Tugboat scheduling problem in large container ports: A case study of the Singapore port

Abstract

In recent years, more and more container ports have become congested because of the large number of visiting ships to the ports. This causes a difficult dispatching and management problem for port operators, that is, the tugboat scheduling problem. To solve the problem effectively from the operational viewpoint, this study proposes an interesting tugboat scheduling problem in a large container port. A mixed-integer linear programming (MILP) model is built for the problem with the objective function of minimizing the total processing cost for container ships. We also consider the constraints of horsepower limitation of tugboats, utilization time limit of tugboats, etc. By using the commercial solver CPLEX to solve the built MILP model in a case study of the Singapore Port, the efficiency of the MILP model is presented. It takes less than 18 hours to reduce the optimality gap to a maximum of 0.9% for solving a real-size instance with 12 tugboats and 100 ships. Moreover, the results of extensive computational experiments also show the applicability and effectiveness of the MILP model to handle real-world tugging operations.