Foreship: Energy density and safety aspects of alternative marine fuels must be addressed in future ship designs

The increasing use of alternative marine fuels due to IMO 2030/2050 regulations is creating challenges that ship designers still need to overcome, according to Helsinki-based ship design and engineering specialist Foreship.

“’Future proof design’ is one of the key words of the shipping industry these days,” Jan-Erik Räsänen, Chief Technology Officer, Foreship told bunkering publication Manifold Times.

“While clearly still challenging, designing ships for lower emissions was more straightforward in the early days because it involved heavy fuel oil (HFO) and marine gas oil (MGO); their superior energy density and relatively high flash point offer great flexibility when designing ships.

“However, while alternative bunker fuels are a good thing due to their lower emissions, they also come with challenges. Ship designers have to consider the energy density, energy content and, due to their low flash points, these fuels must be accessed and stored in separate tanks.”

Challenges of marine engine retrofits to use methanol and LNG

The option of retrofitting vessel engines to use alternative marine fuels such as methanol and liquified natural gas (LNG) also pose their own set of issues, highlights Räsänen.

“Today most shipowners thinking about a retrofit probably consider methanol as their starting point; for ship designers the methanol is a good bunker fuel as it offers flexibility in choosing between different storage tank locations on a vessel,” he explained.

“However, one of challenges for methanol is the need to do more structure-wise when compared to traditional bunker fuels such as HFO and MGO. Designers must strengthen the hull to cope with additional weight from the weight and introduction of cofferdams; containerships will most likely lose cargo space as a result of the conversion.

“Foreship has already done several conversion designs for cruise ships to use methanol, and the conversion can be more straight forward than some might expect, with double bottom tanks and ballast water tanks used to store the bunker fuel. However, doing so comes at a cost – structure-wise.”

Räsänen points out that classification societies also offer initial thoughts on engine retrofit plans to consume methanol. Additionally, engine manufacturers such as Wärtsilä and MAN offer retrofit kits for their own two-stroke engines to simplify the process.

“As such, today we usually ask shipyards to strengthen the hull to accept alternative bunker fuel,  ,”  Räsänen noted, although he expressed reservations on the use of LNG as a future marine fuel. “We are debating heavily on methane slip especially on four-stroke LNG engines,” he said.

‘Methanol-ready’ term overstretched

Moving forward, Räsänen felt the term ‘methanol-ready’ has been over-used, at a time when its definition has not been standardised by class societies.

In general, to secure approval-in-principle (AiP) status as a ‘methanol-ready’, ship owners must agree that a certain number of vessel modifications need to be  carried out so that the ship can consume methanol as a bunker fuel.

However, shipowners can secure the in-principle approval before all of the modifications are carried out, with the ship notated as ‘methanol-ready’ on the basis that it is on the right path.

“This is a departure from the ordinary understanding of what it means for something to be ‘technology-ready’, said Räsänen. “Given what is at stake, it’s essential that these terms aren’t vulnerable to being considered gimmicks.”

Potential risks included ship managers taking a vessel on long term charter on the grounds that it was ‘methanol-ready’ when a full evaluation of its conversion had not been undertaken.

“This AiP has varied between different class societies, and I’d say there certainly needs to be standardisation on what ‘methanol-ready’ notation means – as a matter of priority .”

Photo credit: Foreship
Published: 7 May 2024