In the case of even keel condition, the normal force coef. C_Nand the moment coef. about midship C_m⊗ of a ship-body in turning, are theoretically and experimentally
C_N= 2π/1+2/kcosαcosα{sinα+g(k)ω}+kC_NO(α)+h_Nωsinα
C_m⊗=h(κ)ω-C_m⊗(α)+h_mωsinα where α…drift angle ω…ship's length/turning radius k…aspect ratio of her centre vertical plane. g, h…function of k (theoretical value) k…function of midship section coef. C_NO…normal force coef. when k=0 C_m⊗ (α)…theoretical value of the moment when oblique course with drift angle only. h_N, h_m…non-linear term of α and ω (theoretical value) and especially h_m is very important in turning.
In trimmed condition, the upper results are extended as follows:-
(a) rectangular plate in oblique course C_N=C_NP(1±γ/4d_m)+2sin2α C_m⊗=C_m⊗ (value of mean draft d_m)±1/8τ/d_mC_NP±1/12τ/d_m2sin2α
(b) ship body in oblique course. C_N=C_NP(1±τ/4d_m)+kC_NO C_m⊗=C_m⊗ (value of mean draft d_m)±τ/2d_m(C_NP/4+C_NO/6+C_m⊗0)
(c) ship body in turning. C_N=C_N(value of mean draft d_m)±2π/1+2/kcosαcosαγ/4d_m(sinα+ω/4) When α=0 and ω is finite, C_m⊗=C_m⊗ (value of mean draft d_m)_??_τ/2d_m(1/162π/1+2/kω C_m⊗01/6C_NO) When α≠0 and ω≠0, subtract C_m⊗(α) (oblique course) from C_m⊗ (ω) (upper value) and add h_mω sin α.
Where C_NP=2π/1+2/kcosα sinα cosα τ…trim d_m…mean draft C_m ⊗0…theoretical value of C_m ⊗when k=0.
Upper sign of ambiguous signs shows the trim by bow and lower sign is the trim by stern.

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The roll-stabilizing effect of bilge keels of multiple tandem rectangular plate form was studied by the author by using several models and actual ships, the results being published in the previous paper. After the excellent effectiveness was generally acknowledged, this new type of bilge keels has hitherto been adopted for 17 vessels. But in four vessels of them there occurred the singing of bilge keels in which cracks were produced in spite of their greater strength than those of other vessels. These phenomena are, like the singing of propellers, entirely due to the Karman vortices created from the after edges of plates. Hence if the resonance between the vibrations of plates and Kármán vortices be avoided, this problem will be solved. Experiments were carried out to investigate the frequencies of Kármán vortices with rectangular plates having several sectional forms, and on the other hand a formula for the frequency of bilge keels was obtained theoretically in consistence with the actual singing phenomena. After investigating the bilge keels of 14 vessels by using the new formula, it was found that the vibration of bilge keels of ocean-going vessels would not occur if the ratio of the frequency of plates to that of Kármán vortices did not lie between 0.65 and 1.60.

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In this paper, general methods of limit design and shakedown design of plane structures are proposed. We may design the structures more exactly by them than the method of Symonds and Neal [1].

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The theory of the elasticity of riveted joint was developed by F. Bleich and W. Hovgaard independently by introducing the displacement coefficient of the driven rivet. But in their theories the method of evaluation of the displacement coefficient was not shown and without knowledge of its vales the elasticity of the riveted joint can not be calculated.
In this paper, by considering the bearing elasticity of the plates and the bending of the rivet due to bending moment and shearing force, the method of evaluation of the displacement coefficient is developed and the calculated vales are compared with the various experiments satisfactorily. By the use of calculated displacement coefficient and by the aid of their theories, the distribution of stress and strain can be shown for any riveted joint.

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The phenomenon of the slamming is investigated from the points of view of the ship's motion and hydrodynamics and it is found that the slamming ordinary experienced is caused by pitching, not by heaving. The slamming factor n.i.e. the maximum impulsive pressure due to slamming divided by the hydrostatic pressure due to load draft, can be expressed by equation (11), where P(σ) depends on the speed and the position of the section where slamming occurs, and tanβ on the form of the bottom of that section. Many facts already known about slamming by experience can be clearly explained by (11). Maximum value of n can arrive at about 13 if improper bottom form be adopted. Some suggestions about the form of the forward bottom in order to avoid slamming are also given in Fig. 3 and 13.

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The authors tried to construct the instruments to measure the launching speed and acceleration accurately and directly. In this instruments the speed is obtained by transforming the frequency of A.C. voltage which is proportional to the speed of rotating drum into the electric current by vacuum tubes and condenser. The acceleration is obtained by differentiating the voltage proportional to the frequency by means of CR differential circuits. Each is recorded in the self-recording milli-ammeter.
We used them for the launching of three ships and assured that the results were almost successful.

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This paper deals with the results of three kinds of aerodynamical experiments. Part I is a report on the experiments which were made to know the efficiencies of six types of the cowl-head ventilators in the wind from all directions, namely, circular, elliptical, and obovate types with a vertical and a convex back form respectively. Among these six, the elliptical type with a convex back shows the best efficiency of ventilating.
Part II. deals with the experiments made to make clear the effect of the wind-deflector attached to the wing parts of the navigation bridge of the ocean-going cargo vessel. And a device to improve its efflciency is offered.
Part III. shows the results of wind-tunnel experiments made to minimize the smoke nuisance of ships' stacks.

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In the experiment of the large size models of hatch corner reinforced by the round doubler, we got results as follows;
Test piece; Length over all 3, 850mm Breadth 900mm Parallel part 2, 450mm Opening 680mm×440mm Radius of corner 20mm Thickness of plate & doubler 8mm Radious of doubler 24mm; 34mm & 50mm
(1) The stress and stress concentration, at the point of hatch corner circular end of longitudinal side, are decreased by doubler reinforcement.
(2) The largest stress occurs at the doubler end of longitudinal side, when reinforced by doubler.
(3) The efficiency of doubler increases as it becomes large, but this increment is confined within proper limits.

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As a first step of research on brittle fracture in ship structure, first the effect of notch sharpness on brittle fracture in wide width plate, and secondly the radius of opening corners in semi-box type girder were tested.
Boodberg's experiments⁽⁵⁾ on the wide width effect show the decrease of maximum breaking stress at wide width plate having constant notch sharpness. The author's experiment treated the effect of notch sharpness on the bending strength of wide width plates. The shape of test pieces is shown in Fig. 1. In Fig. 3, the transition temperatures are shown. The nominal maximum stress of wide width specimen (21×63mm) with sharp notch (rad. 0.05 mm) decreases in brittle fracture as shown in Fig. 4. In Fig. 6, the absorbed energy per unit volume at low temperature decreases in the wide width specimen with sharp notch as increase of width.
Fig. 8 shows the effect of notch depth on the nominal maxinum stress and absorbed energy.
Next, the semi-box type girders of rimmed and killed steel, perforated at the centre with round, square, notched, and slit shape, shown in Fig. 9, were tested under tension. The nominal maximum stress and absorbed energy are shown in Fig. 11 and 12. The strength of test pieces of several opening shape are nearly equal at room temperature (30°C), but at low temperature (-30°C), the sharp notch or the defect of welding at opening corners has more remarkable effect in their maximum stress and energy absorption rather than the square corner. The test pieces of killed steel show the parallel increase in their strength.

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The present research has been conducted on the corrosion of the marine engines of about forty sunken ships by means of the field investigation or the deta offered according to the following items:
(a) The relation between the corrosion and the period of the submergence of the materials.
(b) Is there any difference in corrosion due to the kind of the engines
(c) Is there any difference in corrosion between the ships of war-time standardized types and the ordinary ships?
(d)Possibility or Impossibility of the reuse of the refloated engines.
(e) The process of the repairs of the refloated engines.
(f) The condition of the operation of the reused engine.
The results obtained are as follows:
(a) The corrosion makes progress rapidly at the outset. but after a few years corrosion makes progress gradually.
(b) The extent of corrosion of the reciprocating engine is almost similar to that of the diesel engine. In the case of the steam turbine and the mechanical reduction gear, the extent of corrosion is comparatively slight. The boiler may be reused only by replacing the corroded smoke tubes with new ones.
(c) The extent of corrosion in the ships of war-time standardized type is generally very remarable compared with the ordinary ships.
(d) Corrosion generates on both the small-sized and larger-sized materials, but. as the extent of corrosion is more remarkable in the case of the smaller sized materials. the reuse of the smaller sized materials is almost impossible, while the reuse of the latter is possible
(e) The process of the repairs is as follows: After the corroded parts of the engine are boiled in the soda solution, the corroded face of the friction parts are filed off. The other sound parts of the engine may be used without any treatment.
(f) The operating condition of the reused engine is pretty good on the whole.
The present research has been continued by the Maritime Institute since the writer's initial field investigation conducted in April, 1946, at Mitsubishi Dock Yard in Nagasaki on the corrosion of the main engine of the Kongo-maru, the refloated steamer of National Railway Corporation, receiving grants in aid from the Ministry of Transportation. the former owner of the above mentioned Institute and from the Ministry of Education, the present owner of the Institute.
It would be a happy thing. if the present thesis could furnish even a little contribution to the refloating of the sunken ships in the future.

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A system of the combination of a high revolution reciprocating engine and a low pressure turbine, both geared to the main shaft line of a steam ship, has been known in this country as Uraga 2-DC system. A paper was read by one of the authors of this paper, at the autumn meeting of this Society in the year 1936, describing the actual performances of the engines in question. The same system has also been described in the same author's book entitled “Hakuyo Rendo Kiki” (The Marine Combination Steam Machinery).
The present parper deals with some latest improvements upon the design of the part of the reciprocating engine of the said system, and suggestions are given in it to the effect of
1. Adaptability of higher steam pressure and higher temperature
2. Increase of power due to adopting higher piston speed
3. Better efficiency ratio due to improvement of valves and valve operating gears.
4. Improvement of symultaneously operating manoeuvring gears of the engine and turbine, and also suggestion of an electrically operated reversing and control system, which might be worked at remote positions.
This new system will be designated NAC SYSTEM.

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This Optical Torsionmeter is an optical recording type meter designed so as to measure the shaft horse power of small vessel. This meter has several merits as mentioned hereunder
1. It is unnecessary for the length of the parallel parts of its intermediate shaft to be more than 50cm. 2. The space around a shaft to fix this meter does not need more than 13cm. from the surface of the shaft. 3. The meter is comparatively light in itself, and yet bearable against any vibrations. 4. The meter is inertialess during measurement and has high accuracy.
This paper is cancerned to describe the principle and the construction of the meter. And the reports shown in is taken up from the result of the measurement in “Yayoimaru”.

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