Ammonia-fueled container ship design points the way to low carbon future

A Green4Sea Ship Design Award winner in 2024, Seaspan Corporation’s 15,000-teu ammonia-fuelled containership concept is the fruit of an intense collaboration between the owner, Foreship, the Mærsk Mc-Kinney Møller Center for Zero Carbon Shipping and class society ABS.

Approved in Principle by ABS, the forward-looking concept has been optimised for Asia-Europe and Transpacific trading routes, demonstrating how Foreship’s extensive design study focused on servicing the specifics of owner objectives on decarbonization. The project was also connected to the Singapore Ammonia Bunkering Feasibility Study (SABRE) consortium.

Despite its toxicity and stringent handling requirements, ammonia is rapidly finding a position as a practical future marine fuel, not least because OEMs have pushed ahead with developing dual-fuel engines capable of burning the carbon-free substance. Engine makers are now predicting commercial availability for DF engines running on ammonia as soon as 2027.

While future scenarios on the availability, pricing and variable quality of alternative marine fuels are unclear, owners seek to move forward based on known information in the case of a fuel which burns without causing carbon emissions.

The Seaspan concept envisages a ship with a range of 12000 nm and an operating speed of 15 knots, equipped with a dual fuel engine that can run on either ammonia or LSFO to maintain maximum flexibility.

The Foreship study was maker agnostic, with both the MAN 7G90ME-C10.5 and WinGD 8X92DF-2.0 engines considered suitable. Instead, its primary focus was on restricting toxic and hazardous areas to minimize the potential risks that might affect the safety of the ship, persons on board, and equipment. Specifying safe and suitable ammonia fuel supply, storage, and bunkering arrangements were considered to be prerequisites.

Central among the design challenges was the fact that it typically takes more than three times the net volume of ammonia compared to fuel oil for a ship to cover the same distance.

For the 350 m-long vessel envisaged, Foreship determined that an ammonia storage tank of 11,500 cu m would be required to cover the 12,000NM range. To avoid losing container slots, the design solution involved locating the ammonia storage tank entirely under the forward accommodation bay.

The extra capacity needed for ammonia fuel storage has an impact on the ship’s stability and longitudinal strength compared to conventional designs, but Foreship established that the concept complies with intact and damage stability criteria up to a maximum draught of 17m.

Other technical issues relate to Boil Off Gas (BOG) caused by inevitable heat penetration during operation from the IMO Type B Tank specified in the design; the management of this phenomenon is critical.

Foreship notes that ammonia BOG management techniques and technologies are under development, with several already commercially available for maritime use, including reliquification plants. Others are based on existing maritime concepts that need to be further adapted, including gas combustion units (GCU), catalysts, and water catchers/chemical absorbers.

Exact emission levels generated from the combustion of ammonia in this application require further study, and Foreship cautions that attention needs to be paid to the potential presence of ammonia slip, N2O or NOx emissions. However, a preliminary assessment of the ammonia dual-fuel design concludes that its CII rating for all operating scenarios and ship speeds would be A: the highest possible.