A system viewpoint is essential in the study of wave energy converters, since several different energy domains are involved in such devices. In this regard, bond graph, a graphical, port-based approach to modelling engineering systems, serves as a useful tool. This article presents a study of a wave energy conversion system with hydraulic power take-off. With the aid of bond graph, two alternative hydraulic system designs are modelled by assembling hydraulic subsystems/components in different manners. A shallow-water pitching wave energy conversion system is considered as a case study, and selected simulation results using the two alternative hydraulic system designs are presented. In addition, this article suggests how to model by bond graph the dynamics of a multi-body wave energy conversion system.