Numerical modelling of wave energy converters (WECs) can provide insights into device performance at an early stage and help de-risk projects before progressing to more advanced, costlier stages of development. Several software packages have been made available for this purpose in recent years. However, the lack of design convergence in the wave energy industry, with its wide range of working principles and mechanisms, means that many developers have been unable use these tools. Here we show that some limitations can be overcome by using an alternative multibody dynamics approach. A third party multibody dynamics code based on the Lagrange multiplier method, Hotint, has been coupled to Innosea’s existing WEC modelling code, InWave, and verified using existing test cases. This has made the modelling of many new types of mechanisms possible – include closed mechanical loops.