IMO COLREG Rule 14

Rule 14 applies when two power-driven vessels meet on reciprocal or nearly reciprocal courses so as to involve risk of collision; each must alter course to starboard so that each passes on the port side of the other. The situation exists when a vessel sees the other ahead or nearly ahead and by night could see the masthead lights in a line or nearly in a line, or both sidelights. Where any doubt exists as to whether a head-on situation applies, the vessel must assume it does and act accordingly.