Thanks for the informative email. you are absolutely right, it is never a good idea to rely on one means of navigation alone (e.g. GPS). I found that it worked best to use at least 3 means of determining your position in addition to GPS before approaching the coast or a dangerous channel- e.g. compass bearings on adjacent landmarks, radar and depth. when all these are used together and agree, it is usually a good sign that you are on the right track.
Often the charts are correct but the datum on the chart does not correspond to that on the GPS. Many sailors do not know that they have to constantly update their GPS datum for each chart. This is particularly important when you are sailing in foreign waters. This can be done by checking the chart datum and then going to the setup menu on the GPS and making sure the two coincide.
If one were to use only one means of navigation when approaching a coast, my experience is that the radar is often the most reliable, after a careful lookout and common sense. As you point out, a well calibrated depth sounder is also an important tool in these situations. Again, it is good to know how the instrument is calibrated. Some use the actual depth and others the water under the keel for a margin of safety. The less sophisticated depth sounders do not give you a calibration option and the depth is measured from the actual location of the transponder. Knowing the datum from which the depth meter is measuring can be helpful when using the chart depth to determine your position when approaching the coast or sailing in shallow water.
A few other tools that i found useful were a night vision monocular and forward scanning sonar (Interphase Probe). While i agree that approaching a port or anchorage at night is not a good idea, sometimes it is unavoidable. Night vision monoculars allow make it possible to see without destroying your night vision. it is also useful for night watch to see faint lights of adjacent boats which are not visible to the naked eye. The second instrument, forward scanning sonar, is not that expensive and can give a prior warning when approaching an underwater obstruction. Some models will scan both ahead and to either side making it easier to stay in a channel. As you point out, these tools, like the GPS, also have their limitations and a person on the bow with polarized glasses is always the best insurance.
Finally, i think that talking to fellow sailors can be useful but it can also be misleading (point # 3). A VHF call to marina personnel or a harbor master about entering the channel to their harbor, is a good idea when used in conjunction with the other information available (guide books, sailing instructions, ship's instruments and eyeball navigation). I would always qualify the source of the information before relying on it too heavily. I have been heard of many situations where insecure sailors have gotten in even more trouble listening to a well-meaning but inexperienced yachtsmen who are anxious to help but not equipped to do so.... like the motor yacht or catamaran captain with a 3 foot draft giving advice to a yacht that draws 7 feet.
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