Channel Markers and the Light List

Aids to Navigation and COLREGS

Channel markers, buoys, and lighthouses are not defined within COLREGS itself — they are physical infrastructure managed by national authorities (NOAA and USCG in the US, Trinity House in the UK, etc.). COLREGS provides the behavioral rules for vessels; the aids to navigation (AtoN) system provides the landmarks and route markers those vessels use. The two systems work together: COLREGS tells you who yields in a crossing; the AtoN system tells you where the channel is and whether it's safe to cross there at all.

The IALA Maritime Buoyage System governs how buoys, beacons, and marks are colored, shaped, and lit worldwide. The world is divided into two regions: Region A (Europe, Africa, Asia, Australia) and Region B (the Americas, Japan, Philippines, Korea). The critical difference: in Region B (where the US operates), red marks are kept on the right side when returning from sea — the 'red right returning' rule. In Region A, the colors are reversed.

Buoy systems and COLREGS interact at Rule 9 (Narrow Channels): vessels must keep to the starboard side of a narrow channel. The channel markers define where the channel is; Rule 9 defines how to navigate it. A vessel ignoring channel markers and cutting across a buoyed channel creates a COLREGS violation, not merely an aid-to-navigation violation.

The page on Buoys, Markers, and IALA in the Coastal Navigation section covers buoy types, colors, and lateral marks in full detail. This page focuses on the light characteristics that AtoN carry, and how to use the Light List to identify and plan around them.

Light Characteristics

Every light-equipped aid to navigation has a specific light characteristic — a distinctive pattern of flashing or occultation that allows mariners to identify it even when surrounded by other lights. The characteristic is described using a standard notation that appears on charts and in the Light List.

Fixed (F): a continuous, steady light with no interruption. Rare in modern AtoN because it's difficult to distinguish from background lighting, but used for some harbor entrance lights.

Flashing (Fl): a single flash at regular intervals, with the period of darkness longer than the period of light. The most common characteristic. 'Fl 4s' means one flash every 4 seconds. 'Fl(3) 10s' means a group of 3 flashes followed by darkness, repeating every 10 seconds.

Quick (Q): continuous flashing at 50–60 flashes per minute. Used for isolated danger marks and some channel marks. 'Q' alone means continuous quick flashing; 'Q(3)' means groups of 3 quick flashes.

Isophase (Iso): equal periods of light and dark. 'Iso 4s' means 2 seconds on, 2 seconds off. Easy to identify by its perfectly equal rhythm.

Occulting (Oc): a light that is on longer than it is off — the opposite of flashing. 'Oc 4s' means the light shows for 3 seconds and is dark for 1 second. 'Oc(2)' means a group of 2 brief dark periods in an otherwise lit cycle.

Morse Code (Mo): the light flashes a Morse code letter. 'Mo(A)' flashes dot-dash (A in Morse). Used for special marks and mid-channel fairway buoys (which use 'Mo(A)' — white, Morse A).

Color modifiers: lights are white by default. 'Fl R 4s' is a red flashing light every 4 seconds; 'Fl G 4s' is green. Red and green lights typically mark the sides of channels (consistent with buoy colors).

The period is the total length of one complete cycle, including all flashes and all dark periods. 'Fl(3) 10s' has a 10-second period. 'Fl 4s' has a 4-second period. Knowing the period allows you to time a light with a watch and confirm its identity.

Reading the Light List

The USCG Light List is a series of publications (7 volumes covering US and territorial waters) that describes every official aid to navigation — its exact position, light characteristic, structure description, height, nominal range, sound signal (if any), and remarks. It is the definitive identification reference for AtoN.

Why the Light List matters: charts show the characteristic of a light ('Fl R 6s') and approximate position, but the Light List contains details the chart cannot: the exact geographic coordinates, the height of the light above water, the nominal range (how far the light can be seen in clear weather at night), whether the light has a sector (showing red in one arc, white in another), and any operational notes ('PRIVATE', 'MAINTAINED BY...', etc.).

A Light List entry contains:

— Light number: a unique number for each aid in that volume

— Name: the official name of the light or buoy

— Position: latitude and longitude to the nearest second

— Characteristic: the light pattern (e.g., Fl(2) R 5s) — same as charted

— Height: height of the light above mean high water, in feet. Higher lights are visible from further away.

— Range: nominal range in nautical miles — the distance at which the light can be seen in clear weather. This is a function of the light's intensity, not its height.

— Structure: description of the physical mark (red nun buoy, green can buoy, white cylindrical tower with red band, etc.)

— Remarks: sound signal details, operational restrictions, sector information

Using the Light List for passage planning: before a nighttime passage, identify all lights you expect to see along the route, look up their characteristics and ranges in the Light List, and note the sequence in which they should appear. This creates a mental or written schedule of what you should see and when — a deviation from that schedule indicates a possible navigation error.