A buoy used in the IALA maritime buoyage system. The buoy can be can, conical, or pillar in shape, and it sometimes has a topmark which is either can shaped or cone shaped. In IALA region A, lateral marks utilize red and green (in exceptional cases, black) colours by day and night to denote respectively the port and starboard side of a channel when entering it, while in region B these colours are reversed so that red is used to mark the starboard side and green the port. When a ship moving in the direction of the buoyage system (i.e. into a river) comes to a division in the channel, the preferred channel might be shown by a modified lateral mark. For example, if the preferred channel is to starboard the port, or red, lateral mark has one broad green horizontal band, while if it is to port the starboard, or green, lateral mark has one broad red horizontal band.
Subjects: Maritime History.