This study aims to thoroughly understand and analyze the Cargo Oil Pump Turbine (COPT) system on tanker ships through thermodynamic and numerical simulations. The goal is to find the best pump capacities to match different cargo discharge rates and properties. A parametric study has been performed on the COPT system by building a thermodynamic model including exergy analysis, and a numerical centrifugal pump model. The design of experiment applications which are factorial design and response surface methodology (RSM) have determined the the optimal pump capacity The findings demonstrate that the risky flow rate region for the cavitation, if the density and vapour pressure are close to limits, is between 3050-3500 m3/h. The factorial design finds the best operating flow rate for the high capacity demands at 4025 m3/h where the efficiencies are the highest, and the RSM calculates the optimum capacity for the low demands at 1460.34 m3/h.