By experiments with a series of model ships, the virtual water masses of ship while turning were obtained.

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In this paper the Author gives a result of theoretical study, made by him, on the effect of “washing back” the blade-sections of marine propellers. The circular-back or ogival blade-section is taken as basic blade-form, and the effect of making “wash-back” to it is studied for the following two different working conditions.
(1) When there occurs no cavitation : Here the blade-section is regarded as made up of circular-arc triangle, and its lift coefficient is calculated by means of conformal transformation, using some properties of hypergeometric functions.
(2) When cavitation is occurring severely : For this case the flow around the blade-element is reduced to the discontinuous flow past a curved barrier, and lift-and drag-coefficient is calculated in the similar way as the Author's previous paper “On Theoretical Study of Performance of a Blade-element under Cavitation” [Zosenkyokai Zassan, Dec., 1941]
Lastly, the Author gives some numerical illustrations to the result obtained, and shows that, when a moderate amount of wash-back is made, some increase in the lift coefficient may be expected both for two cases (1) and (2), mentioned above.

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There is some analogy between the pressure wave in gas and the long wave on the water surface. Making use of the analogy, we can study compressibility effect in high speed air flow with a shallow water tank. The author investigated the compressibility burble of three airfoils with a shallow water tank and compared with data of high speed wind tunnels. Further, he inquired the influences of the depth of water, draft of model and width of tank upon shallow water tank experiments.

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In the fore part of this paper the author discussed the tension occurred in the towing hawser of ships when they meet regular waves and gusts, assuming that the profile of the towing hawser is a catenary curve and the weight of the hawser per unit length is constant, and neglecting water resistances to the motions of the hawser in water, and the following results are obtained : If so long heavy hawser as T/T_e is very large, where T is a period of free oscillation of the hawser and T_e is a period of encounter of ships and waves, is used, the tension in the hawser is affected only by winds but by no wave, and even this winds' effect is safely so small as the hawser can not be cut off, whereas the tension in a short light hawser is much affected by both waves and winds, and especially, if T/T_e is unity, the tension is steeply augmented from time to time, and finally the hawser will be cut off, but even their effects either can be minimized by adjusting the phase difference between the towing and towed ships to the encounter waves, or can be free from the synchronism between T and T_e, by changing the length of the hawser, the speed and course of the towing ships. It is cleared up that in all cases the smaller towing ship is used, the smaller the effects of waves and winds on the tension in the hawser is.
In the after part of this paper the author discussed similarly as above the tension occurred in the chain cables of mooring buoys when ships moored in sea of some depth of water meet regular waves and gusts, and the following results are obtained : If so large heavy chain cables as T/T_w is very large, where T is a period of free oscillation of the chain cables and T_w is a period of waves, is used, the tension in the chain cables is affected only by winds but by no wave, whereas the tension in short light chain cables is much affected by both waves and winds, and especially, if T/T_w is unity, the tension is steeply augmented from time to time, and finally they will be cut off. It is therefore advisable to use as large heavy chain cables as possible in order to be free from the cutting off.

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This paper treats with the comparison of rigorous and approximate solutions of stresses on the hollow thick cylinder and sphere of cast iron under external or internal hydraulic pressure. Poisson's ratios of 0 and 1/2 for the cylinder and 0 and 1/3 for the sphere are taken into computation of the rigorous solution. The approximate solution is independent of this ratio. The former is only applicable in case of same sign of two different stresses-radial and tangential, and besides does not follow with the superposition law of stress, whereas the latter is free from such restricts. The most suitable stress expression must be adopted by preliminary numerical computations on these solutions. The final conclusion is as follows : --
The effect of Poisson's ratio on stress values is practically a little and the twice superposed values of stresses by rigorous solution are not reliable for the problem, subject simultaneously to external and internal pressures. The tangential stress by approximate solution gives generally an inferior result, nevertheless the radial one a good result.

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