As a lift-based energy-saving device, sails are increasingly deployed on modern ships to reduce fuel consumption and carbon dioxide emissions. This study investigates the performance of a NACA airfoil sail installed on a bulk carrier and identifies suitable areas for sail placement. Computational Fluid Dynamics (CFD) simulations were employed to analyze the flow fields around both the sail and the ship. The simulation results show good agreement with Experimental Fluid Dynamics (EFD) data. A comparison between the onboard sail and a freestanding sail reveals that the hull-induced airflow disturbance alters the lift characteristics of the sail. Furthermore, by analyzing the wind speed distribution above the deck under different wind directions, areas with higher wind speeds were identified, determining a "high-performance zone" more suitable for sail layout. This study provides valuable guidance for developing sail arrangement strategies in practical engineering applications.