To obtain a full understanding of icebreaker propulsive performance, full-scale and model experiments in ice were carried out for an icebreaker PLH "SOYA". A full-scale icetrial was made in February 1997 in the Sea of Okhotsk. A speed trial was carried out with a stopping and a bollard-pull test. Shaft thrust and torque were measured using strain gauges mounted to a propeller shaft. Thrust at zero CPP blade angle was used as its zero-level. Repeatability of the thrust measurement was examined using a bollard-pull test data. It was shown the scatter of thrust data was within 20kN. Model resistance tests in ice were carried out at the ice model basin of Ship Research Institute. The regression model for the model resistance in ice was presented. The predicted full-scale thrust was compared with the measured data and a fairly good agreement was obtained.

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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 vessel is supposed to be towed efficiently with a liglater drafl(about 0.8m) at a maximum speed of about 10 knots (Fn=0.42). A great deal of effort has been made on the course stability for the towed-vessel, what seems to be lacking, however, is an active control of the course stability. This paper is intended as an investigation of the control method for a course stability of the towed-vessel. We conducted the model experiments to investigate the performance of our control method. Also we performed tlte simulation studies to investigate the course stability for our control method. Model experiments were conducted using a 1717><th> scale( 1 .0m) model. The experiments results were used in the control system design and to validate our simulation studies. The results of our experiments and simulation studies are described and discussed.

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We can not watch the structural vibration by the naked eye, because the order of vibrational amplitude is much smaller than the structural dimensions and the vibrational velocity is very fast.Then it is necessary to develop the software with which we can watch the structural vibration mode.In addition, if it is possible to watch the mode by using unmeasured points, such software becomes very convenient tool for us.Autltors developed such software which is including a new function for the animation of vibration mode. This function is that, the frequency response of unmeasured points are calculated with the rotation vector of a measured point. The rotation vector is estimated by using some experimental data of measured points. In this paper, the validity of this method is verified by the application examples of a beam, a plate and a model ship.

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For model experiments of a ship model with forward velocity, it is desirable that directional irregular waves are stationary in space. By making use of wave measurement and numerical calculation,this paper examines homogeneousness of directional irregular waves generated by a signal calculated with a conventional double-summation method in a model basin where side-wall reflections are positively utilised. The measured results indicate that variance of water surface is not stationary in space. In theory, such non-homogeneousness can be caused by the double-summation method for the wave-making signal or side-wall reflections. The numerical calculation of a summation of many cosine waves realised similar non-homogeneousness that observed in the wave measurement. This numerical result indicates that the non-homogeneousness is mainly due to the double-summation method for the wave-maldng signal but not mainly due to the side-wall reflections.

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A linear numerical method to simulate time varying internal pressure of fluid cargo induced by ship motion is presented. The objective of this study is to develop a part of total system by which the safety of the ship structure may be evaluated. Two dimensional problems are solved by finite element techniques while the boundary element method is applied to the problem of three dimensional tank.The effect of small free surface in the air pipe of the full loaded tank is investigated. Special attention is paid to the case where the tank is fully loaded but has no free surface. In this case it is found that the hydrodynamic pressure fluctuation due to heave or sway motion is zero at the gravity center of internal fluid in the tank.

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In order to know the safety margin of an aged FRP boat, we have been performing a series of experimental test program. The program includes tension, compression, bending, fatigue, and impact tests on specimens cut out from the bottom and the side plates of a typical FRP boat used over 17 years.Among the tests, the static ones; those are tension, compression, and bending tests, were completed.In this paper, the test results are compared with the calculations based on Strip Method and a long time prediction. After that the safety margin is discussed.

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This paper is presenting a reasonable numerical calculation method of seismic wave propagation in two-layered medium. The hydrodynamic pressure caused by seaquake is analyzed numerically and its dynamic effects on the floating structure is investigated.In orcler to obtain the solution of the seismic wave field in two-layered medium, the eigen functions on the open boundary and the boundary integral equation are introduced. Furthermore, in order to understand the properties of the effect of the seaquakes on the two-dimensional floating structuare, some typical calculations by using Boundary Integral Equation Method are carried out. Then the effect of seaquake forces acting on the two-dimensional floating structure is investigated from a view point of time structure safty.

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The added mass coefficients of ships are very important to analyze hydrodynamic forces and also simulate mauteuvering motion of ships. Motora carried out the experiments to measure the added masses m_<x,m>y and etc. usixng great numbers of ship forms with conventioal types except block type ships (C_<B = 1.0). The added mass charts based on the experiments and arranged by Motora is well-known owixng to its practicability for the ship design.In our previous investigation on hydrodynamic forces of some block type ships, which resemble very large floating structures and their elements in recent years, our examination of estimating the added masses of the ships (C>B = 1.0) by Motora's charts confirnted that the accuracy was not enough by means of extrapolating the curves on the chart because the block type ship is particular form and is outside of the scope. This paper presents a quick chart arranged with a new parameter to estimate the added masses m_<x,m>y of floating structures with block types, derived from carring out the constant accelerating test and potential calculation to obtain tne hydrodynamic forces of the structures (C<sub>B = 1.0).

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Ships reduce their performance in actual seas caused by natural forces,aging deterioration and biogical fouling. The speed loss,whitch is one of the important index of their performance,is already the performance of the fuel oil consumption and the main engine power with the probabilistic method. Thereafter performance evaluation of ships is attempted. From a prababilistic point of view,the desirable performance is proposed.

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