Running at night
Fog & night · Power & sail
At night you navigate largely by the lights other vessels show. Learn the common light patterns from Rules 20 to 31, keep your own lights right, and protect your night vision: it takes many minutes to build and is lost in a moment.
Safety first
- Distance and speed are much harder to judge at night. A light whose bearing isn't changing may be on a collision course (Rule 7).
- Unlit hazards such as logs, crab-pot floats, kayaks and small boats without lights are nearly invisible at night. Slow down where they are common.
- Shore lights behind a vessel can hide its navigation lights; Rule 6 lists background light as a factor in choosing a safe speed.
Reading other vessels' lights
- Sidelights: green to starboard, red to port, each shining from dead ahead to 22.5 degrees abaft the beam. See both and the vessel is heading at you; see only its red and you are looking at its port side.
- Masthead light: white, shining forward over 225 degrees. A power-driven vessel 50 m or longer shows two, the aft one higher, which also shows its heading. A vessel under sail alone shows no masthead light.
- Sternlight: white, shining aft over 135 degrees. A single white light may be a sternlight you are overtaking, a small boat's all-round light or an anchored vessel.
- Two or three masthead lights in a vertical line and a yellow light above the sternlight mean a vessel towing astern. The tow can be more than 200 m behind, so find it before crossing astern of the tug.
- Vertical all-round lights: red over red, not under command; red-white-red, restricted in ability to maneuver; green over white, trawling; red over white, other fishing; white over red, pilot; three reds, constrained by draft (International rules only).
- At anchor: an all-round white light forward and a lower one aft; a vessel under 50 m may show just one. Aground: the anchor lights plus two all-round reds in a vertical line.
Your own lights
- Power-driven vessel underway (Rule 23): masthead light, sidelights and sternlight. Under 12 m you may instead show an all-round white light plus sidelights.
- Sailing vessel under sail (Rule 25): sidelights and sternlight, which under 20 m may be combined in one lantern at the masthead. With the engine running you are a power-driven vessel under the Rules, so show power-driven lights.
- Rule 22 sets minimum ranges. For boats 12 m to under 20 m: masthead light 3 nm, sidelights and sternlight 2 nm. Under 12 m: masthead 2 nm, sidelights 1 nm, sternlight 2 nm. Check bulbs, lenses and connections before a night run.
- From sunset to sunrise show no other lights that could be mistaken for navigation lights or that spoil the lookout (Rule 20). Bright deck and cockpit lights do both.
Keeping your night vision
- Dark adaptation takes time. A study of ships' lookouts found eyes adapt to dim bridge lighting in about 15 minutes, while adapting to full darkness can take up to 40. A moment of bright light undoes much of it.
- Keep helm and chart lighting as dim as it can be. Red or red-filtered light is the traditional choice and the one international bridge guidance calls for, but any bright light, even red, still costs night vision.
- Turn screens down to their lowest usable brightness and keep phones and flashlights away from the helm.
- The cells that work in dim light sit outside the center of the eye, so a faint light can be easier to pick out a little to one side of where you are looking.
Sources (3)
General guidance for recreational boaters, researched from the sources listed and written in our own words. Your equipment manuals, local knowledge, the Navigation Rules and a qualified instructor come first.