You receive a distress call from a vessel reporting her position as LAT 30°21'N, LONG 88°34'W. Your position is LAT 24°30'N, LONG 83°00'W. Determine the true course and distance to the distress scene by Mercator sailing.
• Mercator sailing relationships between difference of latitude, departure, and difference of longitude • Converting difference of latitude and difference of longitude into a track (course) and distance • Using middle latitude and meridional parts (MP) or a calculator to find course and distance on a Mercator chart
• First, decide whether you are going generally northeast, northwest, southeast, or southwest from your position to the distress position by comparing the latitudes and longitudes. • Compute the difference in latitude and difference in longitude; then think about how Mercator sailing uses meridional parts to relate these to the course angle. • Estimate roughly whether the distance should be closer to 450 or 470 miles based on the size of the latitude and longitude differences, then refine with the Mercator method.
• Be sure you labeled N/S and E/W correctly when finding differences in latitude and longitude. • Confirm you used the correct meridional parts for the starting and ending latitudes (or a consistent middle latitude if using a calculator approach). • Double-check that your final course is expressed as a true bearing from your vessel to the distress vessel, not the reciprocal.
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