Traceable Virtual Sea Trials in the Marine Robotics Unity Simulator for Manoeuvring Assessment of Unmanned Surface Vehicles

Accurate identification of hydrodynamic derivatives is essential for precise control and autonomous navigation of Unmanned Surface Vehicles (USVs). However, acquiring high-fidelity manoeuvring data from physical sea trials is often constrained by cost, safety, and environmental disturbances. Standard manoeuvring trials, particularly Turning Circle (TC) and Zig-Zag (ZZ), remain fundamental to IMO and ITTC assessment procedures because they provide comparable performance metrics reflective of underlying hydrodynamic behaviour. This paper extends the open-source Marine Robotics Unity Simulator (MARUS) by introducing a standardised Virtual Sea Trial framework for automated execution and data generation of TC/ZZ manoeuvres. The framework provides traceable command-actuation logging, system-identification (SI)-focused data conditioning, and automated extraction of IMO/ITTC-aligned manoeuvring metrics. A key contribution is a dedicated TC/ZZ data acquisition and post-processing pipeline, improving the repeatability and auditability of simulator-based manoeuvres while producing SI-ready datasets for hydrodynamic-derivative identification and digital-twin workflows. The framework also provides explicit command-execution separation for differential-thrust steering, where manoeuvre inputs are recorded as ordered rudder-equivalent commands and realised actuation is logged as an execution-level proxy derived from applied thrust. Case study results demonstrate repeatable and IMO-compliant manoeuvre behaviour. For TC tests, the normalised advance differs by approximately 3.9% between port and starboard turns, while the tactical diameter differs by 4.6-4.7%. For ZZ tests, first and second overshoot excesses remain below 1 degree for both +/-10-degree and +/-20-degree manoeuvres, satisfying IMO criteria, while peak yaw rates range from approximately 4.1 to 5.8 degrees/second.