Practical Prescribed-Time Control for Underactuated Marine Surface Vessels: Theory and Experiment

This paper proposes a practical prescribed-time control strategy for underactuated marine surface vessels (UMSVs) with fore-aft asymmetry. A sufficient condition for practical prescribed-time stability (PPTS) is established through a novel time-varying gain function that maps the settling time into a single user-defined parameter. First, the nonholonomic constraint of the UMSV is transformed into an integral cascade system via the hand position approach, which addresses the design challenge from underactuation. Subsequently, input saturation nonlinearity is approximated by a sigmoid function, while model uncertainties are compensated through an adaptive parametric design paradigm. A barrier function-integrated adaptive law is further developed to bound the adaptive parameter without overestimation. Rigorous stability analysis confirms that the tracking error converges to an adjustable bounded domain within the prescribed time. Experimental results validate the efficacy of the proposed controller.