Re: Near-shore tide what to expect. "Need some Guidance"
Here is another article which may help. It explains how GPS finds direction. Because sail boats move at a slow speed (unless you are on an America's Cup team!) and because the current can be significant compared with boat speed then your movement over the ground (which is what GPS measures) can be low enough to confuse a GPS.
www dot gpsreview dot net/electronic-compass/