IALA buoyage · Lateral marks
Preferred channel to port
Differs by region — showing A
A banded junction mark: the channel splits and the preferred channel lies to port — so treat the mark like a starboard-hand mark.
Fl(2+1) G 10sComposite group 2 + 1 every 10 s. Colour: green.Composite group 2 + 1 every 10 s. Colour: green.
Conical buoy; horizontal bands top to bottom: green, red, green; topmark: one cone, point up. Light: Fl(2+1) G 10s.
What it means
At a channel junction, the preferred (main) channel lies to port of this mark. Its base colour and cone shape are those of a starboard-hand mark, with one broad band of the “other side’s” colour.
What you do
To follow the preferred channel, leave this mark to starboard, exactly as you would a normal starboard-hand mark. Leave it to port only to take the secondary channel.
Memory aid
Same trick: top band + shape read like an ordinary lateral. The stripe just warns you there is a second channel on the other side.
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