More things to consider about GPS
As noted, GPS provides very accurate position information. However, many charts currently in use (including those that have been digitized for GPS chartplotters) are based on VERY OLD hydrographic surveys. Your position by GPS may be accurate but the chart that you're using as a reference may not be. To use an extreme example, there are reefs in the Pacific where people have run aground because according to the chart they were several miles away from where the GPS (accurately) said they were. In addition, some things underwater move around (sandbars are a good example), so you may run aground in an area where your GPS and chart tell you that the water is deep. Keep one eye out for new buoys and the other on the depthsounder. Lots of chartplotters show underwater contours which look nice on the display but they too may be based on the original chart (of unknown age and accuracy) that was digitized. Not good. The moral of my tale? Don't believe the hype. A good navigator doesn't rely on a single source of information, nor should he/she trust any source 100%. In addition to a sharp lookout, sounds, boat motion and smell can provide valuable clues to supplement what the chart, compass, depthsounder and GPS are telling you. Unless you have excellent local knowledge, a properly working depthsounder and current tide tables, the prudent thing to do is get out of traffic, heave-to or drop anchor and commence with the horn. Finally, there is a GPS currently being developed that will provide heading when the boat is motionless. It is a fixed unit with two antennas, one at the bow and the other at the stern. It measures the position of each antenna, then calculates heading based on the position of the bow antenna relative to the stern. It's much more precise than an ordinary GPS so it will be pricey. Peter H23 "Raven"
