The use of fossil fuels on commercial ships significantly contributes to the increase of carbon dioxide emission, and adaptation of renewable energy can help control that emission efficiently. Historically, the extraction of wind energy is found to be the best renewable energy solution for commercial ships; and recently, with renewed interest in this area, various wind energy extraction devices are proposed in the literature. This study investigates the effectiveness of one such technology, wing-sail, on a tanker ship. The NACA 4412 series is adopted to design the sail in this regard, and a fowler flap is added to aid the sail in low wind speed. ANSYS Fluent is used to carry out this CFD simulation-based study. The effects of onboard wing-sails under various apparent wind angles, wind speeds, and wing-sail orientations have been examined. The impact of wing-sail on the stability of the ship is also analyzed. It is concluded that the ship can save fuel and reduce carbon dioxide emissions by 1.8% to 2.4% while using the wing-sail with the aid of a fowler flap. Also, this combination of wing-sail with the fowler flap is found to be the best in providing extra thrust for commercial ships without significantly sacrificing its stability.