A yellow buoy or spar buoy, sometimes with an X-shaped topmark, which is used in the IALA maritime buoyage system. It is not primarily intended to assist navigation but to indicate a special area or feature like spoil ground or a military exercise zone. It is also sometimes used as a mark for a traffic separation scheme where use of conventional channel marking may cause confusion, and in this case its topmark, if fitted, is the same as a lateral mark. A special mark can be any shape so long as it does not conflict with navigational marks. To avoid confusion, the yellow lights of these marks do not have any characteristic used for white lights.
Subjects: Maritime History.