Digital route of a maritime autonomous surface ship: from waypoints to a dynamically feasible trajectory

The object of this study is the concept of a “route”, which requires reconsideration. A conventional route is represented by a polyline consisting of waypoints and verified in ECDIS; this is sufficient for a navigator but not for an automatic control system that must execute the route. The article proposes a formalization of the digital route of a Maritime Autonomous Surface Ship (MASS) as an extension of the standard IEC 61174 route format (RTZ) by adding turn arcs with wheel-over points, corridors and safety zones, a speed profile, and time stamps. Conditions for the geometric and dynamic feasibility of the route based on the MMG maneuvering model and the first-order Nomoto model are presented. An “acceptable solution” hypothesis for tactical replanning is formulated, and a fourlevel planning architecture is proposed. A computational experiment involving a 100 m vessel, a speed of 5 m/s (approximately 10 kn), and four route legs demonstrated that, when following the digital route with a specified turn radius, the maximum deviation from the planned trajectory decreased from 35.3 to 11.3 m, the root mean square deviation decreased from 12.1 to 4.3 m, and the maximum rudder angle decreased from 25.1° to 17.6° compared with following a polyline with waypoint switching based on an acceptance circle. The results substantiate the inclusion of dynamic feasibility parameters in the route format exchanged between MASS, shore control centres, and surrounding ships. The “acceptable solution” hypothesis is formulated and a four-level planning architecture is proposed. Further research may include simulation using a more comprehensive MMG model with external disturbances, consideration of deceleration and berthing modes, and cooperative route planning for multiple MASS.