Numerical analysis of escort tug manoeuvrability characteristics - Part II: The skeg effect

This paper presents a CFD-RANS investigation of the effect of the skeg hydrodynamics on the manoeuvrability of an Azimuth Stern Drive Escort Tug. This study is devoted to identifying a proper mathematical model to be included in a dynamic manoeuvring simulator. The hydrodynamic problem is therefore decomposed in the hull and skeg components. The hydrodynamic characteristics of the skeg were so explored by varying its span and chord systematically, allowing deep insight into the physics of both components and their mutual interaction. The distribution of the forces acting on hull and skeg were studied in detail in their dependence from the skeg geometrical characteristics. Suitable mathematical formulations for the skeg forces were implemented in an MMG-like manoeuvring model-based onto the CFD captive simulations. Lastly, the impact on the tug's manoeuvrability of the previously mentioned variations was then investigated. Turning, Zig-Zag, Escort Capability, Escort Mirror ability and Escort Stability manoeuvres were simulated. The results of these manoeuvres are presented, showing the great potential of this manoeuvring model in representing a wider class of Escort tugs.