Any structure exposed to breaking waves, be it a simple breakwater or a complex and expensive marine energy machine, will be exposed to high wave impact loads as overturning wave crests slam into it. The violence of the motion of the water surface as waves break are well-known to surfers who seek out such conditions. Marine renewable energy devices will be hit by the most violent storms that nature can produce, yet they are required to produce significant power when the weather is benign and the waves relatively small. This dichotomy can result in expensive failures such as that of the Osprey, a 2MW wave power prototype device located off the north coast of Scotland, which was damaged and sank in a storm. If marine renewable energy is to play a significant role in meeting the energy requirements of the the United Kingdom, all energy extraction devices must survive for many years and many large storms without damage. Hence accurate design methods are required to estimate the peak hydrodynamic loads occurring in such storms. This project explores the science and engineering required to ensure that renewable energy devices survive extreme conditions, and seeks to identify the upper limit of device operations in less severe conditions. Key to making a significant advance in survivability is understanding how steep and violent waves behave on significant currents. Both wave power machines and marine current turbines are likely to be located in relatively shallow water with relatively fast tidal currents, obviously for tidal turbines this is a virtue! If the current is fast and the water shallow, there will be considerable resistance to the flow close to the sea-bed and less further up towards the surface. Thus, the current is likely to be highly sheared and very turbulent. Add on top of this bulk flow violently overturning steep waves and it is clear that the water will be moving around very fast in local regions. The first part of this project is to characterize the statistics of waves and how this varies over time for decades to decades. Next the waves are combined with sheared currents. Then models of marine renewable energy devices will be exposed to such violent combined wave and current events and the forces measured. Finally we aim to develop and test force computer based computational methods for assessing loads. The overall output from this research project will make an important contribution to removing blocks limiting and slowing down the large-scale implementation of marine renewable energy.