How to Find Latitude and Longitude on a Nautical Chart

Any GPS receiver will find Latitude and Longitude along your sailing routes at any moment. But as a skipper, have you plotted this information onto a nautical chart to check your position? Boost your sailing navigation skills to the next level with this vital sailing skill!

Navigating with Latitude

Cartographers create a grid-like web on your navigation chart. Latitude lines run in a horizontal direction. Longitude lines run in a vertical direction. Imagine the earth, balanced on her axis without a tilt. Wrap a “belt” around the earth, divide it in two and you have the equator–birthplace of Latitude. Label the equator 0 degrees.

Latitude lines parallel the equator to the north or to the south. To plot Latitude to find out where you are, you measure how many degrees you are north or south of the equator. Latitude reaches a maximum of 90 degrees at both north and south poles. Always label Latitude N, if north of the equator, or S, if south of the equator.

In chart navigation, use the scales on the right or left side to find your Latitude. These scales are broken down into degrees, minutes and tenths of a minute, or degrees minutes and seconds. One degree of Latitude equals sixty minutes; one minute of Latitude equals sixty seconds. Here’s a simple way to remember this:

1 degree = 60 minutes.

1 minute = 60 seconds.

Navigating with Longitude

Return to your imaginary globe. To measure Longitude, you again divide the earth in half, but this time lengthwise. Locate Greenwich, England on your globe. Draw a line around the earth that intersects Greenwich and both north and south poles. Cartographers call this the Greenwich, or prime meridian–the birthplace of Longitude. Label the Greenwich meridian 0 degrees.

Longitude lines parallel the vertical Greenwich meridian to the east or to the west. To find longitude, you measure how many degrees you are east or west of the Greenwich meridian. Longitude reaches a maximum of 180 degrees on the other side of the earth, at the International dateline. You must label Longitude E, if east of Greenwich, or W, if west of Greenwich.

Use either the top or bottom of the chart to measure Longitude. Like Latitude, Longitude is broken down into degrees, minutes and tenths of minutes or degrees, minutes and seconds.

How to Convert Increments of Minutes

All nautical charts show minutes broken down into increments so that you can plot parts of a minute. For example, if your gps position shows 23-13N; 82-16W, there are no increments to worry about. But, if your gps position shows Latitude 23-13.278N; Longitude 82-16.786W, you have increments of minutes. Before you plot your position, round off increments to the closest tenth of a minute. Round off like this: Latitude 23-13.3N; Longitude 82-16.8W.

Look at the Latitude scales (right or left side) and Longitude scales (top or bottom) on your chart. Are minutes broken down into tenths or into seconds?

Some charts show degrees, minutes, and tenths of a minute. The minutes will be broken down into 10 small segments. Each small segment equals one-tenth of a minute. Other charts show degrees, minutes, and seconds of a minute. If your chart shows degrees, minutes, and seconds, you will need to multiply the “tenths” of a minute by 6. Follow this example:

GPS reading (with minutes rounded as described earlier): Latitude 23-13.3N; Longitude 82-16.8W.

Multiply the increment of Latitude minutes like this.3 X 6 = 18 seconds.

Multiply the increment of Longitude minutes like this.8 X 6 = 48 seconds.

Plot: Latitude 23 degrees, 13 minutes, 18 seconds; Longitude 82 degrees, 16 minutes, 48 seconds.

How to Plot Latitude and Longitude

Use a pair of dividers to plot your position by Lat and Long onto the chart. Read the degrees and minutes from your GPS. Find the closest degrees and whole minute of latitude on your GPS.

For example, for Latitude 23-13.3N, you would look for 23 degrees, 13 minutes on the right or left side scales on your navigation chart. Push one point of your dividers into the 13 minutes. Open up the other leg 3 small segments (three tenths), above the 13 minute mark. If your chart shows seconds instead of tenths, open up the other leg of your dividers 18 seconds (.3 X 6) above the 13 minute mark. Place a pencil mark where the dividers touch the exact Latitude.

Next, plot your Longitude. Use the same exact method to plot your Longitude. Make sure to use the top or bottom chart scales to plot your Longitude. When you’ve found your Longitude, place a pencil mark where the dividers touch the exact Longitude.

Find Your Exact Position

Align your parallel rules or any other straight edge so that the top long edge touches the Latitude pencil mark. Make the parallel rules or straight edge perpendicular so that when you draw in the Latitude line, it will be parallel to all other latitude lines. Draw a light pencil line across the body of the chart to a location close to where you marked the top or bottom Longitude scale.

Repeat this same method to align and draw in your Longitude line. Where the Longitude pencil line intersects the latitude pencil line shows your exact position. You should now have a cross. Place a dot where the two lines cross. Circle the dot. Erase the light lines drawn from the edges of the chart to clean up the chart and keep your plot neat.

Use these easy steps to find Latitude and Longitude on your nautical chart fast. With these sailing skills, you will be well on your way to become a confident sailing skipper-anywhere you choose to go sailing!

Sailing Navigation Secrets – Mark Your Nautical Chart With Magic Art!

Did you realize that you can make your chart easier to see, with less clutter? And that you can do this with simple office tools to save eye strain, make sailing navigation safer, and chart work easier? Use these easy steps for safer sailing navigation anywhere in the world.

Use “bright and bold” highlights to make vital chart symbols stand out.

Know exact locations of perfect anchorage spots before you arrive there.

Identify reliable depths compared to unreliable depths on your chart or plotter.

Tools You Will Need:

*Pencil

*Direction measuring instrument (parallel rules, Weems plotter).

*Yellow, orange, and blue highlighters.

*Colored blue, green, magenta pencils.

*Fine felt-tip pen.

*Scotch magic tape (permanent or removable.

Scan, Mark, and Protect Your Costly Charts

Master navigators always use a step by step process to plot their sailing routes, scan all along the sailing route for danger, and mark the most important spots like shoals, wrecks, emergency “pull-off-the-road” anchorages, and major aids to navigation that affect your sailing safety.

Follow these seven simple steps in the order shown anytime you plot a course for day sailing, cruising, or distance voyaging. It will keep you safe and you will have the confidence that you can see “at a glance” what lies ahead.

1. Use parallel rules or Weems plotter. Plot each course along your sailing route with light pressure with your pencil. Use light lines in this step. That way, if you need to erase, you can do this without effort or marring the chart.

2. Scan along each sailing course line to make sure the course does not cross over dangerous shoals or shallow depths. If it does, erase that leg and change it to a safer course or break it into two courses to avoid the hazard.

3. Use bright colored highlighters or colored pencils to make dangerous wrecks or important aids to navigation (buoys, lights, or landmarks) near the course.

4. Look for deep water pockets off the course line where you could anchor for rest or in an emergency. Make shoal depth contours stand out by tracing over them with a dark blue colored pencil (or similar marker).

5. Stay in water with a depth at least twice your draft. Coastal charts often show water depth contour lines in six foot increments that begin at 30 feet. That means the next depth contour would be 24 feet, then 18 feet, 12 feet, and 6 feet. Mark the outermost depth contour that’s equal to at least 2X your maximum draft.

Example:

If your draft is 5 feet, you should mark the 12 foot (or higher) contour curve. Set your depth sounder, GPS, or chart plotter alarm to trigger at that depth. This gives you time to turn the boat toward deeper water.

6. Check each course again for dangers. Recheck each plotted course to make sure the direction marked agrees with the direction indicated by your plotting tool. When satisfied, go to the final step.

7. Run a length of tape over the top of each of the light penciled course lines. Run your fingers over it several times to make sure it adheres to the chart surface. Lay a straight edge on top of the tape and darken in each course line with the felt tip marker. This makes your courses stand out in any light or weather condition.

Use your pencil to write the course in degrees magnet on top and the length of the course leg on the bottom of the line. When you label, write onto the tape. This protects the paper chart and the tape surface can be written on and erased as needed.

  1. Captain John’s Sailing Navigation Tip:
    How do you remove the tape when you’re done with the cruise? Use one of these two fast methods. Scotch makes a ‘removable magic tape’ brand. It isn’t as sticky but works well on a dry surface. Or, heat the edge of a blunt kitchen knife with a lighter. Run the knife along the tape and peel as you go. Keep the knife edge warm for best results.

Beware of Spotty Soundings!

Chart plotters fall far short of nautical charts when it comes to detailed soundings. Their small screen real estate forces the manufacturers to sacrifice detail in order to keep the screen uncluttered. This reason alone should be enough to convince any prudent skipper to carry navigational charts.

Scan your chart for signs of inconsistent or scattered soundings. Large gaps between soundings warn that this area hasn’t been surveyed well enough for safe sailing navigation. Keep clear of areas with spotty, inconsistent soundings to avoid grounding or hitting an underwater, uncharted obstruction.

Spoil areas (also called a fish haven or spoil bank) are where debris like garbage, old cars and trucks, and construction site material are dumped. Theses depths change all the time, so they will never be shown. Stay clear to stay safe!

Now you know the fast, easy way to get your chart set up for safe sailing navigation to save you time and effort once you go sailing.