船速に及ぼす風浪の影響について-II(日本航海学会第29回講演会)

抄録

To analyze the effect of winds and waves upon a ship's speed is a very important problem to determine the economical sailing course. But each ship being different from any other in type, size, condition, ability, etc., it is not possible to formulate any universal rules. In this paper, the author has attempted, for an example, to analyze navigational records of fishing training ship "Hokusei-maru" of Hokkaido University. As shown in Fig.1, all data are separated into 7 sections by the directions of the winds. The calculation of speed reduction is by the difference between the standard speed 9.34kt and the log speed converted in the speed when the revolution of the main engine and the angle of blade are standardized, under each condition ; the standard speed is that shown by the sal log when the standard rotation is 300 RPM and the angle of blade is 13.8 degree, and the influences of wind, wave and swell are nil. In Table 1, n… shows the number of data, △… shows the mean speed reduction ; the items of data are 1734 in all. As the speed reduction (△)=aB+bB^2, if a smooth curve is drawn along the points plotted from data, the speed reduction due to wind force is shown by forms (1)〜(7) in each section, as shown in Fig.2. The calculated values by forms (1)〜(7) are plotted and if the smooth curve between the speed reduction and wind direction is drawn, that curve approaches closely to the curve of 5th degree shown by forms (8)〜(14), as shown in Fig.3. In order to get the relation between wave height and speed reduction, the following method was taken for deducing wave height from wind scale, that is, the average value was taken of the grades of wind waves against each wind grade in the navigational records, and the wind grade was replaced by the average value of grades of wind wave scale. The intermediate value between the grades of the scale is shown by the proportional difference. The relation between wind scale and wave height in this observation is expressed by the equation H=0.0697B^<2・1>. Using the relation and relation in Fig.2, the relationship between wave height and the speed reduction is expressed by a simple equation.