Seakeeping analysis of the trimaran ferry ship in short crested sea for a case of East Java water condition

Seakeeping analysis is an important aspect in the assessing of ship performance in wave corresponding to the safety and comfort of ship's crews or passengers. This paper consider to the six degree of freedom (6 DOF) motions of the trimaran ferry ship that was operated in short crested wave of East Java sea, Indonesia. There were some snap shot data representing one year sea condition with of an hour period of snap shot. Based on the snap shot data, the wave spectrums were further generated using the standard ITTC formulation of JONSWAP spectrum. The 3D diffraction analysis was performed to obtain the first-order (high frequency) response motions of ship in regular wave for any ship's heading relative to the waves. The ship's motion responses in multidirectional seas were computed by multiplication of the Response Amplitude Operator (RAOs) and multidirectional wave spectrum. The standard deviations of each motion were obtained by square root of the summation of the total spectral energy of wave. The periods of ship motion were also determined by the division of the total spectral energy to the total spectral moment. The periods and standard deviations were plotted in the scatter charts representing the motion responses for all snap shot data. The cumulative exceeding probabilities of motion were determined, and it was used to examine the response of motions to exceed criteria value.