Question 1

You're entering harbour from seaward and pass a red, can-shaped buoy. Which side should you leave it on?

Accepted Answer

Port (leave it on your left). In IALA Region A, red can-shaped buoys mark the port-hand side of the channel when returning from seaward: leave them to port (on your left).

Question 2

A green, cone-shaped buoy with its point upward marks the opposite side of the same channel. Which side is that?

Accepted Answer

Starboard (leave it on your right) when entering from seaward. Green conical buoys mark the starboard-hand side of the channel on the way in: leave them to starboard (on your right).

Question 3

A black-and-yellow buoy has two black cones on top, both pointing straight up, like an arrow. Which cardinal mark is this, and where's the safe water?

Accepted Answer

North cardinal: safe water is to the north, pass north of it. Both topmark cones pointing up ('pointing to the sky') is the North cardinal's signature: safe water lies north of the mark. Mnemonic: the cones point the way to the safe side.

Question 4

This time both black topmark cones point straight down, and the buoy is yellow over black. What mark is it?

Accepted Answer

South cardinal: pass south of it to stay in safe water. Cones pointing down together is the South cardinal: safe water is south of the mark, so you pass it keeping it to your north.

Question 5

The topmark cones point away from each other (base to base, like a bowtie lying on its side). What does this East cardinal mark tell you?

Accepted Answer

Safe water is to the east: pass on the east side of the mark. East cardinal topmarks point outward (base to base). Safe water is to the east, so pass east of the mark to avoid whatever hazard it's guarding.

Question 6

A black buoy carries two black spheres, one above the other, over a black-red-black banded body. What does it mark?

Accepted Answer

An isolated danger: a discrete hazard with navigable water all around it. Two black spheres stacked vertically, on black-red-black bands, mark an isolated danger: a specific rock, wreck or shoal with safe water surrounding it. Don't cut it close; there's no 'safe side' the way there is with a cardinal.

Question 7

You see red-and-white vertical stripes with a single red sphere on top. What is this mark used for?

Accepted Answer

Marking a fairway centreline or landfall: you can pass close on either side. Red-and-white vertical stripes with a spherical topmark is a safe water mark: used for landfalls and mid-channel approaches. There's navigable water all around it, so pass close on either side.

Question 8

A plain yellow buoy with a yellow X topmark shows up on the chart near a swimming area. What kind of mark is this?

Accepted Answer

A special mark: it flags a feature (cable, race area, spoil ground) rather than a navigational danger. Yellow buoys with an X (or no topmark at all) are special marks. They highlight a feature the chart calls out (anchorage limits, cables, race courses) and don't by themselves indicate which side is safe.

Question 9

A black-and-yellow mark has topmark cones pointing toward each other (like a bowtie lying on its side) over yellow-black-yellow bands. Which cardinal mark is this?

Accepted Answer

West cardinal: safe water is to the west, so pass on the west side of the mark. Cones pointing toward each other (point to point) on yellow-black-yellow bands is the West cardinal's signature: safe water lies west of the mark.

Question 10

Cardinal marks all flash white, but a clock-face mnemonic ties the pattern to direction. Which is correct?

Accepted Answer

East flashes 3 times (3 o'clock), South flashes 6 times plus one long flash (6 o'clock), West flashes 9 times (9 o'clock); North flashes continuously. The clock-face mnemonic: East/South/West flash a count matching their position on a clock (3, 6, 9), with South adding one long flash to avoid confusion with a plain count. North, needing no numeral, flashes continuously instead.

Question 11

On the way in, you left a red can buoy to port, following the conventional direction of buoyage. Heading back out to sea past that same buoy, which side do you leave it on?

Accepted Answer

Starboard: the conventional direction reverses, so the side you keep each lateral mark on flips too. Lateral marks are defined relative to the conventional direction of buoyage, typically the way in from seaward. Reverse your direction of travel and the side you keep each mark on reverses too.

Question 12

A safe water mark's light is described using rhythms like isophase, occulting, one long flash every 10s, or Morse "A", all in white. What's the point of these specific rhythms?

Accepted Answer

They're rhythms reserved for safe water marks, letting you identify the mark type at night from the light alone, when shape and colour aren't visible. At night, shape and colour disappear: the light rhythm is often the only way to identify a mark's type. Safe water marks use a distinct set of white rhythms, separate from the quick-flash cardinal patterns or simple lateral rhythms.

Question 13

There's technically navigable water "all around" an isolated danger mark, yet you shouldn't cut close past one. Why not?

Accepted Answer

The mark sits directly on or very near the actual hazard (rock, wreck): the safety margin around it is meant to be generous, not tight. An isolated danger mark is placed on or very close to a specific hazard. "Navigable water all around" means you can pass on any side, not that you should hug the buoy: give it real room.

Question 14

You spot a plain yellow buoy marking the edge of a swimming area, with no other navigational significance. What kind of mark is it?

Accepted Answer

A special mark: used for many non-hazard purposes, so always check the chart to see exactly what it's flagging. Special marks cover a wide range of non-navigational-danger features: swim zones, cables, race courses, spoil grounds. The chart, not the buoy alone, tells you what it's actually calling out.

Question 15

Chartering somewhere outside Europe, the Med or Asia (the Caribbean or the US, say) puts you in IALA Region B instead of Region A. What actually changes?

Accepted Answer

Lateral mark colours swap (red marks the starboard side and green the port side heading in) while cardinal, isolated danger, safe water and special marks stay the same. Region A and B differ only in lateral mark colours (swapped). Cardinal, isolated danger, safe water and special marks are the same system worldwide. It's worth confirming which region you're chartering in before relying on colour alone.

Question 16

Both North and South cardinal marks show a white light. How do you tell them apart at night, when the topmark isn't visible?

Accepted Answer

North flashes continuously (very quick or quick, uninterrupted); South flashes a fixed count of 6 plus one long flash, then repeats. At night the flash rhythm carries the information the topmark would give you by day: North's continuous flashing versus South's distinctive 6-flashes-plus-long-flash pattern make them unmistakable even without seeing the shape.

Mark	Topmark	Bands	Safe water is
North	Both cones up	Black over yellow	North of the mark
East	Cones point away (base to base)	Black-yellow-black	East of the mark
South	Both cones down	Yellow over black	South of the mark
West	Cones point together (point to point)	Yellow-black-yellow	West of the mark

IALA Buoys and Marks: Reading the Channel

Lateral marks: which side of the channel

Cardinal marks: which quadrant is safe

Isolated danger and safe water marks

Special marks

IALA Buoys and Marks: Reading the Channel quiz