This paper deals with the problem on flow fields around the stern of full ship forms and the estimation of ship wake from model data.
The first part of the paper concerns the measurements of wake in full models and the discussions on the characteristics of flow fields. Wake and pressure were measured by Pitot tube rake and potential wake was separated by measuring wake in models towed astern. Flow observation by tufts was also carried out. Plateau-type distribution of wake and the existence of cross flow and two weak vortices at both sides of the propeller shaft seem to be main characteristics of flow fields in the stern of full forms. Discussion was made on the existence and the cause of cross flow.
The seocond part is on the extrapolation of model wake to full sized ships. Assuming linear superposition of frictional and potential wakes and also similarity of velocity distribution in frictional wake between models and ships, an estimation of ship wake was attempted from the measured model data. Some secondary corrections such as the variation of potential wake between models and ships due to the difference of viscous displacement effect were also considered. Results were shown in the form of wake contours. A comparison of wake shows good agreement between the estimated value and the one obtained from the ship trial analysis.

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According to the slender ship theory, the wave-making resistance of ships is definitely determined by the sectional are a curve alone as far as the so-called, end effect' terms are neglected. As a preliminary verification to this conclusion, a set of three symmetrical models with C_B=0.55 (L/T=20) are tank-tested.
From the presently obtained results a tentative conclusion may be drawn that the designed waterline form atF.P.8¹/₂ affects the wave-making characteristics of ships as seriously as the sectional area curve.

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On three geosim tanker models, 4.2, 7 and 10 m in length, resistance test, self-propulsion test, propeller open-test and wake survey test were carried out. Analyzed results on these models are compared with the standardization trial data of the corresponding actual ship. One of the most important items to be made clear to improve the model-ship correlation seems to be the scale effect on propeller open-characteristics.

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Based on the finding that the wave-making resistance of a slow speed full ship depends solely on the shape of entrance provided the hull form is designed properly, a new method of designing hull form of large full ship is presented. The method consists of the following processes :
(1) The proper shape of run is selected taking the design requirements such as propeller arrangement, prevention of flow separation, etc. into considerations.
(2) Then the optimum entrance shape is determined for the value of C_mH_e/B which is determined from the given conditions on principal dimensions.
(3) Estimating the form factor and the self-propulsion factors for the such determined ship form, the total resistance and SHP can be calculated. Therefore, the optimum hull form with the minimum SHP for the given design conditions can be easily designed.
This method was developed by the authors in Mitsubishi Experimental Tank (Nagasaki) and has been applied to the practical design work resulting in a remarkable accomplishment of economical hull forms.

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Among few methods of roughness analysis of ship hull surface, the one proposed by Dr. Conn, in 1953 is well known. In this method a diagram is drawn showing the relation between the mean apparent amplitude and the apparent frequency of surface roughness. The diagram is easily obtained Providing that the surface roughness is recorded correctly by means of roughness recorders, so this method is much more practical than the troublesome Fourier's Analysis. However, this method gives less information about rough surface.
What we do in the method is to compare the mean height of protuberances between different surfaces. And there is no knowing about the relation between the mean apparent amplitude and energy spectrum of rough surface.
This paper shows theoretically how to read this diagram properly on the base of probability calculation and also presents that the mean apparent amplitude (function of the apparent frequency of surface roughness) is almost independent of the energy spectrum, but depends on the probability density (for instance a normal distribution) of the ordinate of the surface. This means that the height of the surface belongs to a random process and that any rough surface must essentially have the same mean apparent amplitude except that it is proportional to the standard deviation of the probability density of the height of the roughness.
But if we make use of this fact inversely, we can check the validity of the data obtained.
Besides, this paper shows the method to obtain the smallest wave length of the data curve, which gives the order of smoothness of the surface.

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The fluid motion around a ship which moves in regular head seas with a finite forward speed is analysed by means of the slender body theory. Formulas for hydrodynamic forces and moments are given to the ship form of semi-circular cross section.

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Experimental results on unsymmetrical rolling of two ship models, a fishing boat and a cargo ship, are presented.
The model was supported freely, except yawing, in an experimental tank under the action of beam seas, beam wind or both.
The heel angle, the amplitude of rolling and the velocity of drifting were obtained.
In the fisher-boat experiment, observation of unsymmetrical rolling in regular waves due to shipping water was the main subject, while, in the cargo ship experiment, the wave characteristics were kept constant and the wind velocity was changed from zero to 8 metres per second so as to obtain the informations on the combined action of wind and waves.
Unsymmetrical rolling due to shipping water with weatherside heel took place under wave action alone when freeboard was too small or/and effective area of freeing port was insufficient.
It is noticeable that the principle of superposition seems to fail sometimes as to motions of ships under combined action of wind and waves. In other words, these experiments revealed that the rolling amplitude varied with increasing wind speed, the heel angle due to the same wind velocity increased more or less under the additive action of waves and the velocity of drifting was independent of the existence of waves except in case of very low wind speed.

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It is widely known among seamen that the automatic steering introduces sometimes a sluggish yawing with fairly a long period, say, around 100 sec. This is an inherent oscillation of the whole system which is composed of a ship, steering gear and auto-steering device, being naturally accompanied with rudder movement of the same period. This yawing is not vital from the navigational point of view, but it may cause a considerable loss of propulsive power.
An analysis with the equation of motion (Chapter 2) shows that the power loss results largely from an inertial resistance induced by yawing and the resistive component of rudder force. Yawing experiments for free-running models of an oil-tanker and two cargo-boats supported the analysis (Chapter 3 & 4). The incremental resistance is given as Eq. (5) and its rough estimation can be done practically by Eqs. (7) and (8).
Applying these results, the power losses under automatic course-keeping for two typical merchant-men, a tanker and a cargo-boat, are estimated as much as 2 to 5% for reasonable adjustment of auto-steering device and in rather an exceptional case it may reach even 20% of the normal power.

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An attempt is made to establish a simple method of calculating stopping ability of ships as expressed by head reach. The deceleration of a ship is determined by means of one dimensional equation of motion, by abandoning the attempt to satisfy the equation for the rotating system of engine-propeller combination. Assumptions are made that total resistance R is proportional to the square of the velocity and the constant astern thrust T₁ is instantaneously applied which is taken to be value at dead-in-the-water. The final equation of motion of ship can be expressed in the form
T_sdV/ds+V=-K_sn₁²,
and head reach can be obtained as
S=T_s log_e (1+ 1/K_s V₀/n₁²)
Thus if T_s, which is essentially the hull characteristic, and K_s, which denotes the propeller characteristic, are given, the corresponding head reach can be easily calculated.

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In spite of remarkable developments about the research of the ocean wave, the properties of the waves in the closed sea area which are closely concerned with designing small ships are yet unknown.
In this paper, the authors calculated the spectrum of the waves, and reduced the statistical properties of the waves nearly the course of small ships in The Seto Inland Sea.
The observations were carried out with a pressure type wave recorder hanging under the buoy.
And the objected area is about 25 miles square in size, and is almost isolated from open sea. So it may be affimirative that the waves are generated only by the window blowing over the area..
The results are represented in Table 4, Fig. 6, Fig. 7 and Table 9.

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Available data on statistics of wave height and period have been collected on the world sea areas and routes. The purpose of this paper is to establish tentatively standard family of wave spectra for prediction of wave bending moments in rough seas based on such wave data.
Theoretical wave spectra originally proposed byNeumann, Darbyshire, Roll-Fischer and Pierson-Moskowitz were modified realistically to fit the observed sea states and compared with each other. Further, the comparative investigation was carried out on the standard deviations of wave bending moments of two ships in rough seas, which were obtained from those wave spectra and response operators.
There are not so significant differences between the results obtained from those modified wave spectra. The results derived from modified Darbyshire spectra, however, have a tendency rather different from the others. Modified Pierson-Moskowitz wave spectra proposed by I. S. S. C. would be appropriate for short-term and long-term pridiction of wave bending moments in rough seas and acceptable as an interim proposal.

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Studies on the ship behaviour in waves have recently improved so much by the statistical approach, so that we might foresee some quantitative results about the ship behaviour even at the stage of initial design. Sofaras our knowledge is concerned, the data about the destroyer which are available at the initial design stage, are considered very few.
In order to examine the motion of destroyer in rough seas and guess previously some motion of them, the sea tests which covering different sea states were carried out using two sister ships.
The items measured are pitching and rolling angles, acceleration, heaving motion, hull girder stress, local stress on the bottom panel and slamming pressure on the bottom of forebody ; and all of these recorded data are used for statistical and spectral analyses by applying time series procedure.
Theoretical calculations, on the other hand, under the cross flow hyposesis are pursued in order to obtain the response amplitude operators of pitching angle, heaving motion, bending moment and relative motion etc., then the power spectra of them are also calculated by estimating wave spectra of the experimental water areas.
Comparing with both calculated and analysed results, we obtain the facts which distributions of variation in pitching angle, heaving motion and hull girder stress etc. follow to Rayleigh's law, allowing from 67% to 90% confidence limit, and slamming pressures to truncated exponential distribution ; and also from the power spectra the pitching angle, heaving motion and acceleration show good coincidences from the practcal view-point, but on the contrary bending moments some discrepancies especially at the point of maximum magnitudes.
Number of occurrences of slamming impact and the distribution of slamming pressure are theoretically calculated under several assumptions about the threshold velocity and the bottom shape, and their results are compared with recorded data showing some discrepancies for number of occurrences, but for the distribution of slamming pressure good coincidences.

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The recent rapid developments in electronic computers have frequently encouraged parallel developments in methods of analysis of engineering problems. In the field of structural analysis, for instance, great strides have taken place in the use of methods variously termed “matrix methods” or “finite element methods”, and the methods have found wide application in dealing with highly complex structures.
As the first step of their application to analysis of ship structures, computing program for stress analysis of two-dimensional structural members is developed with some numerical examples.

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When a large ore carrier is floating in the full load condition, a large amount of ore load is acting on the double bottom downwards and a large amount of buoyancy is acting on the wing tank upwards. In this case, it is expected that the relative deflection between the side shell and the longitudinal bulkhead increases and induces large stresses in the transvese rings. According to this way of thinking, the authors try to calculate the transverse strength of ore carriers including the relative deflection and the stresses induced by it, and then try to make some considerations upon the effects of shear rigidity of swash bulkheads and of transverse rings.
From these calculations following things are found :
(1) Induced stresses due to relative deflection between side shells and longitudinal bulkheads can not be neglected.
(2) For the purpose of making relative deflection small, it is not effective to set swash bulkheads of reinforced transverse ring type, but is effective to set swash bulkheads of perforated plane type.

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Many parts of a ship, such as bototm structures, decks, and bulkheads consist essentially a plate-stiffener combinations with rectangular boundaries under the action of lateral loads. The stiffener or beam system may consist of orthogonally intersecting beams or beams running in one direction only. The structure may be subjected to lateral loads or it may experience loads in the plane of plating, it may also be subjected to the combined effect of lateral loads in the plane of the plate. The latter two cases involve a consideration of the stability of the system and this report dealt with the problems of plate under lateral loads only. The collapse mode and the corresponding collapse load of stiffened plates were obtained from the experiments and the theoretical calculation. The theoretical analysis were also obtained on the behaviors of stiffened plate above collapse load, and the theoretical calculation are compared with the experiments.
The minimum weight calculation was made on orthogonally stiffened plate which was designed by the criterion developed in this paper.

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In the Previous report the authors showed a method of plastic analysis of plate girders in postbuckling subjected to shear force.
Herein we present a simplified method to determine the collapsing load of plate girders in postbuckling under pure bending.
Namely
m_u=m_cr+β(1-m_cr)
where,
m_u=M_u/M_Y, m_cr= M_cr/M_Y
M_u : Ultimate bending moment
M_cr : Web buckling moment.
M_Y : Flange yielding moment.
β : Effectiveness of section modulus in postbuckling.
The results of tests carried out by the authors, as well as the other research organizations are compared with the theory which showed a good agreement.
A modified interaction curve for collapsing in postbuckling under bending moment and shearing force was introduced.

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As an extension of the contents of our previous papers (1) (2), (3), the collapse loads of particular space frames and semi space frames are dealt with the mechanism method and also the linear-programming method.
In the first place, follwing the introduction, general remarks as to the relation of the redundancy of the frames and numher of assumed plastic hinges with some kinds of basic equations to calculate the collapse loads i. e., the equilibrium equations, the compatibility equations and so on are given. According to these remarks, the equations are induced in the case of the treated structures. Finally, the result of calculation and the results of experiments which were carried out on six specimens are given. Comparing the results of calculations with experimental ones the following were ohtained conclusively.
(1) The difference between the collapse loads by the linear-programming method and ones by the mechanism method is usually slight, excluding the ranges of upper bound.
(2) Experimental collapse loads coincided well. eccept particular cases, with the theoretical resuets.
(3) If a large digital computer can be used, the linear-programming method is superior to the mechanism method in calculation of the collapse loads of high redundant structures.

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The reason of the damage which would often appear on the bottom shell of forebody is simply because of the large impulsive pressure acted thereon, and when the angle between the bottom surface and the surface of oncoming waves becomes nearly zero the water pressure is generally known to become very high.
In order to get the fundamental phenomena on the elastic response of the bottom shell panel having large aspect ratio. the author is now concerned with the basic research of elastic response of high tensile steel plates developed by impact on water surface, from the view-points of both theory and experiment.
The large elastic response of the long rectangular plate due to impulsive water pressure is first solved theoretically by taking the effect of stretching of the plate into consideration, but neglecting effects of higher modes of vibration. Introducing the measured data of impulsive water pressure into the theoretical formula above obtained, the calculated maximum elastic deflections at the center of the plate are compared with those of experiment, indicating good coincidences between them, and both results are further compared with those by theoretical results carried out by Greenspon, which show expanding discrepancies between experimental results corresponding to the pressure increment.
The small elastic response of the stiffened plate is then solved theoretically by considering effects of higher modes of vibration, and the maximum elastic deflections obtained by introducing the measured data of impulsive water pressure into the formula are also compared with experimental results, which show good coincidences between them.

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Under-water explosion produces the Shock Wave and the Pressure Wave in the water, the former propagates at the same velocity of the under-water sound, and the later does more slowly, and so, there are two types of the response of the Structure subjected to the under-water explosion. The representative research can be seen in the report by R. D. Mindlin and H. H. Bleich¹⁾ on the response subjected to the Shock Wave, and in the reports by P. G. Hodge²⁾, H. Kito³⁾, T. Nagai⁴⁾, K. Hanita⁵⁾, and Y. Hommao⁶⁾ on the response under the Pressure Wave. Their conclusionsare as follow ; Mindlin and Bleich : Elastic uniform radial deformation of the circular cylindrical shell.
P. G. Hodge : Plastic uniform radial deformation of the circular cylindrical shell.
H. Kith : Magnification of the amplitude of the initial deflection.
T. Nagai : Semi-experimental formula presenting the total deformation including the effect of the initial static pressure, shock wave, and the pressure wave.
K. Hanita : Semi-experimental formula presenting the buckling distance against the weight of the explosive, but no presentation as to the depth effect.
Y.Homma : Generalized buckling condition by the Energy Method. And a simple example is presented.
Thus, there is no report treating the buckling of the cylindrical shell subjected to the Shock Wave. Auther presents the buckling distance of the cylindrical shell subjected to the Shock Wave against the weight of explosive and the initial static pressure. Many experimental results are explained by the present theory.

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There are many papers regarding with calculation of characteristic value of reinforced rectangular plate in vibration, but in actual calculation we have such trouble as follows ;
(1) it is very difficult to calculate in case of many reinforements
(2) most papers can not be used for various boundary conditions of the plate, especially for elastic built-in edges.
(3) most papers can not be used for various end conditions of reinforcements, especially in case of end blacket of reinforcements.
(4) it is very difficult to calculate in case of high order frequency.
(5) most papers do not consider torsional rigidity of reinforcements.
In this paper, the author removed the above troubles by means of the calculation by electric computer, based on the program of theoretical method which is published already in this society.

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It is necessary for prevention of welded structures from brittle fracture to use steels and electrodes which are suitable to their service conditions and to adopt the suitable welding conditions or heat input. In the previous reports, the mechanism of brittle fracture initiation was studied by using the deep notch test specimens, and the brittle fracture initiation characteristics for various high strength and low temperature structural steels were investigated.
In this paper, the brittle fracture initiation characteristics for the welded joint including the bond and the weld metal, deposited manually or automatically in various heat inputs, of a 80 and a 60 kg/mm² high strength steels were investigated in comparing with that for the base metal by using the deep notch test specimens with welded joint.
In addition, the brittle fracture initiation characteristics for the base metal, the bond and the weld metal, deposited manually, of the 80 kg/mm² high strength steel in the stress relieved condition of 600°C × 1 hr were compared with that in the as welded condition.
Then, the correlation between the brittle fracture initiation temperature for the half crack length of 40 mm and V-notch Charpy transition temperatures were investigated.
Next, the characteristics of brittle crack path along the welded joint of the 80 and the 60 kg/mm² high strength steels deposited in various heat inputs were observed to find the case of crack path in a straight line along the bond or in the weld metal.
Finally, it was proposed what kinds of brittle fracture characteristics or various portions such as the base metal, the bond and the weld metal should be a criterion under a service condition of welded joint, where the longitudinal or the transverse cracks exist under external loading in the direction parallel or perpendicular to the welded joint, respectively.

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The effect of low cycle fatigue on the propagation characteristics of brittle crack in steels has been studied by means of the double tension test. The specimens used were the mild steel for hull structure (i. e. the semi-killed steel) and the ferritic high notch toughness steel (i. e. the Al-killed steel pressed, acceleratedly cooled and tempered), both of which were cumulated with low cycle fatigue previous to the double tension test.
As a result of the study, it has been clarified that the arrest-transition temperature of brittle crack is raised with the cumulation of low cycle fatigue. More details obtained are as follows;
1. There is no clear correlation observed between the increase of the arrest-transition temperature of brittle crack and the variations in the alternate stress of low cycle fatigue as well as in the cumulation number of that.
2. In case of the mild steel for hull structure, the arrest-transition temperature of brittle crack is raised with increase in the cumulated plastic strain below about 25 percent although it is kept nearly constant for the plastic strain above that critical value.

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The Prevention of infestation by mussels and marine organisms is required to decrease of ship fouling and condenser tube corrosion.
The paper is devoted to the research and development of a antifouling device of sea water which is one of electrolysis at the laboratory and an actual ship.
The obtained results are as follows.
1) Current concentration 0.3 A/m³/hr, which is defined by the current of electrolysis at unit flow rate of sea water, is required to prevent grow of marine organisms.
2) But when the sun shine is shut out, required current concentration is decreased to 0.1 A/ m³/hr.
3) The treated sea water is not corrosive for metallic materials such as mild steel and copper alloys.
4) The establishment of this method is proved by the satisfactory results of “Murasaki Maru” at 12 Months.

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Rigid urethane foams have some prominent characteristics as insulation material, such As low thermal conductivity, low permeance, and self-adhesive quality.
Especially, feasibility of foaming directly in the insulation space is its unique characteristic, but this application may lead to considerable non-uniformities of foams.
In this report some experimental studies are presented on these non-uniformities of rigid polyurethane foams.

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It is difficult to adopt the flow line system for assembly blocks, because unbalance of working time at each stage causes vacuum and over flow, from which idle arise.
To avoid these conditions, the flow line is necessary to has buffer area.
By the calculation, buffer area is at least 1.51.75 times maximum length of block.

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Intending to apply an assembly-line-production, a mass production medium, to the assembly of flat blocks, it is essential for the plate joining work which is the beginning of the whole production to be applicable to the assembly-line-production.
The conventional plates joining method is such that the right side of the plates is initially welded and the reverse side is also welded after turning them over. But the busy crane program in many cases prevents a smooth progress of work since the crane is not provided exclusively for this process. So, if such welding method, capable of welding two plates together in one process from the right side to the extreme reverse side, is available, it can eliminate such extra works as turnover and welding reverse side and can creates a smoother flow of material. Of various methods of automatic one side welding, the one we have developed is “Plate sliding type automatic one side welding” that the steel plates to be welded slide themselves through the welding point of a fixed welding machine, under neath which there is a piece of copper plate to keep pushing up the reverse side of the plates being welded.
By this process, the plates are welded together from the extreme right side to the extreme reverse side.
This particular welding method has required us so much study in the process of development especially regarding welding method itself and the holding copper plate system because of the fact that it is different in many respects from ordinary welding methods which hold steel plates to be welded still. As a result of our thorough study, we have successfully developed an automatic one side welding method capable of welding to the extreme reverse side of the plate in one process capable of handling plates, 10 mm to 40 mm in thickness and 10 m to 20 m in length. This new method is now being applied to our hull assembly work in factory.

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In usual launching method, we used two ways having the gauge of about 1/3 to 1/4 of ship-breadth.
On the other hand, there was the single way launching method, in which only one way was placed at ship's centerline. We find many advantages in this single way launching, such as saving of man-hours, saving of material and wide-range for ship positioning, but its application was confined to smaller ship whose max launching weight was about 2, 000 t, because of the problems on ship stability, ship strength, and so on.
The present paper concerns about the modified two way launching method developed by Mitsubishi Yokohama shipyard in which the gauge is so small that it is considered almost single way launching. This single way type launching methad was applied at first to smaller ship, but was extended to larger ship step by step after careful study on ship stability, ship strength and so on. Up to date, eleven ships were launched succsfully by this method including eight fish factory ships whose launching weight was about 8, 000 t and L×B×D 140 m × 24 m × 14.8 m.

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