Chapter 5: Short Range Aids to Navigation
Buoys, beacons and lighthouses mark channels and dangers. IALA harmonised them into two regions whose lateral colours are reversed.
IALA Regions A and B
In IALA Region B (the Americas, Japan, Korea, the Philippines) the rule is 'red right returning': red conical/nun marks are left to starboard when entering from seaward, green cylindrical/can marks to port. In Region A (most of the rest of the world) the colours are reversed — red to port entering. Shape, topmark and light rhythm supplement colour, which is what you rely on at night or in poor visibility.
Cardinal, isolated danger, safe water and special marks
Cardinal marks use black and yellow bands with double-cone topmarks to indicate the quadrant of safe water: North (cones up, Q), East (base to base, VQ(3)), South (cones down, VQ(6)+LFl), West (point to point, VQ(9)). Isolated danger marks are black with red bands, two black spheres, Fl(2). Safe-water marks are red and white vertical stripes with a red sphere, showing Mo(A), LFl, or isophase. Special marks are yellow with an X topmark and are not navigational.
- 3, 6, 9 o'clock rhythm memory aid for East, South, West cardinals
- South cardinal adds a long flash to distinguish it from West
- Preferred channel marks use red/green horizontal bands with the top colour showing the preferred side
Lights and sectors
A lighthouse's nominal range assumes 10 nautical miles meteorological visibility; the geographic range depends on the heights of light and observer. Sector lights show red over dangers and white over safe water; the bearings of sector boundaries are always given as seen from seaward. Loom, and the moment of 'raising' or 'dipping' a light, can give a distance line of position.
Formula cards
Geographic range
D (NM) = 1.17 √h_light(ft) + 1.17 √h_eye(ft)
Use 2.07 √h(m) for metres. Compare with nominal range and take the lesser.
Key takeaways
- • Region B: red right returning. Region A is the opposite — verify the region in passage planning.
- • Shape and topmark carry the message when colour is not visible.
- • Sector-light bearings are quoted from seaward toward the light.
Knowledge check
Immediate feedback with rationales. Answer each question to see the explanation.
Chapter 5 quiz
0 of 3 answered
1.Entering a US harbour from seaward, a green can buoy should be left:
2.A light showing VQ(9) every 10 s with black bands top and bottom over yellow indicates:
3.Nominal range of a light assumes: