Development of the MWU-Based Combined Standard Time Model for Work-Procedure Reconstruction and Man-Hour Estimation in Shipbuilding Outfitting Work

A Standard Time Unit (STU), defined as standard work time per unit workload, supports production planning and man-hour estimation in shipbuilding. This study developed a Combined Standard Time Model (CSTM) that reconstructs outfitting work standards by recombining reusable work actions. Process analysis structured outfitting work into five Basic Standard Units (BSUs), 16 Minimum Work Units (MWUs), and 54 Factors (six quantity-type and 48 condition-type). The same fixed-order MWU candidate set was applied to all ten evaluated materials, while material-specific procedures were represented through MWU selection and Factor settings. Base MWU time units and Factor values were derived from existing STU records supplemented by expert judgment. The absolute percentage errors for the ten materials ranged from 0.178% to 2.514%, and all were below 3%, with a mean of 1.281% and a standard deviation of 0.839%. The paired t-test yielded t = 1.617 (p = 0.140), the Pearson correlation was r = 0.999, and Bland–Altman analysis showed a mean difference of 0.305 min with estimated 95% limits of agreement from −0.863 to 1.473 min. Applied without re-adjustment to 13 further materials not used in parameter setting, the model gave a mean absolute percentage error of 3.387% against the existing unit-rate values. Thus, the CSTM maintained numerical consistency with the existing STUs while enabling a standardized labor-time framework and component-level traceability across the evaluated materials. Because model parameterization and evaluation used the same STU records, the results demonstrate internal reconstruction rather than independent predictive superiority; validation against measured work times remains necessary.