The prediction of the encountered sea state based on the ship dynamic responses

In the paper, a sea state monitoring system on board is developed to assist the ship operator to understand the encountered sea state. It also provides the optimal operational directions to enhance the safety of the ship. The ship motion responses and wave loads, i.e. heave, pitch, roll, vertical acceleration, vertical shear force and vertical bending moment, are adopted as the parameters to estimate the ship’s encountered sea state including the wave height, average period and wave direction. By using the frequency domain technique, we calculate a series of ship motion response and wave loads with respect to different ship speeds, wave heights, average periods and wave directions. Then, based on the significant values through ITTC spectrum, the calculated results are established as the data base to estimate the encountered sea state for the ship. In addition, the time domain technique is also applied to simulate related ship motion response and wave loads in order to verify the validity of the present technique. From the comparisons, we find that the sea state monitoring system developed here can work well and the optimal operation speeds and headings can also be suggested for reference of the ship navigation.