Buoyage
What Is an Emergency Wreck Marking Buoy? Blue and Yellow
Published · Last checked October 2026
An emergency wreck marking buoy marks a newly sunk wreck that is not yet shown on charts or in notices to mariners. It has equal blue and yellow vertical stripes, an upright yellow cross topmark, and shows an alternating blue and yellow flashing light. It may also carry a racon sending Morse 'D' and an AIS signal. Treat it as a serious hazard and keep well clear, because the wreck may not have been fully surveyed.
How to recognise one
| Feature | Description |
|---|---|
| Colour | Blue and yellow vertical stripes, equal in number (typically 4 to 8) |
| Shape | Pillar or spar |
| Topmark | Upright yellow cross (+), if fitted |
| Light | Alternating blue and yellow flashes, Al Bu Y |
| Racon | Morse 'D' (−··), if fitted |
| AIS | May transmit as an AIS aid to navigation |
The upright cross is different from the diagonal X on a special mark, and blue is not used on any other IALA buoy, so the mark stands out.
Why it exists
IALA introduced the emergency wreck marking buoy after a series of collisions in the Dover Strait in 2002. The car carrier Tricolor sank and, despite being marked, was struck by other ships in the following days. The new buoy was designed to look unlike anything else, so that bridge teams notice it immediately.
How it is used
- Laid as soon as possible after a wreck is found, often in pairs or groups around a large wreck.
- Kept in place until the wreck is surveyed, published in notices to mariners and permanently marked, often with cardinal marks or an isolated danger mark.
- Its position is broadcast in navigational warnings by the coastguard on VHF and NAVTEX.
How to pass one
There is no fixed side to pass. Treat it like any uncharted danger: find out from warnings where the wreck lies relative to the buoys, give it a very wide berth, and never pass between buoys in a group unless you know it is safe. If you see an unmarked wreck, or a buoy out of position, report it to the coastguard.
Revise all marks in the buoyage and lights lesson and see what a flashing yellow light means.
On radar and AIS
The racon, if fitted, paints a Morse 'D' (dash, dot, dot) on your radar screen, extending outwards from the buoy's echo. An AIS-equipped buoy may appear on a plotter as a virtual or real aid to navigation, often with a name describing the wreck. In some cases, authorities create a virtual AIS mark over the wreck before a physical buoy can be laid. Treat an AIS wreck symbol with the same respect as a real buoy, even if you cannot see anything in the water. In poor visibility this electronic information may be the only warning you get, so keep radar and AIS running and watched.