Lesson 17 of 40 · Module 3 — Buoyage, lights and the rules of the road

Cardinal marks

North, east, south and west cardinals: shapes, colours, topmarks and lights.

Day Skipper20 minVideo · Notes · Interactive · Exercises
0:00 / 4:28Chapter 1 of 9: Marks named after the compass
Transcript

  1. Lateral marks show the edges of a channel, but many dangers lie out in open water. Cardinal marks guard them using the points of the compass instead. Imagine four lines drawn out from a danger, on the true bearings north-east, south-east, south-west and north-west. They divide the sea around it into four quadrants: north, east, south and west. A cardinal mark is placed in one of those quadrants and named after it, and the safe water lies on its named side: you pass north of a north cardinal.

  2. The north cardinal sits in the north quadrant of a danger, so you pass to the north of it. It is painted black above yellow, with a topmark of two black cones, both pointing up. The cones point to where the black is: up, to the black top half. At night its white light flashes without a break: quick, about once a second, or very quick, about twice a second.

  3. The east cardinal sits in the east quadrant, so you pass to the east of it. It is black with a broad yellow band, and its cones are base to base, a shape some people remember as an egg. Again the cones point to the black: one up and one down, to the black top and bottom. Its light flashes in groups of three: every ten seconds if quick, or every five if very quick.

  4. The south cardinal sits in the south quadrant, so you pass to the south of it. It is yellow above black, with both cones pointing down. Once again the cones point to the black: down, to the black bottom half. At night it gives six quick flashes and then one long flash, of at least two seconds, every fifteen seconds, or every ten if very quick.

  5. The west cardinal sits in the west quadrant, so you pass to the west of it. It is yellow with a broad black band, and its cones are point to point, like a wine glass. The cones point inwards, to the black band in the middle. Its light flashes in groups of nine: every fifteen seconds if quick, or every ten if very quick.

  6. Every cardinal light is white and flashes quick or very quick, so picture a clock face to remember them. East is at three o’clock and flashes three. South is at six and flashes six. West is at nine and flashes nine. North, at twelve, flashes without a break. The south light adds its long flash because quick flashes are hard to count, and six could easily be mistaken for three or nine.

  7. The practice chart has four cardinal marks. The Teeth, east of Gull Point, have North Teeth buoy on their north side and East Teeth buoy on their east. South Brennan buoy is on the south side of Brennan Bank, where the least depth is just 2.1 metres. And West Ledge buoy guards the west side of Head Ledge, the rocks off Kerran Head.

  8. Imagine sailing south past Gull Point, along the east side of the island. North Teeth buoy is a north cardinal, so you keep to the north of it. Then comes East Teeth buoy, an east cardinal: you pass east of it, well clear of The Teeth. At night you would know them by their lights: one flashing without a break, the other in groups of three.

  9. By day, look first at the topmark, then check the colours: the cones point to the black. By night, count the white flashes and picture the clock face. Then pass on the named side, and check the chart for the danger the mark is guarding. Next: the remaining marks, for isolated dangers, safe water and special purposes.

In this lesson you will learn

  • Explain what a cardinal mark tells you, and how the four quadrants are defined by true bearings from a danger
  • Identify north, east, south and west cardinal marks by day from their topmarks and colours
  • Identify them at night from their quick or very quick white lights, using the clock face, and explain the south cardinal’s long flash
  • Decide which side to pass a cardinal mark, and use the practice chart’s cardinals to keep clear of the dangers they guard

What a cardinal mark tells you

In the last lesson you met lateral marks: red and green buoys that show the two sides of a channel, read according to the direction of buoyage. But many dangers are not beside a channel at all. A rock in open water, the edge of a sandbank or a ledge off a headland can be approached from any direction, so “keep it to port” would mean nothing. For these the IALA system uses cardinal marks, which work with the compass instead.

A cardinal mark is placed to the north, east, south or west of a danger and is named after that direction: a north cardinal, an east cardinal, and so on. Its name tells you where the safe water is.

A cardinal mark is named after the side of the danger it stands on — and that is the side you pass: north of a north cardinal, east of an east cardinal.

Cardinal marks are used to:

  • show the safe side on which to pass a danger;
  • show that the deepest water in an area is on the named side of the mark;
  • draw attention to a feature in a channel, such as a bend, a junction or the end of a shoal.

The four quadrants

Imagine four lines drawn out from the danger on the true bearings north-east (045°), south-east (135°), south-west (225°) and north-west (315°). They divide the sea around it into four quadrants:

QuadrantTrue bearings from the dangerMark placed there
North315°–045°TNorth cardinal: pass north of it
East045°–135°TEast cardinal: pass east of it
South135°–225°TSouth cardinal: pass south of it
West225°–315°TWest cardinal: pass west of it
045°135°225°315°NESWDangerBearings are true, measured from the danger
The four quadrants round a danger. Each cardinal mark stands in its own quadrant; the green arrows show the side you pass.

The mark can be anywhere in its quadrant: it is not always due north, east, south or west of the danger. Pass on its named side and the danger is on the other side of the mark from you.

By day: topmarks and colours

Every cardinal mark is painted black and yellow and is usually a pillar buoy (a tall structure on a broad base) or a spar (a tall pole). On top it carries a topmark of two black cones, one above the other. The way the cones point is the most important thing to look for by day: colours can be hard to make out at a distance or against a bright sky, but the shape of the topmark stands out.

North cardinal

Colours: Black above yellow

Topmark: Two black cones, both pointing up

Light: White, VQ or Q (continuous)

East cardinal

Colours: Black with one broad yellow band

Topmark: Two black cones, base to base

Light: White, VQ(3) 5s or Q(3) 10s

South cardinal

Colours: Yellow above black

Topmark: Two black cones, both pointing down

Light: White, VQ(6)+LFl 10s or Q(6)+LFl 15s

West cardinal

Colours: Yellow with one broad black band

Topmark: Two black cones, point to point

Light: White, VQ(9) 10s or Q(9) 15s

There is a neat link between the two: the cones point to where the black is. A north cardinal’s cones point up, so its black is at the top. A south cardinal’s point down, so its black is at the bottom. An east cardinal’s point away from each other, up and down, so it is black at the top and bottom with a yellow band between. A west cardinal’s point towards each other, so its black is a band in the middle.

By night: the lights

When a cardinal mark is lit, its light is always white, and it is always quick or very quick flashing. On the chart these are written Q and VQ: quick is about one flash a second and very quick about two. A number in brackets is a group — Q(3) means the flashes come in threes — and the figure in seconds is the period, the time for one whole group plus the dark gap before the next. LFl is a long flash, at least two seconds long. No colour letter means the light is white. Lesson 19 decodes light characteristics in full.

To remember the lights, picture a clock face:

MarkClock faceLight: quick or very quick
North cardinal12 o’clock: no breakQ or VQ, continuous
East cardinal3 o’clock: 3 flashesQ(3)10s or VQ(3)5s
South cardinal6 o’clock: 6 flashes + long flashQ(6)+LFl15s or VQ(6)+LFl10s
West cardinal9 o’clock: 9 flashesQ(9)15s or VQ(9)10s

East is at 3 o’clock and flashes three; south at 6 flashes six; west at 9 flashes nine; and north, at 12, flashes without a break. A mark may use either speed, so learn both versions of each.

InteractiveThe clock face

Watch the four lights flash together in their real rhythms (the lengths of the flashes are representative). Switch between quick and very quick.

12N3E6S9W

  • North cardinal12 o’clockQ

    White, quick flashing without a break

  • East cardinal3 o’clockQ(3)10s

    White, quick flashing in groups of 3, repeated every 10 seconds

  • South cardinal6 o’clockQ(6)+LFl15s

    White, quick flashing in groups of 6 followed by a long flash, repeated every 15 seconds

  • West cardinal9 o’clockQ(9)15s

    White, quick flashing in groups of 9, repeated every 15 seconds

Each bar is one full period, lit parts in white; the marker shows where each light is now. Flash lengths are representative.

Why the south light has a long flash

Quick flashes are surprisingly hard to count, especially from a moving boat in a seaway. A group of six could easily be miscounted as three or nine — and mistaking a south cardinal for an east or west one would send you round the wrong side of the danger. So the south cardinal adds a long flash after its six, which makes it unmistakable and also marks the end of each group.

Worked example

A light at night off Kerran Head

  1. 1Approaching the island’s west coast at night, you see a white light flashing quick — the kind of light a cardinal mark shows.
  2. 2You count nine flashes in a group, then darkness: nine is 9 o’clock, so it is a west cardinal.
  3. 3Timed from the start of one group to the start of the next, the period is 15 seconds: Q(9)15s.
  4. 4On the chart, that is West Ledge buoy, guarding Head Ledge, which lies 079°T from the buoy, 5.3 cables away.

A west cardinal: keep to the west of West Ledge buoy, with the buoy between you and Head Ledge.

InteractiveCardinal trainer

Name the mark and choose which side you would pass it, then press Check. Try it by day, by night, or mixed. At night, count the flashes in a group: Restart begins a fresh one.

Look at the topmark first, then the colours.

1. What is it?

2. Which side do you pass it?

Score: 0 of 0

Cardinal marks on the practice chart

On the practice chart a cardinal buoy is drawn as a small pillar with its colours and its two-cone topmark, and its light is printed beside it. Admiralty charts also print the colours as letters, read from the top: BY for a north cardinal, BYB east, YB south and YBY west. The practice chart has four:

BuoyGuards (buoy’s bearing and distance from it)Pass to its
North Teeth buoy
North cardinal, Q		The Teeth
000°T, 0.70 M		North
East Teeth buoy
East cardinal, Q(3)10s		The Teeth
101°T, 0.53 M		East
South Brennan buoy
South cardinal, Q(6)+LFl15s		Brennan Bank
180°T, 1.0 M		South
West Ledge buoy
West cardinal, Q(9)15s		Head Ledge
259°T, 0.53 M		West

For Brennan Bank, the bearing and distance are from its shallowest point, the 2.1 m sounding.

Worked example

Which quadrant is East Teeth buoy in?

  1. 1Put the dividers on The Teeth and on East Teeth buoy and measure the bearing from the danger to the mark: 101°T, 5.3 cables.
  2. 2The east quadrant runs from 045° to 135°T, and 101°T falls inside it.
  3. 3So the buoy must be an east cardinal — and the chart agrees: its topmark is drawn base to base, and its light is Q(3)10s.

Safe water lies east of East Teeth buoy: pass east of it, with the buoy between you and The Teeth.

South Brennan buoy shows why the named side matters. It stands 1.0 M from Brennan Bank’s 2.1 m patch, bearing 180°T from it. Half a mile south of the buoy the chart shows about 39 m; half a mile north of it, only 7.3 m, and shoaling. Passing south of a south cardinal keeps you in the deep water. The Teeth have cardinals only on their north and east sides (North Teeth buoy stands 0.70 M from them on 000°T), so a yacht arriving from the south or west has to keep clear by other means: the chart, the depth sounder and the clearing bearings of Lesson 13.

InteractiveExplore the quadrants

Choose one of the chart’s cardinal marks. Then put the yacht on each side of it with the buttons — or tap the chart — and see what the mark promises.

North Teeth buoy (Q) is a north cardinal mark guarding The Teeth, rocks awash at chart datum. It stands 0.70 M from them, bearing 000°T — inside the north quadrant, 315°–045°T.

255101020204644444343434344454442434345404040404038364041363737373939383724133343233373130323333383636193252925342723272932363534312726184166136118197243031373532292824144524187319724273234363328242211937751582229333433302629333429251241022273234343329221680953172252833353533312720110450609981962427313436363533312820322139986587115196253837363332312723221982323293321090807Ldg Lts 000° Oc 4sABCD1242Wk8701020304050607080901001101201301401501601701801902002102202302402502602702802903003103203303403500306090120150180210240270300330VAR 3°00'W (2025)(8'E)Fl(3)10s28m15MIso4s18m10MThe TeethE TeethQ(3)10sN TeethQS BrennanQ(6)+LFl15sHead LedgeW LedgeQ(9)15sOutfallFl Y 5sMew RkFl(2)5sKerran AppLFl10sNo 1Fl G 5sNo 3Fl(2) G 5sNo 2Fl R 5sNo 4Fl(2) R 5sSpireRadio Mast(R Lts)TowerBeacon HillKerran RoadsPORT KERRANISLE OF KERRANGull PointKerran HeadBrennan BankKerran BayISLE OF KERRANPRACTICE CHART · FICTIONAL AREANOT FOR NAVIGATIONDepths in metres below chart datumHeights in metres above MHWSMercator projection · Scale 1:50 000 (approx.)49°40'N49°40'N41'41'42'42'43'43'44'44'49°45'N49°45'N46'46'47'47'48'48'49'49'49°50'N49°50'N51'51'52'52'4°00'W4°00'W01'01'02'02'03'03'04'04'4°05'W4°05'W06'06'07'07'08'08'09'09'4°10'W4°10'W11'11'12'12'13'13'14'14'4°15'W4°15'W16'16'17'17'18'18'19'19'4°20'W4°20'W21'21'22'22'23'23'24'24'NESW
Tap the chart to plot a positionZoom with + / −, drag to pan

Dashed lines: the quadrant boundaries, drawn out from the danger. Green: the side of the mark it tells you to pass. Hatched red: the danger.

Put the yacht half a mile from the buoy — or tap the chart:

✓ North of North Teeth buoy: the side it tells you to pass.

The yacht is 1.2 M from The Teeth, bearing 000°T from them: in the north quadrant. As far as this mark is concerned you are in safe water — keep an eye on the chart for anything else.

On the practice chart, passing three cables outside any of these buoys on its named side keeps you at least 0.82 M from the danger it guards, in at least 11 m of charted water.

Using cardinal marks at sea

  • Identify it properly. By day, read the topmark first, then confirm with the colours. By night, count several groups and time the period before you trust your count. Then find the mark on the chart and check that the name, light and position all agree.
  • Know where north is. Cardinal marks refer to the points of the compass, not to the direction of buoyage, so check the compass when you decide which way to go round.
  • Give it a sensible berth. A buoy swings round its mooring and can drag or be moved, so it may not be exactly where the chart shows it. Pass comfortably on the named side and keep watching the depth.
  • Think beyond the mark. A cardinal guards one danger. The water on its named side is safe from that danger, not from everything, so check your whole route on the chart.

The next lesson completes the IALA system with the marks that are neither lateral nor cardinal: isolated danger, safe water and special marks, and the emergency wreck marking buoy.

Key terms

Cardinal mark
A mark placed in the north, east, south or west quadrant of a danger, named after it: pass on its named side.
Quadrant
One of four sectors round a danger, bounded by the true bearings NW–NE, NE–SE, SE–SW and SW–NW from it.
Topmark
The shape on top of a mark; for a cardinal, two black cones — the key feature by day.
Pillar buoy
A buoy with a tall central structure on a broad base.
Spar buoy
A buoy shaped like a tall pole.
Quick (Q)
A light flashing about once a second (written Q on the chart).
Very quick (VQ)
A light flashing about twice a second (written VQ).
Group
Flashes shown together and repeated, written in brackets: Q(3) is groups of three.
Period
The time for one whole cycle of a light, in seconds: one group and the dark after it.
Long flash (LFl)
A flash of at least two seconds; the south cardinal adds one after its six quick flashes.

Exercises

Check your understanding. You get a second try at each question, then the worked answer. Score 70% or more to complete the lesson — your progress is saved in this browser.

1
You see this buoy ahead. What is it?
2
A buoy is painted black above yellow, with a topmark of two black cones, both pointing up. Which side should you pass it?
3
Which of these lights would you expect on an east cardinal mark?
4
You see this white light at night. Watch it and count the flashes in a group (Restart begins a fresh group). What is it, and which side do you pass?
5
Why does a south cardinal’s light include a long flash?
6
A cardinal mark is charted on a true bearing of 280° from the danger it guards. Which mark is it, and where is the safe water?
7
To check which quadrant of The Teeth East Teeth buoy is in, measure the true bearing of the buoy FROM The Teeth: put A on The Teeth and B on the buoy.
255101020204644444343434344454442434345404040404038364041363737373939383724133343233373130323333383636193252925342723272932363534312726184166136118197243031373532292824144524187319724273234363328242211937751582229333433302629333429251241022273234343329221680953172252833353533312720110450609981962427313436363533312820322139986587115196253837363332312723221982323293321090807Ldg Lts 000° Oc 4sABCD1242Wk8701020304050607080901001101201301401501601701801902002102202302402502602702802903003103203303403500306090120150180210240270300330VAR 3°00'W (2025)(8'E)Fl(3)10s28m15MIso4s18m10MThe TeethE TeethQ(3)10sN TeethQS BrennanQ(6)+LFl15sHead LedgeW LedgeQ(9)15sOutfallFl Y 5sMew RkFl(2)5sKerran AppLFl10sNo 1Fl G 5sNo 3Fl(2) G 5sNo 2Fl R 5sNo 4Fl(2) R 5sSpireRadio Mast(R Lts)TowerBeacon HillKerran RoadsPORT KERRANISLE OF KERRANGull PointKerran HeadBrennan BankKerran BayISLE OF KERRANPRACTICE CHART · FICTIONAL AREANOT FOR NAVIGATIONDepths in metres below chart datumHeights in metres above MHWSMercator projection · Scale 1:50 000 (approx.)49°40'N49°40'N41'41'42'42'43'43'44'44'49°45'N49°45'N46'46'47'47'48'48'49'49'49°50'N49°50'N51'51'52'52'4°00'W4°00'W01'01'02'02'03'03'04'04'4°05'W4°05'W06'06'07'07'08'08'09'09'4°10'W4°10'W11'11'12'12'13'13'14'14'4°15'W4°15'W16'16'17'17'18'18'19'19'4°20'W4°20'W21'21'22'22'23'23'24'24'AB
Distance A→B: 0.45 MBearing A→B: 090°TDrag A and B, or Tab to them and use the arrow keysZoom with + / −, drag to pan
°T
8
South Brennan buoy (Q(6)+LFl15s) guards Brennan Bank. Tap a spot about half a mile from the buoy, on the side where the safe water is.
255101020204644444343434344454442434345404040404038364041363737373939383724133343233373130323333383636193252925342723272932363534312726184166136118197243031373532292824144524187319724273234363328242211937751582229333433302629333429251241022273234343329221680953172252833353533312720110450609981962427313436363533312820322139986587115196253837363332312723221982323293321090807Ldg Lts 000° Oc 4sABCD1242Wk8701020304050607080901001101201301401501601701801902002102202302402502602702802903003103203303403500306090120150180210240270300330VAR 3°00'W (2025)(8'E)Fl(3)10s28m15MIso4s18m10MThe TeethE TeethQ(3)10sN TeethQS BrennanQ(6)+LFl15sHead LedgeW LedgeQ(9)15sOutfallFl Y 5sMew RkFl(2)5sKerran AppLFl10sNo 1Fl G 5sNo 3Fl(2) G 5sNo 2Fl R 5sNo 4Fl(2) R 5sSpireRadio Mast(R Lts)TowerBeacon HillKerran RoadsPORT KERRANISLE OF KERRANGull PointKerran HeadBrennan BankKerran BayISLE OF KERRANPRACTICE CHART · FICTIONAL AREANOT FOR NAVIGATIONDepths in metres below chart datumHeights in metres above MHWSMercator projection · Scale 1:50 000 (approx.)49°40'N49°40'N41'41'42'42'43'43'44'44'49°45'N49°45'N46'46'47'47'48'48'49'49'49°50'N49°50'N51'51'52'52'4°00'W4°00'W01'01'02'02'03'03'04'04'4°05'W4°05'W06'06'07'07'08'08'09'09'4°10'W4°10'W11'11'12'12'13'13'14'14'4°15'W4°15'W16'16'17'17'18'18'19'19'4°20'W4°20'W21'21'22'22'23'23'24'24'
Tap the chart to plot a positionZoom with + / −, drag to pan
9
Heading south at night along the east side of the island, you see a white light ahead flashing quick without a break. The chart shows it is North Teeth buoy. What do you do?
10
An east cardinal shows VQ(3)5s: groups of three very quick flashes, repeated every 5 seconds. How many flashes does it show in one minute?
flashes

0 of 10 answered · 0 correct

Cardinal marks practice

Five fresh questions each time: name a mark by day or night, describe one, choose the side to pass, a quadrant bearing, and the practice chart’s cardinals.