Cardinal Marks are primarily used to indicate the position of a hazard and the direction of safe water.
Cardinal Marks are named after the (4) main cardinal points of the compass (North Cardinal Mark, South Cardinal Mark, East . . . (Ok, so you get the idea.) The attribute that makes the Cardinal Mark so useful to the mariner is that there is no dependency on the position of or the direction of travel of an approaching vessel. The Cardinal Mark will always tell you where safe water lies and that will always be to the named side of the mark.
In the example shown below, the "East Cardinal Mark" indicates that safe water will be found to the east of the mark.
Likewise with the other marks, safe water is always found to the named side of the mark.
All Cardinal Marks are horizontally banded yellow and black and have black cone shaped topmarks. During daylight hours, the band colors, and topmarks are used to identify which cardinal mark you are observing.
A good memory aid to help keep the color scheme straight in your mind is by using the top marks to tell you where the black band/s are located in relation to the yellow band/s.
When lighted, Cardinal Marks will:
The North Cardinal Mark will show a continuous “Q” or “VQ” white light.
The East Cardinal Mark will show a “Q(3) 10s” or “VQ(3) 5s” white light.
The South Cardinal Mark will show a “Q(6) + LFl 15s” or “VQ(6) + LFl 10s” white light.
The West Cardinal Mark will show a “Q(9) 15s” or “VQ(9) 10s” white light.
Quick Flashing (Q) is usually defined as a rate of 50 or 60 flashes per minute. Very Quick Flashing (VQ) is a rate of 100 or 120 flashes per minute.
Another memory aid to help easily remember and identify these lights at night, is to visualize the face of a clock with the cardinal marks at 12, 3, 6, and 9 and equate that to the flash count of the light.
Due to Cardinal Marks’ use of Quick Flashing and especially Very Quick Flashing lights, it often happens that some confusion can arise on the number of flashes observed. To help in preventing confusion between the Marks, a single Long Flash (L Fl) of 2 second duration is added to the South Cardinal Mark.