  A VecTwin rudder system comprises twin fishtail rudders with reaction fins to
increase its performance. With a constant propeller revolution number, the
vessel can execute special low-speed maneuvers like hover, crabbing, reverse,
and rotation. Such low-speed maneuvers are termed dynamic positioning (DP), and
a DP vessel should be fully/overly actuated with several thrusters. This
article introduces a novel and experimental VecTwin positioning system (VTPS)
without making the ship fully/overly actuated. Unlike the usual dynamic
positioning system (DPS), the VTPS is developed for low-speed operations in a
calm harbor area. It is designed upon an assumption that the forces due to the
interaction between the rudders, the propeller, and the hull are linear with
the rudder angles within a range around the hover rudder angle. The linear
relationship is obtained through linear regression of the results from several
CFD simulations. The VTPS implements a PID controller that regulates the
actuator forces to achieve the given low-speed positioning objective. It was
tested in combined automatic docking and position-keeping experiments where
disturbances from the environment exist. It shows promising potential for a
practical application but with further improvements.
