In this study, the hull form and appendage of a 6.5k DWT tanker was improved to reduce greenhouse gas emission under real operation conditions. The hull shape of the existing 6.5k DWT tankers has been designed in terms of performance in ideal conditions of calm sea. Conversely, the performance of a ship in operation should take into account the added resistance due to wind at the actual sea. After optimizing the energy-efficient hull form the regular wave analysis numerically analyzed the additional resistance of the resulting hull form at 11 wavelength ratios. Then, the additional resistance at regular waves was integrated for the wavelength to obtain additional resistance in the irregular waves. Combined with the probability of occurrence of the sea state, it was possible to calculate the daily fuel oil consumption(DFOC) for the real operation condition of the tanker. The entire process of deformation and evaluation of the hull form was performed form the viewpoint of CFD simulation on a free-surface in the presence of regular waves. After that, a series of model tests were performed to confirm that the optimal hull form was improved not only in terms of the performance in waves but also in the calm sea.
As a reinforcement of greenhouse gas (GHG) emission regulations, the International Maritime Organization (IMO) has legislated GHG emission regulations for existing ships. These are the Energy Efficiency eXisting ship Index (EEXI) and the Carbon Intensity Index (CII), which have been in effect since 2023. It is necessary to manage not only the performance in the initial design phase but also the performance in the operation phase. As a result, ship performance under operating conditions has become a major concern for both designers and operator. More specifically, the improvement of ship performance in real operation condition is mainly involved in the reduction of additional resistance by waves RAW, that is, the difference between the total resistance in the waves (equation) and the calm water resistance RT.
