Effective modelling of Wave Energy Converters (WEC) is fundamental in the design and implementation of power-maximizing controllers. It is possible to get accurate dynamic models with system identification techniques based on experimental input-output data. However, even though these techniques are well developed in other application areas they are seldom used in the context of WECs. This work describes the methodology used to model a three-body hinge-barge wave energy device using experimental data. Some identification strategies are discussed to get a linear time-invariant dynamic model. The obtained model is validated against a data set separate from that used for identification, to ensure the generalisation capabilities of the model.