© 2019 Marine Technology Society. This paper presents the results of a study on the effects of the evaporation duct on microwave propagation in the Irish Sea. The evaporation duct is a phenomenon that occurs almost permanently over the earth's oceans and can be exploited to enable over the horizon communications in the marine environment. The study consisted of an experimental test, where signal strength from a shore-based transmitter was recorded at a number of distances. The results of this experiment were compared to simulated values. Atmospheric data used to simulate the signal propagation was taken from weather buoys in the Irish Sea. It was found that the evaporation duct does have an effect on microwave signals and can be used to extend microwave communications beyond the horizon. This could be useful in enabling high bandwidth communications links to or between offshore assets and equipment including navigation buoys, ships, renewable energy infrastructure and lighthouses which are often situated beyond line of sight of land.