Wärtsilä will supply its pioneering Wärtsilä 25 Ammonia auxiliary engines, advanced emissions systems, and integrated controllable pitch propulsion lines for two 51,350 m³ midsize gas carriers built at the CIMC SOE shipyard. Owned by a joint venture between Navigator Gas and Amon Maritime, these vessels will achieve a 90% reduction in greenhouse gas emissions by operating on sustainable ammonia, positioning the fleet well ahead of tightening international maritime climate mandates.
Helsinki, Finland | July 16, 2026 – The commercial architecture of the zero-emission ammonia supply chain has taken a major step forward. Technology group Wärtsilä has secured a breakthrough contract to supply its Wärtsilä 25 Ammonia auxiliary engines for two newbuild 51,350 m³ midsize liquefied petroleum gas (LPG) and liquid ammonia carriers.
The vessels, commissioned by Navigator Amon Shipping AS, a joint venture between gas shipping giant Navigator Gas and Norway’s alternative-fuel pioneer Amon Maritime, will be constructed at the Nantong CIMC Sinopacific Offshore & Engineering (SOE) shipyard in Shanghai, China.
This transaction marks a critical milestone for the maritime energy sector: it transitions ammonia power from experimental testing regimes into integrated, commercially operational hull designs.
The Propulsion & Auxiliary Configuration
Wärtsilä’s delivery scope comprises a fully integrated powertrain and emissions abatement package, ensuring total system optimization across the shipboard electrical and propulsion networks.
Technical Breakdown of the Order
- Auxiliary Power: The Wärtsilä 25 Ammonia 4-stroke engine. First introduced commercially in late 2023, it remains the industry’s benchmark medium-speed platform optimized explicitly to handle the unique combustion properties of liquid ammonia (NH3).
- Emissions Mitigation: A dedicated Selective Catalytic Reduction (SCR) system and an advanced Gas Valve Unit (GVU). The SCR system specifically eliminates Nitrous Oxide (N2O) and Nitrogen Oxides (NOx), ensuring strict compliance with Tier III limits.
- Propulsion System: A highly optimized Controllable Pitch Propulsion (CPP) solution. By integrating the entire shaft line arrangement, the system matches engine torque output with real-time hull resistance to maximize hydrodynamic efficiency.
The Integrated Wärtsilä Ammonia Ecosystem
| System Dimension | Hardware Components | Operational Role |
| Power Generation & Emissions | Wärtsilä 25 Ammonia Engine Gas Valve Unit (GVU) Selective Catalytic Reduction (SCR) | High-efficiency auxiliary power using carbon-free NH3; precise gaseous fuel pressure control; delivers a 90%+ reduction in total lifecycle GHG emissions. |
| Maneuvering & Thrust | Controllable Pitch Propeller (CPP) Integrated Shaft Line Layout | Optimizes hydrodynamic propulsion efficiency and mechanical reliability by seamlessly matching engine torque to real-time hull resistance. |
The Chemistry of 90% Carbon Reductions
Ammonia continues to emerge as a primary pathway toward the IMO’s net-zero 2050 targets because it carries no carbon atoms (NH3). When utilizing sustainably produced green or blue ammonia, total lifecycle greenhouse gas (GHG) emissions are cut by at least 90 percent compared to conventional marine gas oil (MGO) or very low sulfur fuel oil (VLSFO).
Overcoming the Combustion Barrier
Ammonia is notoriously difficult to ignite due to its high auto-ignition temperature and slow flame propagation speed. Wärtsilä overcomes this through precision high-pressure fuel injection and advanced combustion-chamber geometry.
Pure NH3 -> Slow Flame Velocity ->Requires High-Compression / Spark or Pilot Fuel Assistance -> SCR Control -> N2 + H2O
The integrated GVU acts as the safety gatekeeper, maintaining precise control over gaseous fuel pressures while ensuring rapid purging and safety shutdowns in the engine room if any anomalies are detected.
“By selecting the Wärtsilä 25 Ammonia engine, we expect to dramatically reduce the ships’ environmental impact, while supporting compliance with evolving regulatory requirements,” said Mr. Kaj S. Pilemand, Director of Vessel Operations at Navigator Gas.
Order Booking and Project Timeline
The booking structure demonstrates how the joint venture consolidated its machinery contracts across consecutive quarters in early 2026:
| Order Component | Booking Timeline | Expected Delivery to SOE Shipyard |
| Wärtsilä 25 Engines, SCR, and GVU | Q2 2026 | Commencing June 2027 |
| Controllable Pitch Propeller (CPP) System | Q3 2026 | Commencing June 2027 |
Future-Proofing the Fleet
This newbuild order arrives amidst intense regulatory tightening under FuelEU Maritime and the EU Emissions Trading System (EU ETS), which heavily penalize carbon-intensive ton-mileage.
“This project reflects the continued momentum behind carbon-neutral and zero-carbon fuels, with ammonia emerging as one key pathway,” noted Stefan Nysjö, Vice President of Power Supply at Wärtsilä Marine. “It also highlights the growing demand for flexible propulsion solutions that support new, more sustainable operating models.”
By designing these midsize gas carriers to actively consume the very ammonia cargo they transport, Navigator Amon Shipping is mitigating the risks of regulatory obsolescence while setting a new standard for the global gas fleet.
Wärtsilä Marine in Brief
Wärtsilä Marine is a global pioneer in power, propulsion, and lifecycle solutions for the marine market. The company develops industry-leading technologies that advance the maritime transition to new alternative fuels. Wärtsilä supports the creation of an end-to-end digital ecosystem where all vessels and ports are seamlessly connected. Ultimately, Wärtsilä Marine drives the shipping industry forward on its journey toward a decarbonized and sustainable future through its broad portfolio of engines, propulsion systems, hybrid technologies, exhaust treatments, shaft line solutions, digital applications, and integrated powertrain systems. This offering, underpinned by performance-based agreements, upgrades, lifecycle solutions, decarbonization services, and an unrivaled global network of maritime expertise, delivers the efficiency, reliability, safety, and environmental performance needed to support a secure and sustainable future for customers, communities, and the planet.
Wärtsilä in Brief
Wärtsilä is a global leader in innovative technologies and lifecycle solutions for the marine and energy industries. The company emphasizes innovation in sustainable technology and services to help its customers continuously improve both environmental and economic performance. Wärtsilä’s dedicated team of 17,900 professionals across 199 locations in 78 countries actively shapes the decarbonization transformation of heavy industries across the globe. In 2025, Wärtsilä’s net sales totaled EUR 6.9 billion. Wärtsilä is listed on Nasdaq Helsinki.
Source: Wartsila