It had already been a long night, my second in a row without sleep, and I was trying to get to my destination of La Coruna in northern Spain around dawn so that I could anchor and then sleep. I was following the coast some 10 miles offshore with another 20 or so miles to go before I could head more in to the bay and around the peninsular that protected the harbor. Ahead I saw a light, low down on the water and not too far away, showing 3 successive flashes which, because of my familiarity of the Cardinal Mark aids to navigation, I instantly recognized as an East Cardinal. I hadn't expected to see one this far out and it was confusing because to avoid the apparent danger it was directing me to pass between it and the shore rather than head further out. Despite its apparent proximity I found myself heading towards it for an inordinately long time; time enough to consult the chart on several occasions to see if magically it had appeared since my previous look. My anxiety rose with the passing minutes until at last I decided to heave-to on the offshore tack and go below to figure it out. A short rest and a cup of coffee later I suddenly realized that what I had been seeing was not in fact a Cardinal mark close to my position but the three distinct flashes of the Islas Sisargas lighthouse on the mainland some 20 miles or so distant and appearing low on the water because of the curvature of the earth. Once this revelation occurred I was able not only to cease worrying but to fix my position from the light and then carry on safely towards the harbor. This was just one of a number of instances where tiredness had caused me to make an error but that's another topic altogether.
I had thought the lighthouse was a cardinal mark because of the similarity of its characteristic to an East Cardinal Mark. But before I explain this similarity, what are Cardinal marks? For those who venture no further than the coastal regions of the U.S. this system is of academic interest only as though these marks could be used here I do not believe they are. However for those who voyage a little further afield, whether aboard there own boat or on a charter boat away from the U.S., Cardinal Marks will often be observed.
Here in the U.S. we primarily see the Lateral system of buoyage where red and green buoys or top marks are left on the appropriate side of the channel according to the red-right-returning rule. Cardinal marks do not usually mark the sides of a channel but are used to indicate dangers such as isolated rocks, wrecks or other obstructions. They are termed Cardinal Marks because of their use of the Cardinal points of the compass to indicate where the danger lies. Assume for a moment that you are sailing westward along the south coast of some idyllic island but that an underwater reef extends south from the coast for some distance making this a serious danger in your path (Fig 1). A South cardinal mark at the southerly tip of the reef would be all that was necessary to help you avoid the danger. In a similar way North, East and West Cardinal marks are used to indicate dangers from other directions.
Cardinal marks are logical and simple to understand and I can think of any number of situations where they could be used helpfully here but it will probably be a long time before they are! To avoid the danger that they are there to indicate you should stay:
South of a south cardinal mark
West of a west cardinal mark
North of a north cardinal mark
East of an East cardinal mark
Marks are very different to the normal red and green Lateral system marks that are otherwise encountered, though like the Lateral marks they may be either floating aids or fixed marks. Cardinal marks (Fig 2) are colored black and yellow and always have two black cones indicating the type of mark. Two cones points up, is a North Cardinal mark; two cones points down is a south cardinal mark; two cones points apart is an east mark and two cones points together a west mark. The north and south marks are easy to remember when related to a compass rose (where north is up). I was taught the somewhat trite, though useful, way of remembering the east and west marks as follows: Egg, east (the two cones points apart form a rough egg shape); Waisted, west (the two cones points together form a waisted shape). The coloring of the marks coincides with the shapes, the points always indicating black. Thus a north mark has the top half (points up) black and the bottom half yellow. A west mark (points together) is colored yellow, black, yellow.
And now to the light characteristics of these marks which is were I began. The lights are always white and flash either quick (about once per second) or very quick (about twice a second). The number of flashes coincides roughly with a clock face so that the East mark (3 O'clock) flashes three times; a south mark (6 O'clock) six times but is then followed by one long flash ( about 2 seconds); a west mark (9 o'clock) nine flashes; and a north mark has a continuous flash.
And now perhaps you can see how I mistook the lighthouse with its 3 flashes for an East Cardinal mark with its 3 quick or very quick flashes. In fact though they were similar they were not identical characteristics as the lighthouse had a period of 15 seconds - longer than the 5 or 10 seconds for an East Cardinal. If I had been less tired and had timed the light I would not have made the error.