To meet the ship carbon intensity index (CII) due to the strengthened regulations of the International Maritime Organization (IMO), the introduction of rotor sail technology, an eco-friendly technology, has been highlighted. Since the first rotor sail-equipped ship was developed in 1924, various research and development efforts have been made on the same, leading to its commercializations by some overseas companies. In the existing cylindrical rotors, the aerodynamic efficiency decreases after a certain period, as the rotor speed ratio (spin ratio) increases. To solve this problem, in 2019, a new conical rotor, which had already been studied, was used and the conditions were reset to study the optimal aerodynamic efficiency conditions. In this study, considered 12 conditions, wherein different values were assigned to the spin ratio and ratio of the rotor top diameter (d) to end plate diameter (De) for both cylindrical and conical rotor. The results showed that only in the conical rotor, the aerodynamic efficiency remained constant or slightly increased as the rotor spin ratio increased. This could be clearly confirmed under a specific condition, in where the d/De ratio was four.