The fact that partially averaged values is rather important than total mean value is first introduced by Drs. Sverdrup-Munk in their study of ocean wave.
1/q mean value, where q=1 means usual total mean value and q lies between unity and infinity, is connected as follows with the expected maximum value within N samples
N =q· exp (1-γ),
where γ is Eulerian constant.
Above relation shows that “significant mean value” is equivalent to the largest value in several successive samples, which is empirically proved by observations of heights of sea waves.
On regular swells almost all swings are in resonance but in high seas chance of tuning become extremely rare. Number of rolling amplitudes in which one perfect resonance is supposed statistically to be contained is :
ⁿ√N+γ·F(βs) =1.
where ε₀F (βs) and θ₀ are cumulative and resonance angle, and n=2 means “irregular seas” whose. statistical character was analysed by Dr Longuet-Higgins.

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In the open channel containing streaming water the surface pressure distributions over the submerged circular cylinder were measured, and then the forces were calculated by pressure integration. From these results the effect of submersion depth on the forces was discussed in detail. The main results are as follows
(1) In the region of laminar separation and transition, the wave resistance is comparably large. This results from the rearward movement of the position of minimum pressure by the gravity force.
(2) In the region of turbulence separation the form resistance decreases. This results from the rearward movement of the separation point by slackening of pressure increment in the after part.
(3) The effect of laminar flow begins to mixrin the small submersion depth even if the Reynolds number in the large submersion depth is above critical one.

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Following the previous report, it is developed here how to estimate the form drag of a body, especially the pressure one.
The contents are divided into two parts. The first half is the method of calculation of frictional resistance. The principle is just the same as Buri's method, and after reanalysis of the various authors' data numerical constants are modified slightly. The latter half is about the so-called pressure drag and divided again into two cases according to the existence of separation or not. Without separation, introducing a newly defined “pressure thickness”, the pressure drag is obtained as the product of it and the pressure gradient normal to the wall in potential flow. When separation exists, two governing relations are considered in the separating boundary layer which was named by Schubauer. These are the momentum equation and the assumed law of similarity of velocity distribution. Solving the two simultaneously we get the pressure on the layer which may be considered to act also on the body surface.
Numerical calculation is carried out for three kinds of symmetical aerofoils and the comparison with experiments shows a reasonable agreement in practical sense.
Detailed discussion about the position of separation and the effect of Reynolds number is left in future research.

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The influences of variation of number of blades and pitch distribution on characteristics of screw propellers in open water are studied applying the theoretical method of the previous papers (Journal of the Society of Naval Architects of Japan, No. 100 & 101).
The propeller efficiency grows higher with the number of blades if the blade area ratio, pitch ratio and drag coefficient are constant.
The effects of variation of pitch distribution on the efficiency are very small for moderate slip ratios (0.20.5).

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In his first and second reports, the author has publicly announced his study on the theoretical consideration and model experimental results, dealing with the performance of rudders in open water, with special emphasis on the effect of the angular velocity of steering, and he believes that, the general state and tendency of the open rudder have been made clearer.
This third report accordingly treats theoretically the effect of the propeller race on the performance of rudders. From the results of theoretical calculation of the rudder performance, the following results have been obtained :
1. To estimate the rudder force in propeller race, the most important factor is the velocity increasing coefficient of the propeller race, succeeding to the advance speed of the rudder and the helm angle. And 7080% of the total energy of the accelerated water energized by the propeller operates effectively on the rudder.
2. The effect of the angle of incidence generated by the propeller, is of the minor importance as far as the rudder of the symmetrical section is concerned.
3. If the gap between the propeller and the rudder is changed in the range of 0.51.5 R, it has little influence upon the rudder force. (R : radius of the propeller)

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A theoretical consideration of the effect of the propoller race upon the performance of rudders has already been expounded in the third report. In this fourth report, therefore, the author tries to explain the results of his experiment, concerning the model rudders in the propeller race, which was carried out at the circulating channel. From this rudder experiment, the following results have been secured.
1. The increment ratios of the normal force of rudder due to the propeller race are proportionate to the one and a half power of the slip ratio of the propeller.
2. The position of the center of pressure on rudder travels forewards due to the propeller race, and its movement gets larger in proportion to the increase of the slip ratio of the propeller.
3. If the gap between the propeller and the rudder is changed in the range of 1.02.0 R, it affects slightly upon the rudder force. (R : radius of the propeller)
4. The qualitative tendency of the performance of the rudder, of which positon deviates from the propeller center, or of which height differs from the propeller diameter, can be observed by the following method. First, the total area of rudder be divided into two parts. The one is directly affected by the propeller race, and the other is not affected. Then the open results should be applied to the part not affected by the propeller, and the experimental results in propeller race to the affected part.
5. In the propeller race, the effect of the angular velocity of steering upon the performance of rudders was also observed, in the same manner as in the open test.

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The present paper relates to stability problem of auto-piloting of ships with particular reference to “weather adjust” mechanism which induces sometimes a self-exciting severe yawing.
Kochenburger's stability criterion may be utilized for analyzing steering systems involving “weather adjust” mechanism, helm-angle limitation and other non-linear elements. In conclusion, it may be strongly recommended to employ “dead band” element for weather adjust mechanism in place of “back lash” element which has been widely used conventionally. On the other hand, ang-ular velocity control, that means to operate a rudder reacting to angular rate of course deviation as well as to course deviation itself, is decidedly superior to another damping means, “over telemotor adjust” so-called. The synthesis of the angular velocity control may be carried out through Nyquist criterion.

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The Author states in this paper following results out of his research including two actual ship experiments ;
(1) The equation of motion of ships under steering can be reduced to a differential equation of 1 st stage as follows.
T_sdθ/dt+θ=K_sδ
where T_s is a constant which represents the quick responsibility of ships, and
K_s is a constant which represents the turning quality.
Though, T_s and K_s will both vary with the curvature of the locus of ships, according to some experiments, the amount of variation is thought to be not so large.
(2) The ratio K_s/ T_s is a constant, i e,
K_s/ T_s= rudder turning moment/moment of inertia of the ship × rudder angle. and is easily calculated when the dimensions of the ship and rudder are given. So we can get K_s and T_s when either one is given.
(3) It will be most reasonable to get Ks from data of steady turning experiment, i e,
K_s=θ_s/δ
where θ_sis the angular velocity of steady turning
(4) T_s, K_s will both vary with the curvature of the locus of ship's C. G., i e. stronger the curvature, larger the both K_s, and T_s, in other wards, smaller the radius of turning, better the quick responsibility and worse the turning quality. But, the amount of variation is thought to be so small that we can get a close approximation of turning angle curve from initial stage to final stage using T_s and K_s got from the steady turning data.

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When two concentric or eccentric circular cylinders vibrate relatively, the phenomenon of cavitation may be caused by a vibratory hydrodynamic pressure set up in a water bounded by two cylinders. The author confirmed this phenomenon using a model with full scale tail shaft diameter and reported in the previous paper.
In the present paper, the author shows some results found by the experimental resarch using 3 sets of newly built testing machines. The principal contents of these results are as follows :
1) The approximate empirical formula was derived from the experimental reserch to estimate the critical cavitation frequency. The negative amplitude of vibratory hydrodynamic pressure set up in a water is shown as
|h_m|= [0.9+1.6 (α/δ] [1+1.9 (e/δ-α) ²] (10³·a²/δ) (αω²/g)
Where “ω” is the angular frequency of vibration in rad/s, “α” the amplitude of vibration in mm, “a” the radius of inner cylinder in m, “δ” the mean clearance in mm and “g” the accelerlaion of gravity in mm/s².
Using this formula, it is possible to estimate, whether or not cavitation is liable to occur.
2) Relations between a vibratory hydrodynamic pressure set up in a water and the cavitation phenomenon were explained using oscillograms showing the vibratory pressure and results of stroboscopic observation with external synchronizer.
3) The peculiarites of the cavitation and the erosion damage caused dy such cavitation were explained.
4) Using the model test result, one method to avoid cavitation on actual ships was suggested.

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The idea that we calculate the natural frequency of hull vibration and design the ship so as to be able to keep it out from the range of revolution of propeller shaft corresponding to this natural frequency, should be replaced by the positive idea to keep in so small amplitude that can not be the cause of troubles even in the resonance vibration. Because the estimation of the natural frequency of hull has so frequent and so big error that makes the former idea impossible and moreover the operator always insists the latter idea under the necessity of the voyage in every loading and weather condition.
The latter idea requires to decide the allowable intensity of vibration and its allowable exciting force.
This paper shows the method used at the time of preliminary design of the ship to investigate and estimate the kind of natural vibration and its maximum possible intensity at each condition of the ship which may cause troubles, and furthermore to decide the allowable unbalanced force and moment of the main engine for the natural vibration of hull, using the idea of safty factor from the actual data of hull vibrations.

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An investigation is made of the added mass moment of inertia induced by the rotational motion of the prism having hull section on water obtaining the information to estimate the natural frequency of the torsional vibration of ships. The special consideration to the effect of the draught upon the added mass moment of inertia is taken into account in the present study. The experimental studies by use of the prismatic models with the sectional forms of the main stations of the hull of a tanker are also carried out confirming the theoretical calculation. As the result of the present investigation, the convenient formula for estimation of the added mass moment of inertia induced by the torsional vibration of a tanker, as an example, is presented for practical use in design room.

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This is the second report on the strength of the orthogonally stiffened plate, in which the results of the experimental study on the simply supported orthogonally stiffened square plates suffered by the uniformly distributed load are discussed, comparing them with the theoretical value. After precise investigations on the distribution of deflections and stresses, it was concluded that these plates could be sufficiently expressed by the orthotropic plate theory treated in the first report on the same title.

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On the calculation of bending moments of bracketed structures, various results of investigations based upon the consideration that bracketed beams were regarded as beams with variable sections have been published. The author applied the theory of the wedge in bracket parts, obtained various formulas on bracketed beams and showed the method of the calculation of bracketed structures by introducing above formulas into the slope-deflection method.
In this case, the joint rotation due to shearing forces at bracket ends were considered, and it was shown that the effect of the shearing force in the joint rotation can not be neglected in the unsymmetrical structure.

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The effectiveness of the longitudinal members such as deckhouse, superstructure, longitudinal bulkhead etc. contributing to the longitudinal strength of ships have been studied by many investigators.
The authors have tried to analyse these problems applying the theoretical plane stress system of an elastic rectangular plate, noticing that a ship is a structure assembling rectangular plates in three-dimension.
In this first report, they present the deduction of the theoretical plane stress system in a homogeneous elastic rectangular plate so modified the Okubo's theoretical method as suitably applicable to the analysis. As the examples, the stress distributions in simply loaded stress fields are added.

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In order to investigate the critical buckling stress of rectangular plates with longitudinal stiffeners under simple bending moments, the author performed two series of simple bending experiments. The first series dealt with the simple bending experiments of a web plate only, and the second dealt with a box girder with different kinds of web plates. The critical buckling stress of rectangular plates calculated by energy method shows good coincidence with the result of the author's experiments, and there is no significant difference between the experimental results of the critical stresses under simple bending of web plates with a longitudinal stiffener and with two longitudinal stiffeners. Furthermore, it has been made clear that the effect of change of stress distribution over a web plate with longitudinal stiffeners under bending is nearly equal to the effect of the same over a web plate without stiffeners.

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This paper presents the results of buckling test of the reinforced thin sheets panel of high tensile steel under compression. It is well-known that the buckling stress of the reinforced thin sheets panels can be determined by Bryan's formula in the case where its effective stiffener rigidity ratio γeis larger than γemin.
After buckling of the panel, the compressive load still increases in these structures, and reaches the ultimate load when the stiffener collapses.
This paper is primarily concerned with methods of calculating the maximum stress of the stiffener and the ultimate load of stiffened panel.
From the experimental results of series of the stiffener, the following conclusion may be drawn. (a) Buckling stress of the stiffened panel reasonably agrees with existing theoretical results.
(b) A stiffener collapses when the extreme fiber stress of the effective stiffener reaches theyield stress of the material.
(c) The maximum compressive load of these structures can be determined from the buckling stress of the panel and the maximum stress of the stiffener.

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The plastic buckling of plates stiffened by light gage steel, is studied in this paper. It is shown that the ultimate strength of stiffened plate in plastic range is easily calculated by obtaining so-called “Shanley” load (the tangent modulus load) of column which consists of stiffener and effective width of the plate. It is, therefore, quite natural that test results of stiffened plates are plotted on the column curve as shown in Fig. 8.
In the case of stiffener having a thin open unsymmetrical cross-section, torsional-flexural buckling could be frequently expected. This case is also considered in this paper.
The coincidence between test results and calculation is satisfactory.

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The construction of wooden ships is not regarded as a simple beam, but as a group of longitudinal members which are jointed together frames, deck beams, diagonal shell-planks using by nails etc. On the basis of this analogy, anthors find the method how to solve the problem on the strength and rigidity of built-up-beam, and the new way to reserch those of wooden ships.
At the first stage, the authors solve the problem of the multi-layer built-up-beam using by infinite members of shear springs which join each beam and act to reduce the relative slip among each, layer. In other words, this spring action is quite similar to frames, etc. at actual ship.
And solution by this process is proved accurate by the comparison with the results of bending-experiments on simplified models of wooden ships.
We conclude that the strength of ships by ordinary construction system will be solved by this. process as well as other construction system which is adopted for modern wooden ships.

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This series of experiments, requested by the Maritime Board of Self-Defense Force and subsidized by the Ministry of Transportations, was executed, in order to obtain some useful data for designing the wood built hull of such high speed boats as patrol boats, motor torpedo-boats, mine sweepers, etc.
Having done the test upon the panel of double planked shell and the model experiments upon the strength of beams having various kinds of constructions as motor torpedo-boats, the authors were able to find several analytical conclusions as follows.
(1) Not only the bending deflection but also the shear deformation are indispensable as regards the strength of the wooden hull structure.
(2) The double diagonal method is the best way to construct the side shell.
(3) The strength of the wooden hull structure is affected by the end fastening of each plank. (4) The phenomena of shear lag, owing to the weak shearing strength, are observed in the stress analysis of the deck plank.
(5) The stress of longitudinal members fitted inside frames or beams is not so effective.
(6) The panel of glued double diagonal plank in spite of its satisfactory rigidity and strength, has a fault to break suddenly.
Finally, the authors insist that the further investigation should be necessary upon the mechanism of fixing nails, bolts and screws and the shear lag in the panel of wooden plank.

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It is one of the most important problems for engineers to know the relations between welding faults and mechanical properties of weld joints.
In studing such problems, it was labourable and sometimes difficult to obtain the specimens of welds containing the weld faults with same conditions.
Now in this papers, we proposed some artificial methods for each weld faults which are of same sort, same size and same distribution. By such method, we could obtain the quantitative and reproducible datas for our object.
The sorts of artificial faults proposed are blow hole, slag inclusion, poor penetration, crack and undercut and as mechanical tests, static and impact tension tests, static and impact bending tests and fatigue tests were done.
At last we tested the specimens containing naturally produced faults.

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As for the degree of external constraint of welded joints in ship construction, various discussions have long been made in connection with the problems of shrinkage and residual stress, but the magnitude of the constraint has been left unknown. On the degree of external constraint we adopted in this paper the following definition ;
Degree of external constraint=Average value of transverse stress along weld line necessary to produce average dislocation of 1 mm along weld line, we obtained the magnitude quantitatively by applying two methods. The one is the method of measuring the change of root gap due to external load applied transversely to weld line before welding, and the other is the method of comparing average shrinkage along weld line due to welding with the shrinkage in free welded joint.
The main results obtained in this paper are summarized as follows :
(a) Degree of external constraint seems to be independent to thickness of plate and total weight of assembly.
(b) Degree of external constraint is generally very small. About 60 per cent, of total butt joints measured showed the degree of external constraint less than lkg/sq. mm/mm, and none of them showed more than 10 kg/sq. mm/mm.
(c) When the magnitude of degree of external constraint and welding conditions are definite, average locked-in stress increases a little with the increase of the thickness of plate.

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The method of Line Heating is mainly applied to the shipbuilding industry.
It is very effective to releasse the strain of welded structure blocks, and now we began to apply it to bend all sorts of plate into arbitrary curvature.
The mechanism of bending plate by Line Heating is thought as follows ;
1st step : Formation of plastic zone on the heating line from the expansion of the part of the line.
2nd step : Shrinkage of the heated zone and appearance of tensile stress by the existence of the plastic zone.
The worked plate is bended by the tensile stress of 2nd step. The final purpose of applying this method is to have the ability of producing an arbitrary curvature with the most economical working speed. But, it is very difficult to do it because of difficulty of controlling the working conditions.
Line Heating is also as well as any other gas working method very sensitive to the variance of the working conditions.
So, at first we must examine the sensitivity of Line Heating Method to every factor, which constitutes the working condition.
In this experiment we picked up 7 factors which constitute the working condition.
They are tip height of burner, thickness of test piece, pressure of oxygen, torch angle to the test piece, diametre of burner nozzle, volume of cooling water and cooling method.
We used the method of experimental design, orthogonal array L₃₂ (2³¹), to this experiment.
From this experiment we got the main effects of tip height, thickness of test piece, pressure of oxygen, and cooling method.
We could not observe the interactions between tip height and pressure of oxygen and between thickness of test piece and pressure of oxygen.
We could not observe the main effects of torch angle, diametre of burner and volume of cooling water.
From these results only, we may say that the method of Line Heating is most sensitive to the thickness of plate, secondarily to the tip height of burner, thirdly to method of cooling.

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Along with the growing tendency of constructing ships larger than 65, 000 D. W. T. and/or 100, 000 D. W. T., doubling system ought to be adopted in order to maintain the longitudinal strength of the ship for structures such as upper deck and bottom shell plating.
We investigated the nature of cracks at the root of one side full penetration weld joints which are inevitable in doubling system. The summaries are as follows :
(1) Root cracking of one side full penetration welds may be divided into two kinds, notably, cracking in weld metal and cracking in heat affected zone.
(2) Cracking in weld metal originates in the root notch and grows along the grain boundary in dendritic structure.
The cause is considered to be the stress concentration at root notch due to shrinkage.
(3) Cracking in heat affected zone originates in the root notch.
This type of cracking is transcrystalline. It is conceivable to be due to the so-called cold crack.
(4) In order to minimize the root cracking in weld metal, fillet type welding process would be effective.
(5) To minimize the root cracking in heat affected zone, low hydrogen type electrode would be preferable following preheating at the temperature of more than 750°C.

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This report is the second part on the theoretical studies of propagation of brittle fracture. An exact solution of dynamical stress field around a circular hole, enlarging or propagating at the constant speed, under the uniform tensile stress at infinity was obtained.
The equation of motion was solved by introducing a new conception of “expanding coordinates”, in which the radial coordinate expands proportionally with the time. In addition, the released elastic strain energy, the kinetic energy, and the critical stress were also obtained.
The general conclusions obtained are as follows :
(1) The radial displacement and the dynamical stress varies only in the region, in which the longitudinal plane stress wave propagates. (Figs. 2, 3, and 4)
(2) The released elastic strain energy decreases as the crack speed increases. (Fig. 6)
(3) The kinetic energy increases and then decreases with the increased crack speed, and its maximum value is obtained at a speed of about 40% of the sonic speed, (Fig. 6)
(4) The critical stress for brittle crack propagation at a speed of 60% of the sonic speed becomes about 70% greater than that at the extremely low speed. at some temperature. (Fig. 7)

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The use of an abundant explosive energy is one of the successful method to investigate the behavior of the brittle fracture of welded structures. Authors have previously conducted the explosive tests on arc welded mild steel tubes. Recently, however, another phase of study have been made carring out series of explosion tests on the arc welded tube specimens made of high tensile strength steel (“50 kg/mm² Mn-Si steel”, “60 kg/mm² V-Ti alloy steel” and “quenched and tempered steel”).
The purpose of this investigation is the examination of such various effects on the behavior of brittle fracture as that of the quality of steel, welding procedure (manual and submerged welding), stress relieving after welding (600°C, 1 hour heat treatment, the Linde method and peening).
Codes and numbers of specimens are listed in table 1, and the chemical and mechanical properties in table 2. The size of specimens were 400 mm diameter, 800 mm height and 20 mm thickness. The explosive (T. N. T.) was set in the center of a specimen filled up with water and detonated.
The relation between test temperature and circumferential strain at fracture for different series of steel codes are shown in figs. 5 to 7, respectively. Detailed sketches of the fractured specimens are also shown in fig. 8. Figs. 9 to 11 show the relation between test temperature and averaged thickness of shear lips appeared on the fractured surface in the three kinds of base metal, respectively. Similar relationship was observed in weld metal and heat affected zone as shown in fig. 12. It can be seen from fig. 13 that the former is larger than the latter concerning to the thickness of shear lips.
Summarizing the test results the following conclusions are obtained.
1. Comparing the as-welded tested specimens with respect to the effect of the quality of steel on the circumferential strain at fracture, it can be concluded that 50 kg/mm² high tensile steel is the best, and then comes quenched and tempered steel, 60 kg/mm² high tensile steel. And concerning the thickness of shear lips, quenched and tempered steel comes first and then 50 kg/mm² high tensile steel, 60 kg/mm² high tensile steel. In other words 50 kg/mm² high tensile steel is superior for the initiation of fracture, and the quenched and tempered steel for the propagation of fracture.
2. So far as the circumferential strain at fracture the effect of stress relieving heat treatment has not been remarkably observed. But after heat treatment the possibility of crack initiation at circumferential weld can be considered to increase. It may be the effect of the increased brittleness due to heat treatment on weld metal deposited by low hydrogen type electrodes.
3. The effect of the low temperature stress relieving by the Lide method was not appreciable. 4. In all the tested specimens peened on every layer of the outer surface, the crack initiated on the outer surface of the circumferential weld, and the strain at fracture was not so large.
The peening on the last layer can be considered to produce extremely fine cracks and strain hardning of weld metal consequently crack will start more frequently at low strain level in spite of rich ductility the base metal. From the viewpoint of the brittle fracture peening on the last layer should be positively avoided.
5. The difference due to manual and submerged arc welding was no appreciable.
6. With the exception of peened specimens cracks were usually initiated from the inner surface of the pipe, especially from the heat affected zone of longitudinal seam joints, or blow holes in circumferential weld.

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The author investigated the effect of heat treatments (quenching and tempering, normalizing, annealing and etc.) on low temperature impact resistance of pure irons and mild steels.
The structure of pure iron as quenched into water had the higher energy value at low temperature and the lower mean energy transition temperature than the annealed one.
The quenched and tempered structure of mild steel had the highest energy value at low temperature and the lowest mean energy transition temperature. The annealed structure of mild steel had the lowest energy value at low temperature and the highest mean energy transition temperature.
It was found that the structure of mild steel as quenched into water had the lower energy value at +25°C, 0°C, -20°C than the annealed structure and the structure as rolled, but on the contrary had the higher energy value at -40°C and -60°C.
The author concluded that the impact resistance at low temperature depends upon the grain size of ferrite.
The microstructures of pure iron and steel were examined by means of the electron microscope at 25°C, -30°C and -80°C. It was found that there were no difference in these structures.
The author investigated on the electron diffraction figures of iron and steel respectively at +25°C, -30°C and -80°C, and found that the spectrum lines of these specimens were diffused at low temperature.

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A marked tendency to put more and more the V-notch Charpy requirement in force on hull structural steel is seen lately, while it is not always practicable to carry out the test with accuracy. In particular, it is often difficult to prepare the test specimen with accurate V-notch in conformity to rigid requirements of machining tolerance.
The paper shows an examination on the applicability of the pressed-notch Charpy test as a commercial test. And its relation to the V-notch Charpy test is also discussed. Main conclusions are asfollows :
(1) Pressed-notch is very easy to be provided and its acuity can be kept without difficulty.
(2) Ordinary error in notch depth and a little wear of knife edge for pressing do not disturb the test data.
(3) Effect of strain aging caused by pressing notch is also practically negligible.
(4) Percentage of crystallinity is more easy to be recorded accurately in the case of pressednotch than in the case of V-notch.
(5) V-notch Charpy value at 0°C is guaranteed more than 35 ft-lb (6 kg-m/cm²), provided that the material shows cleavage depth not exceeding 5 mm in the pressed-notch Charpy test at room temperature (about+ 20°C).
(6) In due consideration on the fracture appearances and the load-deflection curves for the van der Veen tests with 3 mm and 8 mm deep notches, the author suggests that the resistance of the material to the propagation of brittle crack is well expressed by the pressed-notch Charpy data while the main meaning of the V-notch Charpy data is the resistance to the initiation of brittle crack.

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The Master Butt welding method was adopted on the construction of Hull No. 24, M. S. “TOSEIMARU”, 5, 000 D. W. T. cargo-boat, for the purpose of shortening the time on the slipway and speeding up the building period.
That's to say, two separated hulls (fore and aft, bodies) were built on different slipways, launched individually and then joined each other by the Master Butt Welding method in dry dock.
In this report, it is mainly aimed to judge the suitability of this method, by measuring the movement and the stress of the hull occured and the residual stress on the beads of Master Butt Welding which arises in the process of the work. It is also intended herein to estimate the amount of the restriction which the hull will receive from the keel block during joining work of two bo-dies.
According to the result of analizing these measurements we may consider that even the greatest blocks such as those of some hundreds tons could be welded and combined together under less restriction, as far as they are treated satisfactorily with perfect welding procedure. In other words, two blocks can be drawn each other by rather small force according to the shrinkage of deposit metal.

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船体外板に始めてZn板を使用したのは英国の電気化学者Humphry Davyで, 今から約140年前のことである。我が国で使用されるようになつてからもすでに数十年を経過している。また最近電気防食に関する技術が著しく進歩してきた。それにもかかわらずZn板の装備基準を作ることができなかつた。その原因はZn板の所要量に影響する諸元が多く, それぞれの影響程度が明らかでなかつたためである。特にZn板の性能が一定せず実験毎にかなり大きい相異があることである。しかもZn板の性能は分析成績より良否を推測するだけで実用時の性能を数字的に示すことができないから, 多数の実験を比較検討することが困難であつた。それ故Zn板の所要量を定めるためにはZn板の性能を明確にすることが第一であると考え, 先にZn板の性能試験法について提案した。この試験方法を応用することによりZn板の実用時の性能を数字的に示すことができるようになり, Zn板の取付規準を決定することが可能になつてきた。Zn板の所要量を決定するものはZn板の発生電流と船体の種々の状態における所要防食電流である。なおこの他海水の抵抗等に起因する船体とZn板の間の回路抵抗が問題になる。これ等の問題についての実験結果を述べる。

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When the inner surfaces of oil tanks are electrocoated, they show more polarization than without electro coating. But our experiments pointed out those facts that, after cut down of the current the potential of the surface became positive nearly as well as bare steel, and that, the electricity of caoting on the rusty steel increased in several times of clean surface, and that, the influence of oil films sticked on the surfaces to the effects of electrocoating seems very much complicated.
It should be worthwhile to investigate to know which is more economic the electro coating or high maintenance currents.

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It is very important to use the non-magnetic materials in the equipment of a mine sweeping boat, and these weight is massive compared with the other machinary and fittings.
We determined the chemical composition of a high magnetic steel with the careful consideration from the point of view its use, and carring out tests on mechanical properties, magnetic characters, weldability, castability and forgeability of the material, thus we got good sufficient results for the purpose.

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We know numerous methods of developing shell plate, but these are approximate methods which are founded on the assumption that every shell plate is developable. However, actually some shell plats are formed undevelopable curved surfaces by the process to shrink or to extend some parts of them. Then, if the amount to shrink or to extend is known by simple method, we can develope and mark the figure of such a shell plate on a flat steel plate rationally.
The author intends to explain one method to get the amount to shrink, and to develope such an undevelopable, curved shell plate.

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There are various methods used in the building of a ship on a building berth or in a drydock, but a popular method nowadays is the Block Assembly Method in which sections of the ship are pre-fabricated in the shops or adjacent to the slipways. These pre-fabricated sections are installed on the building berth proper in a pre-determined sequence starting from one point.
The Yokohama Shipyard and Engine Works of Mitsubishi Nippon Heavy Industries, Ltd. has built more than twenty tankers since the termination of the war, but has gradually abolished the aforementioned system of starting construction with only one point, and adopted instead the method of starting construction with the three points e. i., Midship. Bow and Stern, simultaneously. When a number of ships are under construction at the same time, the labour force for hull erection is concentrated on one ship only so that erection of the hull may be completed within the first half of the construction period on the building berth and all the work of hull, machinery, and outfitting may be progressed more rapidly.
This system promotes the progress of construction and also is advantageous in spreading the work over the various shops in the shipyard, promoting efficiency, constant use of facilities, etc.
It may be added as an example of efficient utilization of facilities, that with the above mentioned system one large tower crane is capable of installing the blocks for two 40, 000 DWT Tankers under construction on adjacent berths.

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In this report, the authors have investigated in detail the effect of web dimensions and the crankpin fillets on the statical bending strength of single throw crankshafts by strain gauges.
The conclusions deduced are as follows.
(1) Stress concentration factors (k) are given by the following formulae as for web dimensions when other dimensions are the same :
k∝1/ (b/d)^0.3 (t/d) ^1.2in load bending test,
k∝1/ (b/d^)0.3 (t/d) ^0.8in web deflection test, where, bid and t/d are the ratios of web width and web thickness to crankpin diameter respectively.
(2) The relation between stress concentration factor (k) and fillet radius (R) is expressed approximately by k∝ (1/R/d) ^0.45in both load bending and web deflection tests.
(3) The stress concentration factor (k) of the crankshaft having grooved fillet is nearly equal to that having ordinary circular fillet of the same radius.
(Remark) In this report, k is denoted as follow :
k=Bending stress at the fillet/Bending stress at the lower side of middle of crankpin

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