Preferred channel buoy

A preferred channel buoy marks a point where a channel divides and shows which fork is the main route, the same mark as the IALA junction buoy. It is a lateral mark modified by a single broad horizontal band of the opposite color: in Region A, preferred channel to starboard is red with a green band, preferred channel to port is green with a red band, colors reversed in Region B. Its light is the composite group flashing Fl(2+1) rhythm, the trailing single flash distinguishing it from a plain lateral mark. Treating the body color as the controlling lateral color keeps the ship in the preferred channel; passing it on the other side leads into the secondary channel.