Shojiro Okada

The Experimental Results on the Head-loss of Marine Suction Bell-Mouth and Strainer

This paper deals with the results of comparative experiments carried out with models having several different shapes and sizes of the marine suction bell-mouth and simple strainer for the purpose of examining the head-loss of the bell-mouth and the strainer.The following points were made clear as this experiments.(1) The loss coefficient of bell-mouth, at the range higher than about 1.0 × 105 Reynolds number, attains a fixed value unrelated to Reynolds number, and its absolute value is not much affected by variation in the shape of the open mouth part or in the curvature radius.(2) However, it is greatly affected by the amount of clearance between the open mouth part of bell-mouth and the bottom of tank.(3) As regards the strainer, it was confirmed that its loss coefficient also attains a fixed value unrelated to Reynolds number, but that its absolute value changes in accordance with the ratio of clear of the rose plate.

On the Results of Experiments on Rudders placed behind the Ship

The author discussed the performance of open rudder, particularly the effect of angular velocity of steering in Reports Nos. 1 & 2 of this series of experiments, and described, in Reports Nos. 3 -& 4, the effect of propeller race on the rudder performance. Therefore, in Report No. 5, the present report, the author principally discusses the experimental results pertaining to the effects of wake and propeller as the remaining problem, and lastly he mentions the practical formulae applicable to the normal force of rudder and the position of the centre of pressure, integrally considering Reports Nos. 1-5.The following points were made clear as the results of model experiments of the rudder placed behind the ship and ships propeller.(1) When the propeller is located in.froht of the rudder, the effect of wake can be presumed by considering the mean effective wake fractions within the propeller actuator disc, and when the propeller is not in front of the rudder, by considering the nominal wake fractions around the rudder.(2) As to the effect of propeller race on the normal force of rudder, it is the function of the slip-ratio of the propeller just the same as in the case of open propeller, and its increment ratio is in proportion to 1.5 power of the slip-ratio, but the coefficient is greater than in the case of open propeller.(3) In the case of the rudder behind the right-handed turning propeller situated at the stern, when normal force is zero, the helm angle shifts to the port in many cases, though slightly, but in the case of a great rudder angle, normal force indicates an almost equal value for both port and starboard. The position of the center of pressure alone is affected by unsymmetry of the upper and lower portions in the distribution of wake.(4) Regarding the composite effects on the normal force of rudder located at the stern, the effect of wake and that of race mutually offset and in an ordinary propelling condition, there is shown an increase of an equal degree, or by 10-20%, as compared with normal force working on open rudder at the time of an equal velocity to the ships speed.Lastly, the practical formulae for the normal force and the center of pressure of ruddes in the single screw vessel are given, and the calculated values of the pressent formula were compared to the measured results of the actual vessel.

On the Results of measuring Shaft-Horsepower and Torsional Vibration of Diesel Engines

This paper gives the results of measuring-shaft-horsepower and torque-fluctuation of the intermediate shaft with the magneto-striction type torsionmeter, which is a partly improved one of the shaft-horsepower-meter previously reported.The principal results obtained are summarized as follows:1. The value of shaft-horsepower measured with this new torsionmeter on the sea trial coincides not only with the value calculated from the indicated-horsepower simultaneously measured but also with the model basin prediction when it is standardized.2. The stress on the intermediate shaft due to the torsional vibration is not so large at the usual condition.

On the Process of Improving the Shaft-Horsepower Meter

The authors have reported in 1951, on a system of indicating shaft-horsepower with a wattmeter to which an electric type torsionmeter and an electric tachometer are connected. Since then, further researches have been made with the intention of consummating the shaft-horsepower meter, especially we made our efforts to the simplification of its control, the maintenance of its accuracy, and the diminution of its cost.In this paper, the progress of researches made on improving the shaft-horsepower meter is reported.