  This paper presents the TransBoat, a novel omnidirectional unmanned surface
vehicle (USV) with a magnetbased docking system for overwater construction with
wave disturbances. This is the first such USV that can build overwater
structures by transporting modules. The TransBoat incorporates two features
designed to reject wave disturbances. First, the TransBoat's expandable body
structure can actively transform from a mono-hull into a multi-hull for
stabilization in turbulent environments by extending its four outrigger hulls.
Second, a real-time nonlinear model predictive control (NMPC) scheme is
proposed for all shapes of the TransBoat to enhance its maneuverability and
resist disturbance to its movement, based on a nonlinear dynamic model. An
experimental approach is proposed to identify the parameters of the dynamic
model, and a subsequent trajectory tracking test validates the dynamics, NMPC
controller and system mobility. Further, docking experiments identify improved
performance in the expanded form of the TransBoat compared with the contracted
form, including an increased success rate (of ~ 10%) and reduced docking time
(of ~ 40 s on average). Finally, a bridge construction test verifies our system
design and the NMPC control method.
