Buoyage
What Is a Special Mark? Yellow Buoys and Their Meaning
Published · Last checked October 2026
A special mark is a yellow buoy that is not mainly for navigation. It indicates a special area or feature described on the chart or in sailing directions, such as a sewage outfall, spoil ground, military exercise area, cable, data buoy, water-ski zone or racing mark. It may carry a single yellow X-shaped topmark and, if lit, shows a yellow light in any rhythm not used for white lights. Check the chart to find out what it marks.
How to recognise one
| Feature | Description |
|---|---|
| Colour | Yellow |
| Shape | Optional, but must not conflict with navigational marks |
| Topmark | Single yellow X (saltire), if fitted |
| Light | Yellow, any rhythm not used for white lights, e.g. Fl Y 5s, Fl(4) Y 10s |
What special marks are used for
- Outfalls and intakes
- Spoil grounds and dredging areas
- Military exercise and firing ranges
- Cables, pipelines and ocean data buoys (ODAS)
- Recreation zones: swimming areas, water-ski lanes and speed limit areas
- Racing marks and private moorings
- Traffic separation where conventional channel marks could cause confusion
The chart or local notices tell you what each one means. A yellow buoy off a beach may mark a bathing area you must keep out of, while one offshore might mark a wave-recording buoy.
Can you pass a special mark either side?
Often yes, but not always. Where a special mark has a can or cone shape, it is meant to be passed in the same way as the corresponding lateral mark: can on your port side, cone on your starboard side, going with the buoyage. Where special marks enclose a zone, the question is whether you should be inside it at all. Read the chart notes.
Why they matter
Special marks are easy to dismiss because they are not part of the main channel system, but they often mark things that can hurt you or your boat: shallow outfall pipes, live firing ranges, or swimmers. Plan your passage with them in mind, using the chart symbols guide and the buoyage and lights lesson.
On the chart
Special marks are drawn as buoy symbols tinted yellow, with 'Y' beside them and the light characteristic if lit. Many sit on the boundary of an area drawn with a dashed magenta line and a label, such as 'Spoil Ground', 'Outfall' or 'Firing Danger Area'. The sailing directions and any harbour guide explain what each zone means and whether you may enter it. Range areas around the UK, for example, often have published firing times and a safety boat that will ask you to keep clear. Local water-ski and swimming zones are usually seasonal and may only be marked in summer. Speed limit buoys in harbours and rivers are often yellow too, with the limit written on them.