Cardinal Marks

What a cardinal mark tells you

In short: a cardinal mark is a signpost with a compass in it. It tells you on which side of the mark the safe water is.

Read first: IALA Buoyage System and Light Characters (light abbreviations), then Lateral Marks and Preferred Channel. This is the third topic of the Buoyage area.

• A cardinal mark is named after the compass quadrant where the safe water lies: North, East, South or West.
• North cardinal = deep water to the north of the mark. East = deep water to the east. South = to the south. West = to the west.
• The danger is on the opposite side. A North cardinal sits on the north side of a shoal: pass north of it.
• Cardinal marks are used with the compass, not with the direction of buoyage. They mean the same thing whichever way you are going.
• They are the same in Region A and Region B.

The four quadrants

• The quadrants are set by true bearings from the point of interest (IALA R1001):
  • North quadrant: from NW to NE (315°–045°)
  • East quadrant: from NE to SE (045°–135°)
  • South quadrant: from SE to SW (135°–225°)
  • West quadrant: from SW to NW (225°–315°)
• A mark placed in the North quadrant of a danger is a North cardinal, and so on.
• A large danger may have two, three or all four cardinals round it. Together they draw a box you must stay outside.

What else a cardinal mark can show

• The deepest water in an area.
• The safe side on which to pass a danger.
• A feature in a channel: a bend, a junction, a fork (bifurcation) or the end of a shoal.
• Shape: usually a pillar or spar. The shape has no meaning; the topmark, colours and light do.

Topmarks and colours

In short: two black cones on top, black and yellow bands below. Where the cones point, the black is.

• The colour rule: the black band is where the cones point. Both up = black on top (N). Both down = black at the bottom (S). Pointing out at both ends = black at both ends (E). Pointing into the middle = black in the middle (W).
• Memory hooks: North cones point up like the top of the chart; South point down. East looks like an Egg (or a diamond). West looks like a Wine glass — or a waist, pinched in the middle.
• On the bridge by day: the topmark is often the first thing you can read through binoculars, before the bands. Name the mark from the topmark, then confirm with the colours.

Cardinal lights

In short: every cardinal light is white and quick or very quick. The number of flashes matches the hour on a clock face.

• Speeds: Q = 50 or 60 flashes a minute · VQ = 100 or 120 flashes a minute (IALA R1001).
• Long flash (LFl): at least 2 s. The South cardinal adds it after its 6 flashes so a group of 6 cannot be mistaken for 3 or 9 when the flashes come fast.
• Colour: white only. A red, green or yellow light is never a cardinal mark.
• On the bridge at night: count the flashes in one group and time the period with a stopwatch. If you count “about 9”, wait for the next group before naming the mark.

North and South are easy to swap. One set of revision flashcards once had North as “groups of 6 + 1 long” and South as “groups of 6”. IALA R1001 gives North = continuous Q or VQ and South = 6 + one long flash. The flashcards now agree. Learn it the IALA way: the long flash belongs to South.

Passing cardinal marks on the bridge

In short: translate the mark into a compass side, then into port or starboard for your heading. Never pass between a cardinal mark and its danger.

Steaming North with a North cardinal ahead

• The safe water is north of the mark. You are approaching from the south, so you are on the danger side.
• Stop (or slow right down) at once. Fix your position by every means available and check the chart.
• The water you have just come through was safe: the safe water is right astern. Back out the way you came, then plan a track round the danger.
• Do not try to “just round the mark” — the danger lies between you and the buoy.
• Lesson: a good passage plan never has you meeting a cardinal mark from its danger side. If it happens, your position or the plan is wrong.

Steering 270° and you see a North cardinal

• Safe water is to the north of the mark: you must pass north of it.
• On a heading of 270°, north is on your starboard side. So leave the mark on your port hand.
• Mark fine on the port bow: you are already to the north of it — hold your course and leave it to port with a good margin.
• Mark ahead or on the starboard bow: you are south of it, heading for the danger side. Alter to starboard early and pass north of it.
• General method: name the safe side (N, E, S, W) → compare it with your heading → say aloud “leave it to port” or “leave it to starboard” in the pilotage briefing.

Good habits

• Give cardinal marks a wide berth. The mark shows the quadrant of safe water, not the exact edge of the danger.
• Buoys can drag or be off station. Check the mark against your fixed position, not the other way round.
• If a mark is missing, unlit or not on the chart, slow down, fix by other means and check NP735 and the latest Notices to Mariners.

Cardinal marks on the paper chart and on ECDIS

In short: the MCA syllabus asks you to recognise IALA marks on both a paper chart and an ECDIS. The mark is the same; only the symbol changes.

• Paper chart: a pillar or spar buoy symbol with the two-cone topmark drawn on top, and the colour letters beside it, read top to bottom: BY (N), BYB (E), YB (S), YBY (W).
• A lit mark has a magenta light flare with its character, e.g. “Q”, “VQ(3)5s”, “Q(6)+LFl15s”, “VQ(9)10s”.
• Symbols are listed in INT 1 / Chart 1, Section Q (buoys and beacons).
• ECDIS: an ENC shows cardinal marks with paper-chart (traditional) or simplified symbols, as the operator chooses. Pick the object with the cursor to read the full light.
• On the bridge: when you plan a track past a cardinal mark, check on the chart which quadrant the danger is in and keep a safety margin from the danger itself, not just from the buoy.