Abstract
In the former paper, the author considered the ship's rolling motion in a seaway from view point of forecasting ship's motions on the sea. In that paper, in the case of SEIKAN ferry boat, the maximum angle of roll of ship in the seaway was shown for various wind velocities and 8 principal directions on standard course, when ship was underway at 15 knots. In this paper, from the point of view of safety for the ship's stability, the author has defined the critical anlge of roll due to wave motions, which was decided by the stability standard of sea-going ship, that critical angle can be obtained by use of the following equation: [numerical formula] (3) θ_<max>: Critical angle of roll θ_r: Range of stability D_w: Lever by wind pressure S_d Dynamical stability m_x: Transverse metacentric height Then, under any sea states and wind conditions, it is necessary to manueover the ship to satisfy the following equation for the safety of ship. θ_<max>>θ_w (4) θ_w : Relative angle of roll And the relation between θ_w and maximum angle of roll is given as follows: θ_w=ψ-Ψ'cosφ (6) ψ: Maximum angle of the seaway (Appendix 2) Ψ': Effective wave slope φ: Phase angle (between ship's motion and wave motion) According to the above theory, the author calculated θ_w on the standard course for the same conditions as in his former paper and discussed the matter of the safety of a ship in the seaway.
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