A Virtual Target-Based Underway Docking Procedure for Unmanned Surface Vehicles

Abstract

AbstractThis paper considers the topic of safely docking a small unmanned surface vehicle (USV) with a larger mother ship moving in transit at sea. The proposed underway docking procedure is divided into two distinct phases to ensure a controlled and collision-free operation. Specifically, a safety circle is defined around the mother ship together with a virtual target point that can move along its circumference. During the whole procedure, the mother ship passively moves forward in a straight line while the USV actively tracks the target point using constant bearing guidance. In the first docking phase, the target is positioned at the projection of the USV position onto the safety circle surrounding the mother ship. When the USV has matched its position and velocity with the projected target point, the second phase is initiated by the target point starting to move along the safety circle until its bearing matches up with that of the desired docking point. Subsequently, the target point starts reducing its distance from the safety distance until it becomes equal to that of the docking point such that docking is finally achieved. The suggested underway docking procedure represents a simple and intuitive method which is easy to implement and tune. Its performance is illustrated through a computer simulation with an underactuated USV docking with a mother ship in transit.