Tidal turbine applications will place composite materials such as glass-fibre and carbon-fibre reinforced polymers under surprisingly high pressure due to the significant water depths they operate in (to depths of 50 m). The technical reliability of tidal turbines must be guaranteed despite the high dynamic loads resulting from a combination of plant operation, wind and waves with irregular swell. These external effects could lead to operation downtime and accelerated degradation. Research has already established that (unpressurised) moisture saturation is detrimental to both tensile and fatigue strength of GFRP material compared to its dry laminate performance. This degradation has been shown to be stress dependent. It is possible that hydrophobic coatings could help protect the material while in service. Therefore, two commercially available coatings were applied to 5 variations of composites materials. These materials are commonly used in tidal and wave turbine blades as they have excellent corrosion resistance and mechanical properties. All 5 are subjected to the same conditioning processes. Non-pressurised and pressurised immersion conditioning in water. Glass fibre epoxy (Ampreg), along with a glass fibre powdered epoxy, a glass fibre PEEK composite and a carbon fibre powdered epoxy composites were investigated. The glass-fibre epoxy (Ampreg) was also tensile tested statically/fatigue.