Isolated Danger Mark

Buoy or pillar positioned on a dangerous underwater obstruction.

An isolated danger mark is a navigation aid used at sea to indicate a single, isolated danger (like a rock or a wreck) with safe water around it. It’s a marker to help sailors avoid obstacles that might otherwise be hard to spot.

Isolated danger marks are characterised by:

• Colour: Black with one or more red horizontal bands.
• Topmark: Two black spheres, one above the other, at the top of the mark.
• Light (if equipped): Flashes white, usually in a group of two flashes (to make it distinct from other marks).

These marks are part of the IALA (International Association of Marine Aids to Navigation and Lighthouse Authorities) buoyage system, designed to improve maritime safety.