Did you know that the accuracy of map navigation depends on the map scale used? Or that some nautical charts combine feet and depths or meters and feet for water depth. If you want to become a seasoned sailing skipper, you need to solve the mystery of your title block’s vital treasure chest!
Scan your navigation map for the name of the map anywhere in the unused land area. This title block contains the key information describing the geographic area, type of projection, scale, date, and diagram notes.
All title blocks contain seven key elements that you must absolutely know before buying or using the chart. Follow this simple summary to learn how title blocks appear on nautical charts of the world.
1. Know your navigation area
Look at the location on the earth’s surface to determine the exact boundaries of your navigation map. Here is an example:
UNITED STATES EAST COAST
This description shows you, from top to bottom, the map area shows the United States along the east coast in the state of Maine with detailed navigational information for Penobscot Bay.
2. Make Mercator your projection of choice
Most nautical charts are based on a Mercator projection, which shows longitude and latitude as straight lines. With this projection, navigators can draw sailing courses as straight lines from one point to another. This makes navigation easier and less stressful.
3. Use the largest available scale
Choose a larger-scale chart for the best navigation accuracy. Map scales are expressed as the ratio of one inch to the same number of inches on the surface of the earth.
For example, a chart with a scale of 1: 10,000 means that one inch of the chart must be enlarged 10,000 times to see its actual size. A 1: 80,000 scale diagram means that one inch on this diagram must be enlarged 80,000 times for actual size. The 1: 10,000 scale diagram shows more details, but the 1: 80,000 scale diagram covers more areas. The 1: 10,000 scale diagram is therefore the larger of the two scales.
4th Check the date for GPS compatibility
Make sure your map shows the North American date of 1983 or the World Geodetic System 1984. So if you draw the latitude and longitude of a nautical GPS on your map, it will be accurate. If your diagram shows different date information, you must set your GPS to the appropriate date (see user manual). This will reset the GPS so that Lat and Long match the Lat and Long on the chart to ensure error-free and accurate navigation.
5. Know your depth measurements
Depths can be expressed as feet, threads (1 thread = 6 feet), or a combination of threads and feet, or meters (1 meter = 3.3 feet) and feet. All depths are measured from a low water tidal stage. There’s a huge difference between the meaning of a 3 on a diagram showing feet and a 3 on a diagram showing thread.
The map with the threads would mean you had 18 feet of water above this spot – more than enough to clean the keels of most cruise or racing sailboats. Familiarize yourself with the measurement before using a chart to keep your navigation simple and stress-free.
6th Determine how heights are displayed
Next, look for a statement that tells you how heights are measured. Find a statement that looks something like this: Heights in feet above mean high water. Mean (average) high tide does not take into account periods when tides are unusually high, e.g. B. in spring tides, after heavy, prolonged rainfall or storm surges. For safety, always leave several feet above the specified height to clear the lower steel under the bridges.
For example, if the vertical distance of a bridge reads 45 feet, that is the average height of the lowest steel in the center of the bridge. At full moon, when spring tides occur, you can expect much less leeway at high tide. Play it safe and if in doubt, wait for the tide to ebb.
7th Read your navigation instructions for safety
Take a look around the title block with the numerous notices that contain information about navigation safety. These inform you about shipping routes, dangers, warnings and transmission channels in the event of sea weather in the region and provide important warnings. Take a few minutes to get a full picture of the navigation area.
Use these seven quick and easy map navigation tips to get a fuller understanding of the incredible power of a navigation map. You will become an experienced, confident sailor and navigator – anywhere in the world where you decide to cruise!