Z-Drive Escort Tug manoeuvrability model and simulation, Part II: A full-scale validation

A deep insight into the manoeuvring characterisation of a wider class of Azimuthal Stern Drive Escort tugs (ASD) is undertaken with the scope of defining a real-time parametric manoeuvring simulation code for the free-sailing and towing operations. In the part I of the work a physics-based 4-DOF prediction parametric tool for the dynamic behaviour of the ASD tug has been developed, and a validation with model-scale Escort-towing tests has been presented. In the present paper a second validation methodology, based on full-scale measurements, is discussed. This verification envisages simulator’s capability of describing the free-sailing performance of a different but compatible hull, having dimensions, propulsion, skeg characteristics significantly different with respect to the “parent design” used to develop the tool. The experimental campaign involves the measurements purposely performed during sea trials onto two sister-ship ASD new-buildings (RM3213). Turning circle, zig-zag manoeuvres, and Dieudonne’ spiral tests are deeply analysed and the results used for validation purpose. The simulation results showed a satisfactory agreement with the full scale manoeuvres, positively demonstrating the ability of the parametric mathematical formulations to forecast customised tug manoeuvrability for tug design purposes.