Regions A and B

A lateral mark identifies a side relative to the conventional direction of buoyage. That direction belongs in nautical documents and does not reverse when our boat turns around. Region determines port and starboard colours: A uses red port and green starboard; B green port and red starboard. Begin the figure with its declared arrow, then identify the side before reading colour and shape. A colour rule detached from this reference is incomplete. The arrow expresses a convention, rather than a recommended track or the direction of every vessel’s movement.

R1001 distinguishes an approach from seaward to a harbour, river or estuary from direction determined by the authority, in principle clockwise around landmasses. Portuguese RBMN Article 4 preserves those possibilities. “Whenever entering a harbour” is therefore a partial memory aid rather than the whole definition. In through-channels or where directions meet, the published reference becomes particularly important. Map north and buoyage direction answer different questions; rotating a teaching page changes neither the authority’s convention nor a mark’s identity.