It is necessary to develop technologies to protect the global environment and comply with the International Maritime Organization’s regulations. Although the emissions of nitrogen oxides, black carbon, and greenhouse gases can be reduced by using water-mixed fuel, problems need to be solved before utilizing these fuels for ships in service. In this study, the authors developed a water-mixed fuel supply system and installed it on ships. The effectiveness of this system was evaluated, and the following results were obtained: (1) The results of an analysis using the Stokes equation showed that making the particle size of water as small as possible makes the separation of the fuel and water difficult even if the fuel has a low viscosity and a low density. (2) No additives are required when mixing the fuel and water near the fuel injectors and injecting the water-mixed fuel into the engine before the fuel and water separate. (3) The system the authors developed is suitable for ships in operation as it is equipped with a control device that can switch the fuel types (conventional fuel or water-mixed fuel) in accordance with the operating conditions of the engine (starting, less than 40% load factor, 40% to 80%, 80% or more, blackout). (4) The authors confirmed through a demonstration experiment conducted after installing the "water mixed fuel supply system for ships in service" on the training ship "Tenyo Maru" of the National University of Fisheries that every necessary function of the system works properly, and that the emissions of NOx and BC are reduced by using the system.

International rules are currently being discussed regarding Maritime Autonomous Surface Ships (MASS), and the International Maritime Organization plans to bring the MASS code into force in 2028 as a mandatory regulation. When formulating MASS rules, the level of autonomous navigation is sometimes discussed by using the level of autonomous driving as a reference point. However, as the roles and responsibilities defined by the International Convention on Standards of Training, Certification and Watchkeeping for Seafarers (STCW) are quite different from those of autonomous driving, it is not appropriate to apply the standards for automated driving directly to MASS. Performance indicators for situational awareness system for MASS should vary depending on the ship type and operating mode, but there have not been enough discussions from this point of view. On the other hand, if a proposal separates the performance indicator conditions for situational awareness systems from the perspective of STCW, it will be useful to refer to the standards for automated driving from the perspective of Object and Event Detection and Response (OEDR). In this paper, the authors present regulatory and physical constraints that should be considered when deciding performance indicators for situational awareness systems for MASS, in addition to OEDR for MASS.