Even inexpensive GPSs can come equipped with charting capability. While these charts can be highly useful, they are not a substitute for carrying paper charts. You should also know how to use a compass and carry one at all times because batteries die eventually and you are using a piece of precision electronics in a saltwater environment.
Accuracy of GPS units is variable. Usually, they are accurate to within about 15m, 95% of the time. WAAS can increase accuracy to within 3 meters.
The accuracy of a GPS is also dependent on the operator to some extent. It is important that the operator learn to use the GPS correctly - blind use can get folks lost. See Common GPS Errors.
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