Instructor & student module

Aids to Navigation & Buoyage

Buoyage is one of only three IYT modules graded to "Complete" depth — you must read a mark instantly, by day or night, in either hemisphere. This covers the full IYT Module 21 syllabus: what IALA is, the lateral system and the Region A vs B difference, cardinal marks, and the marks common to both regions — with interactive buoys you can toggle and light up.

What is IALARegion A & BLateral marks Cardinal marksIsolated dangerSafe water Special marksEmergency wreckLight characters

Why it's "Complete": a misread buoy puts the boat on the rocks. The cost of error is grounding — so IYT wants zero hesitation. Venue note: both Lake Ontario and the Bahamas are Region B, so Region A is a classroom item — learn it cold here.

Lesson 1

What is IALA?

IALA is the International Association of Lighthouse Authorities (today: the International Association of Marine Aids to Navigation and Lighthouse Authorities). It's the body that sets and controls the international buoyage system so that a buoy means the same thing the world over.

IALA defines the Maritime Buoyage System, which uses six kinds of mark — each with a distinctive colour, shape and (often) a light:

Lateral — mark the edges of a channel

Cardinal — show the safe side to pass a danger (N/E/S/W)

Isolated danger — sit on a hazard with safe water around it

Safe water — mark mid-channel / safe water all round

Special — mark an administrative area, not primarily for navigation

Emergency wreck — temporarily mark a new wreck (since 2006)

The catch IALA couldn't fix: the lateral system is not standardised worldwide — it runs opposite in the two regions. So step one on any chart is: which region am I in?
• Region A — Europe and most of the world.
• Region B — the Americas (North & South), the Caribbean, Japan, Korea, the Philippines. (Your waters — Lake Ontario & the Bahamas — are both B.)

Lesson 2 · Interactive

Lateral Marks — Region A vs Region B

Lateral marks edge a channel. You read them when returning from seaward (entering a harbour). The shapes never change between regions — a can (flat-top cylinder) is always the port-hand mark, a cone is always the starboard-hand mark. Only the colours flip. Toggle the region and watch:

Region A
Port = RED can, red light · Starboard = GREEN cone, green light. Returning from sea, keep red to port (left).

Region B
Port = GREEN can, green light · Starboard = RED cone, red light. "Red, Right, Returning" — keep red to starboard (right) coming in.

Memory: shape tells you the side (can = port, cone = starboard) in both regions; colour tells you the region. In the Americas, just chant "red right returning." Don't try to pass between a lateral mark and the shore behind it without local knowledge.

Lesson 3 · Interactive

Cardinal Marks

Cardinal marks point to the safe side of a danger using compass directions — a North cardinal means "pass to the north of me; safe/deep water is north." They're yellow and black with two black cone topmarks, and show a white flashing light. Pick a mark:

Mark

North Cardinal

Topmark:

Colour:

Light (white):

Pass:

Live light

The trick that makes it click — the topmark cones point to the black.
• North cones point up → black band on top (black over yellow).
• South cones point down → black on the bottom (yellow over black).
• West cones point in (wine-glass "Waist") → black in the middle.
• East cones point out (egg shape) → black top & bottom.
Lights = a clock face: E = 3, S = 6 (+ a long flash so you don't miscount), W = 9, N = continuous. Pass on the named side; the danger is on the opposite side.

Lesson 4

Isolated Danger Mark

Stationed on or over an isolated danger (a small shoal, rock or wreck) that has navigable water all around it. Pass it on any side — just don't hit it.

Colour: black with one or more broad red horizontal bands.
Topmark: two black spheres, one above the other.
Light: white, Group Flashing (2) — two flashes every ~5 s. (Two balls = two flashes — easy memory.)

Lesson 5

Safe Water Mark

Indicates safe, navigable water all around — a mid-channel, fairway or landfall mark, often the first buoy you meet approaching from seaward. Also called a fairway buoy.

Colour: red and white vertical stripes (vertical — other striped marks are horizontal).
Topmark: a single red sphere.
Light: white — isophase, occulting, one long flash every 10 s (L Fl 10s), or Morse "A" (· —).

Lesson 6

Special Marks

Not primarily for navigation — they flag an administrative or special feature: spoil grounds, pipelines, traffic-separation schemes, jetties, naval exercise areas, speed-limit / water-ski / mooring areas, outfalls.

Colour: yellow.
Topmark: a yellow X (St Andrew's cross).
Light: yellow, one flash every 5 s.

Lesson 7

Emergency Wreck Marking Buoy

Introduced in 2006 (IALA Recommendation O-133) to temporarily mark a new wreck until it's surveyed and permanent marks are set — it replaced the old practice of ringing a new wreck with cardinal/lateral buoys. Keep clear.

Colour: equal blue and yellow vertical stripes.
Topmark: an upright yellow cross (+).
Light: alternating blue and yellow (Al.Bu.Y), 1 s each. Often several are deployed and synchronised around the wreck.

Lesson 8

Light Characters & Flash Sequences

At night you identify a mark by its light character — colour, rhythm and period. The chart abbreviations you must read:

Mark	Colour	Character (typical)	Abbrev.
Port lateral	Red (A) / Green (B)	Any rhythm, can be Fl	Fl R / Fl G
Starboard lateral	Green (A) / Red (B)	Any rhythm	Fl G / Fl R
North cardinal	White	Continuous quick/very-quick	Q · VQ
East cardinal	White	Group of 3	Q(3) · VQ(3)
South cardinal	White	Group of 6 + 1 long flash	Q(6)+LFl · VQ(6)+LFl
West cardinal	White	Group of 9	Q(9) · VQ(9)
Isolated danger	White	Group of 2	Fl(2)
Safe water	White	Isophase / Occ / 1 long / Morse A	Iso · Oc · LFl10s · Mo(A)
Special	Yellow	Single flash	Fl Y 5s
Emergency wreck	Blue + Yellow	Alternating	Al.Bu.Y

Fl — flashing: light shorter than dark

Q / VQ — quick / very quick flashing

Iso — isophase: equal light & dark

Oc — occulting: light longer than dark

L Fl — long flash (≥2 s)

Mo(A) — Morse "A" (· —)

( ) — number in a group, e.g. Fl(2)

10s — the period of the full cycle

Worked read: "VQ(9) W" = a white very-quick light flashing in groups of nine → a West cardinal → pass to the west of it.

Knowledge Check

Aids to Navigation — Knowledge Check

10 questions at IYT exam standard (75% to pass), drawn from the IYT Module 21 knowledge review.