Numerical analysis of escort tug manoeuvrability characteristics

The adoption of RANS techniques is widely spread in terms of resistance and self-propulsion prognosis for merchant and military vessels; however, on the other hand, the captive evaluation of hydrodynamic manoeuvring forces across numerical procedures still concerns great computational effort and challenge. When it comes to deal with Escort or tractor tugs, characterised by rather full hull forms, typical of harbour tugs, with the addition of extensive foiled shaped fore-skegs solutions, the ability of predicting manoeuvring and handling of such vessels becomes a great added value at an early design stage, as an alternative to physical model scale testing, since very scarce data are present in open literature. Escort vessels in particular, both operate at low and high speed, in addition to the typical harbour tasks entailed, making the manoeuvring modelling even more complicated. In present work, a low-speed and high-speed numerical methodology based on the OpenFOAM finite volume method on polyhedral unstructured mesh is investigated and validated against purposely designed model tests carried out in towing tank: Pure yaw, pure drift, drift and yaw, and drift and heel simulation results are compared with experimental data in terms of forces first, and impact on manoeuvring lastly, showing satisfactory agreement with experiments. Finally, Escort capability tests run at tank are compared with a purposely calibrated manoeuvring model on the RANS results.