Z-Drive Escort Tug manoeuvrability model and simulation

The ability to predict the tug's handling, effectiveness, and safety at early design stage is paramount in view of an optimal design process. In this framework, the availability of a reliable manoeuvrability prediction model is beneficial. This paper presents a novel 4-DOF parametric manoeuvrability model dedicated to the manoeuvrability analysis of Azimuthal Stern Drive Escort Tugs. An extensive captive model testing campaign is exploited to develop the mathematical model, conceived following the MMG model concept. The modelling pursues a physics-based approach aimed at characterising the complete manoeuvring hydrodynamics of the vessel. The hull+skeg and azimuthals force contributions are analysed separately and are then coupled to analyse their interaction. A complete, real-time simulator is presented, which is capable of simulating the dynamics of a towing convoy in several real case scenarios. This capability is envisaged to become a very useful tool for the tug designer, allowing to address realistic operational conditions with a focus on manoeuvring capabilities, risk assessment, risk mitigation, operational safety and effectiveness.