Plotting a Course with Compass and Parallel Rulers (No Electronics Needed)

Plotting a course with a compass might sound old school. But when your chartplotter glitches or your battery dies, what then?

Sailors still rely on a pencil, a chart, and a compass for one reason. These tools work when nothing else does. And they teach you to think ahead instead of just following a screen.

This post walks through each step, from setting up your chart to measuring distance and applying variation. By the end, you won’t just know how to draw a line on a chart. You’ll know how to get where you’re going with precision.

Why Should You Learn How To Use a Compass?

GPS is convenient, but you shouldn't rely on it alone. Batteries fail, screens freeze, and connections drop. When that happens, you need a compass.

When you know how to use a compass and plot a course on a nautical chart, you stay in control. You can draw a line from your current position to your destination and steer using bearings, not just pixels.

This isn’t just about having a backup. Using parallel lines, grid lines, and magnetic variation teaches you to read the water like a map. You learn how to orient to true north, calculate declination, and measure distance across latitude and longitude.

To get started, you need the right setup. Let’s walk through the tools you’ll want at hand before you plot your first course.

Gear Up Before Plotting Your Course

Before you can plot a course with a compass, you need the right setup. That starts with the chart itself.

• Choose a chart that fits your route. A harbor chart shows fine detail. A coastal chart covers more distance, but less detail.
• Check the chart’s edition date. Make sure it reflects recent changes. Some hazards appear or shift over time.
• Secure your workspace. If your chart slides while you measure, your bearings and distances can drift. Tape the edges or use chart weights.
• Keep your tools within reach. You’ll want sharp dividers, parallel rulers, a pencil, and a handheld compass. A rubber eraser helps, too.

Once you’ve got everything in place, you’re ready to mark your starting point.

How to Plot a Course Using a Compass

You’ve set up your chart and gathered your tools. Now it’s time to plot your course. Let’s take it step by step.

1. Mark Your Starting Position

Begin by marking your current position on the chart. Use bearings from two or more landmarks.

Choose features you can identify from your boat. Draw a line from each one using your handheld compass. The spot where the lines cross is your fix.

Write the time next to that point using 24-hour format. For example, label it “1430 UTC.” That timestamp allows you to track your progress and refer back to it later if needed.

2. Select and Assess Your Waypoints

Now that you’ve marked your position, decide where you want to go. Use clear visual cues for waypoints, like buoys, headlands, or channel markers.

Check each waypoint’s location for hazards. Stay clear of rocks, shoals, or restricted zones.

Choose points that help guide your route without bringing you too close to trouble. Every waypoint should be easy to recognize and safe to approach.

3. Draw Your Course Line

Use a pair of parallel rulers or a rolling ruler to draw a straight line from your starting point to the first waypoint. Keep your chart steady while you do this. Even small shifts in the paper can throw off your bearing.

Add a small arrow along the line to show your direction of travel. Do this for each leg of your route. This step keeps your course clear if you stop mid-plot or hand the chart to someone else.

4. Measure the True Bearing

Place one edge of your ruler on the course line. Walk the ruler across the chart until it reaches the compass rose.

Read the bearing where your line crosses the outer ring of the rose. This gives you your true bearing in degrees.

For long legs, check the bearing from both ends. That helps spot any errors in ruler alignment or chart scale.

5. Record and Annotate

Write your Course to Steer (CTS) next to the leg on your chart. Label it with true, magnetic, and compass bearings if you know them.

For example, you might write “092°T / 089°M / 085°C” on the leg. That means your true, magnetic, and compass bearings. Add the distance between waypoints and your estimated time of arrival (ETA). Use your logbook to record this as well.

Keeping notes here helps you stay on course while underway. It also helps with tracking if anything needs to change mid-passage.

6. Measure Distance the Correct Way

Use the latitude scale on the side of the chart to measure distance. One minute of latitude equals one nautical mile. Don’t use the longitude scale. It varies with your position on the globe and throws off your measurement.

If your course follows a curve or bends around features, break it into smaller straight segments. Measure each one, then add them together.

7. Apply Magnetic Variation and Compass Deviation

Find the compass rose on your chart. It shows the difference between true north and magnetic north. You may also see a note about how variation changes each year. Apply that update to get the current value.

Then adjust for compass deviation using your vessel’s deviation card. This corrects for errors caused by magnetic fields onboard.

When you shoot an object with a compass and want to translate this point to the chart, use the old mnemonic: “Can Dead Men Vote Twice At Elections?” That stands for Compass, Deviation, Magnetic, Variation, True, and Add East. It walks you through the order of corrections.

When going from the chart to your compass, it goes the other way around. The mnemonic we use for that is a bit more spicy and therefore more memorable: “True Virgins Make Dull Companions - Add Whiskey”. Or for a more PG version, “West is Best, East is Least”

8. Add Chart Notes for Safety and Visual Navigation

Mark areas to avoid, like shallow spots or rocks. You can circle them in pencil or use light shading.

Note any landmarks that help confirm your position as you sail. Lighthouses, towers, or large buildings all help.

Adding these notes turns your chart into a visual guide. It gives you cues to look for during your trip and helps confirm you’re on track.

Practice Compass Navigation with Sailing Virgins

If you want to build real-world sailing skills, there’s no better way to start than plotting and sailing your own route.

Join a Sailing Virgins advanced course and apply what you’ve learned in active conditions. You’ll live on the boat, train alongside other ambitious sailors, and work with expert instructors who have sailed across oceans.

By the end of the week, you can walk away with:

• ASA 105: Coastal Navigation
• ASA 106: Advanced Coastal Cruising
• ASA 114: Cruising Catamaran Endorsement (optional if on a catamaran)

Sail in unforgettable locations like the British Virgin Islands, Croatia, or French Polynesia. Learn to read charts, plot bearings, and steer a course without depending on electronics.

Spots fill up fast, especially during peak seasons. If you’re ready to level up your skills, reserve your spot now!

Contact Sailing Virgins today to get started!