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The aerodynamic properties of a canard-configuration WISES (Wing In Surface Effect Ship) flying over calm water and/or waves are studied from experimental and theoretical points of view. A canard-configuration WISES without PAR (Power Augmented Ram) was originally proposed by Kubo and Akimotol1) and it enables easy detachment from the waves utilizing the large trim angle of the ship induced by the front wing. On the other hand, it has been suspected for the WISES that the stability is one of the serious problems against the disturbance due to the gust or waves. However the aerodynamic properties of WISES for such disturbance have not been yet made clear in detail.In this paper, the model experiment is carried out in a towing tank imitating the WISES flying over calm water or waves, and the aerodynamic properties as well as the aerodynamic interaction effect of wings are investigated. Theoretical computations based on the BEM are also carried out and the results are compared with experiments. Through the study it is confirmed that the effect of the disturbance due to waves on the stability of WISES is scarcely to be considered, and also that the proposed theoretical method can predict aerodynamic properties of WISES in good accuracy.

An overage tanker “ERIKA” was wrecked in 1999 at rough sea off the coast of Brest in France. In consequence of the marine disaster, a large quantity of heavy oil spilled into the sea from the wrecked tanker and all over the coast of France was heavily polluted. In such a case, she should be towed immediately to a safe place to avoid a secondary calamity and minimize the marine pollution. We had a similar marine disaster in the case of Russian tanker “NAKHODKA” which was wrecked in 1997 at the Japan Sea. However, there has been no study of methods for stable towing or of maneuvering motion during the tow of wrecked tanker's fore part. Whenever we encountered such a marine disaster, we have been relying upon our experience and intuition in the towage of wrecked tanker.In this paper, unstable motion and course keeping ability of tow and towed ships at rough sea have been examined as a first step by using measured hydrodynamic forces acting on a tanker model of which fore part is wrecked.

After the marine disaster of “Nakhodka” in 1997 at the Japan Sea, we started in 1998 a five-year research project to develop an “Optimum Towing Support System” (OTSS). OTSS is a simulation system based on the data of external forces on the sea conditions and hydrodynamic forces acting on a hull, rudder and propeller. By OTSS we are able to obtain appropriate guidelines to avoid a secondary accident and to minimize marine pollution. In the simulation, the accurate prediction of hydrodynamic forces acting particularly on a hull would be most important. Using a ten-segmented model ship, we measured the distribution of lengthwise lateral force acting on a trimmed hull in order to investigate characteristics of the hydrodynamic forces. In this paper we report the result of the investigation and propose a theoretical prediction method based on the slender body theory for the hydrodynamic forces acting on a trimmed hull.

Ships disabled from marine disasters are generally towed by tug-boat. Issues concerning tug-towed ship systems are factors such as the length of the towing rope, the location of towing points and the conditions of the disabled ships. Up to the present time, these important factors have been entrusted to the knowledge and the experience of towing operators, and under their supervision, many accidents may occur because there isn't an effective method to tow disabled ships, towing operators are forced to use their own method, creating inconsistency and errors in methodology.In view of the development of the optimum towing method, we estimated the course stability of the tug-towed ship systems including various towing conditions. Furthermore, we examined the manoeuvring performance of the tug and the towed ship systems by using the numerical towing simulations considering wind and wave effects. The towing simulations systematically need to be done which take into account various towing conditions, and which will ultimately lead to guidelines for the safe towing operations.

In order to establish an experimental method to evaluate resistance and running attitudes of planing craft using a very small-scale model, the scale effects on hydrodynamic forces (drag, lift and trim moment) acting on two model ships, a 0.45m model and a 0.9m model, are experimentally investigated by fully captured towing tests. The results demonstrate that the lift and the moment acting on the smaller model are smaller than those on the larger model. The predicted results of running attitudes using the modified hydrodynamic forces obtained for the smaller model, in which the scale effects on the lift and the moment are taken in to account, are in fairly good agreement with the measured running attitudes of the larger model. The residual resistances predicted for the two models based on Froude's hypothesis using Blasius and Plandtl-Schlichting formulae in the prediction of frictional resistance are in fairly good agreement with each other.

This paper describes the application method of CFD (Computational Fluid Dynamics) to the ship manoeuvrability study on the initial stage of hull design. The present method is a method of estimating the linear derivatives of hydrodynamic forces acting on a hull, by using the correlation of CMT (Circular Motion Test) data and CFD computations on two conditions of oblique towing (β=6deg.) and circular motion (r'=rLpp/U=0.2) without drifting angle. Hydrodynamic forces acting on a hull in manoeuvring motion can be calculated by the combination of the linear derivatives obtained by the method mentioned above and the nonlinear ones estimated by CMT database.Authors applied the present method to the estimation of the hydrodynamic forces measured by CMT and the manoeuvring motion at Sea trial, and confirmed its validity.

Marine disasters which cause serious environmental pollution occur frequently. Disabled ships due to marine disasters must be removed from the sea route as soon as possible. Generally disabled ships are towed by tugboats. Concerning the towing problems with tugtowed ships systems, some factors such as the length of the towing ropes, the location of the towing point and the condition of the disabled ships, etc. should be considered. However, these important factors have been left to the knowledge and the experience of towing operators up to the present time. In order to tow disabled ships safely, we need to develop the optimum method of towing systems from the viewpoint of navigational safety.As the first stage of this research, we carried out captive model tests to measure the hydrodynamic forces acting on disabled ships. For the conditions of the disabled ships, we considered the ship which has immersed bow due to large trim angle.Finally, applying the results of the captive model tests, we calculated the manoeuvring motions of tug and towed ships, then estimated the course stability in towing conditions.

Impellers of controllable pitch side thrusters are operated under the condition of the pitch angle twisted largely from the design geometory (0° (zero) pitch angle). Therefore, it is very important to consider changes of the geometrical shapes with the twist of impeller blades and their performance characteristics in the design of controllable pitch side thrusters.In the present paper, two impellers of the forward skew type (A) and the backward skew type (B) are designed and the above-mentioned changes of the geometrical shapes with the twist of impeller blades are calculated and their open water characteristics are investigated theoretically and experimentally. The open water characteristics of these two impellers were calculated by using the propeller lifting surface theory. Then, open water tests were performed by using the impeller models with and without the duct in the towing tank.These results show that the camber of the blade section becomes minus largely with the twist of impeller blades and the open water characteristics with and without the duct deteriorate in case of the backward skew type (B) comparing with the forward skew type (A).

As the Phase II project of “Research & Development of Huge Floating Offshore Platform” carried out by the Mega-Float Technological Association, the proto-type of floating airport using the large floating platform (1000m in length, maximum 120m in breadth and 3m in depth) was installed at the Tokyo Bay in 1999. The model of floating airport consists of mainly 3 floating units with runway such as A, B and C. They were constructed at different shipping yards and connected together on the sea. A and C unit for runway have been constructed at shipping yard in the Ise Bay and B unit has been done in the Tokyo Bay.There are very few data concerning the full-scale measurement of such a flat structure with small depth. However, there is a possibility of the occurrence of various kinds of structures in the future for the development of the ocean space utilization. Transportation by towing has been one of the conventional way of techniques from old times, the limitation of experiment however exists because of its big size. The accumulation of full-scale data is quite important especially in the long distance towing of huge floating structure like Mega-Float unit in the outer ocean.Authors made a full-scale measurement using the floating unit (100m in length, 60m in breadth and 2m in depth) in the phase I project as well as the model experiment in the basin. The towing force and strain on the upper-deck etc. have been measured in both experiments. A floating unit constructed in the phase II project is the same size as the completed structure in the phase I project. The towing force and structural strength of the floating unit have been discussed in this paper.

When a large-sized ship, like a cargo ship or tanker, encountered a marine disaster and lost its ability to cruise, she must be towed immediately to a safe place to avoid a secondary calamity. In such a case, the course stability of tow and towed vessels would become a very important aspect from the viewpoint of safety for ship manoeuvring motion. An exact estimation of the hydrodynamic forces acting on tow and towed vessels is needed in order to predict accurately the course stability of tow and towed vessels by means of numerical simulation. However, any theoretical method estimating the hydrodynamic forces acting on towed vessels has not yet been established, particularly on the damaged vessels with a trim or heel angle. There are very few papers dealing with the hydrodynamic forces acting on capsized vessels with such a posture change as trim or heel angle. Therefore, an accurate estimation of the characteristics of hydrodynamic forces acting on capsized vessels with a large posture change is fundamentally necessary from the viewpoint of the safety in towing vessels.The hydrodynamic forces acting on a capsized model ship with a geometrical configuration and its characteristics have been investigated. The numerical simulation by using the measured hydrodynamic forces acting on the model ship has also been done in order to examine the manoeuvring motion and course stability of the towed capsized vessel.

A numerical simulation method of the motion of a rowing race boat is developed in order to evaluate the performance of oar size and rowing pattern. The driving force of blade is measured experimentally. The resistance of the boat is referred to the experimental result carried out in a towing tank. The motion of crew, which is most important in the simulation, is evaluated from the equation of a boat motion where the other terms are experimentally measured. These measured external forces are modeled by Fourier series or polynominal expressions. The equation of a boat motion is numerically solved by use of Runge-Kutta method.The Simulated boat velocity and force acting on blade are compared with the measured ones. The experiment was carried out in cooperation with the crew at Hiroshima University. Good agreement with the simulated results and measured ones shows that the present simulation method has merit to evaluate the rowing performance. Through the present simulation method, outboard length, blade area, stroke rage and phase of catch are evaluated.

In the old days, flying boats are widely used because wide sea surface could be utilized as run ways without maintenance.But today, utilization of flying boats is only for the rescue in sea disasters. Considering the small land space like Japan, and considering the situation of great efforts are devoted to the feasibility study on floating airport in Japan, further development of flying boats and supporting floating structures will be useful in the future.For the utilization of flying boats, improvement of seakeeping quality is required. So, we considered to develop the experimental guide system for model flying boat in waves.Fortunately we have long towing tank covered by an air tube like building and equipped with directional wave generator. Utilizing this towing tank as air tube, we developed new guiding system for carrying out landing and take off experiments of the total model of a flying boat.Here, we report about this system and example of recorded time history.

An efficient hull form design needs to incorporate some prediction methods which will be able to predict the influence of hull form modification on the ship performance. This paper presents a new and simple prediction method for the form factor which relates directly to the hull form. Six flow-field parameters which have influences on the form factor are proposed on the basis of the result of double-model flow calculation and 3-dimensional boundary layer calculation around the hull form. A regression equation to predict the form factor is made by using 7 parameters (6 flow-field parameters and displacement-length ratio) and model test results in a towing tank. In order to adopt the minimum Akaike Information Criterion (AIC) estimate method in a regression analysis, 7 parameters are selected among many variations.Predicted results for the form factor of full form ship at full load condition by the present regression equation show good agreement within 2% with tank test results. At ballast condition, predicted results show good agreement within 3%. Since flow-field parameters in the present regression equation act as intermediary between actual hull form and ship performance, a designer can easily obtain an information of how to modify the hull form according to the flow-field parameter in order to improve ship performance.

This paper describes the effects of drag reduction by microbubbles injection on very long ship models with flat bottom. The local skin friction and the total drag of 20 m and 40 m long slender ship models were measured in a towing tank with injecting microbubbles from porous plates on the flat bottom. Three cases of injecting position, bow, midship and both, were tested. Microbubbles were observed by CCD camera.The drag reductions by injecting microbubbles were obtained in all experimental cases, and the maximum reduction rate was about 14% in total drag, and about 60% in frictional drag on the part of flat bottom covered by microbubbles. It became clear that the reduction of local skin friction persists for about 40m downstream from the injection point, although the reduction rate decreases with distance. The relation between drag reduction rate and air flow rate, velocity, injection position, etc., are illustrated, and the possibility of energy saving by microbubbles injection is discussed.

We had already reported the developed results on the hybrid type on board measuring method of directional wave spectrum. This method utilize the measured ship motions including relative wave heights and also uses information by radar images on board. By this method, ocean wave characteristics can be observed automatically and quantitatively on board of a running ship. But more data is required for evaluating this method.This time we report about the compared results with that of newly developed directional wave buoy, and also with the experimental results carried out in our towing tank for the improvement of the accuracy of our method.

Flows around two full hull forms in oblique towing or steady turning motion have been computed using a CFD code NICE with the Baldwin-Lomax turbulence model. The computed flow in oblique towing agreed well with experiments in terms of the sway force distribution in the longitudinal direction, as well as the integrated sway force and yaw moment, and the computed hull surface pressure distribution explained well the difference in the sway force distribution on two hull forms. The modified Baldwin-Lomax model gave better results than the original model. Using the same code, flows in steady turning were also computed. Although the agreement with experiments were slightly less satisfactory than those in oblique towing, the modified turbulence model gave better results again.

It was pointed out that there are some weak points on the transverse stability and turning ability in research on the development of Super High Speed Container Ship, so, in the 1 st report, we introduced vertical active fin under the bottom of the ship and reported its basic effectiveness by numerical simulation and model experiment in directional spectrum waves which was generated in the towing tank of Yokohama National University.In this report we introduced optimum regulator for the coupled control of rudder and vertical fin to improve stability and manoeuvrability. In order to carry out numerical simulation of the ship motion in directional following waves, we use experimental data of yaw and roll for estimating wave exciting force. Model propeller used for self propelled experiment was contra-rotating propeller in this time.We also refer to the reason of problem pointed out in the 1 st report that rolling motion became large even in the case of fin was fixed comparing to without fin case.

Investigation of the free surface flow phenomena around the bow of floating models is extremely important to predict resistance components acting on floating bodies. Especially in the case of small scale model experiments, the free surface flow becomes more complicated, because the surface tension effect plays an important role in such cases. In order to make clear this effect, Maruo and Ikehata suggested the experimental technique which could weaken the surface tension effect by the method of spray of the surface activator upon the free surface in front of the model in the towing tank. In the previous work, one of the authors carried out the similar experimental study for 2-dimensional rectangular floating models in the circulating water channel. Since elimination of the surface activator remained and accumulated in the towing tank becomes difficult, the circulating water channel is more convenient for these experiments.In the present paper, the surface tension effect is discussed both experimentally and numerically. As experimental studies, 3-dimensional free surface flow around vertical circular cylinders floating in the circulating water channel can be visualized by means of the same experimental techniques as mentioned above, which can be regarded as typical examples of the free surface flow around floating models with the blunt bow. As numerical studies, simulations of the free surface flow with the surface tension effect are carried out by means of Rankine source method. Through this numerical study, not only simulation of the free surface phenomena but also computations of wave making resistance acting on the floating model with the surface tension effect are expected. Numerical examples are given for a floating vertical circular cylinder and a practical full hull form model.

A pitch, roll and depth controllable towed vehicle has been developed and named as “FLYING FISH”. The towed vehicle equips with an acoustic Doppler current profiler (ADCP), CO2 analyzer and sensors for measuring temperature, salinity, dissolved oxygen, PH, turbidity, chlorophyll.Flying Fish enables us to obtain the space continuous data of physical and chemical properties in the ocean upper mixed layer efficiently. Its maximum submerged depth is 200 m. The length is 3.84 m, breadth 2.26 m, height 1.4 m, weight in air 1400 kg and weight in water is about 0 kg.Numerical simulations were carried out in order to design mechanical parts of the control system and estimate the accuracy of motion control of Flying Fish. The simulations are based on the six degree freedom motion equations for underwater vehicle and lumped mass method for the towing cable. Field experiments were conducted to confirm the performance of Flying Fish and accuracy of numerical simulations. Results of field experiments and numerical simulations are compared.

In the previous paper the author and a co-author analyzed the principal mechanism of propulsion of a ship by “Ro” so as to make an automatic rowing machine of a 1/3 scale model of “Ro”, and carried out open tests and self-propulsion tests of “Ro” rowed by the automatic rowing machine in the towing tank of Yokohama National University. The results of such experiments made clear the hydrodynamic characteristics of “Ro”, such as possibility of high efficiency more than 70% by skillful rowing.In the present paper, the hydrodynamic characteristics of some sections of “Ro” measured in the wind tunnel are reported in CL and CD diagrams in the first stage and the numerical results calculated by the blade element theory of “Ro”, which has been developed originally by the author, using the characteristic diagrams of sections obtained by the wind tunnel experiments are reported in the second stage. Conclusively such calculated results are compared with the experimental results measured by the above-mentioned automatic rowing machine of “Ro”. Calculations are showing good tendency matching with experiments, but the quantitative agreement between the two is not necessarily good.

In this study, a trimaran with small outriggers at both sides is introduced in place of the catamaran. In a trimaran, the wave making interaction between the main hull and outriggers is expected to reduce the wave making resistance. The position of the small outriggers is optimized for optimum wave making resistance by means of a nonlinear programming technique. For fundamental studies of the problem, mathematical hull forms are employed as the main hull and outriggrers. For more practical studies, the high speed hull form of the slender displacement type proposed by Takarada et al is also introduced as the main hull, and similar studies to previous studies carried out. In both studies, model tests based on the optimization results are carried out to verify the hydrodynamical effect of outriggers, including towing tests, wave analyses, and measurements of trim and sinkage.

In the previous report dealing with oblique towing condition, the flow field around tow full ships with different aft hull-forms were investigated by numerical computation and experiments. Thereafter, additional studies of comparison between numerical computation and experiments were carried out for the same ships in steady turning condition. As in the previous investigation, detailed measurement of hydrodynamic pressure on the whole hull surface was executed, and then the longitudinal distribution of sectional lateral force was obtained by integrating the measured pressure along a contour of transverse section of ship's hull at various square stations. The measured pressure on the hull and longitudinal distribution of sectional lateral force were compared with numerical solutions of Navier-Stokes equation. The results are fully described in the present paper. The comparison denotes that agreement between numerical computation and experiments is fairly good. In particular, it should be noted that the difference in hydrodynamic lateral force and turning moment between two ships with different hull-forms can be successfully predicted by numerical computation, and the difference in maneuverability of two ships can be definitely correlated to the difference in lateral force distribution caused by the difference in hull-form by means of numerical computation and experiments as well.

This study is concentrated on the emergency towing arrangements onboard tanker referred in SOLAS Chapter V. The necessity of designing the towing gear at the aft of the tanker is surfaced to facilitate salvage and emergency towing to reduce risk of pollution. Followed up on these requirements, a simulation study centred on the dynamics of tanker-tug tow system is taken up. Three tankers with each of 20000dwt, 100000dwt, and 200000dwt were considered. Four tugs of different pulling capacity of 100kN, 200kN, 300kN and 400kN respectively were considered for towing operation. The important towing parameters like line length, tow speed are mainly decided based on the sea conditions. In a calm sea shorter line length is preferred in general.As the tanker is large in size compared to the tug, the excitations of the tug will be dominant. The wave exciting forces, drag of towed vessels and the line tensions govern the system dynamics. The line is assumed to be finite number of lumped masses and linear springs without mass. Harmonic motions, with the amplitudes and frequencies of oscillation correspond to various Beaufort scales were considered initially. The maximum tension due to the excitation of the towing vessl during its drive to move forward in irregular sea is determined in various cases of sea states. Deformation of line is caused by current and the movement of tug towing the tanker. The towline tensions for various Beaufort scale were determined for the prescribed harmonic motions. The analysis carried out helps compare the maximum line tension to the breaking strength of the line. Lumped Mass method is relied upon for the analysis of extreme towline tensions in random sea. Two conventional types of lines with different diameters were considered for the analysis. ISSC sea spectrum is considered for simulation in irregular sea. This study may help the towing operaters take more care so as to avoid accidents, material loss and loss of life.

Interim Standards for Ship Manoeuvrability was adopted at 18th IMO Assembly in Nov. 1993, and ship manoeuvrability becomes important from the viewpoint of human life safety and ocean environmental protection. In relation to these conditions, it is necessary to examine manoeuvring performance under the external force of waves.In this report, Fujii-Takahashi's semi-empirical equation which can calculate the added resistance in short wavelength region is extended to calculate the surge and sway forces and yaw monent caused by directional spectrum waves having short wavelength. By introducing these forces to M. M. G. model, simulation for zigzag test in short wavelength waves is carried out and compared with the free running model experiment in the towing tank of Yokohama National University, in which directional spectrum waves can be generated. Further, manoeuvrability indices are obtained by K-T analysis of simulation results using 1st order approximate equation.

An ROV developed for survey of the sea bottom over a wide area can be operated both as a towed and a self-propulsive vehicle. Called DELTA, the shape is similar to a delta wing airplane. The vehicle has two-propellers and weight shift apparatus as actuators. The control scheme for the towing mode is different from that for the self-propulsive mode. The direction of DELTA in the towing mode should coincide with that of the mother ship and only the depth is controlled by the trim weight. In the selfpropulsive mode the direction is controlled by the difference between the right and left thruster, and the depth is controlled by the pitch moment generated by the change of the thrust, the motion control is mainly done by the thrusters and the trim weight works to maintain static balance.The dynamic motions of DELTA were investigated theoretically and experimentally. The excellent performances of the vehicle were verified in this study.

The sailing performance of a 10.6 m-LOA ocean cruising yacht was measured by sea test and the results were compared with calculated values. The sea test was carried out to examine the steady sailing performance as well as the dynamic performance in waves.First, the steady sailing performance was estimated by calculating the velocity prediction program (VPP). The VPP calculates the equilibrium sailing state of the boat considering the balance of X, Y forces and K, N moments, respectively. The hydrodynamic force coefficients of hull were derived by the towing tank test using 1/4.275 scale model, and the aerodynamic force coefficients of sail were calculated using the results of a wind tunnel test.Then, the sailing state parameters of the full-scale were measured under various wind conditions. The measured items were wind velocity, wind direction, boat velocity, leeway angle, heel angle and rudder angle. These values were compared with the results of VPP. The both results were in good agreement and this indicates that the calculating method and fluid dynamic coefficients for VPP were adequate.Next, The motion of the boat was measured in conjunction with wave measurement using a throw-in type wave meter. A vertical gyro and accelerometers were used for measurement of rolling, pitching and heaving motion of the boat. These data were analyzed by means of spectral analysis, and compared with both model test and numerical calculations. The model test was performed in regular wave conditions at the towing tank. The analyzed results indicated the sail damping effect on the rolling motion quantitatively and the distinctive feature of motion for the sailing cruiser in waves.

An autopilot system is necessary in order to perform self-propulsion free running test. The autopilot based on the theory like a PID control is generally used in the past. However, a tendency to apply the fuzzy theory to the process control in various industrial fields becomes popular recently. It is because of the fact that the fuzzy control is most similar with the control by an expert, who controls process by his intuition and experience.In this report, fuzzy sets is applied to design the autopilot system to perform the free running model experiment in towing tank with radio controlled maneuvering system. The experiment is carried out in course-keeping and course-changing mode both in still water and directional spectrum waves with fuzzy and PD control. Here three scale factors are used, which have relations with heading angle, turning rate and rudder angle respectively. Further a computer simulation using the M. M. G. model is compared with the experimental results, and a performance index is investigated to appraise the autopilot system and to determine the optimum scale factors.

Although many experiments in irregular waves are carried out at towing tanks, these experiments have been generally carried out without the explanation how long the measuring of waves, ship motion and/or added resistance etc. are required. As the necessary record length effects on the size of towing tanks and model ships and also the power estimation of wave maker, it should be enough investigated. Since under the present situation as experimental accuracy has been discussed severely, this investigation is essential. The matters of experimental accuracy include the accuracy of facilities, measuring instruments and also the accuracy of the data obtained in limited time. The former problem has been studied in many ways but the later problem is still insufficient.We research this problem under some assumptions and apply that procedure to estimate an accuracy of the sea wave-correction for ship trial experimental results, which is performed in only one mile interval.

Focussing on the sea-going maneuverability of a 105-passenger hovercraft, the authors made investigations through series of model tests and computer simulations. The wind forces acting on a scale model, which represents superstructure and cushion form, were measured in a wind tunnel test. Oblique towing tests with self-lifting model were carried out for the hydrodynamic characteristics between cushion skirt and water plane. Regarding the characteristics of control surfaces, the force measurement tests with ducted propeller and rudder in wind tunnel were carried out. Based on these results of model tests, the authors developed a simulation program which employs proper mathematical models for each force components, namely cushion skirt, wind, propellers, rudders and thruster. The output of simulation showed fairly good agreement with the results of actual sea trial. Especially in the case of course keeping in beam wind, the reverse of check-helm direction around Froude number of 1.0 experienced in actual operations were confirmed through computer simulation. Lastly the results of extensive investigations on the sea-going maneuverability of the hovercraft are explained.

The motions in waves of high-speed catamarans with hydrofoils were studied through both nonlinear computer simulation and towing tank tests. The category of the ships of our interests is characterized by a set of fully submerged hydrofoils whose dynamic lift support the majority of the ship weight and a set of catamaran hulls whose displacement gives the support for the rest of the ship weight as well as the longitudinal and lateral stability. We describe the longitudinal motions in head and following waves in this first report. The time-domain non-linear computer simulation was based on the strip method for the forces and moments on the hulls. For the dynamic lift of the hydrofoils, the unsteady components stemming from the wave orbital velocity and the ship motions were considered in the quasi-steady way. The simulation results showed good agreements with the towing tank tests in general. Through the simulation runs and the tank tests for the ship Froude number of 1.0 and the wave length to ship length ratios from 1.0 to 4.0, the motions in following waves were found to be significantly larger than those in head waves. In the high following waves (Hw/L=0.06), the fore hydrofoil went out of the water in the downward slopes of the waves and the ship showed large non-linear motions. This kind of wild motions in following waves are described to be a natural tendency of the ships of the subject category. In order to suppress the large motions, we tried controlling the angle of attack of the hydrofoils by feeding the pitch angle and the pitch rate back. Both the simulation and the tank tests showed significant effects of the control. The amplitudes of the pitching motions were reduced to about 30% of those under no control both in head waves and in following waves. Finally, we studied the effects of the hydrofoil configuration with the simulation. Although the studied cases dis not show good improvements of the wild motions in following waves, the developed simulation program in a good tool for designing this kind of ships considering the motions in waves. In the second report, we intend to survey the motions of six degrees of freedom in the waves from various directions.

Experiments were carried out on the motions of very large offshore structures in directional spectrum waves. A flexible model was used in a conventional towing tank. Directional spectrum waves were applied in two set-ups, one where the model was moored parallel to the longitudinal wall of the tank and the other where the 22.5 degrees angle was given to the model with respect to mean incident wave direction. In both set-ups, two TLP type buoys were used for mooring. The following variables were measured on these two set-ups: motions, structural deformations, drift of buoys and tensions at the mooring tethers. The first report described experiments undertaken in directional spectrum waves, using a rigid model and two models having different flexibility, all of which had a single point mooring system with TLP type buoy. The second report described experiments undertaken in directional spectrum waves, using a rigid model in three different set-ups: on a single point mooring, on a two point mooring system in a head wave condition and on a two point mooring system, but in oblique wave condition. The results described in this report are compared with the results of the experiments reported in the previous reports, in terms of the variance in mooring condition and structural flexibility. It was found that the flexible model having a two point mooring system has a lesser level of slow drift oscillations compared to those observed in the flexible model with a two point mooring. Flexible structures have a bigger bending moment than rigid structures, especially in the long period region. The tension at the tethers of the buoys is not so much affected by the types of models used nor by the mooring system but mainly because of the motion of the buoys themselves.

In order to investigate the propulsive performances of “Ro” that is oriental sweep used to propel a Japanese traditional wooden ship, the authors analyze geometrically the motion of “Ro” when rowing it first of all and make clear the principle of propulsion by “Ro” in the present paper. According to the results of such analysis of the motion of “Ro”, manufacturing of the rowing machine of “Ro” is discussed.The open tests have been carried out by rowing the model “Ro” of 1/3 scale installed on the realized rowing machine. Furthermore the self-propulsion tests of a 4 metres long model ship propelled by “Ro” operated by the rowing machine set-up in the model ship have been performed in the towing tank. As the results of such experiments the hydrodynamic characteristics of “Ro” have been made clear experimentally for the first time. For example, the efficiency of “Ro” is possible to be more than 0.70 in a good case but less than 0.40 in a bad case. In the worst case any thrust cannot be gained. Accordingly the propulsive performances of “Ro” strongly depends on the skill of a rower.

For evaluating speed loss, self-propulsion test and free running test are carried out in directional spectrum waves with a full ship model in the towing tank of Yokohama National University. Such experiments will be the first time in the world. In the free running test, the model has six degrees of freedom as in real condition, and it is controlled to run straightly by using rudder controlling system, therefore the speed loss can be derived directly by considering the relative speed against carriage by using optical position sensor. It is found that the speed loss in short-crested waves is bigger than the speed loss in long-crested waves in short wave length. The experimental results of speed loss in directional spectrum waves are compared with the results of estimation methods which are originated from the added resistance obtained by experiment and theoretical calculation.

Estimation of directional frequency transfer functions of a running ship is important to estimate their behaviours in realistic short crested irregular waves (such waves are called as directional spectrum waves)Of course, there are some theoretical calculation methods for such directional response functions, but it seems that there are not so many experimental results confirming such theoretical ones. For that purpose, square basins are needed.On the other hand, recently the authors developed a wave maker which can generate directional spectrum waves in a long towing tank, and many experiments of running ships were conducted in such waves.In those experiments, obtained results are one dimensional motion spectra and direct comparison with theoretical ones is impossible. So we tried to make inverse estimation of directional transfer functions of a running ship using both one dimensional response spectrum measured in such waves and measured two dimensional directional wave spectrum.Estimated results by present method on heave, pitch, roll and vertical acceleration response functions are reported here, but this method will be also applicable to other situations like motions of a running ship in actual seas by measuring its motions and incoming directional waves.

This paper presents measurements of transverse forces acting on oscillating cylinders towed at constant speeds and the measurements were arranged so that the results can be used in the response analyses of cylinders. The responses of spring supported cylinders and simply supported flexible cylinders were calculated. The calculated responses of the cylinders showed good agreements with the experimental results and calculations by other researchers. The experiments were systematically conducted changing combination of four parameters, oscillation amplitude, towing speed, oscillation frequency and cylinder length. The large number of the experiment cases were conducted and transverse forces and phase differences between oscillation and lift forces are arranged as functions of the four parameters.When oscillating amplitude is small, the frequency of lift force is governed by Strouhal number. The oscillating frequency become to dominante frequency of transverse force as the oscillating amplitude is increased. When the oscillating frequency come close to the Strauhal frequency, the frequency of the lift force is controlled by the oscillating frequency and correlation length become very long. But the correlation length does not become long when the oscillating frequency is distant from the Strauhal frequency. The phase angle, which determine energy exchange between fluid and oscillating cylinder, is changed by 180 degrees as the oscillating frequency coincide with the Strouhal frequency.

A resistance test program of a high-speed semi-displacement craft was performed in sixteen towing tanks (including one circulating water channel) involving thirteen geosim models of 0.4 to 4 meters in length. This work forms a part of the tasks of the High-Speed Marine Vehicle Committee of the 19th ITTC. Analysing sixty three data sets, the following conclusions are obtained. The scale effect is not found in the wave resistance, and on the other hand, it appears in trim and spray calculation. The form factor of frictional resistance can be determined even at high Froude numbers, by the method suggested by Hughes as a function of Froude number. The application of turbulence stimulator is necessary in resistance tests even for larger models at high-speed. Appropriate turbulence stimulator for semi-displacement hull forms should be developed. The characteristics of semi-displacement hull forms in the range of medium Froude numbers (Fn

Hydrodynamic interaction between hull and foils is one of the important aspects for performance prediction of high speed craft lifted up partially by sumberged foils. In order to investigate such interaction, measurements were made of the lift of foils, trim and elevation of a craft model in the towing tank. It was found that the elevation of the model is smaller than that estimated from the measured lift of the foils. This suggests that there exists lift loss due to additional sinkage force acting on the hull as a result of hydrodynamic interaction. Then, numerical calculation was carried out to clarify such hydrodynamic interaction. As expected, it was found that negative pressure is induced by the foil on the bottom of the hull just above the foil, and results in the sinkage force as observed in experiments.

An experimental technique is developed for a vehicle moving steadily in the vicinity of the ground. The towing tank with a steadily advancing carriage is used and the unfavorable effects of the boundary layer on the wall of wind tunnel is fully removed. Experiments with a box-shaped model and a car model revealed some interesting features of lift, drag and side force at various clearance from the ground. Lift force is more sensitive to the boundary layer and it should not be measured in a wind tunnel. The flow with vortices near the bottom surface of the body gives one of the most important effects on the forces.

In the previous report, we derived extensible catenary equations and discussed the fundamental characteristics of catenary. We also descrived the ways to solve the equations under various boundary conditions.In this paper, we introduce a program package based on the extensible catenary theory. Next, a simplified dynamic analysis method is shown. The accuracy of calculation by the program package is verified by comparing with the results of tank tests or calculations with other programs. Finally, initial design method of underwater line structures using the program package is shown and typical line structures such as mooring lines, towing lines and flexible marine risers are designed easily applying this method.

Estimation of directional frequency transfer functions of floating offshore structures is important to estimate their behaviours in realistic short crested irregular waves (such waves are called as directional spectrum waves) Of course, there are some theoretical calculation methods for such directional response functions, but it seems that there are not so many experimental results confirming such theoretical ones. For that purpose, square basins are needed.On the other hand, recently the authors developed a wave maker which can generate directional spectrum waves in a long towing tank, and many experiments of offshore structures are conducted in such waves.So we tried to make inverse estimation of directional transfer functions of a floating offshore structure using both one dimensional response spectrum measumred in such waves, and measured two dimensional directional wave spectrum.Estimated results by present method on heave, pitch, and roll response functions are reported here, but this method will be applicable to other situations like motions of floating structures in actual seas by measuring its motions and incoming waves.

For a preliminaly design of a depth and roll controllable towed vehicle for ocean measurements, three dimensional numerical simulation techniques for calculating motions of a towed vehicle and towing cable are developed. The hydrodynamic coefficients of the towed vehicle and towing cable used in calculations are obtained from experiments in a circulating water tank. The towed vehicle is developed to house a CTD (Conductivity, water temperature and depth) sensor and an acoustic doppler current profiler. The CTD sensor needs the accurate depth control and the current profiler demands a high level of stability in pitch and roll of the towed vehicle. In the design of the towing system and towed vehicle, the special attensions are paid to meet these requirements. The angles of main wings and horizontal tails are under feedback control in order to maintain operation depth and roll stability. The results of numerical simulations confirm the good performance of the system.

Course stability of towed large barges has recently become very important because of the increase of the cargo transportation by "Barge System" in harbor, channel and coastal sea which improves work efficiency and decreases man's work in the collection and delivery of cargoes. Most of existing barges have, in general, large B/d and small L/B ratio that may cause a poor stability on course. Therefore, these barges, which are often installed with a pair of skegs to improve course quality, are towed not to cause yawing motion by the bridle or two lines towing for the safe and quick towing operation. Strandhagen et al., Terao, Inoue, and Bindel reported the worthy theoretical works on this essential problem. These papers offer much knowledge on stability criteion of towed ship, but towing tests to confirm their theories have not been reported as far as we know. In this paper, authors discuss the following several points to clarify the validity of the above mentioned theories. The first point is the theoretical and experimental study on the quantitative difference in derivatives due to skeg section shape. Applying wing theory to skeg, the authors modified the coefficients of Strandhagen's equation of motion, and calculated the additional term of derivative, L sub beta prime and L sub tau prime (corresponding to lift coefficient in wing theory), using the results of forced yawing test (P.M.M.). These values were compared with the theoretical calculation by three dimensional wing theory and obtained an agreement in good order. The next subject is to know the effect of skeg shapes and tow line length on course stability in towing condition. The Routh-Hurwitz's criterion was used to select the best skeg section shape and its attachment angle. In the last step, heading angle or turning rate was simulated by "Random Search Method". The simulated time histories showed a good agreement with the measured phenomena at towing test. As a result of this work, it is verified that the theory by Strandhagen (including our modified equation) gives a good estimation of course stability of towed ship for practical usage.

When travelling in heavy following sea a ship is accelerated on the front slope of a wave and her velocity may become nearly the same as the wave celerity. This phenomenon is called surf-riding and may cause broaching-to, which is very dangerous situation for small craft. The present paper relates to the surf-riding.First, the resistance variation in wave, an important factor of the surf-riding, was treated with both theoretically and experimentally. The usefulness of theory on the Froude-Krylov hypothesis was examined by the proposed theoretical method on the boundary value problem and the captive model experiments.Second, the motion involving the surf-riding phenomenon was realized and recorded in a towing tank. The results show a fairly good agreement with a digital simulation based upon the theory and captive model experiments. Finally the author proposed a diagram indicating the possibility of surf-riding for a given wave and ship on the basis of the present studies. This simulation study proved useful to predict surf-riding of a given ship.

DRAKE (Depth and Roll Adjustable Kite for measuring Energy flux of the Kuroshio) is a towed vehicle developed to carry an acoustic doppler current profiler and CTD sensor (Conductibility- temperature- and depth-sensor). The current profiler demands a high level of stability in pitch, roll and heave of the towed vehicle, so that the main wings and the tail wings are controlled automatically to maintain the submerged depth and roll stability. In a previous report the authors discussed a simulation technique for estimating motions of the towed vehicle and cable. In this paper the structure of the towed vehicle DRAKE and the performance confirmed by experiments on the observation line across the Kuroshio are described,. In the experiments, four kinds of tests are carried out. The first one is the towing test for investigating the static characteristics of DRAKE, such as the main wing angle, trim angle and cable tension versus a command depth. The second one is the steady towing test for the study of the stability of motions of DRAKE when the mother ship is advancing in irregular waves. The third one is the depth change test for the study of the stability of DRAKE in transient motions. The fourth one is the turning test holding a constant depth controlled by automatically produced command signal. These experiments indicated that the performance obtained in experiments are in good agreement with those of theoretical estimations obtained for the previous report.

For analysis of intact and damage stability of semisubmersible type rig, it is important to estimate the magnitude of steady environmental forces such as wind and current forces and moments. Since it is difficult to get the theoretical calculations of these forces and the test techniques need special apparatus, only few researches have been done in these fields.In this paper an attempt to clarify the contribution of various elements of semisubmersible to total force and moment using 1/100 and 1/150 scale test models is made, and the validity of wind tunnel tests in a water channel with wind tunnel facility is discussed.Although the difficulty to simulate the boundary layer on water surface exists, the wind velocity profile required by rules of classification societies was done with success and 6 component forces and moments were measured in this environmental condition.In order to obtain the total force and overturning moment the towing tank test of under water part was carried out, and lift effect on lower hull was observed.Finally the comparison of experimental results and the corresponding calculations obtained from ABS and DnV rules was done and the accuracy of these calculation methods is discussed.

For further improvements of the ship power prediction method by model tests, there were many rooms to obtain the accuracy meeting the present designers' demands. In the IHI towing tank, since its establishment in 1966, steady achievements have been done to satisfy their demands. This paper presents almost all of the measures of improvements conducted and the results obtained in IHI, content of which extends from the facility and test practice to the model-ship correlation. Among them, first it is insisted that the reduction of influence of Reynolds number and disturbances such as the residual current in the tank upon the test results is quite effective for increasing accuracy. Second a theoretical estimation method of propeller open-water characteristics is proposed from the view point of correcting the influence of Reynolds number on its performance. Finally taking the influence of interference between Reynolds number of hull and the propeller loading into account, a new method of ship-model correlation for the effective wake is given. As a result, the average errors of model test results decrease less than 1% and the reliability of predicted ship power gets to more than 97%.

The propeller characteristics, surface pressure distributions and oil film streaks on blades were obtained in the towing tank with a large sized model of which diameter is 0.95 m. Some new facts on the scale effect of propeller characteristics are revealed in the test results. Measured values of the propeller characteristics and surface pressure distributions agree well with those which are calculated by means of the lifting surface theory with the correction for viscous effect. The idea of the so-called equivalent profile method is examined by integrating measured sectional load distributions on blades.

This paper presents results of free-running model tests concerning ship maneuvering motions due to assist tugboats and simulation calculations based on the mathematical model proposed in this paper. The free-running model tests were carried out by the use of wind fans on the model deck which simulate the tug forces. The mathematical model for such maneuvering motions was developed on the basis of captive model tests which consist of the static drift test with whole range of drift angle and the yaw rotating test with several combinations of towing speed and yaw rotating rate. The simulation calculations were compared with the free-running test results for typical maneuvers with tugboats. Through the present study, the following conclusions are obtained.(1) The free-running model tests clarify the basic characteristics of ship maneuvering motions due to tug forces and indicate that such maneuvering motions largely depend on ship forward speed.(2) The simulation calculations show satisfactory agreement with the free-running test results. This indicates that the mathematical model proposed in the present paper is available for describing a so-called low speed maneuvering motion dealt in this study.

In this Second Report, results are presented and discussed of a study of rudder optimisation from the resistance and propulsion points of view. A synthetic method of approach is used in contrast to the analytic method of the First Report. On the basis of Kumano's finding (in 1960-61) that the rudder occupies a near optimum position as a stern bulb aimed at stern wave cancellation, the Authors investigate, by towing tests and wave analysis, several unconventional rudder configurations. Also, possible improvement of self-propulsion factors is investigated in propulsion tests. Up to 7% improvement in propulsive performance is obtained; this is mainly attributable to stern wave cancellation. Viscous scale effects upon the main hull stern wave system are studied in the towed and self-propelled conditions with tow geosim models (L = 2.5 m and 10 m). Order from BSRA as No. 51,914.

The deck wetness and the impulsive water pressures induced by shipping water on the deck are serious problems of a ship operating in rough seas. For these problems, model experiments were conducted in extreme head seas in a towing tank.In this study, relations between the probability of deck wetness and the following matters are discussed :1. significant wave height2. mean wave period3. ship speed4. significant values of ship motions5. relative bow motion.Relations between the peak values of impulsive pressures, relative bow motion and impact velocity of shipping water are also discussed.Moreover, the prediction of the probability of deck wetness was made, applying the empirical expression of the dynamic swell-up proposed by R. Tasaki, and compared with the experimental results. Finally some recorded patterns of impulsive water pressures are discussed in detail.