This paper deals with the free rolling of ship theoretically and experimentally, and the following results are obtained.
(1) The free rolling of ship is made up of coupled oscillations of a horizontal transverse motion of its centre of gravity G with a rotational motion of ship about a longitudinal axis through G. And the horizontal motion is made up of two motions, the one being a damped oscillation and the other a damped translation, but the rotation simply a single damped oscillation. That is to say that, G, about the longitudinal axis through which t1 ship is rotating, translates transversely in the direction against the initial heeling, oscillating horizontally, and at last after the shift of a certain distance the motion is at rest.
(2) C₀, the apparent centre of free rolling, which is the point having a minimum double amplitude of horizontal oscillation 2|ξ|m₀ among the points in the middle line of the ship, is at a distance Y₀ below G. For box-shaped model ship, a ratio Y₀/d, where d is a draught of ship, has a value of about 0.08, and a ratio 2|ξ|m₀/d increases as the initial angle of heel θ₀increases and has a value of 0.03 at θ₀=35°. And these calculated values of Y₀and 2|ξ|m₀ are in agreement with the experimental results.
(3) The actual amplitudes of horizontal oscillations of any point in the middle line_of the ship are larger and more irregular than the calculated ones, but The direction and the amount of the horizontal translation calculated agree with the experimental results AndD, a calculated distance of a horizontal shift of G between the time elapsed from the initial and the final instant of the motion, coincides perfectly with the experimental results, andD/dincreases as θ₀increases and has a value of 0.9 at θ₀=35°.
(4) A damping power oe and α circular frequency ω in the free rolling of the ship are expressed as follows.
α=α₀-C_a,
ω=√ω₀²+C_ω,
where α₀and ω₀are a damping power and a circular frequency respectively in the free rolling of the ship, the horizontal motion of the centre of gravity of which are restrained. Therefore, C_a andC_ω are the effects of the horizontal motion on the free rolling, and the calculated C_a and C_ω agree with the experimental results. For the box-shaped model ship, the calculated C_a/α, C_ω/ω² and (T₀-T)/T (where T and T₀ are π/ω and π/ω₀ respectively) have the following values.
C_a/α : 7%4% in the range of θ₀=0°35°.
C_ω/υ² : about 4% throughout the same range of θ₀ as above.
(T₀-T)/T : about 2%, , , , .
(5) If the effect of the horizontal motion on the free rolling should be neglected as small, the damping power α and the period T, which shall be greatly influenced by the rotational motion, are approximately expressed as follows.
α_??_I₁₀h₁/2 (I+I₁h₁)
T²_??_π²·(I+I₁h₁) /W·h·G₃

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The easy estimation of the speed and power of ships is always quite necessary in the early stages of ship design, and with this purpose several methods have been already published. Among these, Dr. Yamagata's method which was indicated in his paper entitled “An Approximate Method of Estimating the Requisite Horse Power of Propelling Machineries of Cargo Ships” (Jour. of the Soc. of N.A. of Japan, Vol. LXIII.) seems to be the most successful one. But this papal is only concerned to neighbourhoods of normal speed attained at the normal horse power of propelling machinery at full load condition.
Generally, speed trials and other tests on ships are carried out at light condition or 1/5 load condition, except special cases as on oil tankers, and various guarantees in building contract are chiefly appointed on such light load conditions. Therefore, when the principal dimensions of ship and principal particulars of propelling machinery are decided for a new design, it is also a matter of great importance to estimate the horse power-speed curve at such light load condition of the ship.
Since effective horse power-speed curve at any lend condition of a ship can be estimated with sufficient accuracy by means of several methods by papers already published, such as Taylor's, Ayre's, Volker's, Koning's etc., the estimation of shaft horse power-speed curve for a newly designed ship at any load condition may be replaced by the estimation of suitable propulsive coefficient curve for that ship.
The author analysing the results of self-propulsion tests at the Teisinsyô Ship Experiment Tank during past several years, obtained a new method of estimating the propulsive coefficient of cargo ships at full and light load conditions. In the present paper, the values of propulsive coeffi ient are presented corresponding to the adopted standards of cargo ship forms and propellers, and supplemented with correctional valúes for differences between standards and those which may be applied to a particular vessel.

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The effects of deviation of ship form-in brief, the effects of C.B. of ship upon the resistance are calculated theoretically, as an attempt to discover the least resistance ship form.
Since Michell published his mathematical formula for ship wave resistance, the discrepancies between actual and theoretical cases have been researched by means of the model experiments by tank authorities in the world. Wigley, especially, made careful considerations for the effects of viscosity on the wave-making and be introduced an empirical allowance to the ship aft of amidships and calculated the wave-making resistance of the bow and stern separately from Michell's solution.
In these cases, the ships were too slender compared with the sea-going vessels. In the broad ship, however, it is obvious that the aft ship is affected by viscosity and also by eddy-making probably. It may be very difficult to study theoretically these effects on the wave-making.
The author has prepared this paper tentatively without investigating the mechanisms of wave-making in the first place.
It is reasoned mathematically from Michell's formula that the least resistance ship form is symmetrical fore and aft in the perfect fluid, though this is transformed according with its speed. In general, therefore, the best ship form must be asymmetry lengthwise in actual case, this form is shown as follows, adopting two-dimensional flow for brevity, and taking axis of Ox lengthwise, Oy broadwise, and the origin O amidships,
y=F₁ (x²) +F₂ (x),
where F₁ and F₂ are even and odd functions respectively.
A form which deviate from and has same area as the best form is written as
y=F₁ (x²) +F₂ (x) +F₃ (x).
F₃ is odd function and may be small compared with F₁ +F₂, supposing our present ships.
It may be that the wave-making resistance of this form in actual fluid is correspondent with that of a next formula in perfect fluid,
y=F_s+F₃
where F_s is an even function (the best form) and F₃ as before.
In this stage, Michell's formula can be applied. The effect of F₃, the deviation from the least resistance form, can be separately calculated without considering the interferences with the main body F_s, although there are interference-phenomena in the wave syst m.
A following formula was applied,
F₃=y=n {x-k/l- (x-k) ³/l³}
where k and l are parameters to change the deviation.
The additional wave-making resistance due to F₃ is reduced to
R=16ρc²n²/π1/r² [5/3-2P₃ (2p) -1/2P₃ (2q) -2P₃ (p+q) +2P₃ (p-q)+6/r {2P₄ (2p) +P₄ (p+q) -P₄ (p-q)}+6/r² {16/15-5P₅ (2p) +P₅ (2q) +P₅ (p+q) -P₅ (p-q)}+36/r³ {P₆ (2p) -P₆ (p+q) +P₆ (p-q)}+18/r⁴ {96/105-P₇ (2p) -P₇ (2q) +2P₇ (p+q) -2P₇ (p-q)}]

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Results of experiments in open water at the Teishinsho Ship Experiment Tank are presented for 4-bladed propeller series, designed mainly for single-screw mercantile work. Three series of propeller were tested, namely, propellers with increasing pitch, decreasing pitch and constant pitch, all other particulars remained the same.
The general plan of propeller is presented in Fig. 1. All the propeller models had diameter of 0.22m, boss ratio of 0.25, expanded area ratio of 0.40, blade thickness ratio of 0.045 and aerofoil-shaped blade sections. Six pitch ratios were taken for each series, namely, 0.4, 0.6, 0 8, 1.0, 1.2 and 1.4.
The tests were carried out by means of a propeller boat with built-in propeller dynamometer. The immersion of the centre of propeller shaft was equal to 0.9D. The number of revolutions was kept constant at 7.0 per sec, and the speed of advance varied. The measured results were corrected for the static pressure of water on the shaft section, the resistance of the propeller boss and for the shaft frictional loss.
No-dimensional diagrams of the test results are given in Fig. 2. From these diagrams, the design diagrams for our three series of propeller were constructed according to Admiral Taylor's method, and are given in Figs. 35. Also the design diagram similar to Dr. Schmidt's form is given in Fig. 6 for the constant pitch series.
From Fig. 2 and Figs. 35, it can be seen that the difference in pitch distribution usually have no marked effect upon propeller performances in open water. But, as the effect of pitch distribution will be somewhat clearer in a non-uniform flow, propeller tests over a wide slip range in a wake flow are also intended. A part of this research program is now completed, and some remarks on its results are mentioned in the last part of the paper.

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By open and behind experimen's with a series of rudders, the experimental formulae for the normal pressure and centre of pressure were obtained.

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Recently, the importance of inlandwater vessel has greatly increased in our country. In the former part of this paper, the various types of propulsion generally in use for these vessels and their critical velocities in the restricted water are discussed, and in the latter part, a new relation between the principal dimensions is obtained from which a method of determining the principal dimensions is developed, that may be of some use in the initial stage of design.

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The strength of propeller-blade has already been discussed in detail by Taylor in his “Speed and Power of Ships.” But his treatment is based on the assumption of a straight-line law of thrust distribution along the radius. Schoenherr has shown later how to apply the aerodynamical theory to the calculation of propeller-blade strength, which is more rational than Taylor's, but it requires some tedious calculations. The. Authors have constructed an approximate formulae based on the aerodynamic theory for estimating the strength of propeller-blade, substituting the thrust-distribution curve by a suitably chosen algebraic curve. The maximum-thickness distribution which is required in order to make the stress uniform along the radius has also been estimated, and it is found that for this purpose the thickness-curve must be nearly straight but with slight concavity, for propellers of usual proportion.

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The author deduced approximate formulae for calculating, the collapsing pressure of conical and spherical shells under uniform external pressure from the exact formulae for Cylindrical Shells, and showed that the results of collapsing experiments relating to elastic stability of mild-steel shells of the three typical shapes above mentioned can be represented by a single curve.

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The new steel ship construction rules, “Kosenkozo kitei, ” have come into force since April this year, as the or linance of the Department of Communications of our Government, and were substituted for the old ones, i. e., the Part I of the “Zosen-kitei” (“Ship Building Rules”), which enacted in 1916, had already been out of date, notwithstanding the several revisements.
As the new rules greatly differ from the old ones, not only in their method of compilation, but also in the forms and substances, we here give a brief intro luction of the outline.
But the authors have a desire to explain on this subject more or less in detail at the nearest opportunity.

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The general description of making steel materials for marine use at the Yawata Steel Works is given and author's opinion is offered.
When rolling materials are made, it is most important to decrease sorts of rolling materials and to standardize them and to have range in their standard. Because, if we do so, the rolling efficiency is raised and shipment and handling become rapid.
When we use rolling material, we must understand the characteristics of material and, on aecount of carelessness of use and working, we must not damage the manufactured material.

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Twin screw motor ship “Silver Cypress” of 6, 710 G. T. and 7, 000 B.H.P. was built in 1930 by Harland & Wolff at Belfast, Ireland, as an up-to-date cargo boat and was placed in the fleet of the Silver Line Ltd.
While lying at anchor outside the harbour of Manila, in January, 1937 a fire broke out in her engine room and spread to the cargo stowed in the hold immediately forward of the engine room. Moreover, the fire swept into the aft holds engine room, and continued for seven days, destroying the entire cargo.
After the fire was put out, it was found that all of the decks, deck houses, shell plates and equipments on aft half of the ship were completely burned beyond repair. In the engine room, the main motors were hopelessly damaged from bed to cylinder head ; every part of babbit metal at rubbing surface was found to have melted ; and further more all the auxiliary machineries, the dynamos and armoured cables.
Because of the extensiveness and the serious nature of the damage as explained above, the underwriters had no alternative but to condemn the ship and she was sold. to a scrap dealer who towed the hulk to Japan. Later, it was purchased by the Kawasaki Kisen Kaisha who made a most thorough investigation of the matter and decided to have the hulk repaired.
As new steel and iron were not so readily available in Japan then as in ordinary time, every effort possible was made to recover the damaged material for use in the reconstruction work. Also the damaged main motors and auxiliary machineries were repaired without exception. It took 20 months to complete the repairs but now the ship is in excellent condition, both her hull and machinery, and is employed in the service between Japan and America.

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