The roughness effect of the surface of ships has been measured by the scale of sand roughness calculated by Schlichting, but this seems meaningless because of the discrepancies between the nature of the painted surfaces and that of the sand roughened ones. The authors present here a theory of resistance of the wavy roughened surface, based on the mixture length theory containing the viscosity effects which is proposed before by the senior author in this institution.
The numerical calculations for a circular pipe and a flat plate showed the variation of resistance coefficient with Reynolds number is nearly parallel to that of the smooth surface. A method is indicated to find the effect at large Reynolds number from a simple experiment of model plate.

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Since 1949 the experimental towing tank of Osaka University has heen reconstructed, which was lost in 1945 by the unfortunate air attack. This paper treats the design problems during this work.
Some notes of manufacturing and setting the rail are mentioned. Theoretical and experimental analylis of the motion of the towing carriage gives a rational basis of design. As the results, the travel of acceleration and retardation of the carriage is shortened considerably, and in spite of the short tank length (52m) relatively high speed test (5m/s) is possible. The automatic control to keep the constant speed during a test is also constructed. The theory of servomechanism is successful for this design.

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It has been believed that when a ship is steered, it will at first drift outward considerably, and then drawing the Figure of an“S”, cut the original course and will turn gradually inward as is shown in Fig.5 A.1.
In fact, according to results of turning trials of actual ships, some of them drift outward as much as one-third of their length, and a majority of them seem to drift outward to a considerable amount.
On the other hand, accoring to records of the“Turning course recorder”or results of model experiments, it will be noticed, that there is no“drifting out”or such slight“drfting out”that ships seem to deviate tangentially from their original courses.
The Author has investigated into the difference between the results of turning trials of actual ships and that of model ships both theoretically and experimentally, and describes in this paper that the amount of“drifting out”is so small that it does not exceed one per-cent of the ship's length, and he mentions that the present method of measuring the ship's turning path on the turning trial is not sufficiently accurate.
The Author also proposes a method of obtainig more accurate turning path of actual ships.

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Now defunct Japanese Navy prescribed, at its designing of war crafts, in consideration of their stability capacity, the permissible lowest values of GM, OG, Stability range, etc. separately, in accordance with the class of vessels and their sizes.
Later on, however, due to the development of stability theory, it became possible to determine the stability capacity, by applying the organic relation of these values mentioned above and obtaining a value that is the combination of these values.
In this thesis the authors, basing upon the“Theory of Safety Criterion of a Ship”established by Prof. Watanabe, have calculated the Safety Criterion c Value, studying the actual instances of 15 vessels, including destroyers and torpedo boats of the defunct Japanese Navy, and about 90 of their different conditions and analysed them from various angle, such as the transition of the history, and the statistic distributional state.
This study of the authors has led to the possibility to determine the permissible lowest value of safety criterion of naval small crafts.

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The questions to the vibration at the stern of single screw vessels has recently become serious.
That behaviour is original and anomalous compared with the normal type of transverse vibration on ships.
There is increasing vibration amplitude in the after-quarter of the ship, with very little or no vibration noticeable on the hull forward of the after-quarter point.
The maximum vibration occures at the stern of the ship.
The distribution of amplitude along the hull is shown roughly in Fig. 1.
Professor L. A. Baier published his observation and its solution how he had eliminated the vibration at the stern in Trans. of S.N.A.M.E., 1952, Vol. 6.
The author observed similar phenomena on several oil-tankers on service, and found a fact that some parts of engine (including H.P. and L.P. turbine, condenser, reduction gears, piping and etc.) also vibrated transversely.
The frequency of hull and engine is nearly equal to number of blades of propeller×r.p.m. of shaft.
So, the author studied them theoretically in view of the coupled oscillation concerned with hull and engine, and forced by the unbalanced power of propeller.
Fig. 2 & 3 Rough arrangements of hull and engine.
Fig. 4 Whole system corresponding to hull and engine.
Fig. 5 Distribution of force generated by propeller and reaction of engine.
Fig. 6 Diagram of frequency equation-(35).
Fig. 7 Amplitude of several points along the hull; result of equation-(43).
Fig. 8 The modes of hull under forced vibration by propeller ; the eighth mode shows the vibration at the stern.
Fig. 9 Varions type of the vibration at the stern based on forced frequency and stiffness of engine.

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The method of evaluation of the displacement coefficient for various riveted joints was developed and the calculated values were compared with various experimental results in our previous report.
In this paper, to investigate the elastic behaviour of various types of riveted structures by the use of calculated displacement coefficient, tension tests of riveted doubling structures were designed. Comparing the values calculated by measn of the above method with the experimental results, good agreement between them was obtained.
And the latter part of this paper, taking account of the elasticity of riveted bracket connections at the ends of beams of ships, the experimental results at Glengarnock on ships' structural members by B.S.R.A. was discussed with good results.

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The authors performed towing test of a wooden model ship under regular waves and measured the pressure distributions at foreward bottom of the model when she was slamming, by using 19 specially designed pressure gauges.
The maximum pressure observed reached about 4 to 5 times of static pressure under regular waves and position of maximum pressure located about 0.1L from F. P., and dynamical pressure became practically zero at about 0.25L from F. P..
According to the experimental results, maximum pressure seemed to be related to the relative normal velocity of ship to wave rather than pitching or heaving velocity. And this result is expected from rough theoretical consideration written in Appendix and this maximum pressure can also be estimated from the pressure measured by falling test of flat or wedge shaped body on the surface of water.
Slamming appeared when the ratio of length of wave to that of ship became about 1.1 to 1.2 in this test.

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Recently, in many ships, some cracks occurred at the corners of the entrance of house wall. The author considered this cause that, the house wall were subjected to the shearing strain by the difference of the displacements of upper and lower decks and so the large stresses occurred at the corners of the entrance. In order to calculate the shearing strain of the house wall he applied the theory published by W. Hovgaard mutatis mutandis and cleared that the fairly large stresses are possible to occur at the corners of the entrance. The cause of damages of this kind seems to be cleared by this analysis, although this analysis contains some assumptions about the effective area of deck plates, stress distribution in the bulwark plate etc..
The counter-measures of damages of this kind are
1) to enlarge the radius of corners of the entrance as large as possible.
2) to design the situation of the entrance as far as possible from the end of superstructure.
3) to change the connections of house wall from weld to rivet in order to relieve the shearing strain of house wall.
4) to reinforce the corner parts of the entrance.

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This paper presents the results of tests on the five large ship structure specimens which were conducted by the Harima Ship Welding Committee. The tests are made to investigate the extent of stress concentrations and areas affected by structural discontinuities so as to furnish data necessary for improving current design. For this purpose, five specimens are chosen which represent the constructions at the intersection of a bottom longitudinal and a transverse bulkhead as found in a design of 18, 000 D.W.T. welded tanker.
The following problems are presented by the five specimens, i. e. Effects of flanging radius of bottom longitudinal, Effects of tripping bracket on bottom longitudinal, Effects of cutout form and soft toe, Comparison between a through bracket specimen and a non through bracket specimen.
The elastic and failure tests are performed by the 1, 500 tons tester at room tempexature. Stress values in the region of the intersection are compared with stresses in the surrounding area bordering the intersection. Stress concentrations and energy for fracture on each specimen are also compared.
It is concluded from the tests results that the elastic or plastic behaviour and ultimate strength of no. 1_??_4 specimens differed little from one another, and no. 5 specimen shows its superiority as may be reasonably expected.
Lastly, the data are compared with measured stress values in an actual ship while being launched, and the results of earlier American tests sponsored by the U.S. Navy (the Welding Journal, February 1951).

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The stress study on half-size model of the intersection part of bottom longitudinals and transverse bulkhead in tanker was made under tension in testing machine.
The ordinary bracket type, thicker bracket type and lapped bracket type were tested in elastic state and partialy plastic state.
These results suggest that the type without chock (near intersection) is better than that with chock, the thicker bracket has nearly the same performance as the ordinary bracket, and the lapped bracket has large stress concentration at the lapped end.

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We can easily suppose the dynamical stress of ships going in waves is far different from the values of statical stress by standard calculation.
To solve the problems of dynamical strength of ships in waves especially the problems of slamming and its effect on hull strength, we have tried the experiments in model basin by towing 6 metre model ship, made of brass; and measured deck stress, bottom pressure and pitching, heaving motion of ships.
In the present paper, we dealed with the results of the experiments when wave length is equal to ship length, in comparatively light draft, and on various wave heights and ship speeds.
By experiments, we found the physical causes which produce slamming, and we defined the range of ship speed at which slamming occurs as the slamming zone.
At slamming zone, the impact pressure at ship bottom and impact compressive stress on deck increase remarkably as increase in wave height.
We defined the effective wave height ratio by comparing measured stress with calculated ones, and found these values showed a tendency to converge with increase in wave height.

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In case of constructing the welded steel ships, the wavy deformation of the shell plate is liable to occur by the fillet welding of shell plates and frames or floor plates.
This unfairness may not only spoil the appearance of the shell plate but also reduce the buckling strength of it.
This study was performed for the purpose of surveying the mechanism of origination and the method of reducing this deformation.
The specimen used in this experiment is a constrained frame works as shown in Fig. 1. The deformation and the reaction stress originated in the plate due to welding were measured by the dial gauge and the electric resistance wire strain gauges respectively. These measurement were performed after the welding of each layer.
The results obtained are summarized as follows:-
1) Fundamental nature of this problem
This problem of residual stress can be treated as the problem of reaction stress originated by constraining the angular change due to welding. Accordingly, the angular change and the reaction stress can be calculated from the measured deformation using“beam theory.”
2) Effect of welding procedures on the angular change
(i) Weight of deposit metal
Angular change due to welding increases as the increase of the weight of the deposit metal. There approximately exists a linear relation between the logarithm of the weight of the rod consumption and the angular change. Accordingly, it seems to be a benefit-able practice for reducing the deformation and reaction stress to decrease the weight of deposit metal or the leg length.
(ii) Effect of rod diameter
Size of rod diameter seems to have little effect on the angular change when the weight of deposit metal is equal.
(iii) Effect of the degree of constraint
Degree of constraint seems to have a remarkable effect on the angular change.
Accordingly, the additional constraint, such as a kind of strong backs, attached to the shell plate may reduce the deformation and reaction stress.

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The effect of the unfairness in ship bottom plate produced by fillet weld of floor plate and bottom shell on the buckling strength of bottom shell was studied.
By a measurement in actual ship, it became clear that the initial deflection curve of unfairness was parabolic shape, and the initial bending stress existed in bottom plate. The critical hogging stress at which the skin stress of bottom plate reaches to yield stress was calculated for several unfairness.
The allowable limit of unfairness was obtained for various frame space-plate thickness ratios.

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This report is the first part of serial experiements which are being made to survey the effects of welding procedures on the shrinkage, distortion and residual stress of welded joint.

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To investigate the weldability of Japanese commercial ship structural steels, fourteen fully killed and two semi-killed steel plates, 25 to 35mm in thickness, were tested over a range of temperatures employing V-Charpy Test, Austrian-Standard-unnotched-bead-bend Test, and Knoop-hardness Test. Transitions from ductile to brittle behaviors were also observed.
In general, killed steels were found to be more hardenable in the heat affected zone than rimmed or semi-killed steels, and accordingly V-Charpy notch toughness is not enough to evaluate the weldability of killed steels.
The transition temperature determined by Austrian Bead Test was found to be closely associated with the combined parameter of V-Charpy transition temperature and maximum hardness in the heat affected zone. The Austrian Test, therefore, is considered to be a reasonable mean of V-Charpy and maximum hardness tests.
It was observed that with an unnotched bead such as in Austrian Test, the initial crack appeared sometimes in the weld-heat hardened zone in a comparatively hardenable steel. The bend performance, therefore, is greatly influenced by electrode types.

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In the recent construction of steel ships, riveting has been largely replaced by welding. In welding ships, steels are frequently required to be welded in prestrained condition after cold working. One of the most important examples may be the joining of a gusset plate to the margin plate. In such a case it is usualy recommended by Ship Classification Societies that the prestrained area shouldd not be welded in order to avoid deleterious effect of cold working upon welding. It is generaly cosidered that welding of a cold worked steel reduces impact strength and corrosion resistance of the steel.
To investigate the problem, various kinds of tests were performed, that is, tensile, bending, fatigue, and corrosion tests as well as notch brittleness test.
A rimmed steel, 13mm thick and with the manganese-to-carbon ratio>2.5, was employed. After a stress relief heat treatment at 700°C for one hour, specimens were prestrained in a 300 tons tensile testing machine to various amounts of cold working, 0, 2.5, 5, 10%. Specimens were then bead welded with the submerged-arc welding process, and the following results were obtained.
No effect of cold working upon welding was observed in the tensile and the bending tests. In the V-Charpy notch brittleness test, transition temperature seems to be raised with increasing prestrains.
The fatigue test with repeated bending specimens in Schenk's fatigue testing machines, showed that the fatigue strength was increased with prestraining and welding.
In the corrosion test, the steel was made less resistance to corrosion when it had mill scale unremoved, coldworked, while the effect of prestraining-and-welding seemed to be favourable to increase the corrosion resistance.
Summarizing the test results, it may be concluded, that the effect of welding on a prestrained steel is not so deleterious as to be observable in tensile, bending, or fatigue tests, but rather effective to increase corrosion resistance. Therefore the said recommendation does not seem reasonable, and the gussets may be welded to the margin plate on cold worked corners.

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Kawasaki Dockyard completed the floating dry dock of 13, 000 KT. capacity on June 30th, 1953 to fulfil its long cherished ambition.

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Inhibited hydrochloric acid is generally used for removing rust from new boilers and insoluble deposit such as scale from old ones. Addition of reducing phosphoric acid to this acid results in high solubility of metal oxides or salts and anti-corrosive surface after cleaning, and can clean perfectly marine boilers economically even at room temperatures.
Thiourea and fulfurol inhibits the corrosibility of this type of acid and addition of wetting agent lowers this rate of attack.
Details of cleaning methods and results with inhibited reducing acid solution have been reported in this essay.

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