Hydrodynamics-aware formation control for energy-efficient multi-vessel systems: A review

Maritime decarbonization and the emergence of autonomous vessel fleets are motivating cooperative sailing concepts in which formation geometry serves not only as a coordination variable but also as a potential means of reducing hydrodynamic resistance. Although favorable wake and wave-interference patterns can reduce resistance in specific configurations, translating these benefits into deployable formation-control laws remains challenging. The central difficulty is cross-layer: hydrodynamic models must capture spacing- and speed-dependent interaction effects while remaining sufficiently compact, differentiable, and transferable for constrained real-time control. This review examines hydrodynamics-aware formation control for energy-efficient multi-vessel systems using a structured Scopus corpus of 193 publications. It connects three research layers that are commonly treated separately: formation-control architecture, hydrodynamic-interaction modeling, and energy-accounting fidelity. The literature is classified using a five-level evidence axis ranging from single-vessel energy optimization to closed-loop interaction-aware formation control. Empirical, potential-flow, CFD/RANS-based, reduced-order, and surrogate models are compared in terms of real-time capability, differentiability, calibration burden, transferability, and compatibility with MPC and distributed MPC. The synthesis shows that the literature contains substantial CFD, experimental, and offline configuration-optimization evidence, but very limited closed-loop validation in which hydrodynamic interaction, propulsion-realistic energy metrics, actuator constraints, communication limitations, and safety requirements are addressed together. Control-ready hydrodynamic surrogates, propulsion-aware energy accounting, robustness in mixed traffic, and field validation are therefore identified as the highest-priority research directions. A validation ladder and reporting checklist are proposed to improve comparability and support future deployment in inland, coastal, and open-water scenarios.