Lights
What Does a Flashing Yellow Light Mean at Sea?
Published · Last checked October 2026
At sea, a flashing yellow light most often marks a special mark, a yellow buoy flagging an outfall, exclusion zone or similar feature. It can also be an air-cushion vessel such as a hovercraft, which shows an all-round flashing yellow light under COLREGs Rule 23, or a vessel pushing a barge ahead, which shows a special flashing yellow light at the bow. Yellow alternating with blue means an emergency wreck marking buoy.
The main possibilities
| What it is | What you see | What to do |
|---|---|---|
| Special mark | Yellow light, any rhythm not used for white lights, e.g. Fl Y 5s | Check the chart for what it marks |
| Air-cushion vessel (hovercraft) | All-round flashing yellow plus normal steaming lights | Keep clear: it is fast and may change course quickly |
| Vessel pushing ahead or towing alongside | Special flashing yellow light at the forward end of the tow, 50 to 70 flashes a minute | Treat as a towing vessel with limited manoeuvrability |
| Emergency wreck marking buoy | Alternating blue and yellow flashes | A new wreck: stay well clear |
Special marks
Most yellow lights you meet near the coast are special marks. They show yellow in any rhythm that is not used for white lights, such as Fl Y, Fl(4) Y or Oc Y. Find the charted position and the light characteristic: the chart notes will tell you whether it marks a spoil ground, a firing range, a data buoy or a swimming area.
Air-cushion vessels
COLREGs Rule 23 requires an air-cushion vessel operating in non-displacement mode to show an all-round flashing yellow light in addition to normal power-driven vessel lights. Around the UK you are most likely to meet one on the Solent crossing to the Isle of Wight. They are fast, so a yellow flashing light that is moving quickly over the water deserves your attention.
Towing and pushing
Under Rule 24(f), a vessel being pushed ahead or towed alongside shows a special flashing yellow light at the forward end, flashing at 50 to 70 times a minute. With the tug's lights, it tells you there is a long and unwieldy combination ahead.
How to work out which it is
- Watch whether the light moves. A buoy stays put relative to the land; a vessel does not.
- Time the rhythm and compare with the chart.
- Look for other lights around it: masthead, sidelights or a stern light mean a vessel.
- Look for blue flashes in between: that is a wreck buoy.
- Check AIS, which often shows hovercraft, tugs and some buoys.
Revise all vessel lights in the COLREGs lights lesson and the navigation lights guide.
Yellow lights in harbours and ashore
Closer in, other flashing yellow or amber lights may come from shore installations rather than navigation marks. Some ports use amber lights in their traffic signals, and the International Port Traffic Signals system includes yellow lights in some displays meaning that vessels may proceed only when specifically told to. Construction sites, wind farm turbines and vehicles on piers may also show amber lights that are not charted. Check the harbour's own guidance for what its signals mean. Offshore, wind farm structures are usually lit with flashing yellow lights on the outer turbines, and their characteristics are shown on the chart.