Cardinal mark (IALA)

A cardinal mark is an IALA buoy or beacon that tells the mariner on which side to pass by reference to the compass: safe water lies to the named side. The four marks, North, East, South, and West, are named for the quadrant of clear water they guard and read from their double-cone black topmarks and black-yellow band pattern. The topmarks point the way: North both cones up, South both down, East base to base, West point to point. When lit, they show white quick or very-quick flashing in groups keyed to a clock face, N continuous, E three flashes, S six plus a long flash, W nine. Cardinal marks are identical in Region A and Region B.