IALA buoyage · Lateral marks
Preferred channel to starboard
Differs by region — showing A
A banded junction mark: the channel splits and the preferred channel lies to starboard — so treat the mark like a port-hand mark.
Fl(2+1) R 10sComposite group 2 + 1 every 10 s. Colour: red.Composite group 2 + 1 every 10 s. Colour: red.
Can-shaped buoy; horizontal bands top to bottom: red, green, red; topmark: one can. Light: Fl(2+1) R 10s.
What it means
At a channel junction, the preferred (main) channel lies to starboard of this mark. Its base colour and can shape are those of a port-hand mark, with one broad band of the “other side’s” colour.
What you do
To follow the preferred channel, leave this mark to port, exactly as you would a normal port-hand mark. Leave it to starboard only to take the secondary channel.
Memory aid
Read the top band and the shape — they win. Composite light Fl(2+1): “two-plus-one, the channel splits, pick one.”
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