Lights at night

Masthead, side, stern, towing and all-round lights: what a pattern of lights on the dark water is telling you.

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At night a vessel is a pattern of lights. Learn what each light covers and you can tell what she is, which way she is heading and what she is doing, long before you can see her hull. Everything below is from the U.S. Inland Navigation Rules (33 CFR Part 83), which apply on U.S. inland waters, including the Great Lakes; the International Rules (COLREGS) are very close on lights.

The four basic lights

Masthead light: white, over the centre line, shining from right ahead to 22.5° abaft the beam on each side (225° in all). Power-driven vessels carry it; a second one, aft and higher, is required at 50 m and over.
Sidelights: green on the starboard (right) side, red on the port (left) side, each covering 112.5° from right ahead. Under 20 m they may be combined in one lantern.
Sternlight: white, at the stern, covering 135° astern.
All-round light: 360°. Used alone or stacked in vertical lines to say what a vessel is doing.

Night picture, top to bottom: white light, green light, red light.

Both sidelights and a masthead light: a power-driven vessel heading straight at you. Her green light is on your left.

Reading direction

If you see both red and green, she is pointed at you. Red only: you are looking at her port side. Green only: her starboard side. A single white light with no colour may be a sternlight (you are behind her) or an anchor light. With two masthead lights, the lower one is forward, so the line from low to high shows her heading.

Stacked all-round lights say what she is doing

Red over red: not under command.
Red, white, red: restricted in her ability to maneuver (dredging, cable laying, underwater work).
Green over white: trawling. Red over white: fishing other than trawling.
White over red: a pilot vessel on duty.
Yellow over white at the stern: towing astern. Two yellow lights: pushing ahead or towing alongside (Inland Rules).

Night picture, top to bottom: white light (left), white light (right).

Two all-round white lights, the forward one higher: a vessel at anchor (required at 50 m and over; a smaller vessel may show them too).

At anchor and aground

An anchored vessel shows an all-round white light forward and a lower one aft; under 50 m a single all-round white light is enough. Aground, she adds two all-round red lights in a vertical line.