The use of ocean gliders, a class of underwater vehicles for observing the ocean to understand biogeochemical and physical processes, has been pioneered in the North Sea as part of the coastal observatory COSYNA. Since gliders go slow, strong tidal currents are problematic for their navigation. To predict (< 12 h) and reconstruct the local currents and the actual transect under water to know where the measurements were actually taken, an algorithm was developed using glider data only.