IALA buoyage · Isolated danger
Isolated danger mark
Identical in A and B
Black with red bands and two black spheres: a small danger with navigable water all around it. White light Fl(2).
Fl(2) 5sA group of 2 flashes close together every 5 s.A group of 2 flashes close together every 5 s.
Pillar buoy; horizontal bands top to bottom: black, red, black; topmark: two black spheres. Light: Fl(2) 5s.
What it means
Moored on or directly above an isolated danger of limited extent — a rock, shoal head or wreck — that has navigable water all around it. Identical in both IALA regions.
What you do
Do not pass close aboard. Identify the extent of the danger on the chart, then keep well clear on either side.
Memory aid
Two spheres, two flashes — double trouble sitting right underneath.
Source: IALA Maritime Buoyage System — USCG Navigation Center, U.S. Aids to Navigation System