Z-drive escort tug manoeuvrability modelling: From model-scale to full-scale validation

Abstract

A deep insight into the manoeuvring characterisation of a broader class of Azimuthal Stern Drive Escort tugs (ASD) is undertaken with the scope of defining a parametric manoeuvring simulation code for the free-sailing and towing operations. To this end, given a simple set of tug design parameters (main dimensions, skeg size, azimuthal size, propeller pitch, main engines, etc.), a physics-based 4-DOF mathematical prediction tool for the dynamic behaviour of the ASD tug has been developed in calm seas. Two independent validation processes have been provided to prove the suitability of the modelling: the first model-scale, while the second full-scale. The present paper presents the free-sailing full-scale validation of a different but compatible hull, having dimensions, propulsion, skeg characteristics significantly different with respect to the “parent-design” (RM2812) used to develop the code principally. The verification involved the measurements purposely performed during sea trials onto two sister-ship ASD new-buildings (RM3213).