Navigation lights: identify boats and vessels at night

Red, green and white tell you about aspect

Under Rule 21, the port sidelight is red and the starboard sidelight is green. Each covers 112.5°, from ahead to 22.5° abaft its respective beam. A white masthead light covers 225° across the forward sectors; the white sternlight covers 135° aft. An all-round light has a 360° horizontal sector.

A masthead light is defined by its placement and sector, not simply by being at the very top of a mast. Look at the complete arrangement. A single white light can have several explanations, including a sternlight, an anchor light or a permitted small-vessel display. Its colour alone cannot establish the vessel’s status or heading.

Recognise a power-driven vessel underway

The general Rule 23 display includes a forward masthead light, sidelights and a sternlight. A second masthead light is aft and higher: it is required at 50 m and above and may also be carried by a shorter vessel. Smaller vessels have alternative permitted displays, so do not infer an exact length from one glimpse.

Seeing both sidelights with the appropriate masthead aspect can help identify a vessel ahead or nearly ahead. Seeing a green sidelight shows her starboard aspect. Combine that observation with relative movement and risk of collision before classifying the encounter. The large-vessel exercise asks you to read the relationship between the white lights and the visible sidelight.

Learn the vertical combinations in context

Two all-round red lights identify a vessel not under command. All-round red–white–red indicates restricted ability to manoeuvre arising from the nature of her work. A trawling vessel shows all-round green over white; a vessel engaged in fishing other than trawling shows red over white. A pilot vessel on pilotage duty shows white over red.

These are identifying elements of a display, not an exhaustive description of every light carried. A vessel making way may show sidelights and a sternlight in addition, depending on the applicable rule. Fishing gear, underwater operations and towing can require further signals. Read Rules 24–29 when revising those operations.

• Describe the colours from top to bottom.
• Distinguish all-round status lights from directional navigation lights.
• Check for additional lights before deciding what the whole display means.

Separate anchored, underway and making way

Underway means neither anchored, made fast to shore nor aground. A vessel can be underway while stopped and making no way through the water. Anchored vessels generally show the Rule 30 white all-round anchor display; for vessels 50 m and above the aft anchor light is lower than the forward one. The rule contains size and location exceptions.

The anchored-vessel exercise is useful because two white lights can initially resemble a power-driven display. Consider their arrangement and the absence or presence of other evidence. Do not assume every unchanging white light belongs to shore, or every stopped vessel is at anchor.

Practise the observation before the answer

Inspect the scene from the bridge, use the binoculars where available and say which lights you can actually see. Identify the display, then explain what further information you need to choose an action. Revisit the same scene from the chart view to connect your interpretation with the vessel’s orientation.

Rule 20 requires lights from sunset to sunrise, and prescribed lights, if carried, must also be shown during daylight in restricted visibility. Night identification therefore belongs with lookout and fog revision. Before a passage, confirm your own boat’s required display and use the regulations and equipment instructions for installation details.