Pilot Assignment to Ships in the Sea of Bothnia

Abstract

The Maritime Administration in Sweden initiated a study on the best allocation of pilots and its impact on costs and service levels. Pilots are required to guide ships from and to ports along the shipping fairways between the ports and open sea. Transports to and from rendezvous points at sea are made by small vessels. Normally the pilots are qualified to work on a subset of the shipping fairways. Average workloads are known from historic data, but the actual times for the required services are more or less known some 20 + h in advance. The problem studied was a historic data set covering 1 week of operations involving 66 pilot assignments and 21 pilots. A column generation approach was adapted. It includes the solving of shortest path problems in time--space graphs. Postprocessing is applied to handle legality constraints, which involve maximum work time shifts and minimum rest times in between. Set partitioning and set covering models were deployed to identify the final solution. Any multiple assignments associated with set covering formulations were handled by a myopic cost estimation procedure, and a small integer program for surplus removals.