Technical Note: An opportunity cost maintenance scheduling framework for a fleet of ships: A case study

The conventional method towards deriving schedule for a fleet of ships to minimize cost alone has the shortcoming of not addressing the problem of operation revenue losses associated with delays during maintenance at ships dockyards. In this paper, a preventive maintenance schedule for a fleet of ships that incorporates opportunity cost is presented. The idea is to assign a penalty cost to all idle periods that the ship spends at the dockyard. A version of the scheduling problem was defined as a transportation model of minimizing maintenance costs. Fixed maintenance duration and dockyard capacity were the two constraints of the formulation. Relevant data from a shipping firm owing 8 ships and a dockyard in Lagos with a maintenance capacity of three ships per month were collected over a 24-month period. The maintenance cost function was then formulated with the parameters estimated and the transportation tableau set up. The considered eight ships arrived at the dockyard between the 1st and 20th month, and were expected to spend between 2 to 5 months for preventive maintenance. The optimal schedule of the cost function resulted in ships 1 to 8 being idle for 74 months. The results of the study showed that to reduce the cost and delays, decisions for scheduling preventive maintenance of a fleet of ships should be based on opportunity cost.