As the world moves to a greater reliance on renewable energy, a vital component will be the predictability and dependability of the energy source; tidal energy provides such a solution. Horizontal axis tidal turbines are the most mature technology of all the marine renewable energy devices currently under development, as full-scale porotypes are already being tested and operated. As the industry develops and strives for commercial viability, it is becoming increasingly vital to develop a robust understanding of the complex interaction between the tidal flow, turbine blades and the support structure. This study uses an advanced computational fluid dynamics model to explore the operational fatigue loadings induced on tidal turbine blades. Two factors are considered, the presence of a support structure and varying vertical velocity profile of the tidal current. In order to perform the investigation, a model of a concept 16 m diameter horizontal axis tidal turbine with a monopile support structure is created. An investigation of the operational fatigue loadings due to variations in the positioning and the diameter of the support structure, the tidal turbine blade loads were found to varying by up to 43% of the maximum total thrust force. (C) 2020 Elsevier Ltd. All rights reserved.