方形係数シリーズ肥型船の操縦性能 (第一報：水槽試験)

Abstract

Tank tests are conducted to capture the ship maneuverability using ship models with three different block coefficients Cb =0.81, 0.84 and 0.87 of the same principal dimension ratio such as L/B and B/d. First, free-running model tests are carried out to capture the maneuvering motions in a square tank, and next captive model tests are conducted to capture the maneuvering force characteristics using the same ship models. With increase of Cb, turning advance (AD) and tactical diameter (DT) become small in both full and ballast load conditions, and the values of AD and DT satisfy the IMO regulations with sufficient margin. On the other hand, overshoot angles (OSAs) of 10/10 zig-zag maneuvers become large and the course stability becomes worse with increase of Cb. The value of 1st OSA for a ship with Cb =0.87 is on the critical line of the IMO regulation. Reason why the course stability becomes worse with increase of Cb is mainly due to increase of the absolute values of N′υ and Y′γ - m′ - m′χ terms. We investigate the reason why the absolute value of N′υ typically increases with Cb by CFD computations. With increase of Cb, hull lateral force per unit ship length (ΔY) in oblique towing condition becomes large at fore part and just behind the midship position, but small at stern part. As the result, the hull lateral forces (Y) which is obtained by the integration of ΔY become almost the same for three ships due to the cancellation of plus and minus ΔY at fore and stern parts. On the contrary, the yaw moment (N), which is obtained by the integration of product of ΔY and the longitudinal position χ increases with increase of Cb. This feature comes from the effect of negative pressure on the hull surface at face side of the stern part.