Objective function (5) depicts ship voyage fuel consumption. Constraint (6) ensures ship transit between origin – destination port pair. Constraint (7) ensures ship arrival at destination port on or before due date. Constraint (8) ensures that ship voyage fuel consumption does not exceed ship fuel tank capacity. Constraints (9) ensure that time spent at each ship speed level is nonnegative, namely they define domain of decision variable Ts , āˆ€s∈S.