船速に及ぼす風浪の影響について-VII(日本航海学会第34回講演会)

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タイトル別名
  • Study on the Effect of Wind and Wave on a Ship's Speed-VII
  • 船速に及ぼす風浪の影響について-3-
  • センソク ニ オヨボス フウロウ ノ エイキョウ ニ ツイテ 3

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To analyze the effect of winds and waves upon a ship's speed is a very important problem concerned with the selection of an economical sailing course, the estimate of spare fuel and an estimate of the ship's position. But each ship being different from an other in type, size, condition, ability, etc., it is not possible to formulate universal rules. In this paper, the author has attempted, as an example, to analyze the navigational records of the fishing-training ship "Oshoro-maru III" of Hokkaido University. As shown in Fig.1, all data has been separated into 7 sections according to directions of the winds. The calculation of speed reduction has been made according to the difference between the standard speed of 12.03kt and the log speed converted to 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 log when the rotation is 210 RPM and the angle of the blade is 21 degrees, and the influences of wind, wave and swell are nil. In Table 1, t---shows the weights of data (sailing time: minutes), Δ---shows the mean speed reduction. If the relation between the wind force (B) and speed reduction (Δ) are expressed by the equation Δ=aB+bB^2, they have been calculated by the data in Table 1 by means of the least square as forms (1)〜(7) in each section, as shown in Fig.2. In order to get the relation between wave height and speed reduction, he took the following method for deducing wave height from wind scale, namely he got the average value of the grades of wind waves against each wind grade in the navigational records, and replaced the wind grade 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. When the relation between wind scale and wave height in this observation was plotted, it has been shown in Fig.5, and is expressed by the equation (8). The relation between wind scale and wind velocity is expressed approximately by the equation (9), and the relation between wave height and wind velocity is expressed by equation (10). Using the relation of equation (8) and the relation in Fig.2, the relationship between wave height and the speed reduction has been expressed dy a simple equation as shown in Fig.6, cxcept in the case of favorable winds.

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