A graph-rotation model for optimal ship routing in ice conditions

Abstract

Ship independent navigation in ice-infested waters is a risky operation. However, it is widely practiced in the Northern Baltic and other freezing regions. Up to now, there is no conventional algorithmic approach, which provides robust and efficient routes for winter navigation. In the article, we propose a new graph method for algorithmic finding of a route in the complicated environment. This method is based on a concept of local grid rotation and provides optimal routes in sense of its length and number of direction changes. Unlike Dijkstra and A*, the new method allows finding a short route with minimum number of zig-zags, which ensures distance from shores. The presented method is computationally rather efficient and employs extended wave algorithm which has been developed earlier by the authors. We provide the case study of finding an efficient route in ice conditions of the Baltic Sea given by an ice chart. Calculations are performed for a vessel with Ice2 class travelling to Gulf of Bothnia. The route found by the new method is compared with the globally shortest path evaluated by Dijkstra's algorithm on a graph with advanced grid. The new algorithm provided much smoother route with nearly the same travel distance.