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Aids to navigation

Buoyage: marks, safe sides and light rhythms

Try the IALA A buoyage quiz

The essentials

Buoyage communicates navigational information through a combination of shape, colour, topmark, numbering and light rhythm. First identify the buoyage region and the mark family, then decide what the mark says about the safe water or feature. At night, use the complete light characteristic and verify it against the chart rather than relying on colour alone.

By · Reviewed 2026-09-08 · independent learning guidance

Scope: The lateral examples here are framed around IALA Region A. Confirm the buoyage region, current charted position and local navigation information before interpreting a real mark.

Why does the buoyage region matter?

IALA lateral marks use different red and green assignments in Regions A and B. That makes region a first-step question whenever a lateral mark is involved. Cardinal, isolated danger, safe water and special marks follow shared international families, but their exact use still depends on the charted local situation.

How should a cardinal mark be interpreted?

A cardinal mark names the side on which safer water lies relative to the danger: north, east, south or west. Its paired black-and-yellow pattern, cone topmarks and white-light group reinforce the same identity. Learn the system as one repeated code, then place it against the charted hazard before altering course.

What makes night identification reliable?

Observe colour, rhythm, group and period for long enough to distinguish the full characteristic. A glimpse can make different lights look alike. Compare the observation with the chart, expected bearing, surrounding lights and the vessel's position; if the evidence does not agree, do not force a match.

  • Identify region before interpreting a lateral mark.
  • Read a mark as a complete visual system.
  • Use the chart and position to confirm what you see.

Primary references used for this guide

Compass is an independent revision publisher. These maintained official, regulatory and standards-body references anchor the scope above; always check their current operational material for a real passage.

Check your understanding

Buoyage questions

4 selected answers

What colour is a port-hand mark in IALA Region A?

A port-hand mark is red in IALA Region A.

Read the answer

What is an isophase light?

An isophase light has equal periods of light and darkness.

Read the answer

What should you do with a yellow special mark?

Check the chart and current publication to identify its purpose, limits and route implication

Read the answer

Which mark sits on or close to a small hazard with navigable water around it?

An isolated danger mark, with the chart used to resolve the danger's extent and passing distance

Read the answer