Numerical investigation of control strategies on a coupled ship propulsion system in waves

This paper investigates two engine control strategies—constant rack (CR) and speed controller (SC)—for a coupled ship propulsion system in regular head waves. The study decomposes the efficiency chain into components to identify physical mechanisms behind performance differences. By integrating a mean value engine model with a time-domain ship simulator, we analyze transient interactions between hull, propeller, and engine under realistic seaway conditions. Results demonstrate that CR achieves superior fuel efficiency (up to 2.49% improvement), particularly in long-wavelength seas. This advantage stems from reduced turbo-lag effects and more stable air–fuel dynamics that minimize transient thermodynamic losses. However, CR induces significant engine speed fluctuations that may limit practical application. In contrast, SC provides better speed regulation but increases fuel consumption due to turbo-lag and unsteady air–fuel dynamics. Hydrodynamic effects contribute through control-strategy-induced variations in ship speed and wave resistance, though to a lesser extent. These findings highlight the importance of modeling both engine dynamics and nonlinear hydrodynamic effects when evaluating propulsion control strategies.