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Ammonia has moved from whiteboard idea to real metal in the water. By early 2025 there were hundreds of ammonia-fuelled or “ammonia-ready” vessels in the orderbook, mostly carriers and bulkers, with the first deep-sea ships expected to start running on ammonia around 2026 as two-stroke and four-stroke engines from MAN, WinGD and Wärtsilä leave the testbed and hit commercial service.
What is it and Keep it Simple...
Ammonia as a marine fuel is basically bottled hydrogen without the carbon. It carries energy in the nitrogen–hydrogen bond, so when it burns there is no CO₂ in the exhaust. Instead of running engines on fuel oil or LNG, the ship uses liquid ammonia stored in insulated tanks, mixed with a small pilot fuel to ignite it in the engine.
On board, ammonia needs its own fuel system: dedicated tanks, double-walled piping, ventilation, leak detection and scrubbers to deal with any accidental release. It is toxic and pungent, so the fuel system is kept in gas-safe spaces with strict separation from accommodation and working areas. Engines are either new dual-fuel designs or retrofits that can burn ammonia plus a small percentage of pilot fuel, with controls tuned to manage NOx and nitrous oxide (N₂O) emissions.
The big attraction is its zero-carbon exhaust when the ammonia itself is produced from renewable power. The big challenge is making enough green ammonia, moving it safely through ports and bunkering, and proving that day-to-day operations on trading ships can handle the toxicity and new safety rules without adding unmanageable complexity for crews.
Ammonia as Marine Fuel: Advantages and Disadvantages
Category
Advantages
Disadvantages
Notes / Considerations
Climate and emissions
✅ No CO₂ in the fuel molecule, so combustion does not directly emit CO₂.
✅ When produced from renewable electricity (green ammonia), it can be close to zero well-to-wake carbon.
✅ Can materially reduce GHG footprint versus conventional fuel when paired with good NOx and N₂O control.
❌ Risk of nitrous oxide (N₂O) formation, a very strong greenhouse gas, if engine and aftertreatment are not optimised.
❌ If ammonia is made from fossil gas without CCS (“grey”), total climate benefit is much lower.
❌ Slip of unburnt ammonia (“ammonia slip”) is a local toxicity and environmental concern.
Ask for well-to-wake GHG numbers, not just “zero CO₂ at the stack,” and check how NOx, N₂O and ammonia slip are managed and monitored.
Engines and tech status
✅ Major engine makers (MAN, WinGD, Wärtsilä) have tested ammonia four-stroke and two-stroke concepts and are lining up first commercial engines and retrofits around 2025–2027.
✅ Early pilot vessels, including ammonia carriers and offshore vessels, are scheduled to enter service around 2026.
✅ Dual-fuel designs can switch between conventional fuel and ammonia, giving flexibility during ramp-up.
❌ Technology is still at early fleet introduction stage; long-term performance, maintenance and degradation data are limited.
❌ Most engines require pilot fuel (often 5–10%) and specialised components, increasing system complexity.
❌ Limited yard and retrofit experience compared with LNG or methanol.
Focus first projects where cargo, trading pattern and charter backing justify a pilot; avoid treating ammonia as a drop-in swap for the whole fleet.
Safety and toxicity
✅ Clear IMO interim safety guidelines and class guidance now exist for ships using ammonia as fuel and for using ammonia cargo as fuel.
✅ Strong odour helps detect small leaks compared with some odourless gases.
✅ Dedicated fuel spaces and gas-safe concepts can keep crews away from routine exposure.
❌ Ammonia is acutely toxic and corrosive; even small leaks in confined spaces are dangerous.
❌ Requires robust double barriers, ventilation, detection, emergency shutdown and personal protective equipment procedures.
❌ Crew training and drills must go well beyond conventional fuel handling.
Treat ammonia fuel risk more like a cargo chemical hazard than like conventional bunkers; embed this into design reviews, SMS and port procedures from day one.
Energy density and design
✅ Liquid at moderate cryogenic conditions compared with hydrogen, so storage and handling are technically familiar to gas carriers.
✅ Proven experience with ammonia cargo tanks and systems in the gas carrier segment can be leveraged for fuel systems.
❌ Lower volumetric energy density than fuel oil, so fuel tanks take more space and may reduce cargo capacity or range.
❌ Additional cofferdams, ventilation trunks and segregation constraints complicate internal layout.
❌ Retrofitting on compact hulls is more difficult than for methanol or LNG.
Run early concept studies on tank size, location and impact on deadweight and stability before committing to ammonia on a given design.
Fuel supply and bunkering
✅ Global ammonia production and trade already exist for fertiliser and chemicals, with key export hubs in several regions.
✅ Pilot projects show that ship-to-ship and terminal ammonia bunkering can be designed and operated safely with the right controls.
✅ Many national strategies list green ammonia as a priority export fuel for shipping.
❌ Green ammonia volumes are still small and expensive; most current ammonia is fossil-based.
❌ Dedicated bunkering infrastructure at major ports is only at pilot or early planning stage.
❌ Long-term fuel price and availability are highly uncertain compared with conventional fuels.
Align any ammonia-fuel vessel project with concrete supply and bunkering plans at specific ports, not just high-level national strategies.
Regulation and training
✅ IMO has adopted interim safety guidelines and is updating the IGC Code to allow ammonia cargo as fuel on applicable ships from 2026.
✅ Class societies have started issuing guidelines for ammonia fuel system design, bunkering and operation.
✅ Work has begun on training frameworks for seafarers on ships using ammonia as fuel.
❌ Rules are still evolving; designs approved under interim guidance may require updates as the permanent code matures.
❌ Training standards, simulators and practical courses are still ramping up, especially outside key early-adopter regions.
❌ Different flag, port and class expectations can add paperwork and complexity.
Build projects around class and flag that are already active in ammonia rulemaking, and budget time and cost for regulatory learning curve.
Commercial and fleet strategy
✅ Strong decarbonisation narrative and potential for very low GHG footprint can support green charters, finance and premium cargo contracts.
✅ Ammonia-ready and ammonia-fuel orders can hedge against stricter GHG rules and future fuel mandates on key trades.
✅ Dual-fuel capability provides downside protection if ammonia cost or availability disappoint.
❌ High CAPEX and integration cost, especially for early movers and retrofits, with uncertain payback windows.
❌ Revenue upside depends on charterer willingness to pay for green tonnage and on policy support (tax, ETS, fuel standards).
❌ Technology and fuel risk may limit resale value if market preferences shift toward other fuels.
Start with a small number of vessels on well-defined trades with supportive charterers and lenders, and treat them as learning platforms for the wider fleet.
Transition role
✅ Offers a route to very low GHG deep-sea shipping without on-board carbon capture.
✅ Synergies with ammonia cargoes and existing chemical logistics chains on certain routes.
✅ Can be part of a multi-fuel strategy alongside methanol, LNG, biofuels and future hydrogen derivatives.
❌ Not a “one size fits all” solution; likely to suit specific ship types, trades and owners rather than the entire global fleet.
❌ Competes for renewable power and hydrogen with other sectors, which may affect long-term cost and availability.
❌ Requires long-term policy stability to justify investment at scale.
Treat ammonia as one option in a portfolio; compare it with other alternative fuels on a route-by-route, vessel-by-vessel basis rather than in isolation.
Summary: Ammonia fuel promises zero-carbon exhaust and deep cuts in shipping emissions, but it arrives with serious safety, supply and cost challenges. The upside is a powerful long-term decarbonisation tool for certain ships and trades; the downside is early-stage technology, toxic handling requirements and a fuel and regulatory ecosystem that will not fully mature until the 2030s.
Pilot ships are moving from drawings to water: The first offshore support vessels, ammonia carriers and demonstration projects are starting sea trials and early operations with dual fuel ammonia engines. These are still small in number, but they give owners real data on handling, reliability and crew workload.
Engines are leaving the testbed: Major engine makers now have commercial two stroke and four stroke ammonia designs that are installed on newbuilds and approaching first service. Most designs use a small amount of pilot fuel and promise efficiency close to conventional engines when tuned correctly.
Safety rules and class guidance are in place: Interim IMO guidelines and updated class rules give a clear framework for fuel system layout, ventilation, leak detection and emergency response. Projects that stick closely to these rules are getting approvals, although engineering and review time is still longer than for conventional fuel.
Supply and bunkering are still the bottleneck: Ammonia production exists at scale for fertilisers, but dedicated marine fuel supply and bunkering at ports is only developing at a handful of hubs. Many early ammonia fuel ships will start life running conventionally or on partial ammonia until local infrastructure catches up.
Costs are high and depend on policy: Green ammonia is significantly more expensive than fuel oil, and early engine and fuel systems carry a first mover premium. Where carbon prices, green corridors, or long term green charter deals are available, the projects look more attractive than in pure fuel cost comparisons.
What owners are learning so far: Ammonia works best when there is a committed cargo owner or charterer, clear port pairs with future fuel supply plans, and internal risk appetite for a pilot project. It is not yet a simple fleet wide fuel switch but a targeted bet on future regulation and green premium demand.
Ammonia Fuel vs Conventional - Cost, Carbon and ROI
Training values - replace with your own data
Baseline On Conventional Fuel
Ammonia Fuel and Engine Behaviour
CAPEX, Carbon Price and Green Premium
Key Results
Annual useful energy demand
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Baseline fuel use and cost
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Ammonia, pilot and remaining fuel cost
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Baseline CO₂e vs ammonia CO₂e
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Baseline total cost vs ammonia total cost
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Net annual impact
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Payback (discounted) and NPV / IRR
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This model compares a notional conventional fuel case with a dual fuel ammonia case using simple energy and cost logic.
It is for training and pre feasibility only. Replace all numbers with your own fuel use, prices, engine data, well to wake
emission factors, carbon costs, CAPEX, OPEX and green premium assumptions before using it in any real decision or external
communication.
By late 2025 the orderbook for ammonia fuelled and ammonia ready ships had grown to well over one hundred hulls, and the first commercial engines and vessels are scheduled to enter service from 2026 under new IMO interim safety guidelines for ammonia fuel systems. For most owners, that means ammonia is no longer a theory but still very much a pilot stage option, best suited to specific trades where cargo interests, ports and financiers are prepared to share the risk and where green fuel supply can be tied to long term contracts.
