This paper presents an effective autonomous follow-the-leader strategy for Azimuthal Stern Drive vessels.
The control logic has been investigated from a theoretical point of view. A line-of-sight algorithm is exploited
to ensure yaw-check ability, while a speed-check feature is implemented to track the velocity of the target along
the path. For this purpose, a linearised manoeuvrability model for azimuthal drive surface vessels is presented.
A model-based control synthesis is proposed to ensure the stability of the closed-loop system and robust PID
controllers are designed by using Linear Matrix Inequalities technique. The control strategy has been successively
validated in two steps, initially by using simulation techniques, and then experimentally using an outdoor scenario
with model scale tugs.
The path planning, navigation, guidance and control modules are studied, detailed, and digitally implemented
on-board of the model scale tugs. The models are supplied with GNSS+INS navigation system. Low-level
management and control of Azimuthals angles and shaft revolutions is implemented on-board. High-level decentralised
path planning, guidance, and control sequence evaluation are dealt with at a remote ground station.
In particular, the presented follow-the-leader strategy meets the most generic needs of platooning convoys,
and, in the specific instance, of Escort convoy tugs. The operative profile of the latter concerns long-lasting and
routine chases with the continuous demand of tuning heading and speed to track the target vessels, until the rare
occurrence of an emergency event. In a realistic scenario, the proposed control system would be beneficial for
the tug master’s lucidity and alertness, while reducing avoidable risks.
At the end of the paper, the results of the experimental campaign are shown to demonstrate the effectiveness
of the proposed control logic.