Abstract
This paper introduces two applications of an ontology-based fuzzy system to marine system : a ship's steering control system and a collision avoidance system for ship. In the steering control system, an ontology-based fuzzy support agent consists of linguistic instruction ontology and a fuzzy support agent on which a ship's steering controller is based. In the second system, ontology is applied to identify a new case in a fuzzy CBR for ship collision avoidance support system.