Cardinal marks. Cardinal marks are used in conjunction with the compass to indicate where the mariner may find the best navigable water. They are placed in one of the four quadrants (North, South, East and West) bounded by inter-cardinal bearings, from the point marked.
Cardinal marks take their name from the quadrant in which they are placed.
The mariner is safe if he passes N of a North mark, E of an East mark, S of a South mark and W of a West mark.
Cardinal marks may be used to:
Indicate that the deepest water in an area is on the named side of the mark;
Indicate the safe side on which to pass a danger;
Draw attention to a feature in a channel such as a bend, junction, bifurcation, or end of a shoal.
Topmarks. Black double-cone topmarks are a very important feature of Cardinal marks; they are carried whenever practicable, with the cones as large as possible and clearly separated.
The arrangement of the cones must be memorised.
Colours. Black and yellow bands are used to colour Cardinal marks.
The position of the black band, or bands, is related to the points of the black topmark, thus;
North - Points up Black band above yellow band;
South - Points down Black band below yellow band;
West - Points inward Black band with yellow bands above and below;
East - Points outward Black bands above and below yellow band.
Shape. The shape of Cardinal marks is not significant, but in the case of a buoy it is a pillar or spar.
Lights. White lights are exhibited from Cardinal marks which are lighted. Their characteristics are based on a group of quick or very quick flashes which distinguish them as Cardinal marks and indicate their quadrant.
The distinguishing quick or very quick rhythms are:
North - Uninterrupted;
East - 3 flashes in a group;
South - 6 flashes in a group followed by a long flash;
West - 9 flashes in a group.
To aid the memory, the number of flashes in each group can be associated with a clock face, thus:
3 - o’clock East;
6 - o’clock South;
9 - o’clock West.
The long flash (of not less than 2 seconds duration), immediately following the group of flashes of a South Cardinal mark, is to ensure that its 6 flashes cannot be mistaken for 3 or 9.
The periods of the East, South and West lights are, respectively, 10, 15, and 15 seconds if a quick light, and 5, 10, and 10 seconds if a very quick light.
Quick lights flash at a rate between 50 and 79 flashes per minute, usually either 50 or 60. Very quick lights flash at a rate between 80 and 159 flashes per minute, usually either 100 or 120.
Retroreflectors. One or more white bands, letters, numerals or symbols of retroreflective material are used in the Standard Code to distinguish unlighted Cardinal marks.
Blue and yellow bands on the black and yellow parts of the mark are used in the Comprehensive Code, thus:
North - Blue on the black part and yellow on the yellow part;
East - Two blue on the upper black part;
South - Yellow on the yellow part and blue on the black part;
West - Two yellow on the upper yellow part.