Analysis of a Marine Accident And Freak Wave Prediction With an Operational Wave Model

In the past, a number of ships have sunk near Japan, and some cases are thought to be due to the “Freak Wave”. To avoid such accidents, it is important to investigate under what sea states those accidents occurred and utilize such knowledge to predict where and when such dangerous and freakish sea appears. We have conducted a wave hindcast simulation to reproduce the sea state at the time of the ONOMICHIMARU accident by an operational third generation wave model. Detail analysis of the sea states and wave spectra revealed that the cause of the accident may be related to the occurrence of the freak wave. Unlike the report from the earlier investigation that suggested a possibility of a crossing sea, we discovered that a uni-modal wave spectrum narrowed before the accident creating a condition favorable for the freak wave occurrence. The Joint-Probability-Density-Function of the spectral bandwidths (frequency and direction) is suggested to be used as a visualization tool to indicate the freakish sea state so that the ships are able to avoid the risk of encountering freak waves.