Study on the Effects of Wind and Wave on a Ship's Speed-VIII

Abstract

The author had already analyzed the navigational records of several ships and investigated the effects of the winds and waves on ships' speeds, but each ship was different from each other in type, size, condition, ability, etc., it was not possible to formulate any universal rules. Hereupon, if I make the assumption that speed reduction of each ship follows a common formula, I can express an experimental equation as to speed reduction corresponding to sea condition, and it is also easy to compare the characteristics of any ship. The assumed equation to suit the object must be simple in form within the limits of the possible, so that a ship's speed V be given in the following formula, V=a-bcosθ, and can be applied to three ocean-going ships. As a result, the coefficients a, b are kept in line with certain curves as shown in Fig.4 (a)(b), on the assumption that a=a'-cB^n, b=dB^m, those points fitting closely. Accordingly, the speed equation is expressed as follows: speed=a'-cB^n-dB^mcosθ (where B: Beaufort scale, θ: Wind direction) Secondly, as to the three coasting vessels, the coefficients a, b are shown in Fig.5 (a)(b), and they are expressed by the following equations: a=a'-c'D^n, b=d'D^m, accordingly, speed=a'-c'D^n-d'D^mcosθ (where D: scale of wind waves) Furthermore when I indicate a ship's speed in connection with a wave height (H), it is expressed thus: speed=a-bH-cH^mCosθ, as shown in Fig.6 (a)(b) and Fig.7 (a)(b).