The significance of onboard maritime English communication has led to the needs of innovation in language teaching strategies and instructional design. Mostly Indonesian seafarers faced serious problems to join ocean-going vessels due to maritime English proficiency. This study attempted to capture the essential demands of Indonesian seafarers joining an ocean-going vessel for their communication techniques using maritime English, with the goal of having a greater impact on the development of instructional design for Indonesian curriculum. Semi-structured interviews were conducted with 14 Indonesian seafarers assigned to different ocean-going vessels of various sorts, sizes, and foreign flags. Semi-structured interview was performed with three maritime English lecturers from different maritime education institutions in Indonesia. This study employed qualitative research by combining theory and using NVivo 12 Plus software as the coding method to understand and analyse data. The first finding indicated that operational maritime communication strategies such as in routine and special-message communication like safety, distress and urgency communications were required to create communication patterns. Second finding denoted challenges faced by Indonesian seafarers in having maritime communication such as unclear meaning resulted from improper word choices, different accents and pronunciations of the different socio-cultural of radio officers they spoke to, and due to sentence construction. The third finding revealed the focus of materials for each language skill for communication onboard. The whole findings implied that maritime-ESP teaching should reform with solemn education packages and instructional design heading toward the communicative competence to prepare cadets with the required needs of their future seafaring job.