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Chapter 4 - Using the Chart Screen
Understanding electronic charts
Each Navionics chart cartridge contains electronic chart data from several paper charts. Electronic charts have much of the information from the original paper charts, although spot depth soundings, some nav aids, and other data may be missing. When used with caution, electronic charts open up a world of navigational accuracy and simplicity.
CAUTION!
Don’t become overly confident when using electronic charts.
Always be cautious!
Chart boundary lines
The 958 displays the boundary line of each chart on the
CHART screen. To turn this feature off, press the CHART
SETUP key on the CHART screen, then press the CHART
DETAIL key and turn off the CHART EDGES option.
Chart details
If you move from a highly detailed chart to a less detailed one, you may see a sudden change in the detail shown on the screen, just as if you had changed from one detailed paper chart to a less detailed one. You may be able to use the displayed boundary lines to predict when this change in detail is going to happen.
Page 38 958 Operator’s Manual, Rev. A
Chapter 4 - Using the Chart Screen
Understanding nav aids
The nav aids on the CHART screen represent a variety of standard “aids to navigation” used on coastal and inland waterways throughout the United States. Nav aids are displayed on the CHART screen as colored circles with white letters. Most of these aids comprise buoys, lights, lighthouses, and daybeacons, which typically are maintained by the U.S.
Coast Guard. Nav aids warn you of hidden dangers, such as underwater hazards, and to help you to safely navigate specific waterways and channels.
CAUTION!
Nav aids have been converted from official paper charts into the electronic format on your screen, and therefore aren’t necessarily as accurate as the paper charts. You can expect about a 95 percent accuracy rate. In some areas, only the most important nav aids may be shown.
Buoys
Buoys are the most common type of nav aid. The 958 shows green and red channel markers as green and red circles, respectively.
Approach buoys are shown as circles with black on the upper half and white on the lower half.
Sound buoys (featuring an audible signal, such as a bell, gong, or whistle) are identified by a description in the INFO BAR such as BELL , WHIS , GONG , or HORN) .
Some nav aids have no chart symbol, and are shown on the
CHART screen as text only.
When you move the cursor onto a nav aid, the 958 displays a description in the INFO BAR at the bottom of the screen, along with the distance and bearing from your vessel to the nav aid.
958 Operator’s Manual, Rev. A Page 39
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