When using a GPS, what important detail should sailors be aware of?

Sailors should be particularly aware that the speed over the ground as indicated by a GPS device can differ from the sailing speed toward their intended destination. This distinction is crucial because the speed displayed by the GPS measures the vessel's actual movement over the Earth's surface, taking into account any current, tide, or wind that may be affecting the craft's progress.

For instance, if a sailor is sailing into a strong current, the GPS may show a certain speed over the ground that is significantly less than the speed the vessel is capable of under sail. Conversely, if the current is assisting the vessel, the GPS reading may indicate a higher speed over ground than what the vessel is achieving purely through its own sailing ability.

Understanding this difference helps sailors plan their course effectively, adjust their navigational strategies, and estimate arrival times more accurately. Recognizing the realities of how external factors influence the vessel's overall speed allows for safer and more precise navigation.