Recently, the need of measurements of the boundary layer around a ship model has been stressed in connection with turbulence stimulation used at the ship experimental tank. The author observed, formerly, the transition in the boundary layer along a flat plate by finding the velocity fluctuation through use of hot wire. And now the experiments on four ship models (2.5 m Hakubasan-Maru model, and 1.7 m series models-A, B and C) were carried out by the same method.
As a result, the state of the flow in the boundary layer around ship models was observed, and the areas of laminar, transitional and turbulent flows on ship models were determined. The effect of turbulence stimulation by a trip wire or plate studs was confirmed by this means, thereby making it clear that the area of the transition was considerable at low speed in spite of the use of these device. Moreover, it was found that the area of laminar or transitional flow was larger on the full ship model than the fine model.

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From the standpoint of lifting-line theory, the wall effect of tank side is considered on the lift and resistance of the submerged hydrofoil of finite span.
The main results obtained are as follows
(1) The lift increases and the resistance decreases due to the wall effect, but those amounts are comparatively small.
(2) A correcting method for the wall effect is proposed.
(3) A minimum allowable breadth of the experimental tank for neglecting the wall effect should be more than twice span of the submerged hydrofoil.
(4) Some special cases are examined and compared with the previous results.

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There are many reports saying that the trial results of supertankers, which have been built in recent years, show much smaller power than the tank test prediction. Main reason of the trend may be due to deficiency of the method of residual resistance.
The authors try to develop a new method of correlation between models and ships. The method is based on the assumption that the flow fields around models and ships are similar to each other including their boundary layers, and only their thicknesses are different according to their respective Reynolds numbers. Thus the form effects on frictional resistance become linearly proportional to the corresponding plane friction, viz. they follow the law of Reynolds instead of Froude. This is a result similar to the Hughes proposal, except that in the case of actual ships the value of plane friction should be corrected by the roughness allowance. The formula of prediction of the effects between ships and models is
C_F8=C_Fm×C_fp8+ΔC_f/C_fpm
Applying the method to some results of supertankers, reasonable explanation for property of resistance is gained as seen in Figs. It is hoped that queer phenomena as negative ΔC_f may be removed by the use of this method.
A method of estimation of the form effects for fuller ships like tankers is also proposed. Comparison of the calculated figures with the tank tests shows a close agreement. The method assisted by the use of Taylor chart may be convenient to initial designers.

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Rolling amplitude of a ship decreases as the natural period increase. This fact is true not only on smooth swells, but also on confused seas.
If we suppose that there are two ships simultaneously whose each period is T₁ and T₂, then the ratio of expected maximum value of rolling amplitude is approximately
θ₁/θ₂=1/(T₁/T₂)²
so that if T₁<T₂, θ₁ is considerablly larger than θ₂.
The author examined these results on the long records of weather ships at X-ray (39 N, 153 E) and Tango (29 N, 135 E), whose types are different and the period is about 7.60 sec. and 12.32 sec respectively.
For a ship whose period is long, rolling amplitudes are comparatively stationally and regular as the ship tends to prefer and select swells, but on the contrary to this, for a ship which has short period resonance waves are usally confused seas, so that statistical amplitudes are not narrow banded but widely spread and these distributions are the same as that of Drs. Longuet-Higgins.

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The author has tried to set the theory of approximation in the problem to get the water pressure acting on fixed cylindrical ships amongst waves by the method used in the theory of acoustics and optics.
The method of approximation differs from case by case as the ratio of wave length to ship length.
In the one case, the wave length is very longer than the ship length, the knowledge of the virtual inertia coefficients in the uniform flow teaches us fairly accurate approximate values of wave pressure.
In the other case, the wave length is very shorter than the ship length, the method of approximation is of the geometrical optics and the wave pressure so obtained seems to be acceptable.
The theory up to the present, Froude-Kriloff's and T. H. Havelock-H. Maruo's, is usefull only in the case that the wave is incident longitudinally to the ship and that this length is longer than the ship length while the theory proposed here covers other ranges and cases in which the refered theory says nothing of.

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To examine the validity of the Froude-Kriloff Hypothesis, the exciting forces and moments of waves acting on ship models were measured. The results are shown in many figures in this paper. The differences of the Froude-Kriloff Hypothesis from the actual conditions are based on the facts that the incident waves are disturbed by the ship models.
It must be noted that the wall-sides of the experimental tank affect on the heaving forces remarkably at the wave length which is same with the tank breadth.

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The dynamical effect of a free water surface in on open tank with a rectangular section is investigated considering the effect of the surface waves occurring in the tank.
The results of the theoretical calculation show that the dynamical influences are large when :
1. the tank is located upwards.
2. the natural frequency of the ship is large.
It may also be certain that the rolling motion caused by an exciting moment having a frequency coinciding with the natural frequency of the tank water becomes extinct in short time.

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In the present paper an empirical formula (1) for the fin resistance is obtained after analysing the results of the rolling experiments on the action of a full-sized bilge plate. And a method of approximate calculation of the rolling resistance to actual ships by the bilge keels is found by adding the above-mentioned fin resistance to the surface resistance calculated by the method given in the first report.

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This paper relates to steering test results for a super-tanker model with four alternative rudder sizes.The test follows the frequency response procedure which has been developed by the authors. To increase relative rudder size from 1/77 to 1/61 results only a little gain of turning ability and a moderate improvement of stability on course and quick-responsibility in steering. Comparing the present results to Kempf's zig-zag test results for several similar actual ships, it seems that a considerable nonlinear effect is included in a steering motion as hard as usual zig-zag tests.

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In many branches of the “Ship-hydrodynamics”, the fields concerning the interaction among a hull, a propeller and a rudder have many unsolved problems. The author has specially interested in the problems concerning a rudder, and so had reported the measured results of the twisting moment acting upon the actual ship's rudder-stock, in 1953.
However, the phenomenon appeared in the experiments of the actual vessels were very complicated and difficult to solve. So that, the author had promised further investigations by model experiments. The author, recently, had a chance for this further investigation to carry, as a result of the completion of the model experimental equipments, water circulating channel, and planned the general research of ship's rudder from the hydrodynamical standpoint.
This first report treats theoretically the effect of the angular velocity of steering on the performance of an open rudder. From the results of theoretical calculation of the non-uniform vortex theory, the author finds as follows : -
1. The twisting moment acting upon a rudder-stock grows larger than the values at steady state, by the effect of the angular velocity of steering.
2. The lift can be divided into two parts at this unsteady state. One of them acting on the point behind a quarter of the chord-length of the rudder from its leading edge, and the other acting on the middle point of the rudder.
3. The lift, which acts on the quarter point, is a function of angular velocity and helm angle, but the other lift, which acts on the middle point, is a function of angular velocity only.
4. The growing-up tendency of a twisting moment in affected seriously by the position of the centre of the rudder-stock. In the case of general merchant vessels, this increment of twisting moment gets larger accompanied to increasing of distance of the centre of rudder-stock from the leading edge.

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The author has already developed a theoretical consideration in the first report, which deals with the effect of the angular velocity of steering upon the performance of rudder.
This second report contains the results of model experiments, which were carried out at the circulating channel. The forces and moments acting upon the rudder were measured at both states, steady and unsteady. The measured increments of the twisting moment are compared with the theoretical values, which had reported in the first report. Generally the tendency and values of the measured increment coincided with the calculating ones.

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Applying the theory of free--running screw propellers in the previous papers (Journal of the Society of Naval Architects of Japan, No. 100 & 101), the influences of various factors on screw propeller characteristics were studied.
The effects of blade-outline and blade-area were calculated in this paper, and the results show good accordance with experimental trend.

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Open water tests of AU-series propeller models varying the number of blades from 4 to 7 were carried out in Experiment Tank of Transportation Technical Research Institute. The tests contained next two series.
Series No. I ; Expanded area ratio was kept constant and contour of blade was varied as shown in Fig.1.
Series No. II ; Contour of blade was kept constant and expanded area ratio was varied as shown in Table 1.
All propeller models have a constant pitch ratio of 0.80.
Results of tests are shown in Figs.2 and 3, and results of analysis are shown in other figures and tables.

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Regarding the problem of vibration at the stern of single screw vessels, active research is recently in progress in many of the countries and several treatises have been made public in which the problem has been touched upon.
For example, the followings may be mentioned :
On vibration at the stern studied by Baier (S. N. A. M. E. 1952)
Vibration at the stern as referred to in the treatise on vibration re Gopher Mariner by Mc Goldrick (S. N. A. M. E. 1955)
Vibration at the stern as referred to in the treatise on research of hull vibration by Ramsay (T. I. N. A. 1956)
Vibration at the stern as referred to in the treatise on research of hull vibration by Kumai (I. S. P. Vol. 4, No. 32, 1957)
The Writer stated in the “International Shipbuilding Progress, Vol. 2, No. 10, 1955” certain fundamental theories on vibration at the stern under the title of- “A Contribution to the Vibration at the Stern of Single Screw Vessels”, and these theories are herebelow further developed more extensively.
The principal outcome of the research is : -
Upon detailed analysis of the vibrations which are collectively called in the terms of “vibration at the stern”, it was found that those vibrations are caused by different causes, and can be classified as follows :
Forced type stern vibration
Resonance type stern vibration
Associated type stern vibration
Apparent stern vibration
The forced type stern vibration takes place on ordinary vessels where the hull vibration is concentrated to approx. aft 1/4 L of the hull, and this phenomenon is conspicuous in large-type vessels. The cause for this vibration is a superposition of forced vibration of higher mode.
The resonance type stern vibration takes place in cases where the hulls are equipped with coupled oscillatory system composed of engines, boilers, unsupported deck, etc.
The “zone of vibration at the stern” is determined by the co-relation between the distribution condition of natural frequency of the hull and the blade frequency of out-of-balance force caused by propeller, and if the resonance frequency of the whole system, including the coupled oscillatory system, is within the zone and also if the blade frequency coincides with it, there occurs an extremely violent vibration at the stern in resonance condition. Such is called resonance type stern vibration.
In regard to the associated type of stern vibration, the mode of vibration will be of interest, however, from purely vibrational point of view, it is rather out of question because none of this type of vibration is violent. This type of vibration is created by an interference between the exciting force of the propeller and the reaction of coupled oscillatory system, the two forces simultaneously acting upon the hull.
Regarding apparent stern vibration, it is sometimes called “stern vibration”, because of the fact that, when hull vibration occurs, the amplitude of vibration is liable to appear in large amount in the vicinities of both forward and aft ends of the vessel due to the strength of hull scantling being smaller at forward and aft than at the midship portion of the vessel.
However, the Writer would like to distinguish this type of vibration from the other three types, and give thereto an appellation of “apparent stern vibration”.
The reason is that this type of vibration substantially differs from the other three types, and besides, the distribution of the vibration along the hull does not form stern vibration in a true sense of the term.
Lastly, the Writer will describe as to the principle of preventing the vibration of the hull, for the purpose of giving an example of practical appliance of this research.

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The present paper deals with some computations on the higher natural modes and the response of the hull vibration of a large tanker excited by propeller blade exciting force. The calculations are carried out under the assumption of the shearing vibration of the beam of variable cross section. The results of the response calculations are checked by which obtained from the generator survey on two tankers. The propeller blade exciting forces are estimated from the accelerations measured on several types of the large tankers in aid of the calculation. Also the allowable exciting force to maintain hull vibration within acceptable limit of an acceleration is estimated by the present calculation.

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In order to study the motion and stresses of ships in rough water, several research committees of the Shipbuilding Reasearch Association of Japan have made a number of experiments on boards for some years. To determine the actual wave profile, the author, as a member, have tested a recording device which can show continuously the wave profile along the ship's outside-wall.
The device consists of electric contacts distributed over the outside of the hull. The contacts and lead wires were sticked directly to the shell planks with resin, without any machining or drilling procedure.
The outline of this device and some test results are explained in this paper.

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A calculation of the stress distribution of ship's superstructure is presented, which is introduced by combining author's former calculation of the shear lag distribution of house wall with H. H. Bleich's bending theory of superstructure, so the effects of bending and shear lag are both taken into consideration in this calculation. The numerical calculation of one example is carried out by this theory and by H. H. Bleich's theory respectively, and the results obtained by each theory are compared with a good agreement except in the vicinity of the superstructure ends.

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In the previous reports, No. 2 and No. 3, the authors presented the methods for the bending calculation of deckhouse and superstructure, but in their calculations, the effect of openings in the wall of superstructure was not considered.
In this paper, to investigate the effect of openings on the longitudinal stress distribution of superstructure, the effective cross sectional area and the effective moment of inertia of the superstructure were determined taking into consideration of the deformation of the openings, and using these, the experimental results were analysed.

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In genral the object of a bracketed connection is to increase the strength and rigidity of connected parts. For determining bracket sizes investigations of the stress distribution in the bracket and variations of the bending moment of structural members due to bracket sizes should be carried out.
In this paper investigations of the stress distribution in brackets and economical shapes of brackets by photoelastic method are described in part I, and the theoritical analysis of bracketed beam in part II.
Experiments were carried out on three kinds of series specimens. According to test results the stress in bracket is smaller than the stress in the adjacent member. But discontinuity at ends of the bracket brings about the stress conncentration, therefore special attentions must be taken about this matter. Furthermore the diameter and the position of centre of the circular hole in brackets were studied.
On the theoritical investigation of the bracketed beam, the author adopted the two dimensional theory in the bracket part, and found the stress function which satisfies boundary condition at several points. From the results displacements in the bracketed beam and staically indeterminate quantities in the fix-end beam and so on were obtaind. It could be confirmed that theoritical values of the stress. coincide thoroughly with experimental values.

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On the distribution of bending moment of bracketed structures, various results of investigations based upon the consideration that the brackets were regarded as beams with variable sections have been published. There are, however, few experimental data which justify the investigations of this kind.
The authors conducted an experiment using a model of rectangular bracketed structure with different aspect ratios, whereupon it was found that, when the brackets were regarded as beams with variable sections, effective brackets (see Ref. (6)) should be taken into account.
On the other hand, introducing the span point (see Ref. (6)), they developed an approximate calculation method by which the distribution of bending moment of bracketed structures could be obtained. The results obtained by this calculation were proved to be in good consistency with those obtained by the experiment.

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Because the commonest element of the ship's structure is the orthogonally stiffened plate, the investigation on such structure is indispensable for designing, for instance, deck, bottom and bulkhead of ship.
In this first report, the theoretical solutions of orthotropic plates with various end conditions under various lateral loads are given employing the general solution of the basic equation, for the sake of analysing the orthogonally stiffened plate.
Some considerations are also performed in case added stiffener is installed on stiffened plate, as the center girder on the bottom in actual ship.

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In the strength calculation of hull construction members, the mutual interference of respective members should naturally be taken into consideration. However, since such a calculation is very complicated and difficult, the strength calculations in the past have been limited to the extent of two dimensional ones. In view of this situation, this paper deals with three dimentional strength calculation which are considered to be generally practicable. By using Hardy Cross Method in the calculations of transverse members and normal functions in the calculations of longitudinal members, calculations of a sufficient accuracy have been attained with the effort of as small as 5 to 6 man days.

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Reversed bending fatigue tests in sea water under the impressed current cathdic protection were carried out. The lower the electrochemical potential the higher the fatigue limit, and in spite of a large quantity of absorbed hydrogen, no deterioration of the fatigue strength was observed. It is supposed that the distortion of the lattice structure produced by the absorbed hydrogen is favorable to the fatigue. Relations between potential, cathodic current and applied stress were also considered.

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If a rectangular beam is heated such that the temperature is uniform in the upper fraction keeping the rest unheated and then wholly cooled to the room temperature, the residual bending deformation is occured plastically.
The author analized the phenomena as one of the fundamental problems of thermo-plastic working, which is distinguished from the usual plastic working.
In theoretical study, the following assumptions are used : 1) The elastic constants and thermal expansion coefficients do not change during the process. 2) The decrease of yield stress is proportional to the increase of temperature. 3) We use Prandtl-Reuss stress-strain equations and von-Mises yield criterion as the plastic laws of material. 4) The depth of heated region is less than one half of the height of beam, and the temperature changes discontinuously at the boundary of heated zone. 5) Navier's hypothesis is applied to the bending deflection of beam.
Under these assumptions, the characteristics of plastic behaviours of beam are studied. The numerical calculations are performed for initially unstrained beam and the results are compared with the experimental deta with fair agreement.

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This report is the first part on the theoretical studies of propagation of brittle fracture and deals with the axissymmetrical case of the radial crack around a circular hole propagating at Speed V in the stress field of uniform tensile stress p at infinity. An approximate solution of the dynamical stress field and the extended Griffith's conception were obtained.
The general conclusion obtained are as follows :
(1) The dynamical stress field is affected by the crack speed.
(2) The critical stress for brittle crack propagation is affected by the crack speed as the results of change in the released elastic strain energy and the kinetic energy with crack speed.
(3) There exist the minimum critical stress depending on the temperature, arresting transition temperature, the minimum and the maximum critical speeds for brittle crack propagation under the consideration of the plastic strain energy near the top of crack.

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Residual welding stress having no effect on the ductile fracture of welded structure might play an essential role in the case of brittle fracture. It is well known that the actual damages of brittle fracture occurred at cosiderably low stress level, and this is a very important particular nature of brittle fracture. The brittle fracture may propagate at low stress level after it is once produced, but considerably high stress must be applied in order to initiate a brittle fracture. Therefore, some special treatments such as additional shock are usually applied in the tests on crack-propagation characteristics of steels.
There rises a question in what kind of mechanism the brittle fracture was initiated and propagated in the actual damages. There is a doubt that residual stress caused by welding may be one of main factors which might induced the initiation of brittle fracture at low stress level in the actual damages. The possibility of this sort was once showed by Wells in England. Wells successfully realized a complete fracture of welded joint under considerably low stress using welded joints having pre-existing sharp notches. However, the occurrence of fracture at low stress level was limited to only one case, and the reproducibility of this kind of fracture must be ascertained the further investigation.
The authors tried an experimental investigation on this problem, and clarified the fact that residual stress may have an important effect on brittle fracture.
The main results obtained are summarised in the following : -
1) When the testing temperature is high enough to produce shear fracture (higher than T₁ in Fig. 6), fracture stress is very high and residual stress has no effect on fracture stress.
2) When the temperature is below the fracture transition temperature but above the arresting temperature of base metal (between T₁ and T₂ in Fig. 6), brittle crack may be produced under low applied stress. But the crack will be arrested after running a certain length, and complete fracture of joint is produced at high stress level (nearly equal to the yield stress). Thus the existence of residual stress produces no effect on the load carrying capacity of welded structure.
3) When the temperature is below the crack arresting temperature (below T₂ in Fig. 6), brittle crack will be initiated at low stress, and in this connection, two different cases will be occurred in accordance with the level of applied stress at the crack initiation.
(a) If the level of applied stress at crack initiation is lower than the value of critical stress of brittle fracture, the crack will be arrested after running a certain distance, and the final fracture stress will be as high as yield stress of the base metal. Concequently, the final fracture strength of welded joint is not affected by the existence of residual stress.
(b) If the level of applied stress at crack initiation is higher than the value of critical stress, the crack will propagate through the whole width of material and the welded joint will be failed in single stage at low stress level. In this case the existence of residual stress has a serious effect on the load carrying capacity of welded structure.

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When cutting the mild steel plate by oxygen, some deformation remains frequently due to the effect of local heating and cooling. The influence of this deformation makes the further works difficult.
Several methods to prevent this kind of deformation have been reported recently, but it seems to us that these methods do not always meet our satisfaction.
For this purpose, we have discovered a new and quite interesting method, applying water quenching right after oxygen cutting, which enables us to reduce the amount of deformation almost to zero without giving any harm to the material.
In this research, we found out the suitable quenching condition and investigated the influence of this process to the material.
The following results are summarized from the experiment.
1. According to the quenching condition, shown in TABLE 10, we could reduce the amount of deformation more than 1/10 of the one caused by ordinary oxygen cutting.
2. The change in material characteristics throughout this process is out of question, namely, after electric arc welding no difference is found in material characteristics comparing with the ordinary process. On the contrary, the free edge as cut, not intended for electric arc welding, is inferior for cold bending and brittle fracture. But we can eliminate this inferiority by applying a simple additional treatment.
3. To apply this process, it is not necessary to arrange any special apparatus but only a simple water nozzle with its holder, rubber water tube and some water.
Therefore, this process is easy to manage and is very much economical, as for, we are possible to carry on the further works without any fairing.

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The best method for the examination of the characteristics of Zinc anode is the testing of anodic polarization. The experimental sesults of the above method in usefull to the design of cathodic protection.

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Kawasaki Dockyard created a new ship-building method for large tankers (D. W. 38, 000 tons and above) on march 1957. Under the new method, a large stern block as much as 3, 000 tons which was previously assembled on the assembling plat form is shifted on to the adjacent berth where the remaining part of the ship is built in about 2 1/2 months and whilst the latter work is going on, almost all fitting work, installation of engine etc, are completed and then the ship is launched.
There is so short a period of time (about 1 month) from launching to delivery that the conventional docking prior to sea trials seems to be unnecessary. In order to carry out the new fitting out method without docking, the authors have planned some fundamental studies as follows : -
1) How to make the perfect protective organic coating on ship bottom whilst on berth.
2) How to minimize the damage of hull and the scratches of protective coating by any accidents during launching and whilst fitting out.
3) To protect the ship bottom against corrosion and rusting by cathodic protection (sacrificial anode system) during guarantee period.
4) How to keep ship bottom clean after launching and during service whenever she'll be launched, especially before sea trials. For this purpose we must have the special A/F paints which are properly controlled in initial leaching rate of toxics immediately after launching and have long life of anti-fouling facilities.
Having made experiments for the above mentioned 4 subjects, the authors have had the successful results for item 4. Now the authors feel no fear about fouling of ship bottoms even if we carry out the new fitting method without docking. This paper shows how we got the new special A/F paints suitable for no docking system.

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Kawasaki Dockyard Company, breaking out of the old shell of hull building technique, has adopted a new shipbuilding technique conceived under a new idea. Under this new idea a large stern block previously built is shifted on to an adjacent building berth and there outfitting of the stern parts is continued. In parallel with such work the rest of the hull construction and the outfitting work are kept on while engine installation, electric wirings, and deck outfitting are completed, and then the ship is launched.
The objectives of such procedure are to shorten the time needed for all the outfittings, which are usually carried out on the launched ship moored to a wharfside, and also to do away with subsequent docking.
Briefly speaking, the summary of shifting work is as follows : The 2, 800 T stern block is pulled transversely along eight rows of greased sliding ways and then made to slide down two rows of greased standing ways longitudinally by means of a single wire rope, respectively.
The pulling arrangements including wire and winch etc. are planned on assumption that the frictional coefficient of the grease during the shifting is 0.03. The speed for pulling and sliding is fixed at 500mm/min.
Various measurements are carried out during the shifting. With regard to the stresses caused in the hull during the shifting and readjustment of its position, their maximum values in tension and compression are found to be 2.1kg/mm² and 0.8kg/mm², respectively, which do not differ much when compared with those (1.9kg/mm² in tension, 3.4kg/mm² in compression) measured in hydraulic test of the same stern block. So the figures are by no means serious as hull stress.
Frictional coefficients of the grease, which were experimentally within the range of 0.0110.017 for 20T/M² pressure, were found to be actually 0.029 in maximum, 0.010 in minimum for the lateral shift and 0.022 in maximum, 0.010 in minimum for the longitudinal shift, respectively.
These values of coefficient obtained in actual shifting corresponded, in minimum side, to those of experimental result.
Sand jacks were used in making minute adjustment for the final position of the stern block when it was settled on the berth after a long shifting work.

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The large stern block of the 38, 000 DWT tanker (total moving weight 2, 800T) was shifted laterally and longitudinally on March 12, 1957 in the shipyard of Kawasaki Dockyard Company.
Before the planning of the above-mentioned shifting, authors made experiment on the frictional coefficient and characteristic of the grease to be used. As a result of this experiment, it was found that the frictional coefficient of the grease is very large at the beginning of the shifting, but suddenly decreases and becomes constant within 0.0110.017 after moving the distance of 20mm, the pressure on grease is 2030 T/M² and so it was ascertained that the greased sliding way could be used for the shifting work, when the shifting equipment, which is planned based on the frictional coefficient of the grease as 0.029 in case of lateral shifting, and 0.010 in case of longitudinal shifting, is reinforced by the pushing arrangement at the start of shifting.
Authors also planned the lateral shifting by pulling the center of resistance position by means of only one pulling wire rope.
As a result of the analysis of miscellaneous measurements and recordings of the actual shifting, it was also ascertained that the above plannings and results almost agree, namely the frictional coefficient of the grease was max 0.029 approximately in case of lateral shifting, min 0.010 approximately in case of longitudinal shifting, and the difference between lateral pulling position and the center of resistance position was within±200mm.

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