Recognize GPS Limitations
"Get on the same sheet of music" is a frequently spoken saying and this has application in GPS also, and this may be a justificaton for getting the map feature - if a justification is desired. GPS coordinates are based on a particular projection for which charts were drawn of which a common one is NAD 27. If you're in low visibility and in close to hazards the GPS should be set to the same coordinate system as the chart being used. Even then, some charts, or portions of charts, are based on very old surveys and may be in error. If checking the projection of the chart being used is a problem then consider the map feature.Another limitation with GPS is moisture between the unit and the satelite. My first experience with this was on a moonless night in a sou'wester somewhere between Cape Scott and Cape St James in fog and drizzle. The GPS started showing it's hourglass for long periods of time - not a good place for this to happen especially when it's comming up on time to make landfall with rocks between the boat and your destination. The GPS does not like it when things are wet, such as a wet coachroof (when the unit is below deck). Don't get in the position where you have to bet your life on it. Have backup positioning alternatives such as dead reconing,depth sounder, and radar, and maybe even an RDF such as a cheap radio with a directional antenna.Many people mount electronics around their compass - make sure there is no magentic field influencing the compass card. I tried to install a hailer talk-back mike and found it had to be about 5 feet away before the infuence was negligible. My compass is a Venus, not a Ritche.Which brings up another point, when traveling, anchoring, or running aground in low visibility conditions one needs to emit the appropriate horn signals per the Col Regs. So, in addition to the GPS, a high-output hailer with coordinated fog horn would be a good adjunct. I mount my fog horn on the pulpit (away from the helm) with a pair of Vice Grips, when needed, and run the 16 ga conductors back to the hailer. Hope this didn't get too windy - was only going to write a little bit.