In marine engineering programmes, simulators are the key infrastructures to support learning outcomes comply with the designated minimum competencies within the International Convention on Standards of Training, Certification and Watchkeeping for Seafarers (STCW). The practical training concept in full mission engine room simulators (FM-ERSs) includes the key aspects such as competency selection, scenario description, task identification, observation procedure, data gathering, initial condition preparation, briefing, conducting exercises, assessment and debriefing. At this insight, the learning outcomes are highly depending upon assessment system aligning with the knowledge, understanding and proficiency to consistently prove whether the competencies are achieved or not. To achieve a comprehensive competency analysis, this paper offers a methodological approach based on Technique for Order Preference by Similarity to Ideal Solution (TOPSIS) method. The proposed assessment system is demonstrated with different scenarios (i.e. test, start and prepare D/G-II for standby) applied to 16 marine engineering students in a team context. The demonstration study yields the individual performance and team achievements through the given tasks. Consequently, the suggested assessment system contributes to marine engineering competencies in term of enhancing learning outcomes, instructor capability, course and infrastructure development. Furthermore, the assessment approach can be extended to practical studies in other disciplines.