The Concept of Determining a Ship’s Route Based on the Capability Plot and Dijkstra’s Algorithm—Finding the Ship’s Route Between Anchorages

Determining the route from the starting point to the destination is one of the first tasks performed when planning a ship’s voyage. Before the computer age, routes were plotted manually by seafarers based on maps. Nowadays, algorithms are used for this purpose, which make it possible to reach any port in the world. In scientific publications, one can mostly find algorithms that generate global routes based on historical weather and traffic data on major sea lanes. Such routes do not take into account the current hydrometeorological conditions in the area where the ship is currently located, so that disturbances generated by environmental forces can increase energy consumption. A solution to the problem can be local routing based on the currently prevailing hydrometeorological conditions. With this approach, it is possible to respond to dynamically changing sea conditions, determine the route along which the impact of environmental forces on the hull will be least severe and minimize fuel and energy consumption. This paper presents an algorithm that determines the local passage route of an offshore ship using the example of a vessel moving to an anchorage to drop anchor. The algorithm defines a grid of points between the start point (the vessel’s current position) and the end point (the anchor position), and then determines the transition weights between each grid point based on the vessel’s capability plots. Finally, a modified Dijkstra algorithm determines the route where the sum of the transition weights will be as small as possible. During the tests, it was found that the time needed to find the passage route depended on the chosen grid density of the waypoints and was as follows: for a 6 × 6 grid—0.05 s, for an 11 × 11 grid—0.36 s, for a 16 × 16 grid—0.47 s and for a 21 × 21 grid—0.85 s. It was also found that the algorithm identified a route where the impact of environmental forces on the ship’s hull was 13% less than the direct route to the destination, resulting in a 7.5% reduction in energy consumption. The operation of the algorithm for determining the passage route was demonstrated in the anchor design tool developed in the Unity3D environment.