Medium-Range Scheduling for a Freighter Fleet

A model of Matson Navigation Company's freighter movements has been created to schedule voyages between the West Coast and Hawaii for periods of three months. The model describes the ships and port facilities; it regards the West Coast as consisting of three port areas. Ship timings are based on average values; no stochastic variables are used. Inputs to a run include cargo forecasts and initial positions of the ships in the fleet. Decisions on ship movements are made sequentially on the basis of calculated voyage profit and service requirements. Twelve cargo classes and six port pairs are considered, but of 72 possible combinations of cargoes and port pairs, only 29 actually occur. Programming is in GPSS-III for the IBM 7094. IBM 360/30 programs were written to facilitate entry of data and also to tabulate the output in several types of management reports for easier analysis of results. A three-month period, in one-hour increments, takes six minutes to run on the 7094. The model utilizes the computer to obtain schedules in the region of optimum profit, consistent with certain rules laid down by management. The model has been used in planning activities of the current fleet and in studying requirements for the future fleet. It offers the following advantages: computational accuracy in production of medium-range schedules; incorporation of profit criteria in many schedule decisions; speed of testing many alternatives; and consequently, more responsive and satisfactory fleet scheduling than could be done by normal manual methods.