Whilst energy can be efficiently extracted from waves by a device exhibiting sloped motion, sustaining that performance in a deep water environment would conventionally rely on a costly support structure. Introduced herein, the WaveTrain device provides an alternative approach to retain the benefits of sloped motion, using a series of joints and struts to mechanically interconnect a series of sloped modules, each of which houses an internal water column to allow reaction against the surrounding water inertia. With a view to maximal power extraction in a real wave climate, this paper presents an optimisation of key parameters associated with the geometry and mass distribution. This relies upon an efficient hydrodynamic model, whose development is presented, particularly with respect to the use of ‘generalised’ modes to model hinges, for which a somewhat didactic treatment is given. A genetic algorithm, tailored specifically to handle the discontinuous parameter space and the numerical hydrodynamic model, is then used to identify design criteria that are essential for optimal power extraction. Five necessary but not sufficient criteria are presented, in addition to guidance regarding the remaining parameters, which is used to briefly highlight the potential benefits for the practical engineering design.