Design for maintainability is a systematic and proactive approach that integrates operational and maintenance considerations into the early stages of designing complex products such as marine vessels. Studies indicate that applying design for maintainability principles has a decisive impact on both the economic efficiency and operational readiness of fleets. However, traditional ship design remains primarily focused on criteria such as speed, seakeeping, and stability, while neglecting the critical role of maintainability in maritime missions. This conceptual paper, based on a systematic synthesis of literature, standards, and ship design experience, presents an integrated framework of key principles. Through thematic analysis, five fundamental principles were identified: accessibility, standardisation, modularity, reliability, and condition monitoring. Potential implementation barriers, including system complexity, budgetary constraints, siloed design practices, and human factors, were discussed alongside technology driven solutions such as artificial intelligence, the Internet of Things, 3D printing, and digital twins. The interdependencies among the principles were also examined. This framework provides strategic guidance for designers and maintenance decision makers, though empirical validation remains a direction for future research.