# IALA Buoyage System — Complete Rules Reference

Source: IALA/AISM Publication R1001 (5th edition, 2010); IHO S-57 Object Catalogue; INT-1

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## Region Overview

| Region | Coverage |
|--------|----------|
| A | Europe, Africa, Asia (including Middle East, India, SE Asia, China, Australia, New Zealand) |
| B | Americas (North, Central, South), Philippines, Japan, South Korea |

The only practical difference between Region A and B is the **lateral mark colour convention** (red/green sides are swapped). All other marks (cardinal, isolated danger, safe water, special) are identical.

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## 1. Lateral Marks

### Lateral marks — Region A

| Mark | Colour | Shape | Topmark | Light rhythm | Light colour |
|------|--------|-------|---------|-------------|--------------|
| Port hand (pass on port side) | Red | Can / Cylinder | Red can (if any) | Any (Fl R common) | Red |
| Starboard hand (pass on stbd) | Green | Conical | Green cone point up (if any) | Any (Fl G common) | Green |
| Preferred channel — port hand (modified port) | Red with green band(s) | Can | Red can | Fl(2+1) R | Red |
| Preferred channel — stbd hand (modified stbd) | Green with red band(s) | Conical | Green cone point up | Fl(2+1) G | Green |

### Lateral marks — Region B

| Mark | Colour | Shape | Topmark | Light rhythm | Light colour |
|------|--------|-------|---------|-------------|--------------|
| Port hand | Green | Can / Cylinder | Green can (if any) | Any (Fl G common) | Green |
| Starboard hand | Red | Conical | Red cone point up (if any) | Any (Fl R common) | Red |
| Preferred channel — port hand | Green with red band(s) | Can | Green can | Fl(2+1) G | Green |
| Preferred channel — stbd hand | Red with green band(s) | Conical | Red cone up | Fl(2+1) R | Red |

> S-57 CATLAM attribute: 1=port, 2=starboard, 3=preferred_channel_to_stbd (vessel keeps to starboard = mark acts as port), 4=preferred_channel_to_port

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## 2. Cardinal Marks (same in both regions)

Direction refers to where the mark is placed relative to the danger (e.g., a North cardinal is placed NORTH of the danger — pass to the north).

| Mark  | Topmark              | Colours (top→bottom)  | Light rhythm               | Light colour |
|-------|----------------------|-----------------------|----------------------------|--------------|
| North | 2 cones point UP     | Black over Yellow     | Q (60/min) or VQ (100/min) | White |
| East  | 2 cones base-to-base | Black/Yellow/Black    | Q(3) 10s or VQ(3) 5s       | White |
| South | 2 cones point DOWN   | Yellow over Black     | Q(6)+LFl 15s or VQ(6)+LFl 10s | White |
| West  | 2 cones point-to-point | Yellow/Black/Yellow | Q(9) 15s or VQ(9) 10s     | White |

Memory aid for topmarks: cones point TOWARD the black portion.
- North = both black (top), cones point up
- South = both black (bottom), cones point down
- East = black both top and bottom, cones point apart (base together)
- West = black in middle, cones point together

> S-57 CATCAM: 1=North, 2=East, 3=South, 4=West

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## 3. Isolated Danger Mark

Placed ON or OVER an isolated danger of limited extent with navigable water all around.

| Attribute | Value |
|-----------|-------|
| Colour | Black with one or more broad horizontal RED bands |
| Shape | Pillar or spar |
| Topmark | 2 black spheres (vertically in line) |
| Light | Fl(2) White |
| Light period | 5s typical |

> S-57 layers: BOYISD (buoy), BCNISD (beacon)

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## 4. Safe Water Mark

Indicates safe navigable water all around — used for mid-channel, landfall, or fairway axis marks.

| Attribute | Value |
|-----------|-------|
| Colour | Red and white vertical stripes |
| Shape | Spherical (preferred), pillar, or spar |
| Topmark | Single red sphere |
| Light | Iso W, Oc W, LFl W 10s, or Mo(A) W — any white rhythm not used for other marks |

> S-57 layer: BOYSAW

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## 5. Special Purpose Mark

Not primarily intended to aid navigation — marks a special feature or area.

| Attribute | Value |
|-----------|-------|
| Colour | Yellow |
| Shape | Any (optional X topmark) |
| Topmark | Single yellow X (optional) |
| Light | Yellow, any rhythm not already used by other marks in the area |

Uses: traffic separation schemes, spoil grounds, military exercise areas, cables/pipelines, ODAS buoys, recreation areas, ferry crossings.

> S-57 layer: BOYSPP

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## 6. Emergency Wreck Marking Buoy (EWMB)

Introduced by IALA 2006, for newly discovered dangerous wrecks before standard survey/marking.

| Attribute | Value |
|-----------|-------|
| Colour | Blue and yellow vertical stripes (alternating) |
| Shape | Pillar or spar |
| Topmark | Single upright yellow cross |
| Light | Al.Bu.Y 3s (alternating blue / yellow) |
| AIS | AIS AtoN transmitter active if fitted |
| RACON | Morse "D" (— . .) if fitted |

Deployed in pairs when possible, one on each side of the wreck. Removed once proper marks or formal notices are in place.

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## 7. New Dangers (S-57 / ECDIS)

A newly discovered hazard (shoal, wreck, obstruction) not yet charted or inadequately charted is marked by:
- One or more cardinal or lateral marks as appropriate
- Identical mark may be doubled for emphasis
- ECDIS may show a "New Danger" highlight

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## 8. Fairway and Mid-Channel Buoys

On wide rivers, lakes, and channels a single line of buoys may be laid along the fairway centreline — these are safe water marks (red/white) or may be lateral depending on the traffic pattern.

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## 9. Light Phase Descriptions — Standard S-52 / INT-1 rhythms used on IALA marks

| Rhythm | Typical period |
|--------|---------------|
| Q      | 1s (60/min) |
| VQ     | 0.5s (100–120/min) |
| Fl     | 3s–10s depending on group count |
| Oc     | Equal or longer eclipse; period 4s–12s |
| Iso    | Equal on/off; period 2s–8s |
| LFl    | Flash ≥ 2s; period 10s typical |
| Mo(A)  | Morse A (. —); period 6s |

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## 10. S-57 Layer to IALA Mark Type Mapping

| S-57 Layer | Mark type    | AidsMonitoring classify() result |
|------------|-------------|----------------------------------|
| BOYLAT / BCNLAT | Lateral buoy / beacon | LATERAL_PORT, LATERAL_STBD, LATERAL_PREF_PORT, LATERAL_PREF_STBD |
| BOYCAR / BCNCAR | Cardinal buoy / beacon | CARDINAL_N/E/S/W |
| BOYISD / BCNISD | Isolated danger | ISOLATED_DANGER |
| BOYSAW | Safe water buoy | SAFE_WATER |
| BOYSPP | Special purpose buoy | SPECIAL |
| LIGHTS | Light (point) | LIGHT_POINT |
| LNDMRK | Landmark | LANDMARK |
| RTPBCN | Racon | RACON |
