Extraction of energy from ocean waves is a high-priority sustainable-energy initiative in the UK. The Offshore Wave Energy Ltd wave energy convertor (OWEL WEC) is a floating rectangular box which captures waves at one end and extracts their energy though a power take off (PTO) system at the other end. The Surrey team is providing underpinning modelling and mathematics to this project. The modelling requirements of the OWEL WEC design dovetail with research at the University of Surrey on interior fluid sloshing, external water wave dynamics, coupling between vessel and fluid motion, and modelling of the PTO as a gravity current interaction. The outcome is direct impact on the wave energy industry and indirect impact on the environment and the economy.