IALA buoyage · Lateral marks
Port-hand lateral mark
Differs by region — showing A
Marks the port (left) edge of the channel when travelling with the direction of buoyage — a red can in Region A, a green can in Region B.
Fl R 4sOne flash every 4 s — dark longer than light. Colour: red.One flash every 4 s — dark longer than light. Colour: red.
Can-shaped buoy; solid colour: red; topmark: one can. Light: Fl R 4s.
What it means
The port-side limit of the navigable channel, taken in the direction of buoyage (normally from seaward into harbour). The flat-topped can shape means “port side” in both regions; only the colour flips.
What you do
Going with the direction of buoyage (e.g. entering harbour), leave this mark on your port side. Leaving harbour, keep it to starboard.
Memory aid
Region A: “Is there any red port left?” — red = port = left, and port wine comes in a can-shaped bottle. Region B flips the colours (green can to port) but the can shape still says port.
Region A vs Region B
Same mark, same meaning, same shape — only the colours flip. Select a region to preview it site-wide.
Source: IALA Maritime Buoyage System — USCG Navigation Center, U.S. Aids to Navigation System