The present paper is aimed to clarify the effect of flap on the unsteady lift and moment of the hydrofoil in still water and regular waves.
A method for obtaining the additive bound vortex distribution due to flap is shown, from which the lift and hinge moment can be easily calculated. And, as a concrete example, the coefficient of the effeck of the free water surface on the lift and hinge moment is shown.
By superposing linearly the four basic types of the unsteady condition of hydrofoil, the lift is obtained and discussed for the several conditions of practical interests.

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Detailed discussions are given to the problem of minimizing the theoretical wave resistance with special reference to the existence of the solution of the calculus of variation.
Rigorous solutions are given to the integral equations which express the condition of the minimum wave resistance of strut-like ship forms with infinite draft under various side conditions.
The solution determines the optimnm shape of water line.
Optimum curves of sectional area of slender ships are calculated in a similar way. Resistance experiments are carried out with respect to the optimum forms, showing a good agreement with the theoretical result.

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Three kinds of 'Waveless Form theory are at present schemed at the ship model basin of University of Tokyo. The first one is the theory that waveless hull may be given by using bulb to the simplified main hull, while the second one is the theory that the least wave making condition will be realized by the complicate wave interference due to complicate hull geometry. The last one is the combined idea of the above-saying two theories.
As the result of the basic research concerning to the theory of the first kind, the hull form with the bulb of the smallest size and of the least projection outward from the main hull has been strongly desired for practical application from the structural and the operative point of view.
After discussing the possibility of these desires, experiments are made to assure using mathematical hull forms (named U-series models), of which source distribution is uniform for draftwise direction. However these U-series models have more or less curved bottoms, so further experiments are needed to verify that the waveless form could be realized even with a conventional flat bottom hull. On the other hand the wavemaking effect of the lower part near the midship is believed to be comparatively small. Therefore the authors adopted UF-series models to examine for flat bottom hulls, cutting off artificially the bottom of U-series models.
Further approximate approach is required for such a shallow draft ship as a coaster or a ferry boat. As an example, the SEIKAN-ferry boat is served for further approximation, only keeping the load waterline of fore-half body exactly the same as given by the stream-line calculation of planned source distribution.

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As a continuation of a study on form effects on viscous resistance of ships, this paper deals with the pressure resistance of a two dimensional streamlined body. The effects of the boundary layer on pressure distribution over the surface of the body are explained, for the region of small curvature of streamline, as the sum of the displacement and the pressure thickness effects. It is shown that, at the tail end of the body with finite angle, special consideration must be paid to the action of viscous stress. It is suggested that the pressure of actual flow at the tail end may be approximated by the pressure of ideal flow at the edge of the boundary layer and the pressure resistance coefficient based on wetted surface area can be estimated by the formula
1/4α²δ (L) /L,
where α is the full angle of the tail end, L the length, and δ (L) the boundary layer thickness at the tail. Finally an approximate methed for calculating a form factor due to pressure resistance is presented.

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It has become a established theory that the ship motions in irregular waves are estimated from the transfer functions of ship motions and the Neumann spectra. But, according to this method we can only know the information of ship motions in irregular waves to be defined by spectra. Therefore it has a weak point, because we can not directly compare the actual ship performances in a certain wave height or a certain wind wave scale with the estimated qualities from it.
This paper makes a proposal to exclude that fault of the conventional method. In the first place, the author investigated the relation between wind velocity and mean wave height in average sea states. Next, he tried on to substitute the assumed partially developed Neumann wave spectra for the average relations between wind velocity and mean wave heights. Hereupon, the significant wave heights of the assumed spectra are equal to the average wave height of actual average sea states. Moreover, he calculated the ship motions in that assumed spectra by the ordinary method. Then, it is considered that the calculated values by this method are equivalent the ship motions in average sea states.
The obtained results show that the estimated values by the use of the fully developed Neumann spectra develop a tendency to over estimate, and that estimations give the inverse qualities at comparative calculations between various ship forms is possible.
Then he predicts the critical ranges of the navigation in the averge sea state arising from severe ship motions or seasickness. Moreover, the cumulative occurance frequency of ship motions are predicted.
The used ship forms for calculations are four kinds of destroyers. In this report, pitching and bow vertical accelerations in head seas are calculated.

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The forced oscillation method is a very suitable method to find out the characteristics of oscillations, and several types of forced oscillation generater have been developed. However, most of them are designed for the model towed by or running under the tank carriage, which can be used as a platform to endue the force. For the investigation of the rolling characteristics, it is desirable to use a completely free running model, for example in a square shaped basin, because the experiments by the model can be carried out without any wall effects and any complicated techniques. For the completely free running model, very few oscillation generater can be used except the weight shifting type. At first, we also used this type, however, the oscillater produces the movement of the centre of gravity together with the inclining moment, that makes the scope of analysis of the oscillation characteristics limited.
Recently, we have completed a new type forced oscillation generater to use on the free running model test. As is shown in Fig. 2, the new oscillater is composed of two gyroscopes, which have their axis vertical and are turning in opposite direction. The angular velocity is given to the gyroscope around the y axis oscillatory, then the forced oscillatory moment is produced around the x axis as the precession moment. As the direction of rotation and the given angular velocity of each gyroscope is reverse each other, only the forced moment on the same direction around the lateral axis x is produced, while the reaction moments are cancelled each other. Moreover, even if the model perform the pitching motion, the rolling moment is not produced. The superior character of this method to Gerritsma's and Golovato, s methods is that the oscillation can produce the pure sinusoidal forced moment by giving the sinusoidal angular velocity to the gyroscopes. The characteristics of oscillation can be obtained by measuring and analysing the motion of the model.
Here, as the first attempt, we have carried out the forced rolling experiments by the free running model to obtain the rolling characteristics, especially when she is advancing with forward speed. The results are summarized as follows ;
1. The rolling characteristics of ship while she is advancing are essentially the same with that while she is drifting. Even in rolling, it is sufficient to consider the effect of the nonlinearity of damping term in the equation of motion, and the non-linearity of restoring term can be neglected, so far as the amplitude is modelate.
2. Comparing the forced rolling tests in still water with the rolling tests in regular beam waves, it is concluded that the amount of forced moment of the wave affecting on the ship with advance speed is almost the same as that affecting on the ship in drift condition.
3. The effects of forward advance speed on the roll damping of the ship were made clear quantatively as well as qualitatively. The damping of roll increases with the increase of the advanced speed of ship, and around the service speed of the ordinary ships, say at Froude number of 0.2 to 0.3 it becomes about 1.5-1. 8 times the damping in drift condition. It is very interesting to find that the damping of ship has usually a hump and a hollow at the same range of the Froude number.

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Tank experiments for a destroyer model have been carried out at Meguro Model Basin to investigate the longitudinal bending moments in regular waves. This paper describes the test procedure, test results, and some conclusions.
The hull of the model, 8 m long, was made of wood and separated in eight blocks at seven sections. Each block of the hull, 1 m long, was jointed by a steel girder whose longitudinal bending rigidity was similar with the actual ship.
Bending moments at seven sections were obtained by measuring the bending strains on the steel girder by means of resistance strain gages. Tests were made in regular waves having heights of h/L=1/50, 1/30 and 1/20, and lengths of λ/L=0.6, 0.8, 0.9, 1.0, 1.1, 1.2, 1.5, 2.0 and 3.0.

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In the previous paper, the authors presented the results of theoretical evaluation of heave, pitch, .shearing forces and bending moments of a destroyer in regular head waves. In this paper, they tried the theoretical evaluation of heave, pitch and midship bending moments of the same destroyer in oblique head waves, and eslimated the statistical values of them in irregular head seas by means of St. Denis and Pierson's method. The derived statistical values were compared with those calculated approximately in long-crested irregular head waves.
The statistical heaving amplitudes in irregular head seas are nearly equal to the approximately calculated values in long-crested irregular head waves. However, those of pitch and midship bending moment are rather smaller than the approximately calculated values.
The amplitude of midship bending moment calculated by the conventional method without Smith's effects is nearly equal to the average of 10% highest values in not-fully developed storm seas corresponding ot 25m/sec. winds of 40 hours duration, and that caluclated with Smith's effects is nearly equal to the average of 10% highest values in fully developed storm seas corresponding to 20 m/sec. winds.

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The initial deflections exist between frames for the stiffend cylinders fabricated by welding. In this paper the influence of the initial deflection to the elastic behavior of a cylinder subjected to external hydrostatic pressure was studied using the mathematical expressions for the intial deflections as follows
(1) w_i1=δ (1-4ξ²)
(2) w_i2=δ/w_ξ=0-w_ξ=1/2 (w-w_ξ=1/2)
(3) w_i3=A sinh _κ2ξ sin _κ1ξ+D cosh _κ2ξ cos _κ1ξ+k
A theoretical analysis indicates that the influences of initial deflections are different by its forms.
The pressures at which the total stress on the surface of the cylinder with initial deflection w_i3 equal to the yielding stress of material were calculated for the cylinders having diffrent dimentions. Results of these calculations are shown Fig. 4, which are nondimentional plots of ψ=qa/Yh versus ν²=b²/ah.

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The problem of pure bending of a thin strip in its plane is treated as one of generalized plane stress for a strainhardening rigid plastic material. The method is based upon the deformation theory of plasticity, and the material is assumed to follow the yield condition of von Mises. The solution can be obtained solving a basic non-linear differential equation numerically. Especially for the rigid perfectly plastic material, a heuristic solution is found in closed form. Some numerical results are presented and an approximate expressions for stress and strain distributions are derived. These results are compared with experimental measurements.
Consequently, it is shown that the effect of any strainhardening characteristic on the strain distribution is very small, but is large on the stress distribution and the foregoing analysis is useful for practical purpose.

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This paper presented the results of uniform pressure tests carried out on 3 series of plated grillages. The purpose was to providing information on the elastic and plastic behavior of the stiffened panels, and particularly to find the collapse mode of the stiffened grillages. The analysis on the elastic stress, deflection in both elastic and plastic, and the collapse load were given to compared with the results of experiments.

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In order to take charge of the part of horizontal loads, braces are commonly used in the frame structures. Designing elastically these structures, in many cases the calculation becomes rather complicated and moreover it is difficult to decide the optimum scantling of the brace. In this paper the bracing systems of plane and spacial structures were studied by plastic design method to obtain strength of braced frame structures. Experiments were carried out on 16 portal frames and 10 spacial frames. Comparing the results of calculation with the experiments, the followings were obtained conclusively.
(1) The test results show reasonably a good agreement with the calculations, revealing applicability of plastic design to bracing structures. (see Fig. 2, 3, 10, 11, 12 and 13)
(2) In the case of plane frames, when horizontal loads only, collapsing load of a frame increases proportionally with the sectional area of bracing, on the other hand when both horizontal and vertical loads are applied, a diagram of collapsing load versus the sectional area of bracing may have knuckle points so that the optimum design could be attained. (see Fig. 2 and 3)
(3) The bracing systems in the experiments are slightly different from the actual systems, but the same methods of calculation could still be applicable to more complicated frame structures.

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When side walls of a ractangular tank, which is filled with water, are vibrating, the inside water will also make a vibratory motion. This motion of water lowers considerably the natural frequency of vibration, of side-walls of the tank. This effect is conveniently expressed by “virtual mass” of water. In the previous reports, I to VI, of the same title, the author has made a theoretical study on the value of the “virtual mass”, and examined various factors affecting it. These calculations were made by assuming, tentatively, the mode of vibration of rectangular elasticplate which constitute the side-walls of the tank. And, the velocity potential for the vibratory motion of water, caused by this vibration of sidewalls, was found. The question of degree of accuracy of the result obtained by this method, will naturally be raised, and some examination was made in report II of the same title.
In the present report, this question of degree of accuracy of the author's procedure in previous reports, is examined. It may be said that, we are dealing with a problem of hydro-elasticity. Here, the equation of vibratory motion of a rectangular elastic-plate subjected to lateral load (which is the water pressure caused by vibratory motion of water), is taken as the basis of our discussion. And magnitudes of correction terms are deduced from it. It is concluded that, at least for rectangular plates of ordinary proportions, the approximate formula given in previous reports, may be said to be fairly accurate.

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Measurements of the propeller-induced oscillating pressures induced on the hull surface were made on a destroyer in her sea trial and the results were compared with those of the model tests previously made by one of the authors. Both results agreed well. Further the authors present an empirical formula for estimating the total surface force induced by a propeller on a flat bottom near propeller.

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Generally speaking, intensity of restraint in a weld joint increases according to the decrease of temperature. In many cases, however, the intensity of restraint is defined by the final value of it.
In the present paper, considering the change of restraint during welding, relations between shrinkage speed and cracking during and after welding were investigated.
In the previous report, experiments were conducted under the condition such that the speed of shrinkage is kept almost constant and it was reported that cracking is occurred in narrow range of temperature for both weldments of a mild steel and a high strength steel. However, in this report, the effects of shrinkage speed were investigated for both weldments of a mild steel and a high strength steel of 60 kg/mm² strength level.
The results obtained are as follows ;
(1) Shrinkage speed and magnitude of reaction stress were widely changed by changing the gauge length of restraint, and weld cracking was occurred in wider range of temperature.
(2) In mild steel weldments, weld crack is occurred only during cooling and crack intiation is not observed after cooled to room temperature.
(3) However, in high strength steel weldments, crack initiation is observed during cooling and also after cooled to room temperature.
(4) Especially the cracking after cooled to room temperature occures at a lower reaction stress range and the incubation period for these crack initiations (abont 20 hours after welded) was measured.
The incubation time is insensitive to the applied reaction stress. Such cracking would be “Delayed failure” by hydrogen embrittlement.

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In the previous report, a method of theoretical analysis for the shrinkage of a finite-sized rectangular plate due to spot heating was presented. It was shown that the calculated shrinkages in case of a square plate where heating was applied on its centre lines gave an excellent agreement with the measured ones.
In the present paper, numerical calculations were conducted for a square plate where spot heat was applied on an arbitrary point situated on neither centre lines, as well as for a rectangular plate where heating was done on a point on either one of its centre lines.
Based on the results of theoretical analyses obtained from both the previous and the present reports, approximating formulae were deduced for estimating the shrinkages of a rectangular plate due to spot heating.
Physical meaning of these formulae is simple and self-explanatory, making the formulae easy to remember and convenient to apply in practice.
It is also shown that the average shrinkage due to spot heating on a rectangular plate is inversely proportional to the breadth, or the shorter side of the plate, and that the length, or the longer side, has practically no effect on the average shrinkage.

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Investigations were further performed about the effects of high temperature prestraining on the retained ductility and the notch toughness of various structural steels, and compared with the results of previous reports for a killed mild steel. Seven high tension steels, whose tensile strengths were ranging from about 50 to 85 kg/mm², were used for experiments.
It was found from the retained ductility test that the loss in retained ductility by high temperature prestraining was generally slighter for those high tension steels than the killed mild steel. At the same time it was revealed by V-notch Charpy test that the prestraining at 300°C was most harmful to the notch toughness of steels tested. But the loss in notch toughness after such treatment was fairly less compared with a marked decrease experienced in the killed mild steel.
It was suggested from the above results that the high tension steels tested might be less susceptible to the damage of thermal strain cycle during welding than mild steel.

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A brittle fracture propagation test was carried out to find relations among the crack propagation velocity, dynamical stress distribution, temperature and applied stress. To simplify the test condition, isothermal double tension test was used and test temperatures were made low enough to get nearly elastic cracks. The test results were compared with the previous calculation and some considerations were made on the surface plastic work-done.
The main results are as follows,
1) The stress distribution around a propagating crack is obviously different from that of a stationary crack. Along the crack path, there is a region where the normal stress perpendicular to it is lower than the mean stress. This minimum stress is depends on the crack velocity. These results show good agreement with the calculations.
2) Crack velocity depends on both temperature and applied stress. When the applied stress is not changed, the lower the test temperature is, the higher the velcoity is and for a temperature the higher the applied stress is, the higher the velocity is. Taking the surface plastic work-done into considerations, this is explained.

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Exponential expression for temperature dependence of the effective surface energy of brittle fracture was early proved its validity by Y. Akita and K. Ikeda. G. R. Irwin's stress intensity factor at instability point K_C was lately applied by M. Yoshiki, T. Kanazawa and S. Machida to the crack-arrest phenomenon of double tension test. Combining these two approaches, the authors propose a new expression for double tension test data, i. e. the formula (7) in conjunction with the formula (4) and Fig. 1. If the material constants K₀ and T₀ are given, the conventional σ-T curve of double tension test can be drawn by calculation only. Examples of the calculated curve are given in Fig. 10, where the curves for C/B=0.2 and C/B=0.6 are corresponding to the transition curves for the iso-thermal test and for the temperature-gradient type test respectively. So far as the ferrite-pearlite plates are concerned, K₀ (kg/mm²·√mm) for the double tension test can be predicted from the pressed-notch Charpy fracture transition temperature _PT_C (°K) through the formula (13) and Fig. 6.
In the light of the experiments illustrated in Fig. 8 and Table 1, the effects of the parabolic crack-front and the temperature-gradient on the double tension test result are discussed. Figs. 7, 9 and 10 are also associated with the discussion, and it is concluded that the arrest-transition characteristic of steel plate in service condition may be represented by the double tension σ-T curve for C/B=0.2. This agrees in principle with the idea previously suggested by one of the authors that the service performance of plate can be predicted by the iso-thermal double tension σ-T curve.

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The effect of corrosion on the propagation rate of a fatigue crack was studied to get the relation between an applied stress and the corresponding fatigue life. From the theoretical analysis it was found that the corrosion fatigue, even if there is no effect of creep or strain rate, is strongly time dependent.
Rotating bending tests on the high tensile steels were carried out at the frequencies of stress of 140, 20.5 and 3.5 cpm, to compare the theoretical analysis and the following conclusions were obtained.
1. The crack propagation rate in sea water is larger than that in air, and dc/dN would be expressed by eq. (7).
2. The propagation of a fatigue crack is affected by the frequency of stress and the propagation factor in air, k₀ increases with the decrease in frequency. On the other hand, the propagation factor in sea water changes as k₀exp. (q₀N/ω) and consequently the effect of the frequency is more remarkable.

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The authors investigated into the causes of failures frequently occurred in propeller shafts in way of the big end of cone part, using the results of a series of rotary bending fatigue tests with large specimems carried out by the Research Laboratory of the Nippon Kaiji Kyokai.
According to the results of investigations, the failure of shafts is assumed to occur in such a manner that micro-cracks produce in these parts of the shaft at an early stage under low stress reversals, and the cracks so produced propagate due to the excessive stress of the shaft when the ship is in rough sea, causing the failure of the shaft.
The results of a careful examination of the relationship between the shell patterns on cracked surface and the roughness of sea indicate that the propagation speed of cracks is in the order of 0.050.08μ/cycle and the stress which shaft is subjected to is considered to be±1214kg/mm², which implies that there is a large possibility of failure if microcracks have produced.
Accordingly, the authors would like to emphasize that utmost caution should be paid to the watertightness and workmanship of press-fitting the propeller at the big end of cone part so as to prevent from the initiation of miro-cracks, and further that in rough seas, ships should be handled with care so that the stress produced in the shaft may be as small as possible.

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Ship's hull under construction undergoes various deformations, such as bending up and down or athwartships and shrinkage fore and aft. The major elements to cause such a deformation are (1) loading (hull weight and water weight), (2) temperature variation, and (3) shrinkage force due to welding.
The deformation of ship's hull is complicated, because the above elements affect the ship simu ltaneously and the intensity of element itself varies with time. Thus, while the length of ship, for instance, varies every moment with atmospheric temperature and sun shine, it tends to be shortened as a whole due to the welding shrinkage force. Furthermore, because of the nature of wood, the ship's bottom lying on wooden blocks lowers with time even if the load be kept constant.
The present paper is concerned with the result of deformation measurement on actual ships, theoretical investigation, and practictal applications in ship-building in connection with, for example, the hull supporting method on berth and the method to find the most favourable propeller shaft center line.

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The hull construction work is composed of many unit processes including template production, marking, flame cutting, fitting, welding and so on. Inaccuracy of the geometry of member is produced during the each unit work ; errors increase at a later stage of the hull construction because of the accumulation of errors.
A statistical analysis was made or errors produced during unit processes at various stages of the hull construction. Measurements were made of errors which occurred during the hull construction of an oil tanker and a bulk carrier.
It has been proved that the errors follow the Gauss distribution. Values of mean deviation, , and standard deviation, σ, for the each processes were determined. It has been confirmed that the standard deviation of errors observed at a stage of hull costruction can be expressed as the summation of the deviation of errors produced during the preceding stage.
Using the result of statistical analysis, the following actions have been made ;
1) The toleran ce of inaccuracy at each of the unit processes has been established.
2) Quality control of each unit process has been established.
3) A standard procedure has been established to minimize the correction which may be required at joints between members to be welded at the erection stage.
4) An attempt has been studied to improve the structual design to minimize joint accuracy at the erection stage.

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The purpose of the paper is to propose a design procedure for preliminary ship-lines using a high speed digital computer, which derives prismatic curve, offsets and hydrostatic data with which given characteristics are satisfied, from the standard series having block coefficient within the range from 0.65 to 0.85.
The method is outlined as follows : -
The data of the prismatic curves and lines' offsets of the standard series, which are provided beforehand as basic data, are loaded in the high speed digital computer (I.B.M. 7090 is used in this case) with the object program for the calculation.
By these data and object program, the computer calculates and prints out the prismatic curve, offsets and hydrostatic data having given characteristics such as principal dimensions, prismatic coefficient, midship section coefficient, longitudinal centre of buoyancy, sharpness of shoulder of prismatic curve, shape of section of body and sheer.
In the first part of the paper, the principles of the method are described. In the second part. the standard series of prismatic curves and lines are illustrated in detail. Finally an outline of the procedure of the calculations of prismatic curve, lines etc. is given, using I.B.M. 7090, and an example is also presented.

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