  A two-phase model predictive controller (MPC) is proposed for underactuated
surface vessel operation in confined environments. For general driving
maneuvers (phase one) the ship's geometry is not considered explicitly while in
more restricted areas (stage two) which occur, e.g., in mooring maneuvers, the
ship's geometry is approximated to ensure collision avoidance. To remove the
dynamical constraint in the problem setup, the differential flatness of the
fully actuated system is exploited and the flat outputs are parameterized using
B-spline functions. Underactuated behavior is retained by means of inequality
constraints that are imposed on the non-controllable input. In an effort to
solve the MPC, a static nonlinear optimization problem is formulated and
feasibility w.r.t. obstacles and actuator constraints is ensured at collocation
points. Static obstacles are considered as constructive solid geometry
functions in the MPC which also takes into account disturbances induced by
wind.
