Recently, several attempts have been made to estimate the ocean wave spectrum from the vessel motion using the Kalman filter. The Kalman filter has the advantage of real-time estimation, lower cost, and easier installation than other instruments. However, when a vessel is less responsive to high-frequency waves, over-estimation occurs at high frequencies. Therefore, there is a limit in the estimation. In this paper, an improved configuration of Kalman filter is tested to reduce overestimation at high-frequency region, which came from the intensive heuristic analyses. Generated motion data was used to acquire the corresponding estimated wave spectra.
Recently, in the industry of ship, the most important topic is an unmanned ship or smart ship. If an unmanned ship becomes reality, it is possible to reduce the operating cost and the incidence of ship accidents. In addition, human loss caused by pirates can be prevented (Minter, 2017). For the unmanned ship, several issues need to be solved. Route optimization is also one of the important issues (Jokioinen, 2015). The calculation for optimizing the route includes several parameters, including the additional resistance acting on the ship by the ocean waves. Additional resistance induced by ocean waves can be calculated from the wave spectrum. In other words, the wave spectrum is necessary for route optimization.
There are many ways to estimate the wave spectrum such as using radar (Al-Habashneh, Moloney, Gill, & Huang, 2018), satellite (Jackson, Walton, & Baker, 1985), or buoy (Gorman, 2018). Moreover, there is a technique of estimating the ocean wave from the ship motion measured by the motion sensor equipped on the ship using Kalman filter. This is relatively low-priced and has an advantage that the wave spectrum can be easily estimated on the ship's passage, even on far from the coast. It is founded that the number of active merchant ship around the world by 2017 is 50,000 approximately (Statista, 2017), which means there are already around 50,000 of potential sensors of the vessel over the world.
