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Tide Stream Compensation Theory

With modern GPS and other electronic navigational aids there are many mariners who no longer go to the trouble of tide stream heading calculation, or are no longer required to learn or use the technique when plotting a course between waypoints. However, it is a fact that GPS does not compensate efficiently for tidal drift. Neither does it know the most suitable tide time to make a passage making best use of the assisting or opposing streams along a route. GPS and a plotter is undoubtedly an easy and accurate way of navigating from one position to another but it is not so good at working out an accurate ETA or saving time and fuel by choosing the best possible departure time.