It is doubtless that sea surface is the most reasonable and convinient route to transfer the huge badies of caissons from the factory where they are built to the place where they are to be set up. The present experiments were carried out to get the necessary data for the transportation of caissons. The apparatus of experiment are rather rude and the method of analysis is not so rigorous, but the results obtained are useful enongh for our practical purposes.

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In Mitsubishi Experimental Tank (Nagasaki), investigations have been made into the repeatability of self-propulsion tests on full ship forms by repeating the resistance tests, the self-propulsion tests and the propeller open-water tests for a 7m wooden model of a typical tanker.
The self-propulsion factors deduced properly from the self-propulsion tests are scarcely affected by water temperature, and the standard deviations of the self-propulsion factors from their mean values are about 0.006 for e_r, about 0.005 for w_m and about 0.01 for t, and the estimated standard deviation of SHP of the actual ship due to the dispersion of the self-populsion factors is about 1.5%.

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This paper treats the analysis of the time optimal control problem in the steering of ships. The equation of steering motions of ships can be described as a differential equation of [1st] order as follows :
Tdψ/dt+ψ=Kδ
where T is a constant which represents the quick responsibility of -ships, and K is a constant which represents the turning quality.
The performance of the turning motion of ships is decided by these maneuverability indices, T and K.
On the other hand, some optimal control problems in automatic control system are solved by application of the Pontryagin's Maximum Principle.
The problem of optimal control treated here is to minimize the steering time which ships take to turn an assigned turning angle, by application of the Pontryagin's Maximum Principle and maneuverability indices T and K. The turning test on the actual ship proved this method was proper.

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In regard to the angular velocity of a main steering gear, American Bureau of Shipping and Nippon Kaji Kyokai establish the following rules :
In American Bureau of Shipping, the steering gear shall be capable of moving the rudder from 35 degrees on one side through 30 degrees on the other side at an average rate of travel of not less than 2 1/3 degrees per second. Also, in Nippon Kaiji Kyokai, the main steering gear should be capable of moving the rudder from 35 degrees on one side through 30 degrees on the other side within 28 seconds with the ship runnning ahead at the speed specified in art. 13 part 2 of the N. K. rules.
At the present stage, these rules are uniformly applied to all vessels, regardless of size and values of maneuverability indices T and K. The writer thinks that the application of these rules to all vessels is not proper, especially for such ships of slow response as supertankers or such ships required of quick response as catcherboats when in turning motion.
From the viewpoint of Optimal Control, the writer considers the angular velocity of the main steering gear should be matched with the performance of the steering motion of ships. The next new rule has been obtained as follows :
The optimum steering gear shall be capable of moving the rudder from 35 degrees on one side through 30 degrees on the other side at the rate which is 0.96 times of the maneuverability index T, with the ship running ahead at the speed specfied.

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Double wall caisson is a type of open dredge caisson applied to the foundations of long span bridges over water, for example, the foundations of Mackinac Strait Bridge in U. S. A., and is now considered to be applied to the foundations for the Bridge interconnecting Honshu with Shikoku in Japan. This report describes the results of our study on the method to build this type of caisson on the shipbuilding berth, and its merits are as follows :
(1) The caisson is capable to be built up in laying condition on a berth due to its shallow draft after launching. And as the result of it, remarkable decrease of building time and cost can be achieved.
(2) The caisson, whose height is larger than its diametre, can be built up in one body and assembling work at site can be eliminated.
(3) The caisson can be easily towed in laying condition compared with upright condition.
The fact was found that a small quantity of water poured into the compartments of the double wall could upend the caisson from laying condition to upright condition, due to free water effect in floating body.
This phenomenon was investigated experimentalily by models of six different heights, and we obtained diagrams for transitions of the stability curve due to the quantity of the poured water inside of the double wall (see Figs. 8-13), and for critical quantities of poured water to upend the caisson and differences of floating drafts on each floating conditions. (see Figs. 14-16 and Table 1)

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It is well known that the strip theory is based on many assumptions. In those, three-dimensional effect, advance speed effect, viscosity effect and section-shape effect are investigated in this paper, and correction coefficients are given for them. The accuracy of the strip theory are examined comparing the responces, with and without correction, of the ship in regular head seas.
The effect of viscosity and section-shape can be ignored, practically. But three-dimensional effect and advance speed effect are rather large over the wide range of λ/L.
To verify the practical accuracy of the strip theory, much should be investigated, such as nonlinear effect and restricted water effect.

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Several methods were recently proposed for the purpose of direct determination of wave-making resistance from the measured wave pattern. Among them, the method based on the Fourier transform of the wave profile at the longitudinal cut seems to be very excellent. The authors applied this method to the measured wave profiles of two models of the simple shapes and computed their wave-making resistance. The comparison of the above results with those of towing test showed a good agreement. It is also discussed in the present paper how to estimate the unavoidable error due to the measurement at a finite distance sideways from the ship, since this method of wave analysis is derived from the asymptotic expression of the wave pattern at an infinite distance from the ship.

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A new ship model basin of Ishikawajima-Harima Heavy Industries Co., Ltd. was established at Yokohama in January 1966. It consists of a towing tank (100m×10m×5m+10m×2m×1.5m), model manufacturing shops and laboratories.
The towing carriage is made of steel box girders and its maximum speed is 5m/sec.
The remarkable features of this model basin are as follows :
(1) The Thyrister Leonard System is adopted to the speed regulation of the towing carriage. Then the sufficient steadiness and setting accuracy of the speed of the carriage are preserved.
(2) The application of sequence program with punched cards made possible to simplify the measuring work and only one or two persons are needed for the ordinary experiments.
(3) In the self-propulsion tests, the rate of propeller rotation is automatically corrected according to the relative speed between the carriage and the model. By this method the self-propelled model settles into a steady speed in a comparatively short time, therefore in spite of short length of the tank, sufficiently reliable data are obtained.
(4) All experimental data in ordinary tests are detected directly by digital transducer.
(5) The special detecting mechanism is used for the thrust measurements, which needs no slide coupling and the small displacement of the propeller shaft is converted to the phase difference between a couple of pulses.

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In order to serve the improvement of performance prediction of high-speed vessels, theoretical and experimental investigations into the propeller cavitation in oblique flow condition have been carried out.
A series of supercavitating propellers were tested in cavitating oblique flow condition. The test results show that in non-cavitating condition the variation of propeller characteristics due to the shaft inclination is related closely with pitch ratio but little with expanded area ratio, while in cavitating condition the variation decreases with cavitation number and the effect of geometrical particulars of propeller is not so clear as in non-cavitating condition.
In view of the analysis and the application of the test results, a quasi-steady method was developed to calculate the propeller characteristics in oblique flow condition from those in axial flow condition. The comparision of the experimental and the calculated results showed pretty good coincidence.

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This paper presents results of experiments on the transverse loads acting on the T2-SE-Al tanker model in regular waves. Hydrodynamical pressures were measured at five locations, two on the bottom and three on the side, along the girth of the midship section. Relative water level with respect to the hull at the midship was also measured. Tests were made in regular head waves having lengths of 75, 100, 125 and 150% of model length. Approximate calculations of pressures on the bottom were carried out by means of the strip theory and compared with experimental results. Good agreement between calculated and experimental values was found.

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A computer program for the calculation of heaving and pitching motions of ships in regular waves, by the strip method, was developed by Fujii and other. The authors tried to extend the program to calculate longitudinal wave bending moments and shearing forces in regular waves, not only at midship but also various position along the ship length.
The fundamental equation of motion is based on Watanabe's theory, and added mass coefficients and damping coefficients are obtained by the Tasai's method.
The formulae of wave bending moments and shearing forces are those which are proposed by Fukuda.
Some calculations on a gigantic tanker both in regular and irregular head waves are carried out and the results were compared with the requirement of a classification society.

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In order to examine exactly the strength of transverse rings of oil tanker with long cargo tanks, it is necessary to take into consideration the effects of deformation of the longitudinal members which support the transverse members. Much investigation has been done in regard to this problem as the shearing deformation of wing tank. It seems to us that the shearing deformation will occure not only in wing tank but also in centre tank. The authors try to make the three dimensional strength calculation for all tank parts and then try to analize the results of experiment on an actual ship and to make some considerations upon the longitudinal members.
From this study following things are found :
(1) The deformations and the stresses in the transverse ring of a big tanker can be estimated with good accuracy for the practical uses by this method.
(2) The shearing deformations in the cross section increase the stresses in the lower part of the transverse ring.
(3) In way of the tank parts, the shearing force seems to be more shared by the longitudinal bulkhead and to be less shared by the side shell than what is usually considered.

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In order to investigate the transverse strength of bulk carriers, experimental tests have beer made on six newly built ships, including 16, 000 DWT class to 55, 000 DWT class bulk carriers. The tests have been carried out under such loading condition of filling sea water into their top side tanks, and the measurements have been made on the hold frame stresses as well as on the vertical and the horizontal deflections of upper deck construction.
Based on the results of these, analytical formula has been deduced to calculate the hold frame strength, which can illustrate fairly well the mechanical behavior of bulk cargo carrier constructions, and the frame stresses have been evaluated for various loading conditions.
The general conclusions obtained from this investigation are as follows.
(1) Degree of the end fixty of hold frames is usually lowered by the deformations of hopper or top side tank constructions in the plane of their transverse cross section. In this analysis, an equivalent span of the hold frames is introduced to calculate the frame stresses instead of directly considering the effect of their plane deformations.
(2) The load carried by web frames and ordinary frames is almost proportional to their values of the moment of inertia, and thus the bending moment in extraordinary large sized web frames becomes comparatively large one.
(3) The effect of load acting on the bottom structures on the magnitude of frame stresses is usually significant.
(4) Fairly high stresses might take place in hold frames under certain loading conditions, e. g. in an empty hold under fully loaded draft condition.

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In this paper studies are made on the application of displacement method to the analysis of two-different types of problems in two dimensional theory of elasticity.
The first study is to develope the computer programming for stress analysis of mixed boundary value problems which are frequently encountered in engineering practice and yet reliable method of analysis is not well established. Taking a perforated square plate streched in one direction by a certain prescribed edge displacements as an example, stress distribution around a hole was calculated. Comparative study of the results obtained with that of previous study in which the plate is streched by uniformly distributed edge loads showed significant difference on the stress concentration factor and stress distribution.
Computer programming is also developed for analysis of thermal stress problem under arbitrary temperature distribution. Thermal stress distribution of a rectangular plate under a given temperature distribution was also studied and good agreement was confirmed with the results of previous investigation. Study on the application of this method to the initial stress problem such as residual stress problems due to welding or heat treatment is underway.

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In this paper the axi-symmerical deformation of hydrostatically loaded elastic-plastic cylindrical shells and posibility of axisymmetrical collapsing from these elastic-plastic deformed conditions are studied. From calculating about the some numerical examples, relations of pressure and deflection are obtained, and it is shown that there exist two modes of collapse corresponding, respectively, to short shell with hearvy frames and long shell with weerk frames.

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This paper treats the transmission of the vibrational waves through a beam with many appendages.
The conclusions are as follows.
1. When beam system has many appendages which may have couplings between flexural and longitudinal waves, the amplitudes of flexural waves (progressive and near field waves) and longitudinal waves (progressive waves only) of adjacent beam elements both sides of an appendage can be related with matrix. So the amplitudes of both extreme ends can be connected by the products of matrices when the appendages, which must not necessarily be same property, are attached in arbitrary distances.
2. In the analysis of flexural wave transmission problems, matrix mentioned above can be simplified in the relation of progressive flexural waves only when masses, which have no coupling properties, are installed in larger distances in comparison with wave lengths.
3. The transmission waves can't always be attenuated even if another new masses were fitted. The ratio of amplitudes of adjacent beam elements can't be determined locally but the boundary conditions of whole system must be considered.
4. The idea that the magnitudes of transmission energy are expressed by the amplitudes of progressive and near field waves clarifies the mistake of “propagation constant” mentioned in other literatures.
5. To check the above theory, the bending wave propagation on a beam with lumped masses was measured. In general, the theory and the experiments were fairly in good agreemant.

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The paper deals with the estimation of natural frequencies of the vertical vibration of ship hull, taking into account the recent investigations on the effects of fineness of the hull, shear deflection and rotatory inertia and the virtual inertia coefficient of the water. Some empirical factors obtained from the observations on board actual ships are shown. Here are also put forward new empirical formulae for estimating inertia coefficient of the water surrounding a vibrating ship based on the data obtained from several ship-shaped models.

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The numerical solution techique was applied to the equations of the coupled torsion-horizontal vibration of a beam, and the computing program by means of a digital computer was made.
Using the above-mentioned program, preliminary calculations were made for the uniform beams, the main result of which is that, in almost of all the case of the uniform beam, the horizontal and the torsional modes of coupled vibration have the same number of nodes. Another result is that the corresponding horizontal and torsional modes can have different number of nodes if the distance between centre of mass and of torsion varies along the length of the beam. The calculation were also made for 4 actual ships and the results were compared with measured ones. For the ships in the present calculation the effect of coupling on the frequency is small and can be neglected for the calculation of lower modes such as excited by reciprocating machinery. Although the errors between computed and measured frequencies are about 10%, the improvement of computing accuracy can be expected by further study on the virtual mass of the water and on the rigidity and the centre of twist of the ship with hatch openings.

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Experiments were made to investigate the notch toughness of bead welded high tension steels, WT 50, WT 60 and WT 80. Kinzel bend test and Double Blow impact test were performed to make clear the characteristics of fracture initiation in the heat affected zone of weldments. As the results of experiment, the following were revealed.
(1) The bend angle at maximum load was proposed as the most suited criterion to measure the ductility transition in Kinzel bend test. It was shown using this criterion that the weldments were remarkably notch brittle as compared with base plates.
(2) Energy for fracture initiation (W_i, ) vs. temperature curves were measured in Double Blow impact test, and a ductility transition temperature, (T_rEi) 2, was determined from these curves. The adverse effect of welding was marked in WT 60 and WT 80, whereas such effect of welding was unexpectedly slight in WT 50.

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An investigation was performed into the effect of mechanical stress relieving on low load fracture of welded wide plate, reported by Prof. H. Kihara and his research group, and the analysis of the effect was made, based on the concept of the flow and fracture stress curves.
In the analysis, the history of plastic stress and strain at the tip of the notch was pursued by taking into account of so-called Bauschinger's effect and also introducing the concept of Orowan's plastic constraint for a sharp notch. And a reasonably assumed value was used for the strain concentration factor of the notch.
The result of the investigation showed that this new method of analysis was succeeded in clarifying quantitatively the mechanism of recovery in fracturing load due to mechanical stress relieving.

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In the preceeding reports, the authors discussed on the several kinds of crack arrester model with application of two dimensional elasticity theory of cracked plate. Numerical calculations and some preliminary experiments showed that the brittle crack propagaion arrest could be explained by a relatively simple fracture mechanics criterion based on Kc-concept.
In this report integral stiffener type arrester model is considered. An approximate calculation was made to see the effect of geometrical factors of the stiffener, such as its breadth and depth, on the stress intensity factor of the crack running perpendiculer to the stiffener. Some experimental checks were tried using the double tension with integral arrest stiffener model and the results showed a good agreement with the theoretical estimation.
A further study on several other types of arrester is now in progress and the paper on it will be reported in near future.

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Previously the authors investigated the effect of low cycle fatigue on the brittle fracture propagationarrest characteristics of ship steels. This paper concerns with some fundamental aspects of brittle fracture initiation from fatigue crack. It is of practical interest to know quantitatively to what extent the fatigue cracks, once they happened to grow in ship hull members, should affect the susceptibility to catastrophic failure.
Toughness of ship steel against brittle fracture initiation was investigated using wide plate specimen (300 & 500 mm wide) containing fatigue crack. Some observations on fatigue crack growth rate were also made. The steels tested are 15 & 20 mm thick ordinary ship steel plates and fatigue loading considered here is repeated tension.
The followings have been obtained conclusively :
The material deterioration due to repeated plastic straining seems to be relatively slight.
The specimens with low cycle fatigue crack showed higher toughness than that of the base plate specimen with machined notch, for which the tilting of fatigue crack and the residual compression stress developed in crack tip zone seemed to be responsible.
On the other hand reduction in fracture toughness is observed in the specimen with high cycle fatigue crack where the above two factors are almost absent.
A simple expression is formulated with respect to fatigue crack growth rate under general yielding condition.
Further investigation is required to ensure the validity of the conclusions obtained here.
Additional research program on high strength steel for ship structure is now in progress.

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This paper describes the two step low cycle fatigue tests on hourglass shaped specimens of a 60 kg/mm² high strength steel. Strain controlled tension-compression fatigue tests were performed to study the damage processes in low cycle fatigue. The cycle ratio in the first step was varied in five conditions.
It was found that original material of the 60 kg/mm² high strength steel showed in the general the similar behaviors to the 80 kg/mm² high strength steels which were studied in the previous report. The relation between longitudinal plastic strain amplitude and crack initiation life for original material indicated the linear relationship in the log-log plot. The materials which were damaged by the first step strain cycling of longitudinal true strain amplitude of 0.05 with the cycle ratio of 0.19, 0.38 and 0.57 on the crack initiation basis, showed the knuckled line relations of ε-N_c curves. The knuckle point was found on the strain level in the first step. The value of index in the Manson-Coffin equation for materials damaged by the first step strain cycling is smaller than that for original material in the case of step-up test. For step-down test little difference was found between the indices for the original and the damaged materials.
The mean value of the usage factor on the crack initiation basis was 0.82 to 1.09, and that on the failure basis was 0.93 to 1.01. Cycle ratio in the first step scarecely affected the static fracture ductility of damaged materials. On the contrary significant decreasing tendency of the cyclic fracture ductility was observed for damaged materials with increasing cycle ratio in the first step as a parameter, where the cyclic fracture ductility was defined as the product of total true strain amplitude and kth power of cycles to crack initiation in the second step. The cyclic fracture ductility for materials tested by step-down method was always higher than that for specimens tested by step-up method.

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This report presents an experimental study investigating the dynamic pressure exerted on tank walls of ship by swashing internal fluid.
The case, in which no obstacles such as swash bulkheads or deep girders existed in the tank, was reported already in the previous report.
In this paper, the case, in swich a swash bulkhead was inserted at the center of the tank, was dealt with.
In the present experiment, second to the experiment described in the previous report, the bulkhead was made of strips, and its breadth and the height of its center were changed systematically, in order to observe the influence of the bulkhead.
From this experiment, we derived the experimental formula for the force acting on the end bulkhed and the swash bulkhead.
In the third experiment, the swash bulkhead of the practical type were tested. The results of this experiment were compared with the ones of the second experiment, and experimental formula were reformed for the use in the actual swash bulkhead.
From the above results, the effectiveness of the swash bulkhead was examined as follows.
At first, with a view to observing the burden of the end bulkhead, the maximum waterhead which could occur on the end bulkhead was calculated by the experimental formula, and the extent of reduction of maximum waterhead by the insertion of the swash belkhead was examined. Then the limit percentage of the swash bulkhead, which is useful for the reduction of the burden of the end bulkhead was calculated for the arbitrary tank length.
Then, in view of minimum weight design, the effectiveness of swash bulkhead was exmined, considering the total force on the end bulkhead and the swash bulkhead.

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Measurements on the dynamical forces by the water in a tank and the stresses induced by them were carried out on an ore carrier. (The ore carrier was used in order to avoid danger of gas explosion caused by measuring instruments.) Measuring items are the accelerations of ship motions, the dynamical pressures by ballast water and the stresses due to them. Results are as follows.
(a) The motion of the water is very dull in the tank which has many transverse members in itself such as side tanks.
(b) But in the tank located at fore part of a ship, the motion of water is considerably larger than in the midship tank.
(c) The load on a swash plate is much smaller compared with its strength.
(d) At slots of a horizontal girder web plate, there may occur tearing forces of remarkable magnitude in a severe case.

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Measured stresses and deflections are compared with calculated ones. Method to calculate the correct bending moment at lift by the stern, considering the effect of inertia force of virtual mass, is established. The values of virtual mass coefficient kw lied between 2.23.0. The contributions of the super structures to the longitucinal strength and rigidity are discussed. Strength of stress concentrated parts at double bottom is examined and the parts are proved to be safe from fatigue failure.

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Model tests of tanks are carried out by the experimental design method.
Flow rate, nozzle height, and nozzle diameter of inflow gas are selected as elementary factors which affect the gas purging efficiency.
The results of variance analysis are as follows.
1) The case that difference of densities of inflow gas and initial gas in tank is small.
Flow rate is, only, considered as significant factor at 5% level of significance.
The relation to purging efficiency is shown in fig. 10.
2) The case that the density of inflow gas is larger than the initial gas density in tank.
Nozzle height is, only, considered as significant factor at 5 % level of signficance.
The relation to efficiency is shown in fig. 11.
3) The case that the density of inflow gas is smaller than initial gas density in tank.
Nozzle height and nozzel diameter are considered as significant factores at 5% level of significance.
The relations to puring efficiency are shown in fig. 12.

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