An appropriate schedule of the operations for the maintenance (both long and short term) of offshore renewable energy devices can be a crucial key factor for assessing the economic viability of marine energy projects. Moreover, floating devices suffer from a higher uncertainty in the determination of loads and failure occurrence. For these reasons, in this work a methodology based on Global Positioning System (G.P.S.) signals for mooring integrity monitoring is introduced. Indeed, besides the already widely used Automatic Identification Systems (A.I.S.), which provides alerts for drifting devices, it is proposed here a more advanced methodology enabling the detection of line failures or simply broadcast alerts if the device position reaches a contour line, previously calculated and provided by the floater and mooring designers. Different position monitoring strategies and contour line will serve to identify when a simple visual inspection is required, a mooring line is broken or whether the device is freely drifting away or not, to plan maintenance operations.