Much attention has been paid in recent years to the determination of design loads for moored floating structures and the application of established methodologies for fixed structures have been found to be ineffective. This paper experimentally investigates extreme responses of a lazy S moored 1:20 scale model of Mocean Energy’s Blue Star wave energy convertor (WEC) along the 1 year return contour. The device is a hinged raft type WEC and the extreme responses studied include mooring loads and snatch load events. Long irregular wave time series are used in the estimation of extreme value distributions of the mooring load for particular sea states. Conditional random response wave and constrained new wave profiles are used to study and support the predictions. Wave calibration and the impact of wave breaking on the physical realisation of response conditioned focus waves and extreme value distribution (EVD) predictions are discussed.