A linearised frequency domain numerical model of small seabed-mounted bottom-hinged wave energy converters is developed that accounts for vortex shedding at body edges and decoupling at large angles of rotation. The numerical model is verified and calibrated using data from wave-tank experiments. It is found that in general the device capture factor increases with both the device width and wave frequency due to increasing wave force. The model also indicates that for typical flap dimensions and incident wave amplitudes the peak in capture factor at the body’s natural pitching frequency is suppressed due to viscous losses and motion constraints. The effect of viscous losses and motion constraints are also responsible for limiting the increase in performance that is obtainable with phase control. Three cost functions, power per unit displaced volume, power per unit structural task and power per unit surge force are produced and applied to the results of a parametric analysis. Three distinct regions of the design space are identified; EB Frond and BioWave are found to sit in one region, WaveRoller in another region and Oyster in the final region. Characteristics are identified for each region and related to the distinct designs of the commercial systems identified.