<jats:title>Abstract</jats:title> <jats:p>Uncertainty in a complex socio-technical system, such as ship, is given. Yet, surprisingly, most of the ship operations were done without any significant problem. In this case, the ship officer as the operator plays an important role in maintaining ship safety. Human performance is unpredictable and varies on the condition. However, variation in human performance is more likely to produce acceptable outcomes than adverse outcomes. Therefore, this study aimed to determine how human variability performance in specific officers onboard contributes to successful ship operation. Evaluation of officer variability performance for establishing safety in everyday ship operation has been done using Functional Resonance Analysis Method (FRAM) in this study. FRAM is Safety-II based tool that provides concepts and models for safety analysis that use terms called function to describe system activities. An essential feature of FRAM is the mean that is necessary to explain the activity of a system in which the functions are mutually dependent. System activities are modeled in terms of how the system works to ensure that it performs systematically. Key functions of officer activities onboard are generated through observation in training ship Fukae-maru owned by Kobe University. As a result, FRAM could define how officer variability performance contributes to system propagation and create a safe ship operation.</jats:p>