Identification of Vertical Centre of Gravity and Ship Mass Using Phase Resolved Wave Prediction Through In-Service Onboard Measurements

Abstract The loading condition of container ships varies with each voyage, significantly impacting their motion behavior. Accurate knowledge of this loading condition is essential to avoid dangerous situations. The presented method provides real-time vertical centre of gravity (VCG) and mass estimation with Prolate spheroidal wave functions (PSWF). PSWF enable the reconstruction of ship motions from measurements and their transformation into encountered wave profiles. This study investigates three methods to extend the procedure in order to estimate ship mass and VCG. The first method solves ship mass parameters and encounter angle iteratively, the second simultaneously and the third with a roll differential equation. Verification with numerical data leads to precise parameter reconstruction, while model test validation indicates that nonlinear effects reduce the accuracy. The iterative procedure leads to the smallest deviations from numerical and model test data. Higher wave steepness reduces prediction accuracy in wave angle and profile estimation, but has less influence on VCG and ship mass accuracy. Full scale validation using estimates for mass and VCG results in similar estimation accuracy as using the estimated values as fixed parameters.