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Did you know that the accuracy of chart navigation depends on the chart scale you use? Or that some nautical charts combine feet and fathoms or meters and feet for water depth. If you want to become a more skilled navigational master, you will have to unravel the mystery of the treasure chest from the vital title block of your chart!

Scan your navigation chart somewhere in the unused land area to find the name of the chart. This title block contains the most important information describing the geographic area, projection type, scale, datum, and chart notes.

All title blocks contain seven key elements that it is vital that you know before buying or using the chart. Follow this simple summary to learn how title blocks appear on any nautical chart in the world.

1. Know your navigation coverage area

Look at the location on the earth’s surface to determine the exact limits of your chart. Here is an example:

EAST COAST OF THE UNITED STATES

MAINE

PENOBSCOT BAY

From top to bottom, this description tells you that the area on the chart shows the US, along the east coast in the state of Maine, with detailed navigational information for Penobscot Bay.

two. Make Mercator your preferred projection

Most nautical charts are based on a Mercator projection, which shows lines of latitude and longitude as straight lines. This projection allows mariners to draw navigation courses as straight lines from one point to another. This makes browsing easier and less stressful.

3. Use the largest scale available

Choose a chart with a larger scale for the best navigation accuracy. Chart scales are expressed as a ratio of one inch compared to the same number of inches on the earth’s surface.

For example, a table with a scale of 1: 10,000 means that one inch of the table would have to be magnified 10,000 times to show the actual size. A table showing a scale of 1: 80,000 means that one inch on that table would have to be magnified 80,000 times to get the actual size. The 1: 10,000 scale chart shows more detail, but the 1: 80,000 chart covers more area. So the 1: 10,000 scale table will be the larger of the two scales.

Four. Check datum for GPS compatibility

Make sure your chart indicates the 1983 North American Datum or the 1984 World Geodetic System. That means when you plot latitude and longitude from a nautical GPS on your chart, it will be accurate. If your chart shows different reference information, you will need to set your gps to the proper reference (see owner’s manual). This resets the GPS so that its latitude and longitude match the latitude and longitude on the graph for accurate, error-free navigation.

5. Know your depth soundings

Depths can be expressed in feet, fathoms (1 fathoms = 6 feet), or a combination of fathoms and feet or meters (1 meter = 3.3 feet) and feet. All depths are measured from a low tide stage. There is a big difference between the meaning of a 3 on a graph showing feet and a 3 on a graph showing fathoms.

The fathom chart would mean you have 18 feet of water above that spot, more than enough to clear the keels of most cruising or racing sailboats. Understand sounding measurement before using any chart to keep your navigation simple and stress-free.

6. Determine how heights are displayed

Next, look for a statement that tells you how heights are measured. Find a statement that looks like this: Heights in feet above mean water level. Mean (average) high tide does not take into account periods when tides have exceptional heights, such as spring tides, after prolonged heavy rains or storm surges. For the sake of safety, always allow several feet of clearance above the listed height to clear bottom steel under bridges.

For example, if the vertical clearance of a bridge shows 45 feet, that is the average height of the lowest steel in the center of the bridge. On a full moon, when spring tides occur, you can expect much less headroom at high tide. Play it safe and wait for low tide when in doubt.

7. Read your navigation notes for safety

Look around the title block of the chart for the many notes that contain navigational safety information. These inform you about ship routes, hazards, warnings, marine weather broadcast channels in the area, and provide important warning information. Take a few minutes to get a complete picture of the navigation area.

Use these seven quick and easy chart navigation tips to gain a more complete understanding of the amazing power of a navigation chart. You will become a safer and more skilled boater and skipper, wherever in the world you choose to sail!

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