Ana Pacheco Jiménez

Livestock carriers contribute to greenhouse gas emissions through the continued use of conventional fossil fuels. This study presents a theoretical, steady-state case study of replacing the Wärtsilä W7X35 diesel engine of the livestock carrier Motor Vessel MV Ganado Express with a Wärtsilä 46F methanol-fueled engine (7500 kW, operated at 81.2% load to deliver the required 6090 kW), using published specific fuel consumption values and emission factors. Fuel consumption and exhaust emissions were estimated with a bottom-up method over a 24 h sailing period, and the annual well-to-wake (WtW) greenhouse gas fuel intensity (GFI) and compliance costs were assessed for 2028–2035 against the two-tier targets of the IMO Net-Zero Framework approved at MEPC 83. Because methanol is a carbon-bearing fuel, tank-to-wake carbon dioxide emissions are nearly unchanged, declining by only 5.4%, whereas nitrogen oxide emissions fall by 73.2% and sulfur oxide emissions are eliminated. The decarbonization benefit arises instead on a well-to-wake basis: with renewable e-methanol, annual lifecycle emissions fall from 29,897 to 2291 tCO_2eq. Diesel operation exceeds both targets from 2028, at a compliance cost rising from USD 0.91 to 3.85 million per year, while e-methanol remains in direct compliance throughout the period. E-methanol nevertheless remains the more expensive option, the annual cost gap narrowing from USD 15.1 to 12.2 million by 2035.

Hydrogen appears in almost every maritime decarbonization roadmap, yet it barely sails: 19 vessels against more than 1600 powered by liquefied natural gas. This study combines an analysis of the global alternative-fueled fleet and orderbook (3094 fuel-vessel records) with an assessment of 26 international and European governance units, two of which are documented absences of an instrument, grouped into the seven conditions a hydrogen vessel needs to be built, certified, crewed, insured, financed and refueled. None of the 26 fully covers the condition it addresses, and the deficits run across all seven domains. Nor does binding demand regulation reach hydrogen where it is currently viable: the tonnage threshold it applies makes eligible nine out of ten LNG or methanol vessels and only two out of ten hydrogen vessels, a difference that narrows but does not close once adjusted for vessel segment. We term this pattern governance misalignment: conditions that must be met simultaneously but advance at different speeds, with unequal legal force, with ambiguous signals, and across fleet segments that do not coincide. The obstacle is not the absence of regulation but its lack of synchronization, a diagnosis replicable for any fuel whose deployment depends on several regulatory domains.

Trim optimization is widely promoted as a low-cost lever for reducing ship fuel consumption, yet most estimates of its benefit come from calm-water simulations or empirical models, leaving open whether the effect survives where sea state, wind and speed vary jointly with trim. This study analyzes 139 voyages of a Ro-Ro/Container vessel on a fixed interisland route (Puerto del Rosario–Las Palmas de Gran Canaria, Canary Islands), combining loading-computer hydrostatics, flow-meter fuel records, AIS-derived speed and course, and hourly sea-state observations. A naive comparison across trim bins reproduces the ≈4% saving commonly cited for moderate stern trim, but the difference is not significant (Welch t-test, p=0.80) and is no longer identifiable once significant wave height (Hs) and speed over ground are controlled for (p>0.7 in every specification). Over the interquartile trim range these operations explore, the 95% confidence interval for the trim effect spans −1.4% to +1.7% of specific consumption, excluding savings of the magnitude reported under controlled conditions. Trim is itself confounded with sea state: bow-down voyages occur, on average, in significantly higher sea states than moderate stern-trim voyages (p=0.009). Added resistance from wave height is significant in head seas (p<0.001) but indistinguishable from zero in beam seas (p=0.42). For this vessel and route, trim adjustments within the range routinely used are therefore secondary to weather-driven resistance, while the wider envelope simulated under controlled conditions remains beyond the resolution of operational data, with direct implications for how trim optimization tools are calibrated and how their recommendations are presented onboard.