Abstract: The chapter deals with developing small and cheap autonomous underwater vehicles, AUV, entrusted of extended manoeuvrability for surveying and docking missions, requiring accurate path tracking and attitude control, capable of travelling at low speed, down to the proper depth, to accomplish the assigned tasks with reliable autonomy and without relevant impact on the surroundings. The to day available AUVs, generally, make use of several propellers, distributed around the body, to achieve the desired mobility with full attitude control. The solution requires the closure of multiple loops between sensors and actuators, highly cross-coupled and dependent on dynamics non-linearity and marine surroundings disturbances. The prospected solution considers a properly shaped vehicle, to grant minimal drag for lowering power consumption. A single rear propeller has in charge propulsion and manoeuvring. The propeller can be oriented around two axes, say, pitch (for heaving) and yaw (for veering); the screw (hydrodynamic) torque is balanced by variable tilt fins, either, by counter-rotating vanes. A three degrees of freedom parallel-kinematics robotic wrist provides the joint path-and-attitude selection and the twist off-set, by driving the propeller assembly through three independent actuations. The devised submarine wobble-free autonomous navigator, SWAN, is a considerable upgrading of the vectored thrust planning, due to the innovative robotic actuation, permitting the joint heave and veer setting up, with the total balancing of the screw effect around the vehicle axis. The attitude preservation is important figure, each time the AUV's mission requires the accurate angular positioning of the carried instrumentation. The solution makes use of a ductrestricted propeller, with externally driven pitch-and-yaw bending and twist to counter-act the screw torque by continuous rotation, either, by tilted fins. The balancing wile assures local hover or docking, accomplished by active duct counter-rotation, while steady surveying missions exploit the reactive mode, for optimal efficiency. The through-out discussion of the prospected innovative robotic actuation is given, with characterisation of the basic functional and structural features, with account of the on-duty properties and of the conditioning design specification. This way, the noteworthy SWAN's peculiarities emerge, to equip advanced AUVs. The vectored control strategies are also discussed in the chapter. To that purpose, different AUV moving modes (approach to desirable point of space, approach to desirable point of space with desirable orientation, moving on the desirable spatial trajectory, etc.) are taken into consideration. The related examples algorithms, which operate on the heave and the veer setting and on the twist compensation, are investigated, for each navigation mode, also discussing the manoeuvrability abilities of the enhanced vectored propeller actuation, with added autonomy for docking and hovering. The chapter intends to provide full design and development frames of the advanced SWAN solution. The results, obtained by modelling the competing navigation modes, are addressed to document the effectiveness of the innovative robotic actuation, and to show how to work out the duty-oriented solutions, with the resort to the special purpose parallel wrist, in driving the manoeuvring thrust.
