INTERNATIONAL JOURNAL OF ROBUST AND NONLINEAR CONTROL Int. J. Robust Nonlinear Control 2008; 18:570–585 Published online 14 May 2007 in Wiley InterScience (www.interscience.wiley.com). DOI: 10.1002/rnc.1224 A combined first-/second-order sliding-mode technique in the control of a jet-propelled vehicle G. Bartolini 1 , N. Orani 1 , A. Pisano 1, * ,y , E. Punta 2 and E. Usai 1 1 Department of Electrical and Electronic Engineering (DIEE), University of Cagliari, Piazza d’Armi, Cagliari 09123, Italy 2 Institute of Intelligent Systems for Automation, National Research Council of Italy, ISSIA-CNR, Via de Marini 6, Genoa 16149, Italy SUMMARY This note concerns the design and practical implementation of a position/attitude sliding-mode controller for a surface vessel prototype. The prototype is equipped with a special, recently patented (Italian Patent, 2005), propulsion system based on hydro-jets with adjustable output section. The sliding-mode control design is based on the combination between three instances of a second-order sliding-mode velocity observer (Automatica 1998; 34:379–384) and a simplex-based sliding-mode controller (Int. J. Robust Nonlinear Control 1997; 7(4):321–335). We first describe the structure and the working principle of the prototype. Then, we detail the derivation of the motion observer/controller. Finally, we discuss the major implementation issues and show some experimental results. Copyright # 2007 John Wiley & Sons, Ltd. Received 25 May 2006; Revised 23 March 2007; Accepted 2 April 2007 KEY WORDS: marine vessels; simplex vector method; higher-order sliding modes 1. INTRODUCTION The motion control of marine vehicles is a challenging problem for several reasons: the nonlinear, multi-variable, strongly coupled and uncertain nature of the dynamical phenomena involved; the difficulties in retrieving accurate and reliable localization information; the heavy environmental disturbances [1–5]. Rotating thrusters are commonly used as actuators in both underwater and surface marine vehicles. It is known [4] that the produced thrust is proportional to OjOj; O being the thruster rotating speed. Clearly, this property compromises the manoeuvrability of the vehicle near the zero speed, and its interaction with the wind and wave disturbance can lead to limit cycles of the closed-loop positioning control system [4]. For this reason, rotating thrusters are often doubled, *Correspondence to: A. Pisano, Department of Electrical and Electronic Engineering (DIEE), University of Cagliari, Piazza d’Armi, Cagliari 09123, Italy. y E-mail: pisano@diee.unica.it Copyright # 2007 John Wiley & Sons, Ltd.