Current Greenhous gas emissions (GHG) from maritime transport represent around 3% of global anthropogenic GHG emissions and will have to be cut in half by 2050 to meet Paris agreement goals. Liquefied natural gas (LNG) is by many seen as a potential transition fuel for decarbonizing shipping. Its favorable hydrogen to carbon ratio compared to diesel (marine gas oil, MGO) or bunker fuel (heavy fuel oil, HFO) translates directly into lower carbon emissions per kilowatt produced. However, these gains may be nullified once one includes the higher Well-to-tank emissions (WTT) of the LNG supply chain and the vessel’s un-combusted methane slip (CH₄) from its combustion engine. Previous studies have tended to focus either on greenhouse gas emissions from LNG in a Well-to-wake (WTW) perspective, or on alternative engine technologies and their impact on the vessel’s Tank-to-wake emissions (TTW). This study investigates under what conditions LNG can serve as a transition fuel in the decarbonization of maritime transport, while ensuring the lowest possible additional global warming impact. Transition refers to the process of moving away from fossil fuels towards new and low carbon fuels and engine technologies. Our results show: First, the importance of applying appropriate engine technologies to maximize GHG reductions; Second, that applying best engine technologies is not economically profitable; Third, how regulations could be amended to reward best engine technologies. Importantly, while the GHG reduction of LNG even with best engine technology (dual fuel diesel engine) are limited, ships with these engines can with economically modest modification switch to ammonia produced with renewable energy when it becomes available in sufficient amounts.

The development of autonomous ships is at an advanced stage. It seems to be just a question of time before such ships become available at an industrial scale. In this paper, we investigate the economic advantages of utilizing autonomous over conventional ships. We consider a shipping network composed of conventional mother ships and autonomous daughter ships that perform cargo transshipment at specific ports. The mother ships sail between Europe and the Norwegian coastline and are conventional due to international regulations. The daughter ships serve small ports located along the Norwegian coastline and are autonomous. We apply this concept of mother and daughter routes to a Norwegian shipping company that transports containers between a continental European port and 21 ports scattered along the Norwegian coastline. Furthermore, we extend this case to a shipping network of 42 ports to study a possible increase in the activity of the company. For solving the corresponding optimization problem, we present a path‐flow‐based model formulation and a heuristic route generation method. We carry out extensive computational experiments that consider differently sized problems, various demand scenarios, advanced routes structures, and sensitivity analyses for cost rates and the degree of automation of the maritime transport system. The results provide evidence that autonomous ships might contribute to considerable cost savings.