Ship scheduling of fertilizer products

This article describes a Mixed Integer Programming model to schedule ships with a variety of fertilizer products into eight ports on Australia's eastern and southern seaboards. The objective is to minimise freight, discharge and inventory holding costs while taking into account demand for product and warehousing constraints. Major planning decisions are made on a monthly basis for a 12–15 month planning horizon. To improve run-time performance extra integer variables are introduced to provide strong cuts and binary variables are introduced gradually throughout the planning horizon over several optimisation runs. The model is used for operational planning and budgetary purposes and interfaces to the outside world through a friendly matrix generator and a modern spreadsheet system.