Comparing with experimental results, the rudder resistance calculated by NICE-code is over-estimated in self propulsion condition particularly. This causes bad influence upon the accuracy of calculated self propulsion factors, for example 1-t etc. In this study, the arrangement of grid near the leading edge is studied to calculate the rudder resistance accurately. First, the viscous flow field around a two-dimensional Joukowski aerofoil is computed with H-type grid. As suggested by the potential theory, fine grids are needed near the leading edge to follow numerically the very steep pressure gradient there. Secondly, the fine grids are applied to compute the viscous flow field around the rudder behind ship. As the result, estimated rudder resistance with finer grid, shows better agreement with experimental results.

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For energy conservation reasons, viscous drag reduction is of great interest for full scale ships. A lot of references report skin friction or total drag reduction when bubbles are injected into the boundary layer on the hull. As experiments on a full scale ship are almost impossible and in order to understand how experimental results can be applied to full scale ships, the influence of the hull size on the trajectory of bubbles injected on the bottom of geosim ship hulls was investigated. After a description of the experimental work, the numerical scheme used to compute the bubble trajectories is explained. Then the experimental and numerical results are presented and discussed. The influence of the scale effect and of the injection location is shown.

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In this paper, a verification of cavity model for the analysis of partially cavitating for two dimensional hydrofoil by using a potential surface panel method is presented. A type of cavitation that is applied for calculation is sheet cavitation. Using the Green's theorem, the normal dipoles and sources distributions on surfaces of the foil and cavity may constitute the perturbation velocity potential. The source singularity plays an important role in the cavity surface and is determined by an iterative process. We verified a various cavity models in the transition zone and it is concluded that a closed type models approvable to physical phenomenon. The effect of hydrofoil thickness on the cavity shape is investigated. That is the bigger hydrofoil thickness generates the shorter cavity volume. As for a closed type model, some quantities, for example, cavity shapes, surface pressure distribution and other hydrodynamical characteristics have been calculated. The calculated results are in good agreements with other numerical calculations.

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Heave and pitch motions of a ship model running in following and quartering seas with very low encounter frequency were measured in a seakeeping and manoeuvring basin and well compared with some theoretical predictions. As a result, it was concluded that, when the ship meets danger for capsizing in following and quartering seas, heave and pitch motions can be approximated by simply tracing their static equilibria. Further, up to the steepness 1/10 they can be regarded as linear with respect of wave steepness.

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The high-speed-towed fish preserve is a new type vessel about 15.6m long with a fish preserve capacity of 200m^3. The ship will be able to be towed efficiently with a lighter draft(about0.8m). Since the maximum speed of the ship is over 8 to 10 knots (Fn≧0.33). But it depend on a tug boat's power. The course stability of the ship will affected by the ship's speed, the trims and towline's positions. It is important to clear the relation between ship's speed and course stability. In this paper, we present the course stability characteristics in high-speed range. Also we discussed the effect of the trims and towline's positions. We conducted circular tank experiment tests using l/25th<sup>scale(0.624m) modeles and simulation studies of the course stability. The results of our experiments and simulation studies are described and discussed below.

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Floating breakwater system to reduce high waves has been used in recent years because it has advantages of sea water circulation and lower cost especially in deep sca. Now, plans are proposed to construct very large offshore structures of floating type such as a floating airport. Therefore, the effectiveness and capabilities of wave protection of floating breakwater in oceans are investigated in this paper. A new multiple floating breakwater, which consists of several single floating breakwaters, is proposed in this paper. The separated region method is modified to calculate resulting wave reflection and transmission coefficients of the multiple floating breakwater. A mathematical model based on the separated region method is obtained to evaluate the performance. Numerical results based on the proposed method are compared with several previous numerical and analytical results. Good agreement is found between the present results and others. the transmission coefficients of the multiple floating breakwater are searched thoroughly, and interesting properties of the multiple floating breakwater have been obtained. These properties are very important in designing the multiple floating breakwater in occan engineering.

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The load fluctuation acting on a propeller blade in the condition that the prpeller blade exposes partially over the water surface had been investigated experimentally. The experiment has made clear the interesting phenomenon that the negative torque acts on the blade at the moment when it passes through the water surface from water to air. And the former report proposed the hypothesis that the negative torque is due to the force caused by the change of the added mass of the blade along the rotational direction. In order to confirm the above hypothesis, the forces acting on a horizontal cylinder passing through the water surface are experimentally investigated in this report. The experimental results are compared with the calculated results. The calculation is carried out according to the theory that the test cylinder is acted by a force system of 5 component, that is, the inertial force, the drag, the buoyancy and the force caused by the change of added mass. The last component acts in the same direction with the cylinder motion from water to air. It is called here a negative force. The calculated results are in approximate agreement with experimental results. The existence of the negative force component is confirmd.

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