In this study, a free-running model with an outboard motor is development and the results of free-running model tests are compared with maneuvering motion simulations using data tables of fluid forces measured in full captive model tests to verify the validity of the proposed measurement range and number of measurement conditions. It is found that differences in draft between free-running test and captive model tests can cause the fluid forces acting on the hull to become relatively larger than the thrust, resulting in an underestimation of simulated ship speed. However, by correcting for displacement effects the simulation results more closely matched the experimental data. It is also found that minor variations in drift angle significantly influence discrepancies between free-running test and simulation results, including the turning radius, acceleration behavior, and heading changes after steering. Furthermore, reducing the number of test conditions for measuring thrust and rudder forces led to discrepancies between the simulated and experimentally observed ship speed and drift angle under very low-speed forward or reverse-propeller conditions.

　The aim of this study is to develop a simplified mathematical model for low-speed manoeuvring motion, which involves significant lateral and rotational motion compared to forward motion, making low-speed manoeuvring critical. To simulate the manoeuvring, it is necessary to model the hydrodynamic forces on a hull, the propeller forces and the rudder forces. Hydrodynamic forces on a hull are highly non-linear and complex, requiring detailed modelling. In addition, various propeller and rudder operations during port manoeuvres require the models to be extended to four quadrants. This study employs the following methods to create a simplified model: a polynomial model using cross-flow drag terms to simplify the non-linear hydrodynamic forces, extending the propeller forces to four quadrants by modifying the thrust coefficient in the first quadrant, and extending the rudder forces based on the slip ratio. Finally, the validity of the model is validated by comparison with free running test results.

　This paper discusses the numerical characteristics of time-domain dynamic analysis of floating structures considering instantaneous phase difference between the floating body and waves. It was confirmed analytically that the nonlinearity induced by considering the instantaneous position of the floating structure causes a slowly-varying drift motion similar to wave drift force even when the analysis considers only first-order diffraction forces. However, its frequency characteristics would seem to be essentially different from that of the wave drift force obtained by potential theory. Subsequently, this paper investigates the numerical model that removes the low frequency motion caused from the nonlinearity of the instantaneous position of the floating structure by using a low pass filter. This model would be effective for time-domain analysis of wave frequency and low frequency motions simultaneously. Finally, these models are compared with the commercial code OrcaFlex, and it is confirmed that the numerical results obtained by the presented method and the numerical results by OrcaFlex are equivalent.

　Stiffeners are essential members of ship hull structures composed of stiffened panels, and their scantling formulae against lateral pressure are important for designing safe and rational hull structures. In typical scantling formulae of classification societies, the reduction in the fully plastic moment due to the shear stress is not directly considered in the current design.

　In this study, we first derived a simple formulation of the shear stress effect with the simultaneous action of an axial stress under a given stiffener configuration and showed that the reduction of the fully plastic moment can be calculated using three non-dimensional parameters. Based on the formulation, we discussed how each parameter contributes to the fully plastic moment as well as the condition under which the shear stress can be effectively neglected. Subsequently, we used finite element analysis (FEA) based on the residual deflection criterion, thereby verifying the validity of the theoretical proposals. Finally, we proposed a scantling formula, rationally taking account of the shear stress effect.

　In recent years, the increasing size of container ships has led to more frequent occurrences of elastic vibrations such as whipping and springing, which superimpose on wave responses and reduce fatigue life. Therefore, the importance of fatigue assessment considering elastic vibration is increasing. In this study, fatigue assessment using several spectral methods was conducted on stress measurement data from two large container ships, and the effectiveness of each method was examined. The spectral methods employed included the narrow-band method, the Jiao method for bimodal processes, and the DK method for wide-band processes. Their results were compared with those from the rainflow counting method. The results showed that the narrow-band method and the Jiao method tended to evaluate fatigue damage on the conservative side, while the DK method tended to yield less conservative (riskier) evaluations. The narrow-band method did not accurately reflect actual phenomena, as it deviates from actual rainflow counting. On the other hand, the DK method was found to be a good model that captures the real physical behavior.

　Therefore, a correction factor was introduced to the probability density function of the DK method to extend the distribution toward the higher stress range. By using the ratio of zeroth moment of the wave component and zeroth moment of the elastic vibration component, conditions likely to cause significant whipping were identified, and a formula for determining the correction factor based on this value was proposed. This approach enabled more accurate estimation of fatigue damage.

In this study, we assessed the impact of discharged water from a 1 MW-class Ocean Thermal Energy Conversion (OTEC) plant on marine ecosystems (corals) in Kume Island, Okinawa. Based on field survey data, including detailed topographic data, numerical simulations were conducted using a physical model (MEC model) and an ecosystem model (NPZD model). Through the simulation with different discharge water qualities and discharge locations, the extent of the discharge water’s impact was compared. The results suggested that while the cooling effect of the discharge water could expand the area suitable for coral habitats, the increase in nutrient concentrations might have a negative impact on corals. It was also found that this negative effect could be reduced by discharging the water separately after secondary use. Furthermore, the diffusion range of the discharge water was influenced not only by the depth of discharge, but also by the surrounding topography. Sensitivity analyses of tidal currents and diffusion coefficients confirmed that their impact on the spread of discharged water was limited.

　After a massive earthquake, there is a high likelihood of a severe shortage of land transportation capacity for a certain period. This shortage could significantly hinder the maintenance of social order and the early recovery and reconstruction efforts. As a mitigation measure, preemptive consideration of utilizing maritime transportation is highly valuable. This study assumes the Nankai Trough earthquake as a case of a massive earthquake and examines the transportation of disaster-related cargo. The target term is the pull-type transportation period, the recovery period and the reconstruction period. Given the severe post-disaster transportation constraints, a web-based reservation system is assumed for operating ferries and RORO ships as tramper vessels. To optimize vessel allocation under these conditions, a planning method was developed by integrating a genetic algorithm with a transportation simulator. Linkage Learning Genetic Algorithm (LLGA), which organizes chromosomes in a circular structure, was introduced. Various modifications were also added to better suit maritime transport. As a result, a feasible and practically implementable tramper allocation method was obtained.

　Correlations between hull form factors and behaviors of hydrodynamic force acting on lateral motion ships were investigated, and response to water depth change at shallow water area was clarified. The shallow water effects to maneuverability were well known by the ship operators, however, the accidents caused by that factor will not disappear. Recent increase of ship size is significant, and the needs for attention on shallow water effects has been serious.

　Present paper describes the results of investigation on the dependencies of shallow water effect to hull form factor by means of series model tests made by numerical simulations. Hull form factors were represented by the principal dimensions ratio and fineness coefficients. The investigation was made even at the extreme shallow water area; H/d< 1.20, and the behaviors of lateral force was examined. The behaviors of lateral force were evaluated by utilizing the multiple regression analysis that enables us to know the sensitivities for each parameters qualitatively.

　Obtained results show that the main factors for determination of behavior characteristics could be L/d and B/d for aspect ratio, and C_B especially C_P × C_M would be dominant factors for fineness of hull forms. Present conclusions have been much with the investigated results of previous work that clarified the correlation with drastic flow structure change caused by the blockage effects at ship bottom.

　This paper presents a mathematical framework for defining and managing the transformation between engineering bill of materials (E-BOM) and manufacturing bill of materials (M-BOM) specifically within shipbuilding. Unlike traditional manufacturing sectors, shipbuilding exhibits substantial differences in data structures between E-BOM and M-BOM due to unique design and production processes. To address this complexity, we introduce a mathematical formulation based on mapping functions: a partition mapping (φ) and a hierarchy reconstruction mapping (Ψ). The partition mapping systematically defines how each component in an E-BOM is divided or consolidated in the corresponding M-BOM. The reconstruction mapping translates parent-child relationships from E-BOM structures into production-oriented M-BOM configurations. Through the application of these mappings, we provide a unified, flexible theoretical framework for clearly expressing transformations between diverse BOM structures. The validity and applicability of the proposed formulation were verified using a simplified ship hull model, demonstrating consistent and practical representation of various E-BOM granularities into an M-BOM. Our results confirm that this mathematical framework effectively captures and streamlines the transformation process, providing a solid foundation for optimized data management and future system integration within shipbuilding PLM systems.

In this study, a numerical method was developed to predict the adhesion of water spray and the amount of ice on a ship's superstructure, facilitating a quantitative evaluation of hull icing during ship operation in cold regions. Using OpenFOAM, fluid dynamics simulations were performed to analyze the behavior and adhesion patterns of water spray and calculate ice accretion rates based on the structural characteristics of each component. The results indicated that wind speed and inflow angle have a considerable effect on the distribution of water spray and ice accretion. For example, under an inflow angle of 30° and a wind speed of 20 m/s, a noticeable accumulation of ice was observed on the port-side crane. These findings demonstrate the critical role of detailed numerical analyses in understanding ice accretion patterns and provide a foundation for designing effective countermeasures against hull icing in cold regions.

　In 2023, the Society of Naval Architects and Ocean Engineers awarded the Antarctic research vessel, icebreaker SOYA a ship heritage award. SOYA is renowned for its contribution to the establishment of Syowa Station and the foundation of the Japanese Antarctic Research Expedition. However, its ice navigability from a naval architecture perspective is not well understood. In this paper, The author estimates the ice navigability of SOYA based on current technology, verifying the accuracy of these estimates using contemporary data, such as the SOYA's navigation records. Continuous icebreaking capability is estimated that SOYA can break ice up to 70 cm thick at 3 knots, which is less than half the thickness that the current Antarctic research vessel SHIRASE can break at 3 knots (150 cm). According to the latest ice class rules by the International Association of Classification Societies, hull plating is generally PC5 to PC7 in strength, but in some hull areas it is below PC7. This indicates that the structural strength is much lower than that of SHIRASE (equivalent to PC2). Although no serious navigational accident occurred, significant damage was observed at the joints between the cast steel components and the main hull in the bow and stern areas, as well as in the bulge sections.

　There has been a trend toward decarbonization and carbon neutrality and the development of energy production technologies that do not generate carbon dioxide is being promoted. One such production technology is green hydrogen production. Specifically，possible measures include supplying the electricity used for hydrogen production from renewable energy sources such as offshore wind power，and filtering seawater to obtain the pure water necessary for hydrogen production in order to avoid competition with domestic water supplies.

　This study examined an offshore hydrogen production plant that uses electricity generated by offshore wind power to filter seawater using the RO method to obtain pure water，and then produces hydrogen by electrolysis.

　Furthermore，a challenge with RO is membrane fouling caused by raw water quality，which hinders maintaining flow rates and extending membrane lifespan. A solution requires pretreatment to improve raw water quality.

　This study clarified the applicability of a filtration method using a spring filter and diatomaceous earth as a filtration aid (hereafter referred to as the SP/DE method) as seawater pretreatment for RO filtration. The technology for seawater filtration to obtain pure water suitable for hydrogen production was investigated by combining the SP/DE method with high-pressure/low-pressure RO methods. This technological investigation involved designing a filtration system and conducting filtration experiments using the system. Both lake water and seawater were used as feedwater.