Optimization in Roll-on Roll-off shipping
Speaker: Professor Kjetil Fagerholt, Norwegian University of Science and Technology.
Roll-on Roll-off (RoRo) shipping is a specialized shipping segment where the vessels are designed to carry wheeled cargo, such as cars, high and heavy vehicles (e.g. trucks, agricultural and construction vehicles), and other types of breakbulk cargo (e.g. turbines, train coaches, boats) that can be placed on trolleys for loading and unloading. RoRo vessels have built-in ramps that allow the cargo to be efficiently rolled on and off the vessels, and come in four main types varying in their ability and flexibility to handle the different types of cargo: 1) pure car carriers (PCCs), 2) pure car and truck carriers (PCTCs), 3) large car and truck carriers (LCTCs), and 4) general RoRo vessels. The first vessel types are designed to carry cars but have also a few hoistable decks that allow also for taller cargoes. The latter types are optimized for carrying more high and heavy and breakbulk cargoes, but can also carry cars. The largest RoRo vessels have a capacity of around 8,000 so-called car equivalent units (CEUs), which is a measure based on a Toyota Corona 1967 model.
This presentation gives an introduction to the RoRo shipping segment and, based on a research collaboration with one of the major RoRo shipping companies in the world, discusses some important planning problems where optimization can provide valuable decision support. At the operational planning level, we present the stowage planning problem for a RoRo vessel visiting a given set of loading and unloading ports along its voyage. If we look at the stowage on one deck on board the vessel at a time, this is as a special version of a 2-dimensional packing problem where we want to utilize the vessel’s capacity so that we can carry as much cargo as possible. However, the problem has a number of additional considerations. One wants for example to place vehicles that belong to the same shipment close to each other to ease the loading and unloading. Another important consideration is that one wants to minimize shifting, which means temporarily moving some vehicles to make an entry/exit route for the vehicles that are to be loaded/unloaded at the given port.
We also present the fleet deployment problem arising in RoRo shipping. This tactical planning problem consists of assigning available vessels in the fleet to voyages along given geographical trades. The results from fleet deployment, in addition to which ship will perform which voyages, are sailing routes for the ships in the fleet, i.e. each vessel is assigned a sequence of voyages to perform, possibly with ballast (empty) sailing between the last port call of one voyage and the first on the next. Since the selection of vessel speeds heavily influences on the fuel consumption and costs, we also include sailing speed on each voyage as a decision variable.
This presentation provides an overview of mathematical optimization models and solution methods for both problems along with some computational results and discussion.