The following documents the essential features of the international 'IALA A' scheme of marine buoyage and is intended for use by users of this scheme. Readers should be aware that there is also a 'B' scheme (used in the Americas, Japan and the Philipines) which contains important detail differences (notably, the reversal of lateral mark orientation and bouy shape).
Marine navigation in tidal waters is aided in most (but not all) countries by an international system of buoys, which mark the essential navigational features necessary to ensure safe passage of a vessel. The following is by no means exhaustive, but details the essential navigational marks. The reader is referred to their national maritime authority for further information - in the U.K. Admiralty chart no. 5011 provides a complete listing of navigational marks and buoys.
Lateral marks are used to define the edges of navigable channel or estuary and are always oriented in the direction of the flood tide (i.e. the rising tide). The two essential marks are the:
Red Can, which defines the port (left-hand) side of the channel. This is a cylidrical shaped buoy and is coloured solid red.
Green Cone, which defines the starboard (right-hand) side of the channel. This is a conical shaped buoy(point uppermost) and is coloured solid green.
Submerged rocks or wrecks etc., are marked with a:
Danger Mark, which is a tall cylinder or spar placed directly over the hazard. These are coloured black/red/black in horizontal stripes.
The safe route past a hazard is marked using a:
Safe Water Mark, which is placed in the centre of the safe channel. This buoy may be spherical or cylindrical and is coloured red and white in vertical stripes. This is the only buoy to use vertical stripes.
The safe water to the north, south, east or west of a point of interest (which may be a rock, shoal or similar danger) is marked using a unique buoy for each cardinal compass point. These marks should always be passed on the named side of the buoy (e.g. a north cardinal should be passed to the north). The four marks comprise:
North Cardinal, a tall cylinder, coloured black/yellow in two horizontal stripes (black at top).
South Cardinal, a tall cylinder, coloured yellow/black in two horizontal stripes (yellow at top).
West Cardinal, a tall cylinder, coloured yellow/black/yellow in three horizontal stripes (yellow at top).
East Cardinal, a tall cylinder, coloured black/yellow/black in three horizontal stripes (black at top).
The above lists the essential internationally recognised navigational marks. There are of course many others, which may be readily identified using relevant maritime publications.