This paper concerns the implementation of hybrid drive lines in marine applications with the main aim to improve the longitudinal dynamics during acceleration. The main concern is the optimal use of the combination between internal combustion engines and electric motors limited by battery capacity and thermal load. We use physical and data based modelling to derive a suitable model for control design. Based on a chosen cost function we finally compute a control law to assist the combustion engine during acceleration phase while battery charge conditions and thermal constraints can be taken into account via a cost function parameter. © 2010 IFAC.