Isolated danger mark

An Isolated Danger Mark, as defined by the International Association of Lighthouse Authorities, is a sea mark used in maritime pilotage to indicate a hazard to shipping such as a partially submerged rock.^[1]

Isolated danger marks are recognisable by the following characteristics:^[1]^[2]

Generally a pillar or spar shape, but could alternatively be any other shape as long as the shape is different from those used for lateral marks.
Coloured black with one or more broad horizontal red bands.
Always having a topmark attached which is two black spheres stacked vertically.
If a light is fitted, it is white in colour and has a light characteristic of group flashing 2 (abbreviated as "Fl(2) W"). Two flashes of white light in succession are followed by a longer duration of darkness.

Footnotes

^ ^a ^b "R1001 The IALA Maritime Buoyage System". International Association of Marine Aids to Navigation and Lighthouse Authorities. Retrieved 2025-07-09.
^ "R0110 – Rhythmic Characters of Lights on Aids to Navigation". International Association of Marine Aids to Navigation and Lighthouse Authorities. Retrieved 2025-07-09.

International association of maritime aids to navigation and lighthouse authorities (2010). "Maritime buoyage system and other aids to navigation" (PDF). IALA-AISM. Retrieved 11 August 2019.
Service Hydrographique et Océanographique de la Marine (1 September 2016). Signalisation Maritime (PDF) (in French). France: SHOM. ISBN 978-2-11-139457-5. Retrieved 11 August 2019. {{cite book}}: |work= ignored (help)