience.

Shipping’s energy transition will not be won only by those who correctly identify the dominant fuel of the future. It will also be shaped by those who build ships capable of remaining valuable as that future changes. For owners, that may prove to be the most important competitive advantage of all.

This article was written by Antonios Trakakis, energy transition solutions technical director at RINA