Studying acting forces exerted on a fixed or free-moving body and its movement in a flow field, Morison’ s equation is widely used. Since this equation includes quadratic drag force term, engineers prefer to simplify it by linearization. This paper shows the error effect that should be tolerated by use of the Fourier coefficients. Results are as follows: 1. In case, the velocity of the body is approximately expressed by first-order component with angular velocity ω, exerted non-linear drag force is expressed by sum of the Fourier coefficients with angular velocityω and its nth components, and it changes the non-linear equation of motion into the linear one. 2. The inertia force of Morison's equation is expressed as the first order component of the body motion with angular velocityω and acts as the principle driving force of the body. 3. The first order component of the drag force acts as the frictional force and the higher order components of that act as the driving forces. The latter's effect results in infinity at the point of resonance（ nω=ω0） and substantially decreases when it apart from the point. 4. In case of the studied cases here, the simple harmonic action of motion with ω/ω0 is possible to replicate the simple harmonic free-body motion under the estimated relative error of 10 percent by the linearized equation of motion.

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The ship roll motion has a significant impact on its safety. Therefore, it is imperative to estimate the parameters in the equation of the ship roll motion. However, as the effect of the nonlinearity of the ship roll motion becomes more prominent, estimating the parameters becomes more difficult. This research proposes an estimation method that helps overcome this problem. The authors estimated the parameters in the equation of motion using real-coded genetic algorithm, differential evolution （DE）, and particle swarm optimization（ PSO） from roll decay data. The results confirmed that it is possible to estimate the parameters with consistency and high accuracy.

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In this study, visualization of water flow in a fish farming tank was conducted using computational fluid dynamics（ CFD）. Here, a cylindrical tank with diameter of 0.5m, height of 0.5m, and surface height of 0.4m was employed. A L-shaped pipe （internal diameter: 0.016m） was used for inlet. The angle between direction of the inlet flow and x axis was defined as inlet flow direction θ, and set as 0 and 60° . To validate the CFD results, flow velocity of the tank was measured using PIV experiment and electromagnetic velocity meter, and CFD results showed good agreement with these experiments. Regarding the velocity distribution, vertical circulating flow was confirmed when θ ＝ 0° , and horizontal circulation was observed when θ ＝ 60° . As for the particle path line visualization, a half of particle sank in the bottom when θ ＝ 0° . In contrast, when θ ＝ 60° , all particles were floated around the surface. The air age was also visualized to evaluate the freshness of water. The air age of θ ＝ 0° was shorter than θ ＝ 60° . From these results, it was considered that θ ＝ 60° was suitable to prevent particles from sinking the bottom; however, θ ＝ 0° was better considered the freshness of water. Finally, we concluded that we can comprehend the flow characteristics of fish farming tank using CFD analysis.

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The large-mesh midwater trawl, bottom trawl with the knotless Dyneema netting, tuna longline, squid jigging machine and drift net were equipped on the research and training vessel Shinyo Maru Ⅳ of Tokyo University of Marine Science and Technology. In this paper, the composition and the performances of these fishing equipment were explained. In addition, the outline of the sampling trawl with canvas kites（ Larva Catcher） and autonomous multiple Codend Opening/Closing net（ COC-MOHT） equipped on Shinyo Maru Ⅳ were also introduced. By using these fishing equipment and sampling gears in combination with various hydroacoustic instruments, it is possible to conduct the effective fisheries resources surveys and many different types of fishing practices for sustainable fisheries in the future.

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We used UAV（Unmanned Aerial Vehicle） for the part of the investigation for the operation and maintenance at the fishing port facilities. The decrepit degree diagnosis at the facilities which used UAV can implement work correctly and safely. The settlement of the precast concrete armor unit and crack width on the concrete structure were measured using UAV. The extraordinary acceptance standard of the sinking of the precast concrete armor unit is defined as being 'the height which exceeds a block 1 layer'. The measurement accuracy which used UAV was judged enough. The threshold of the crack on the breakwater was 10 mm wide but could measure a crack well of the degree from the image which was photographed from the 20 m height.

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We studied the image analysis technique of aerial photographs by drone for the large-scale survey of spatial distribution of seaweed bed. The pixel of aerial photographs of coastal area of Bikuni and Furubira, Hokkaido, were grouped to 7 elements （three species of seaweed, sand bottom, sandy shore, rock bottom and rocky shore） by the supervised classification which used the field observation data of seaweed distribution and bottom materials as teachers. It was possible to estimate the seaweed distribution at the area shallower than 3 m in water depth. For estimation at the area deeper than 3 m in water depth, it is necessary to correct the color tone of aerial photographs.

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Recent rapid developments in UAV （unmanned aerial vehicle）, or drone, technology have made it easier than ever to take aerial photographs. In this study, we tested the efficacy of using a consumer drone as a tool for aerial photography studies of seagrass/seaweed vegetation, tidal flat topography mapping, and epibenthic fauna research. By using the consumer drone（ DJI Phantom 3 Professional） and an autonomous flight planning application （Pix4Dcapture） both seagrass/seaweed vegetation and tidal flat topography were photographed from a vertical position at a height of 100 m. Oblique drone aerial photographs were also taken at the tidal flat to map a wider area than that captured by the vertical imagery. The orthomosaic maps were created by using PhotoScan Sfm software on both the vertical and oblique photographs. Tidal flat epibenthic fauna was photographed from a height of 2 m and 10 m. In general the equipment system used in this study was suitable for the seagrass/seaweed vegetation and the tidal flat topography mapping, at least for objective areas that were relatively small （less than 1 km2）, but it was not suitable for the tidal flat epibenthic fauna study. Hence, improvements to the equipment system, e.g., higher resolution of images, zoom control, and a mechanism to estimate the image area would be valuable for future marine research applications.

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