Navigation Plotting On A Nautical Chart


While marine GPS and other electronics have managed to revolutionize marine navigation, navigation plotting is still an ideal way of laying a safe course, fixing the position, and even reassuring the position. Plotting a course on a nautical chart is an imperative job that expert and beginning sailors should master.

Nautical charts and sea maps represent an unbroken thread between sailors throughout sailing history. Navigation plotting is only difficult if you do not know how to do it. In this article, we will make plotting a course on a nautical chart easier by showing you the steps you need to follow.

What Exactly Does “Plotting a Course on a Nautical Chart” Mean?

The modern navigation charts offer a graphic image of the varying marine environments, including the sea bed arrangements, currents, water depths, location of dangers, etc. The nautical charts aid in both inland and ocean navigation.

Nautical charts are generally based around sets of geographical coordinates which can be used when describing the specific water location. An extensive set of symbols help in realizing the location.

By making use of the latitude-longitude system, navigators can measure the geographical location using the scales available on the chart’s outer border. By drawing a straight line between 2 points on the map, it is possible to work out the compass direction for the desired route and the distance necessary to work out the ideal course between the selected points.

Tools Necessary for Navigation Plotting

1. Applicable Nautical Chart

You can find a wide variety of nautical charts, including ones that cover an entire country and the surrounding areas to those which offer close-up views of single channels. You must invest in a sea map that best covers the areas you intend to explore after wearing your sailing shoes and packing your marine binoculars.

2. Parallel Plotters

These feature a mounted ruler that makes it easier for you to plot the courses. They allow you to draw parallel lines more easily.

3. Dividers

Despite not changing much for over 400 years, a divider is an ideal tool for measuring distance. It is important to note that varying models will offer varying degrees of convenience. Finding a model that offers the best convenience is always a good idea.

4. Chart Corrector Pen/No. 2 Pencil

The 2B pencil is soft and hence kind to the chart. This makes it an ideal scribing tool for navigation plotting. A chart correction pen is an ideal tool for making adjustments and changes when plotting a course on a nautical chart. Make sure the corrector pen features ink that does not bleed after drying.

5. Stopwatch

The stopwatch will help you know when you reach the end of each course line. All you will need to do is keep an eye on the time needed to run the course line once you rig your sailboat and decide to start your trip.

Step by Step Navigation Plotting


Assuming that you already know about boating safety and you have all the tools mentioned above, will show you the steps you need to follow when plotting a course on a nautical chart.

1. Grab your parallel plotter and draw a straight line from the point of departure to the destination point. You can draw as many course lines as you need to complete your trip.

2. Lay one of the edges of the parallel rulers along the course line you drew in the first step and then roll it to the closest compass rose on the nautical chart. Ensure that the edge intersects the crossed lines in the middle.

3. Read where your course line intersects with the inner degree circle to figure out your magnetic bearing. Write the course on the nautical chart, above the lines you plotted, in degrees magnetic (For example, C 234 M). For each course you drew on your nautical chart, do this.

4. Using a combination of the dividers and the distance scale available at the bottom or the top of your chart, determine the distance, in nautical miles, of each course.

This can be done by simply placing one end of the divider at the starting point and the other end at the stop or the turn. Next, while making sure you do not move the dividers, place them on the scale and read the distance. Repeat this for all the course lines you drew and then note the distance below each course line (For example, 1.5 NM).

5. Calculate the time you will need to run every course line. This will involve determining the average speed you will be using after putting on your sailing sunglasses and the current conditions.  This should be noted on top of the course line next to your bearing (For example, 10 KTS).

6. Continue calculating the time you need to run every course by multiplying the course distance by 60. Next, divide the obtained number with the predetermined speed.

The result you should get will be the minutes and seconds it should take to complete the plotted course line. Repeat this for all the lines and note the time at the bottom of each course line (For example, 7 mins 55 sec).

7. The last step will involve running the course using your stopwatch. At the starting point, come up with a predetermined speed and make sure you point your inflatable boat (Note: you can use other types of boats) in the direction you had plotted on the chart, ensuring that you keep the magnetic compass heading continually.

Start the stopwatch and then run a steady course and speed for the time you had calculated for the initial course. When the time is over, turn the boat and then follow your next compass heading. Now, reset the stopwatch for the new course.

Globo Surf Overview

When plotting a course on a nautical chart, it is important to make sure that you are plotting in ideal water depth. This will keep the underside of the boat safe when you start running the course. It is crucial to remember that safety comes first. Hence, you can deviate from the course you had plotted to avoid collision or unsafe conditions.

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Globo Surf
My name is David Hamburg. I am an avid water sports fan who enjoys paddle boarding, surfing, scuba diving, and kite surfing. Anything with a board or chance I can get in the water I love! I am such a big fan I decided to start this website to review all my favorite products and some others. Hope you enjoy!