Wärtsilä Ammonia Engine to Power Two New Gas Carriers

Ammonia-Fuelled Auxiliary Engines Ordered for New LPG Carriers

According to a report by The Maritime Executive, technology group Wärtsilä has secured an order to supply its Wärtsilä 25 Ammonia auxiliary engine for two newbuild midsize LPG/liquid ammonia carriers, each with a cargo capacity of 51,350 cubic meters. The package also includes a selective catalytic reduction (SCR) unit for NOx abatement and a gas valve unit (GVU), aimed at improving both emissions performance and operational efficiency.

The vessels are under construction at the Nantong CIMC Sinopacific Offshore & Engineering yard near Shanghai. Ownership sits with Navigator Amon Shipping AS, a joint venture between Navigator Gas and Norway’s Amon Maritime. Wärtsilä will additionally provide the ships’ propulsion package, including a controllable pitch propeller system intended to boost shaft-line efficiency and reliability.

Order Timeline and Delivery

Wärtsilä booked the order for the engines, SCR, and gas valve unit in the second quarter of 2026, with the controllable pitch propeller contract following in the third quarter. Equipment deliveries to the shipyard are scheduled to begin in June 2027.

Ammonia’s Role in Decarbonisation

Ammonia is increasingly viewed as a viable carbon-free marine fuel that could help the industry meet the IMO’s 2050 net-zero target. Wärtsilä has been active in this space since 2023, when it introduced what it describes as the sector’s first commercially available four-stroke engine solution designed for ammonia fuel. The company states that when run on sustainable ammonia, its engines can cut total greenhouse gas emissions by at least 90 percent compared with conventional diesel units.

Kaj S. Pilemand, Director of Vessel Operations at Navigator Gas, said the choice of the Wärtsilä 25 Ammonia engine reflects an expectation of substantially reducing the ships’ environmental footprint while keeping pace with tightening regulations. Stefan Nysjö, Vice President of Power Supply at Wärtsilä Marine, framed the project as part of a broader push toward flexible propulsion systems suited to lower-emission operating models, noting that ammonia is emerging as one of the key fuel pathways for the industry.

What It Means for Owners and Surveyors

For ship owners and technical managers, this order is another sign that ammonia-capable machinery is moving from pilot projects into mainstream newbuild specifications, particularly for gas carriers already equipped to handle ammonia as cargo. Using the cargo itself as a potential fuel source offers an operational logic that other vessel types lack, which may explain why LPG/ammonia carriers are early adopters of this technology.

However, the introduction of ammonia-fuelled auxiliary machinery raises new questions for vessel inspection and condition assessment practice. Ammonia is toxic and corrosive in ways that differ meaningfully from LNG or conventional fuels, and surveyors will need to pay close attention to fuel supply system integrity, gas valve unit performance, and SCR after-treatment condition during periodic and pre-purchase inspections. Bunker surveys and fuel-system audits on these vessels will likely require updated protocols to verify safe containment, leak detection, and crew handling procedures specific to ammonia fuel, rather than relying solely on conventional diesel or LNG survey checklists.

As more ammonia-fuelled and ammonia-ready vessels enter service over the coming years, owners and charterers should expect classification societies and flag states to refine inspection regimes accordingly. In the meantime, operators bringing these ships into service would be well advised to build ammonia-specific expertise into their condition survey and technical due diligence processes well ahead of delivery, rather than treating it as a standard afterthought once the vessels are already trading.

The two carriers are expected to enter the fleet as part of a broader wave of alternative-fuel newbuilds aimed at aligning gas carrier operations with tightening international emissions standards.

Reviewed by Ibrahim Halil Ceylan, Marine Surveyor at Apeks Marine.