Using STPA for hazard identification and comparison of hybrid power and propulsion systems at an early design stage

The decarbonization of the shipping industry is a hot topic and new emission reduction goals, regulations, and initiatives all over the world underline its importance. These goals apply to the ocean going fleet, as well as coastal shipping and fisheries. Both academia and industry, work on the development and testing of new technologies to reach emission reduction targets. Besides technical feasibility and economic viability, the safety of new power and propulsion systems must be considered in this process. In this paper, the Systems Theoretic Process Analysis (STPA) method is used for hazard identification and comparison of two alternative hybrid power and propulsion systems for a small-scall fishing vessel. The assessment method allows for identifying focus areas for hazard reduction in a systematic manner. System safety requirements derived from the assessment can be considered when designing power and propulsion systems. Based on the results, a discussion of the method and the usefulness of the results is given. The main findings are that the assessment provides valuable insights into the hazards introduced by new power and propulsion systems in a qualitative manner. For a quantification of the risk, further work and an extension of the assessment are needed. The STPA results show that especially the control of the power sources and their interactions internally and externally with the consumer side are crucial. Therefore, special attention should be given to the design of the automated control system, feedback system, and user interaction with the system.