Block erection in the event of delays in shipbuilding: A scenario-based approach

Ships are constructed from individual steel structural units called blocks, which are typically erected into the ship one by one in a sequence. This sequence, the block erection schedule, is the main schedule in shipbuilding, and it is followed in other production phases. However, the problems in the production of the blocks can delay the arrival of the blocks in comparison to what was initially scheduled. To deal with these delays, this article studies five different planning methods: erecting blocks unfinished; the use of inventories; the use of rush jobs; sequence changes; and, if the delays cannot be dealt with, delaying the completion of the ship. In order to do that, a mathematical, scenario-based mixed-integer linear programming model is formed. The model is used with numerical results to show that the block structure, delay conditions, and the tardiness costs have significant effect on the optimal use of planning methods. Results show that inventories should be used when delays are probable, whereas blocks should be erected unfinished if the delays are very uncertain and there are high tardiness penalties. The uses of rush jobs and sequence changes depend on the structure of the ship.