On predicting boat drift under time-varying and uncertain sea environment and boat parameters

A theoretical model for predicting steady boat drift for search and rescue missions is being extended in this work to situations involving time varying environments. The drift models are based on the laws of physics which govern the motion of a floating body in time-dependent wind and surface current fields. The nature of a sea environment is addressed through uncertainty analysis with interval mathematics and nonlinear programming. In terms of the empirical aerodynamic force coefficients of the boat or any other drifting object, external wind field, and current field, the drift velocity of the boat being searched for can be obtained numerically. Two theoretical models are presented. One of them, a simplified version, ignores the boat's accelerations. Field experiments previously performed are described. Five sets of measured field data or are selected to verify the presented models. Predictions of both theoretical models are compared with the measured field data. The result shows that the both models' predictions are in agreement with field test results and, with a prescribed uncertainty, the predicted path falls within the same range as field test result. This illustrates that both models can provide reliable drift regions for search and rescue.