An approach to estimate vertical center of gravity, draught and RAO from ship motions based on prolate spheroidal wave functions and time-series filtering

• For synthetic time series, the estimation uncertainty was below 2 %, for realistic time series 15 %. • RAO estimation uncertainty is lower than VCG, draught estimation uncertainty. • Accurate estimation of vertical center of gravity, draught and RAO required time-series filtering. • The approach requires few hours of ship motions to estimate vertical center of gravity and draught in full-scale conditions. The motion behavior of a ship is significantly influenced by its draught and the position of the vertical center of gravity (VCG). Accurate estimation of these two parameters enables determination of the response amplitude operator (RAO). This study presents a method to estimate draught, VCG, RAO and wave spectral parameters based on prolate spheroidal wave functions and time-series filtering. The method requires only measured motion data and predefined RAOs as input. Validation is performed by comparing the estimated parameters with known reference values from numerical simulations and model tests. A main contribution is the automated identification of time windows with high estimation accuracy. For numerical and model test cases, RAO, VCG and draught showed deviations of approximately 15 %. The accuracy of the applied RAO database and non-linearities are the main source of uncertainty. Estimations required a few hours of measurements in full-scale. Application to full-scale measurements provides predictions with comparable accuracy to which obtained numerically, indicating that real-time onboard application is possible.