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IALA Special Marks

Special marks identify areas or features described in nautical publications, not the sides of a channel.

Decide

An interactive 3D illustration is shown here. The same content is described in the rule text and key takeaways below.

Step 1 of 2

Which mark is it?

The mark in plain words

  1. What do they indicate?They identify an area or feature whose nature is described in charts and nautical publications; confirm its meaning there.
  2. What colour are they?The mark is yellow, a clear visual clue.
  3. What is on top?If fitted, it shows a yellow X, the St. Andrew's cross.
  4. Do they mark channel sides?They generally do not replace suitable lateral or cardinal marks; check the chart or nautical publication.
Special marks: yellow buoys with a yellow X, fencing off a swimming area near the beach.

See it in 3D

Turn the mark to inspect its colours, shape and topmark, then switch to night to see its light.

An interactive 3D illustration is shown here. The same content is described in the rule text and key takeaways below.

How you recognise it

Colour
Yellow
Shape
Optional, without conflict with navigational marks
Topmark
Single yellow X-shape (if fitted)
Light · colour
Yellow
Light · rhythm
Any rhythm not used for other marks

Frequent mistakes

  • Wrong: "A special mark can never be near a hazard."

    Right: It may mark a dangerous floating object as a MAtoN; check the publications.

  • Wrong: "Yellow tells me exactly what is there."

    Right: The chart or nautical publication defines the specific area or feature.

  • Wrong: "It is a lateral mark showing which side to pass."

    Right: It generally does not replace suitable lateral or cardinal marks.

Exam keys & interpretation

  1. Yellow + X does not indicate a lateral channel: the mark identifies a special area or feature.
  2. If asked what it means, check the chart or nautical publication instead of guessing from the buoy.
  3. Yellow light: look for a rhythm not reserved for cardinal, isolated danger, safe water or MAtoN marks.

How to read it

Think of it as a yellow label: it flags a special area or feature, but the chart explains its meaning.

The X and light help you recognise it; the nautical publication tells you what is there.

Key points

  • Yellow throughout the mark.
  • Yellow X on the topmark, if fitted.
  • The yellow light uses a rhythm not used by other marks.
  • Check the chart: it does not replace suitable lateral or cardinal marks.

Test your knowledge

Question 1/4

You see a yellow mark with an X topmark. What kind of mark is it?

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Full lesson & sources

Special marks indicate an area or feature whose nature is described in charts and nautical publications. They generally do not replace suitable lateral or cardinal marks. A Mobile Aid to Navigation (MAtoN) may, however, mark a floating object that poses a collision hazard.

  • Colour: yellow
  • Topmark (if fitted): single yellow X-shape (St. Andrew's cross)
  • Light (if fitted): yellow; any rhythm except those reserved for cardinal, isolated danger, safe water or MAtoN marks
  • Shape: optional — any shape not conflicting with lateral or safe water marks

Examples include: ocean data acquisition systems (ODAS), traffic separation marks, spoil ground marks, military exercise zone marks, cable or pipeline marks, recreation zone marks.

Reviewed by Ramon Curto, Nautical teacher at IECNPC · Last reviewed: