Under the linearized free surface condition, wave resistance of a silmple form is calculated analytically. In this computation a double-body potential is used as the zero-order approximation as it is done conventionally. It is then shown that the wave resistance differs in general according to the kind of surface singularity distributions even if the so called line integral is taken into account. The author explains the reason for the indeterminacy of the wave resistance. It comes from the usage of singularity distributions, expressed in terms of the double-body potential, in the potential-expression which was originally derived from Green's formula under the linearized free surface condition. When using Green's formula, it should be noticed that the double-body potential does not satisfy the usual linearized free surface condition but the rigid-wall condition. By taking this fact into account, the indeterminacy of wave resistance is eliminated. It is then concluded that the wave resistance is uniquely determined and independent of the kind of singularity distributions.

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In the previous papers, the propulsive performance and its scale effect of a full ship, which consists of an actual hull form and an infinitely bladed propeller, were calculated theoretically by utilizing the measured hull resistance and the wake data for a geosim model. In this paper, it is investigated that the effect of a streamline rudder on the propulsive performance of the full ship. The rudder is considered to be a rectangular wing with thickness. The load distribution on the rudder is represented by vortex systems and rudder thickness is expressed by doublet distribution. The rudder plane is divided into a lot of small rectangles, on which the load distribution is assumed to be constant in the spanwise direction of each rectangle. Then the mutual interactions of the hull, the propeller and the rudder are elucidated. Following conclusions may be drawn from the calculated results: (i) In case of a ship with a single screw and a single rudder, a rudder has a considerable effect on the propulsive performance. (ii) Thinner rudder is more favorable to the propulsive performance. (iii) When the area of a rudder plane is constant, a rudder of higher aspect ratio is recommended. (iv) The screw propeller which has larger effective pitch ratio attains higher propulsive efficiency.

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Measurements of the velocity distributions in the turbulent boundary layer on the after body of a ship model of C_b=0.57, which is expressed by means of conformal mapping, are carried out by use of five-hole spherical probe in the towing tank. The ship model is 8.0m long and Reynolds number is 1.166×10^7. The boundary layer calculations for the ship model are performed by three different methods using the momentum integral equation. The measured velocity profiles and integral parameters are compared with the calculated results. Agreement of the measured and the calculated results is fairly good with respect to the main flow characteristics. However, further researches are necessary even for a finer ship form such as the one used in the present study in order to improve the accuracy of the prediction for the flow near separation and the reversed cross flow. A calculation method, which employs Coles' wall-wake law as the velocity profile family and the entrainment equation for three-dimensional flow as the auxiliary equation, seems to be better than other two method used in the present study.

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A method is presented for calculating the three-dimensional boundary layers from laminar flow to turbulent flow by applying the Cebeci and Smith's method, where the empirical model of eddy viscosity is used as the Reynols stress. At first, the fundamental equations for the three-dimensional flow and for the flow on the symmetry plane are presented, and the boundary and initial conditions are given analytically. Next the procedure for numerical computation is discussed. Finally, the results calculated for a flat plate and a ship hull form are compared with measured data. As a conclusion, it may be said that the results calculated by this method agree very well with the experimental data in spite of very simple model.

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The authors present the correction method of long-term wave frequency based on the observed data, by using the correlations between the observed and measured wave data. They have investigated how the accuracy of the long-term prediction results of the ship response is affected with the observation error of wave data. It was concluded that, (a) The long-term prediction results of hydrodynamic pressure on the water line and bilge based on observed wave frequency are somewhat smaller than those based on the corrected wave frequency. There is no significant difference between the long-term prediction results of hydrodynamic pressure on the keel centre line based on the observed wave frequency and those based on the corrected wave frequency. (b) There is no significant difference between the long-term prediction results of vertical wave shearing force based on the observed wave frequency and those based on the corrected wave frequency. And the similar results are obtained for the vertical wave bending moment. (c) The long-term prediction method based on the observed wave frequency would be acculate enough for practicl purpose.

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As the continuation of the previous papers (Transactions of the West-Japan Society of Naval Architects, No.47 (1974), No.49 (1975), No.52 (1976) etc.), the author develops a method to evaluate hydrodynamic characteristics of a ducted propeller and a rudder taking account of their mutual interactions. Applying this method, he calculates numerically the forces and the moments acting on the ducted propeller and the rudder where the helm angles of the rudder are given.

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Meteorological tide effects on ship's speed as a periodic variation of 10.916 minutes, whose wave height is 34.68cm and whose wave slope is about 1.264×10^<-4>rad for fundamental stationary wave and 0.898×10^<-5>rad for progressive wave. Consequently, horizontal compoment of ship's weight remains more or less to her own speed is several percents. The period of prevail of this sort of long wave is estimated about several hundred years, and the most typical period is found as 1020.99999 years with other famous period of Meton's 19.00023 years and Saros 18.03001 years. The most prominet altitude of front is about 62.45% of tropopause of 19461m altitude above Ocean, which sometimes seems to disturbe Decca method.

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The flow field by the arbitrary forced motion of flap of wave maker was investigated. By a simple two-dimensional linearized theory, the velocity potential in the fluid domain are represented by distributions of the time dependent Green function on the flap. Therefore, numerical calculation for obtaining transitional wave making phenomena and experiments measuring wave height time history caused by the various flap motion were performed. The agreement between the results of experiments and numerical calculations are fairly good.

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In reference to the estimation method of drifting force acting on a floating body in waves, Tasai pointed out a problem about the disagreement between theoretical and experimental results. In Tasai's paper, however, the theoretical results by Maruo in the two-dimensional case were discussed by quoting the experimental ones by Suyehiro and Tasai obtained for the three-dimensional bodies. To look into the pertinent disagreement, therefore, it will he necessary to make detailed investigations into difference in the two- and the three-dimensional problems. In the present paper, the author carried out an investigation to ascertain the validity of the evaluation of drifting force based on Maruo's theory, confining the problem to two-dimensional cases. The two-dimensional experiments were conducted for two models; a semi-immersed circular cylinder and a catamaran hull composed of semi-immersed circular cylinders. Comparisons were made of the measured results with the theoretical predictions based on exact treatment of the linear potential theory. Calculated results were all in fairly good agreement with the measured ones. From these results, it is inferred that the cause of the disagreement pointed out by Tasai may be due to the effect of the three-dimensional motion of fluid. In order to clarify the problem, therefore, studies on the three-dimensional problems such as the one by Kudo will be called for.

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To investigate the manoeuvring characteristics of ship, we have well known the available theories, in the use of slender body theory or low aspect ratio lifting surface theory, for predicting the hydrodynamic force and moment acting on ship hull. But we can't almost see the work which dealt with the hydrodynamic ones acting on ship hull in trimmed condition, notwithstanding the manoeuvring characteristics of ship are greatly affected by her load condition. In this paper, it was made clear the relations between hydrodynamic derivatives on ship manoeuvring and ship's load condition by the use of slender body theory. With these numerical results, we may coclude that the hydrodynamic derivatives on ship manoeuvring are greatly affected by trim quantity, however there are no influence of change of draft at a fixed trimmed condition. And the numerical results, we may represent the following approximate formulae for predicting the hydrodynamic derivatives on ship manoeuvring in trimmed condition. [numerical formula][numerical formula][numerical formula][numerical formula] where d_m and τ represent the mean draft and trim quantity respectively, [numerical formula].

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