Steady Wave Forces and Moment Acting on Ships in Manoeuvring Motion in Short Waves

In order to evaluate manoeuvrability of ships by analyzing manoeuvrability test at seas effects of steady wave forces and moment must be estimated correctly since it is inevitable that ships suffer those external forces at seas. Short waves induce larger steady wave forces than long waves and short waves exist anytime at seas. These are among reasons why short waves' effects on ships in manoeuvring motion must be investigated.Formula for estimating steady wave forces and moment acting on ships in manoeuvring motion is presented by applying Ohkusu's method for calculating added resistance of ships in head wave condition to manoeuvring condition that includes oblique, turning and their combined motion. Model experiment is carried out to measure steady wave forces and moment acting on a ship in oblique and turning motion in short waves with motion of wave period not constrained.Calculated results by present method are compared with experimental data and those by other methods of calculation. It is found that present method well describes property of steady wave forces and moment acting on ships both in oblique and turning conditions. Effects of oblique and turning motions on steady wave forces and moment are discussed based on present calculation.