PART 6


BASIC NAVIGATION & PILOTING CONCEPTS Think “navigating and piloting” and most boaters immediately imagine GPS screens and chart plotters because these are the most common sources of access to navigation data. The prima- ry tools, however, are the paper chart and a good pair of eyes. GPS makes using both of these easier, and a plotter in the right hands can render the paper almost redundant, but the naviga- tor has to assume electronics will fail. This chapter deals with the concepts needed to pilot safely in daylight.


The Chart


There are two basic types of charts: paper charts and electronic charts. To use a paper chart all you need is vision and some simple instruments while electronic charts can only be operated through an electronic chart plotter.


Most nautical charts use a Mercator projection to transfer the image of Earth’s spherical surface onto a flat piece of paper. The primary advantage of a Mercator chart is that lines of latitude and longitude form an easy-to- use rectangular grid, which allows compass courses to be drawn as a straight line from one place to another.


Paper charts typically show areas of water and adjacent portions of coast- line together with information useful for navigation, such as navigation aids (i.e., beacons and buoys), underwater features and landmarks on shore. Symbols and abbreviations are frequently used to convey this information, many of which are largely self-explanatory, but NOS (National Ocean Ser- vice) Chart No. 1 is a helpful reference for any you don’t find obvious. The title block contains a great deal of important information, including units of soundings (water depths) and heights of land elevations. On this chart soundings are in feet. Other charts may have them in fathoms (1 fathom = 6 feet), fathoms and feet, or meters. If fathoms are used, fathoms with a feet subscript may be used in shallower water. For example, a depth of 4 fathoms and 3 feet would be indicated as 43. If the soundings unit is in meters, the soundings will be indicated in meters and tenths of meters with the tenths shown as a subscript. Thus, 1.3 meters would be 13. Note also the depth contour lines. These are often picked out in colors, making them easy to spot at a glance. If your chart doesn’t cover enough ground for the passage you want to make, you might change to one drawn to a larger scale. This will show a wider spread of coastline, but will have less detail. So for safe piloting, you’ll probably need both.


Line of longitude Line of latitude


Lines of longitude appear parallel on the chart, but they converge toward the poles (see globe).


Scale


Soundings in feet Chart datum (WGS84)


Heights in feet


Title block includes chart datum, scale, and measurement units for soundings and heights. Date that the chart was issued along with any corrections are located in bottom left corner. Keep current charts on board and update them with Local Notices to Mariners changes.


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