How to plot a course on a nautical chart from a reference port

This article explains how to plot a course on a nautical chart, which is vital for reaching a destination effectively and, above all, safely. To do so, it is important to take into account a number of factors that ensure smooth sailing.


What do I need to plan the destination?

By complying with these points, you can use a nautical chart and plan a course safely:

  • Nautical chart knowledge: First and foremost, it is essential to know the nautical chart to be used. You must be able to identify the different chart components, such as the scale, compass points, lighthouses, sea bed, reefs and hazards.
  • Starting point: This is the reference port from which the sailing starts.
  • Final destination: This must be marked on the nautical chart, so the navigator can determine the distance and the general direction to be taken to get there.
  • Measuring instruments: To plot a course on a nautical chart, measuring tools such as a compass, marine compass or GPS.
  • Weather and sea conditions knowledge: It is essential to know the weather and sea conditions before planning a course on a nautical chart. For example, you need to know about strong winds, currents and tides, for example, which may affect the course and sailing.
  • Maritime regulations knowledge: These set out the rules and procedures to avoid collisions at sea. They also determine the exclusion zones designated to protect sensitive areas, such as coral reefs or nature reserves, which may affect your course and navigation.

Types of nautical courses

Courses can be of different types, each with its own features and considerations. Here are the most common ones.

  • Celestial: Used when navigating in a direction that leads directly to a star. This course is useful in good visibility conditions, but can be more difficult to follow in bad weather or poor visibility.
  • Magnetic north: This is based on the direction of a magnetic compass needle. This course is suitable for sailing in waters with few hazards or in a known coastal environment.
  • True north: This bearing is based on the true direction of a place or point on Earth, taking into account the Earth’s rotation and magnetic declination. This heading is useful in poor visibility conditions, but requires a GPS or satellite navigation system to determine the true direction.
  • Hazards: Used when navigating around obstacles or hazards, such as reefs, the seabed or sandbanks.
  • Weather: Used to avoid adverse weather conditions, such as high winds and storms.


What do I need to plan the course ahead?
Plotting a course on a nautical chart is crucial for reaching the desired destination effectively, safely, and incident-free. Image by Freepik.


How to read a nautical chart

Before plotting a course on a nautical chart, you have to know how to read it:

  • Contour lines: These show the shape and depth of the seabed. It is important to pay attention to deep and shallow areas to avoid hazards and obstacles.
  • Symbols and legends: These represent a wide range of information, such as hazards, signs and obstacles. It is important to know the symbols and legends to correctly interpret the information on the chart.
  • Scales: They show the relationship between the dimensions on the map and the dimensions in the real world to calculate distances and determine the size of obstacles and hazards.
  • Degrees and directions: These are used to determine the direction and location of objects on the map.
  • Tides and currents: This information can help the navigator anticipate when it will be easier or more difficult to navigate in an area and therefore adjust the plan accordingly. If the navigator does not take tides into account when plotting a course, he may encounter water that is too low to navigate, which can damage the boat or even ground it. And if he does not assess the currents, he may end up in a very different position than planned.


General tips for charting a course

  1. Understand nautical charts: contour lines, symbols, legends, scales, degrees, directions, tide and current data.
  2. Consider hazards and obstacles: such as sandbanks, rocks and strong currents to plan a course to avoid them.
  3. Tides and currents: These can affect the direction and speed of the vessel, so it is important to consider them when plotting a course.
  4. Check and update the course regularly: During navigation, you have to check and update the course regularly to ensure you stay on the desired course and avoid deviations.


Ways of measuring nautical headings

The most prominent course measurement formats are described below:

  1. Compass points: Can be measured in terms of cardinal directions, which are used to describe direction in terms of north, south, east and west.
  2. Degrees: Can also be measured in degrees, with a 360-degree scale divided into four quadrants, each representing a cardinal direction.
  3. Thousandths: Degrees can also be measured in thousandths, which are more precise units than degrees, and are used in navigation with electronic instruments.
  4. True course: The direction in a straight line from a point of origin to a destination.
  5. Magnetic heading: Magnetic heading is the direction of an object relative to the Earth’s magnetic north.
  6. Magnetic variation: The difference between true north and magnetic north, which is used to correct the heading to account for magnetic influences on navigation.
  7. Magnetic deviation: The deviation that occurs in a compass due to magnetic influences on the vessel, which is used to correct the heading to account for these influences.

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