Containers lost at sea are a hazard for shipping. The maritime authorities thus wish to be able to announce their positions to the navigators, or to recover them. In the event of containers loss, the calculation of the trajectory enables to locate the dangerous area for navigation and to search for the containers. A numerical model has been developed and configured to provide a tool to forecast container drift at the sea. This paper summarises the key features of the model and presents four simulations in hindcast mode. Three cases are real losses ('Churruca', 'Sherbro' and tank containers), one is an experiment (Dourvarc'h). A basic physic of the container has been implemented in the hydrodynamic code developed by Meteo-France. This aspect constitutes a new approach in the prediction of objects drifting on the sea. We demonstrate by the analytical calculus and with the four studied cases that the immersed fraction initialised in the initial condition is a key parameter. The results have also shown the role of the wind direction and intensity on the trajectories simulations and the sensitivity of the model to the container buoyancy term. (C) 2002 Elsevier Science Ltd. All rights reserved.