Sea state estimated from ship motions by a statistical approach

In theory, a sea wave spectrum is calculable given the ship motions in the seaway and its motion transfer functions. In practice, the complex nature of sea waves, and the influence of ship speed and heading relative to the waves, makes an analytical solution extremely difficult. This paper considers the problem from a purely statistical point of view with the aid of an extensive set of seakeeping trials results. Multiple linear regression is used to deduce the relationship between the RMS ship motions in five degrees of freedom, and the significant wave height measured by a waverider buoy. It is shown that the significant height may be estimated with around 10% error by this method for a wide range of conditions. A test with ‘blind’ data confirms that the approach provides a robust and successful calculation