Real-Time Estimation of Sea Spectra Based on Motions of a Running Ship : Full Scale Trial

Abstract

There is no need to say that the real time and quantitative estimation of sea state around a running ship is very important on the view point of prevenlting marine casualties or keeping safety sailing. Up to this time, as ship borne wave recorder, there is well known Tucker type recorder and ultrasonic relative wave recorder which is overhung from a ship bow also exist. However, those recorders have a weak point that they are influenced by the rocal disturbance from the hull of a moving ship. Moreover, the buoy or throwed away type is also developed, but it is difficult for usual use and was used for experimental use only in the past. Therefore, it is actual circumstaces that the estimation of sea state from running ship is mainly depending on visual observations, but this method is difficult to apply at night and individual differences are large especially about the estimation of swell. On the other hand, present report concerns about the development of a system on board which can estimate wave spectra or its statistics in real time by introducing a cheap microcomputer. This system is based on the method of estimating wave spectra by using the known frequency transfer functions of ship motions and measured ship motions by sensors on board like accelerometer and vertical gyro. Here, the wave direction is also obtained from ship borne rader. By this relatively cheap system, even at night, we can make usual estimation of sea spectra and then sea state sitting in a running ship, and also we can contribute to the accumulation of reliable data of ocean waves.