In this study, we quantitatively evaluated the applicability of an integrated operational framework combining a heavy-class remotely operated vehicle (ROV) with manned diving systems, including the surface-supplied diving system (SSDS) and self-contained underwater breathing apparatus (SCUBA), under predicted tidal conditions at the Sewol ferry disaster site. A 31-day tidal-current dataset was analyzed to assess operational durations, phase-based deployment strategies, and personnel requirements. The results showed that integrated ROV–diver operations substantially expanded operational availability compared with standalone diving, increasing deployable time by 26.4% for SSDS and 54.7% for SCUBA. During neap tides, SSDS enabled long-duration deployment, whereas SCUBA maintained operational efficiency through rapid preparation and high mobility. Under spring tide conditions, the limited diving window made the heavy-class ROV the primary platform for search, inspection, and hazard-removal tasks. In this phase-based framework, sensor-derived information from the ROV supports underwater environmental assessment, target detection, hazard identification, and decision-making on the transition between ROV operations and diver deployment. Personnel analysis further showed that actual requirements were substantially lower than arithmetic estimates and represented only 6.6–10.1% of the Sewol response workforce, indicating the feasibility of coordinated ROV–diver missions. These findings provide a quantitative basis for developing standardized procedures and integrated command structures for large-scale underwater search and rescue operations.