Integrated Planning of Asset-Use and Dry-Docking for a Fleet of Maritime Assets

In maritime industry, moving assets (e.g., naval ships, dredgers, pilot vessels) are subject to obligatory inspections that are based on calendar time. These inspections consist of exhaustive operations that need the assets to be towed into specialized facilities referred to as dry-docks. In addition, there are maintenance operations that need to be carried out as a result of usage-related deterioration of the assets, also requiring the assets to be dry-docked. In practice, a common approach for a fleet of assets is to synchronize these inspection and maintenance operations to avoid unnecessary dry-dockings. However, when and how these operations, some of which are calendar-based and some of which are usage-based, should be synchronized, and whether synchronizing them is always optimal remain as important questions. Since how an asset is used influences when it requires maintenance, answering these questions requires solving an integrated planning problem that combines the planning of asset-use and the planning of dry-docking. Operational constraints such as the locations of assets (i.e. the existence of dedicated assets that must be used at a particular location and flexible assets that can be used in multiple locations), limited dry-docking capacity, and the requirement to meet the demand for asset-use in each location make the problem even more challenging. We formulate this real-life problem as a Mixed Integer Linear Programming (MILP) model. The resulting optimal policy is compared with a benchmark approach from industry to quantify the benefit of integrated planning for asset-use and dry-docking