Selective Waiting-Time Reduction in Indonesian Fiberglass Shipbuilding: A Digital Lean Simulation Framework

Background: Uniform waiting-time reduction in fiberglass shipbuilding may compromise essential technical processes, including curing, inspection, and safety checks. Therefore, waiting time must be classified according to its technical function and potential for reduction. Objective: This study develops a simulation-based Digital Lean Manufacturing framework for selectively reducing waiting time in Indonesian engineer-to-order fiberglass shipbuilding. Methods: A single-case study was conducted at PT Teluk Naga Bahari, Indonesia, covering eleven production stages. Value Stream Mapping (VSM) was integrated with deterministic discrete-event simulation using AnyLogic. Waiting time was classified into avoidable waiting (AW), reducible technical waiting (RTW), and fixed technical waiting (FTW). Five scenarios (S0–S4) were evaluated using waiting time, lead time, and Process Cycle Efficiency (PCE). Results: The baseline recorded a cycle time of 157 days, waiting time of 67 days, lead time of 224 days, and PCE of 70.09%. Waiting time comprised 15 days of AW (22.39%), 24 days of RTW (35.82%), and 28 days of FTW (41.79%). Scenario S4 achieved the greatest simulated improvement, reducing waiting time to 44 days and lead time to 189 days while increasing PCE to 76.72%. Lead time decreased by 15.63%, while FTW was preserved. Conclusion: Selective waiting-time classification enables targeted efficiency improvements while preserving essential technical constraints. However, simulated reductions in RTW require material and process validation before implementation. The framework provides a transferable decision-making approach for fiberglass shipyards.