Dr. M. Yamagata investigated the minimum Reynolds' numbers (Rc) for resistance measurements of various ship forms and found that 1) they vary with ship forms, 2) the tendency of their variation is reverse in the case of discontinuous forms to that of the usual hull forms. We can also find the fact that the smaller the Reynolds' numbers, the greater the specific residuary resistances. These phenomena present themselves in many other experiments, the use of different formula of frictional resistance cannot always erase them out.
Are the causes of these facts to be found in the laminar boundary layer itself or in the phenomena of the turbulent layer?
The author has investigated this problem and reached to the following conclusions;
1) In the case of discontinuous forms, the separation of boundary layer is forced to occur in the region of fore body. With the fuller forms, the transition is difficult to take place, the boundary layer may separate in laminar condition for low Reynolds' numbers, while the finer forms come into turbulent state. This condition may explain the trend of Rc curve for Cb.
2) In the case of usual ship forms, the effects of Reynolds' number present themselves as the movement of the turbulent separation point, the position of which moves ahead with the reduction of Reynolds' number as the stern wave front advances.

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In order to know the pressure distribution on the bottom of the hydroplane, it is necessary to solve an integral equation of two independent variables x and y. However it is almost impossible to solve this equation for the three dimensional motion, the author has found rigorous solutions for the two dimensional case, and, using these solutions with a consideration which resembles to that of Prandtl's lifting line theory, he has reduced the general equation to an integral equation of only one variable y. This simplified equation seems to be soluble by a comparatively simple manner.

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In this paper applying the thin wing theory, the effect of immersion on the characteristics of the submerged hydrofoil is examined. The main problems considered are as follows;
(1) Substituting the submerged hydrofoil by a single vortex, the fundamental properties of the effect of immersion are clarified.
(2) Expressions for the lift, wave resistance and profil form of an arbitrary vortex distribution are introduced.
(3) An applicability of thin wing theory to the submerged hydrofoil is discussed.
(4) A relation of types of vortex distribution to the wave resistance is examined.

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When a directionally stable ship deviates slightly from her course owing to some external disturbances she can return to a new state of equilibium without any steering.
But in this case the ship's new track is quite different from her original one. In order to keep her course, the helmsman has to use the rudder continuously. In this respect, it is of much importance to study the course-keeping quality of a ship in steered conditions.
The author has studied the motion of a ship when steered, on the assumption that the rudder angle is given directly proportional to the angle of yaw and the distance of deviation from the original track.
The following results have been obtained:-
(1) When the helmsman gives a rudder angle directly proportional to the angle of yaw, the ship's head may come back again onto her course, but in general it is impossible for her to reach her original track.
(2) When the helmsman gives a rudder angle directly proportional to the distance of deviation from the original track, the ship tends to come back onto her original track, but in this case an initial deviation or yaw increases with a sinuous course.
(3) When a rudder angle is given to follow the two modes of steering above mentioned, the ship may come back again onto her course and keep her original track.

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This work is one of a series about the corrugated bulkhead of my previous paper. Now the foundamental problem as Fig.1 is discussed. Mathematical techniques used here are of the method by Dr. Ota and Handa (published previously in this society council), moreover a general theory of complex variables.
The results obtained here are not so easy for numerical treatment as expected, but this investigation will give one hint for exact or apploximate solution tried later on this work.

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Formerly few studies proposed on the stability of the rectangular plate with elastically built-in edges except those in “Theory of Elastic Stability” by S. Timoshenko. The author derived a new idea by using infinite matrix method, which can be apply under the condition of different elastic constant of opposed edges.

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It is familiar that stress concentration and triaxiality have great influence upon the transition temperature of notch sensitivity of mild steel. So I performed impact tests of various notched specimens, and studied the influence of the followings : i.e. (1) Notch radius, and Thickness of specimens, (2) Notch angle, and Notch depth, (3) Side notches,
A 13mm. thickness rimmed steel was used for the tests.
Using the theory of the notch sensitivity of mild steel stated in the 1st. report, I obtained curves of mean energy transition temperatures vs. stress concentration and triaxiality matching very well with the experimental results. And also I verified that there is a certain relation between the absorbed energy at 0°C and the temperature on the 2.6kg-m/cm² (15Ft-Lb energy of the standard specimen) absorbed energy level.
Some detailed discussion about absorbed energy will be left to the next report (the 3rd. report).

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An oil-tanker “Seiho Maru” was built at Kawasaki Dockyard in January of 1952. The authors considered that the lines of such a large and full ship as “seiho Maru” should be determined from the point of view of arrangement, construction and equipment as well as propulsive performances. Therefore, in this report, comparisons were made for two kinds of lines on basis of arrangement, construction and etc., one of which was the original form of “Seiho Maru” and the other modified form. Then, for three kinds of lines, adding a thirdform to the former two lines, comparisons were made on a base of propulsive performance.
It will be shown from their results that a certain lines may be determined so as to have a superiority in every point of view.

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From the view point of study of safety at launching work and design of launching trigger, it is quite indispensable to grasp the accurate magnitude of starting force of ship at launching.
Authors tried to measure actually the starting force of ship by means of magneto-striction type pressure gauge placed between launching trigger and hydraulic ram.
The magnitude of starting force thus measured by authors are much greater than that calculated from the theory and the data accepted up to now, and we discovered that the apparent frictional coefficient calculated conversely from the measured starting force lies between 0.005 and 0.012.
We believe the magnitude of actual starting force depend not only upon the quality of grease, but upon the quality and quantity of soft soap and especially upon the exposed scope of grease.
The value of frictional coefficients gained by authors are that considered the all factors mentioned above.

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Authors measured the launching force by a new method. The method is as follows:
The launching force was obtained by observing the change of current due to the change of magnetic flux in the search coil around a Ni-Cr-Mo steel bar of 28m/m diametre and 470m'm length, attached in the ram of the hydraulic trigger and compressed by the launching force.
Applying this method to the “Steel Ball Launching” of several ships, authors show the statical fricitional coefficient is about 0.020.

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Among many shell expansion methods, “The Base Line Method” is the most simple and practical.
We can draw the expansion of shell plates on the flat steel plates immediatly after the frame and seam battens are provided. The other methods need the complete expansions on the mould loft before marking on the steel plates.
But the base line method cannot be applied to such twisted plate that the angle between frame lines and seam lines are far from right angle. Because the base line on the Body Plan does not correspond to the straight line on a flat steel plate used in marking.
Assuming that a shell plate is divided into small parts by many planes parallel to the frame line, the line, straight or curved, which passes through middle points of every frame, will work as an axis of torsion of each part.
We have to expand twisted shell plates relying on this line. We cannot obtain good expansion of these irregular plates by any other method without consideration of the matters above-mentioned.
There is to be a special curve on the twisted plate that was straight when the plate was flat.
Authors found out the simple practical way to draw this special curve on the Body Plan. It needs only five or ten minutes to draw the curve. We name this curve “The Corrected Base Line”.
Using the corrected base line we can expand most accurately in the same way as the ordinary base line method.
We applied this method to almost all shell plates of ordinary cargo ship. The results were satisfactory and we could cut down the labour to expand shell plates.

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Lately highly welded vessels began to be constructed in Japan, and this tendency has brought a revolution into method of fabricating the hull.
Now nearly all component parts are prefabricated on the ground, which inevitably forces the main effort to be concentrated on the welding skids.
The authors show the generality of ships constructed at Kawasaki Dockyard as of 1951, the proposed utilization of the welding skids, and the actual utilization record of the skids area by major ships.
Basing upon these actual data, they defined the “Coefficient of Welding skids” which indicate the possible turn-over of the welding skids.
By the use of the coefficient of skids, they analyse the relation among the skids area, the capacity of plater's shop and the number of erection berths, then they attempt to set a limit of skids area necessary for the construction of welded ships.

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As the windlass frame of a cargo-ship was broken in a harbor in the course of leaving the shore, we carried out the material test of the anchor chain and the windlass frame including destructive test and strength calculation of the frame, and the measurement of the deformation and the calculation of load on the anchor chain to investigate the causes of its failure.
Results of these tests showed that there was no defect in the material of the frame and anchor chains. It could be suspected that there might have been some traces of minor cracks at the fractured surfaces of the frame prior to its failure, but it is highly questionable due to the various opinions regarding its existence. The microstructure of the part of the material which was doubted to be incipient cracks seems to be a little inferior to the other parts. But the starting point of the fracture was not found in that part but in the part which is sound. And from the view point of propagation of the cracks we are sure that the cause of the fracture is not in the materials involved.
In the destructive test of the windlass frame the breaking load was found to be 112tons which coincides both with the results of strength calculation and the measurement of the deformation of the chain links inside the hawse pipe. At the outside of the hawse pipe the load acted on the chain cable was found to be 220-240tons considering from the measurement of the deformation of the links and this value is comparatively consistent with the calculation. This load is much larger than the breaking load of 174tons specified in the AB rule and it is reasonably believed that the anchor chain itself was about to break. According to the above consideration it is within reason to believe that the cause of the trouble lies in some undue large load which acted on the windlass frame. If we make the strength of windlass frame much stronger than chain cable, the breaking of anchor chain would take place prior to the frame failure and it would then be easier to handle the situation. But the windlass frame of any ship today are equipped with almost the same strength for a given requirement and we don't believe that the frame of this particular ship was especially weak in comparison with other ships.

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During the last year a considerable amount of information has become available regarding the employment of bunker oil in diesel ships.
We wish that the fuel bill of diesel ships as a result of using bunker oil instead of diesel fuel are equal as that of turbine ship of using high temperature and pressure steam as possible.
The comparative tests on the purification of bunker oils between Sharples type and De Laval type were carried out at Kobe Shipyard & Engine Works, Central Japan Heavy Industries, Ltd.
As our shop tests proved, it is necessary to have a very high separating efficiency for purifying bunker oil so completely that it can be used without additional trouble in a diesel ship, and the disc type is therefore not suitable for this purpose.
The O.S.K. Line new vessel, the “Atlas Maru & Andes Maru” has been arranged to operate on bunker oil.
She is propelled by Central Japan Sulzer 10 SD 72 engine of 7000 B.H.P., and equipped with four Sharples centrifuges of “18B” type.

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We made various experiments on the ship's fire-proof paint for selecting which paint to make use of.
(1) We adopted the organic fire-proof paints for the steel plates of cabins. Though complete fire-proof ability was not obtained, they are fine, easy to paint, water-proof and anti-corrosive. While some inorganic ones showed complete fire-proof ability, but generally other abilities were inferior to the former.
(2) We adopted melamine resin baking enamel for the steel furnitures, because it excels in appearance, hardness, water-proof ability, and considerable fire-proof quality.
(3) For wooden products, fire-proof paints must have property to swell and become porous when they are heated by fire. Some of them were comperatively successful in it, but water-proof ability and fineness were inadequate.
(4) To protect ships from fire, we must build the fire-proof construction such as fire-proof sections, remove inflammables and disuse wood in advance of using the fire-proof paint.

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