You are called to the bridge at 0230. The OOW reports a confused cluster of lights ahead: a white flash, a green flash, and what looks like a red sector. You are approaching an unfamiliar port in IALA Region A. Before you can direct the OOW, you need to know — with certainty — what each light means and what it demands of you as Master.
The two IALA regions
IALA Region A covers Europe, Africa, most of Asia, Australia and New Zealand. IALA Region B covers the Americas, Japan, South Korea and the Philippines. The critical difference: in Region A, red buoys are left to port on entry and green to starboard; in Region B this is reversed — red right returning. A Master transitioning between regions must brief the team and update the voyage plan accordingly; an incorrect assumption here puts the vessel on the hazard the buoy is marking.
The five mark types
- Lateral marks — define the sides of a navigable channel. Shape and colour depend on the region and whether you are inbound (conventional direction of buoyage) or outbound.
- Cardinal marks — indicate the safe side on which to pass. Named for compass quadrant; topmarks are two black cones in orientations that correspond to the quadrant (north: both up; south: both down; east: points together like an egg; west: points apart like a waist). Light characteristics: north = VQ or Q uninterrupted; east = VQ(3) or Q(3); south = VQ(6)+LFl or Q(6)+LFl; west = VQ(9) or Q(9). All-white lights.
- Isolated danger marks — mark a small hazard with navigable water around it. Black with red horizontal band(s), two black sphere topmark. Light: Fl(2) white.
- Safe water marks — safe water all around (mid-channel, landfall). Red and white vertical stripes. Light: Isophase, Occulting, one long flash every 10 s, or Morse 'A' — all white.
- Special marks — indicate a feature shown on charts (cables, separation schemes, spoil grounds). Yellow. Light: yellow, any rhythm not used by white lights.
Emergency wreck marking buoys — not part of the original five categories but now included in IALA documentation. Blue and yellow vertical stripes, pillar or spar, Morse 'U' blue/yellow alternating. Placed by an authority to mark a newly-discovered wreck before permanent marking is established.
Applying this at command level
Back on the bridge: the white flash is an isolated danger mark — the hazard is directly below it, do not pass over it, pass either side with adequate clearance. The green flash is a lateral mark — in Region A leave it to starboard inbound. The red sector of the light structure ahead tells you that your present heading crosses a defined dangerous arc. Alter course now to enter the white sector before closing the fairway. Issue the helm order, log the decision, and confirm the new track clears all hazards on the chart.
The Master's role is not to read the chart instead of the OOW — it is to hold the complete mental picture so that when conflicting or confusing information arrives, the correct interpretation and the correct order come instantly.