Nonlinear maneuvering and control of ships

We address the problem of maneuvering ships onto curves or paths in the plane. To do this, we introduce the Serret-Frenet equations and show how these fit the scope for control design with 3 degrees-of-freedom (DOF) hydrodynamic ship models in the loop. The Davidson and Schiff (1946) linear parametrically varying ship model is used in the design, and we show how we can manipulate this by introducing acceleration feedback and by moving the body-frame freely. This simplifies the control design in such a way that we do not have to deal with zero-dynamics. Instead we use a 3-step backstepping design and theory for interconnecting subsystems. Real data from a 175 m container ship is used in a computer simulation to validate the design.