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.
An interactive 3D illustration is shown here. The same content is described in the rule text and key takeaways below.
Buoyage Reading Order
Read the mark in a fixed order: topmark, colour pattern, light rhythm, charted meaning, then the safe side or action required.
Confirm the conventional direction of buoyage from the chart or pilotage plan before deciding port-hand or starboard-hand treatment.
Treat every mark as one aid among several.
Cross-check with charted depth, position, radar, visual bearings and the planned track.
Exam Focus
For cardinals, use the cones first, then the colour bands, then the flash mnemonic.
If those three agree, the answer is usually secure.
For lateral marks, the region only changes the colours, not the core idea: the mark still identifies the side of the channel in the conventional direction of buoyage.
Key Takeaways
All yellow colour scheme
X-shaped (cross) topmark in yellow
A special mark may also identify a dangerous floating object as a MAtoN
Indicates special areas — check nautical publications for details
Common Mistakes
Assuming there can never be a hazard near a special mark
Not consulting charts/publications for what the mark indicates
Test Your Knowledge
Practise this topic and review the explanation for each answer.
More rules in this Part
- IALA Lateral Marks (Region A & B)Lateral marks indicate port and starboard sides of channels. Region A: red to port. Region B: red to starboard.
- IALA Cardinal MarksCardinal marks indicate the direction of safe water relative to the mark using compass quadrants (N, E, S, W).
- IALA Isolated Danger MarksAn isolated danger mark is on or near a danger with navigable water around it. Consult charts and nautical publications for the extent of the danger and safe passing distance.
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