Optimizing the woodpulp stowage using Lagrangean relaxation with clusters

The cargo stowage process in ships consists in arranging items into holds. This paper approaches the problem of finding the maximum number of stowed units of woodpulp into holds of dedicated maritime international ships. This problem, essentially three-dimensional, can be reduced to the two-dimensional case due to constraints provided by the transport, and becomes similar to the manufacturer's pallet loading problem. We present in this paper a formulation to the woodpulp stowage solved by a Lagrangean relaxation with clusters (LagClus) that considers the conflict graph generated by overlaps of woodpulp units. Computational tests are performed and compared with the real results obtained in Brazilian ports. The results obtained by LagClus were better than the real results, and consequently it can provide savings if we look at the shipping logistics costs.