Navigation lights and day shapes

Lights and shapes tell you what she is

In Lesson 20 you met the steering and sailing rules, which decide who keeps out of whose way. They only work if you know what the other vessel is — a ship, a yacht, a trawler with her nets out — and which way she is heading. At night all you can see are her lights. By day, vessels in special situations also hoist black shapes. Part C of the collision regulations (Rules 20–31) sets out exactly which lights and shapes each kind of vessel shows, and Annex I gives the technical details.

When? Rule 20 says lights are shown from sunset to sunrise, and also by day in restricted visibility (they may be shown at other times whenever it seems necessary). Between sunset and sunrise no other lights may be shown that could be mistaken for them, make them harder to see or spoil the lookout — so keep deck and cabin lights under control. Shapes are shown by day.

Two terms matter here. Rule 3 defines under way: not at anchor, made fast to the shore or aground — even if she is drifting with her engine stopped. The rules also distinguish a vessel making way: actually moving through the water. Several vessels show sidelights and a sternlight only when making way, which tells you a lot.

The building blocks (Rule 21)

Every navigation light is defined by its colour and the arc of the horizon it shines over. The arcs are measured from the vessel’s own bow, so they turn with her.

The masthead light and the sidelights cover the same 225° forward; the sternlight covers the 135° astern. From any direction you see either her forward lights or her sternlight — never both, except in a narrow band at the boundary.

Rule 22 sets how far the lights must be visible on a dark, clear night. A vessel of 50 m or more needs a masthead light visible at 6 M and sidelights at 3 M. A boat under 12 m needs a masthead light of only 2 M and sidelights of just 1 M.

Which way is she heading?

Because each light shows only over its own arc, the lights you can see tell you where you are relative to her — and so which way she is heading:

• Both sidelights (on a power-driven vessel, with her masthead light above them): you are right ahead of her, and she is heading straight for you.
• Green only: you are looking at her starboard side, so her bow points to your right.
• Red only: you are looking at her port side, so her bow points to your left.
• Sternlight only: you are more than 22.5° abaft her beam and she is heading away. If you are catching her up, you are the overtaking vessel and must keep out of her way (Rule 13).

A vessel of 50 m or more carries two masthead lights, the after one higher. They work like a transit: when they are in line she is heading straight at you, and as she turns they open out, with the lower, forward light pointing the way she is heading. Watch them: they show an alteration of course sooner than her sidelights do. The head-on rule (Rule 14) uses exactly these clues — masthead lights in line or nearly in line, and/or both sidelights.

Power-driven vessels (Rule 23)

A power-driven vessel under way shows a masthead light forward, sidelights and a sternlight. A vessel of 50 m or more must also show a second masthead light, abaft of and higher than the forward one; a smaller vessel may.

Small craft have simpler options. A power-driven vessel under 12 m may show an all-round white light and sidelights instead of a masthead light and sternlight. One under 7 m whose maximum speed is no more than 7 knots may show just an all-round white light, with sidelights if practicable.

Sailing vessels and rowing boats (Rule 25)

A sailing vessel under way shows sidelights and a sternlight — and no masthead light. She has two options:

• Under 20 m she may combine all three in one tricolour lantern at or near the top of the mast. It uses less power, and is less likely to be hidden by waves or the headsail.
• Any sailing vessel may add two all-round lights at or near the top of the mast, red over green — “red over green, sailing machine” — but never together with a tricolour.

The rhymes in quotation marks in this lesson are old memory aids used by sailors, not part of the rules.

A sailing vessel under 7 m shows these lights if practicable. If not, she must have a torch or lighted lantern showing a white light ready to show in time to prevent a collision. A vessel under oars may show the sailing-vessel lights, or else must keep such a torch or lantern ready.

A yacht whose engine is driving her — even with her sails up — is a power-driven vessel. By night she shows a power-driven vessel’s lights: masthead light (often called the steaming light, part-way up the mast), sidelights and sternlight. By day she shows a cone, point down, forward where it can best be seen.

At anchor and aground (Rule 30)

A vessel at anchor shows an all-round white light in the fore part, and a second, lower all-round white light at or near the stern. Under 50 m she may show a single all-round white light where it can best be seen instead — on a yacht, often at the masthead. By day she shows one black ball forward. A vessel of 100 m or more must also light up her decks, and a smaller one may.

She is not under way, so she shows no sidelights or sternlight. Two white lights and no coloured ones, the forward light higher, mean a large vessel at anchor.

A vessel aground shows her anchor lights plus two all-round red lights in a vertical line; by day, three balls in a vertical line. Keep well clear: she has found shallow water, and you could too.

Exceptions: a boat under 7 m at anchor away from channels, fairways, anchorages and the routes other vessels normally use need not show the anchor light or ball, and a vessel under 12 m aground need not show the extra red lights or the three balls.

Vessels that can’t easily keep out of the way (Rules 27 and 28)

Three kinds of vessel warn you that they cannot manoeuvre freely. Their signals are all-round lights by night, and shapes by day, in a vertical line where they can best be seen.

• Not under command (NUC): through some exceptional circumstance — an engine or steering failure, for example — she cannot manoeuvre as the rules require. Two all-round reds: “red over red, the captain is dead”.
• Restricted in her ability to manoeuvre (RAM): the nature of her work limits how she can move — dredging, surveying, laying or picking up a cable or pipeline, servicing a navigation mark, transferring people or stores while under way, or a tow that stops her changing course.
• Constrained by her draught (CBD): a power-driven vessel whose draught, compared with the depth and width of water available, severely limits her ability to turn off her course. Showing her signal is optional.

A RAM vessel at anchor also shows her anchor lights, or the ball by day.

Two variations on RAM: a dredger or vessel working underwater with an obstruction on one side adds two all-round reds (two balls by day) on that side, and two all-round greens (two diamonds) on the side where you may pass. A vessel supporting divers that is too small to show all of these shows the red, white, red all-round lights and, instead of the shapes, a rigid replica of the International Code flag “A”, at least 1 m high. Vessels under 12 m, except those supporting divers, need not show the NUC or RAM signals at all.

Fishing vessels (Rule 26)

A vessel engaged in fishing is one using nets, lines, trawls or other gear that restricts her manoeuvrability — a yacht trailing a mackerel line doesn’t count. She shows two all-round lights in a vertical line:

• Trawling (dragging a net or dredge through the water): green over white — “green over white, trawling at night”. A trawler of 50 m or more also shows a masthead light abaft of and higher than the green; a smaller one may.
• Any other fishing: red over white — “red over white, fishing at night”. If her gear reaches out more than 150 m from her, she also shows an all-round white light (by day, a cone point up) in the direction of the gear.

Both add sidelights and a sternlight only when making way through the water. By day both show two cones with their points together. She shows these signals whether under way or at anchor; when she is not fishing, she shows the ordinary lights for a vessel of her length.

Towing (Rule 24) and pilot vessels (Rule 29)

A power-driven vessel towing astern shows two masthead lights in a vertical line — or three if the tow is longer than 200 m, measured from her stern to the after end of the tow — plus sidelights, a sternlight and a yellow towing light above the sternlight. The vertical line takes the place of one of her ordinary masthead lights, so a tug of 50 m or more also shows a second masthead light. If the tow is longer than 200 m, the tug and the tow each show a diamond by day. The vessel being towed shows sidelights and a sternlight, but no masthead light.

A pilot vessel on duty shows two all-round lights at or near the masthead, white over red — “white over red, pilot ahead”. Under way she adds sidelights and a sternlight; at anchor, her anchor light or lights. Off duty she shows the ordinary lights for her size. The rules give her no day shape: by day, look for PILOT painted on her side.

The figure shows white over red with a green sidelight: a pilot vessel on duty, under way and heading to your right. Pilot boats often come out to meet ships near harbour entrances, so expect them to manoeuvre quickly.

Day shapes

By day, the special situations are shown by black shapes hoisted where they can best be seen. Annex I sets their sizes: a ball at least 0.6 m across; a cone as tall as its base is wide; a cylinder twice as tall as it is wide; a diamond two cones base to base; and at least 1.5 m between shapes. Vessels under 20 m may use smaller shapes.

Putting it together: identify, then decide

Identifying a vessel is only half the job: the point is to know what to do. Lesson 20 set out the responsibilities between vessels (Rule 18), and the lights and shapes in this lesson are how you know which line of the table applies.

Rule 18 applies except where Rules 9, 10 and 13 say otherwise: an overtaking vessel always keeps out of the way; in a narrow channel, vessels under 20 m and sailing vessels must not impede a vessel that can navigate safely only within it; and in a traffic separation scheme they must not impede a power-driven vessel following a traffic lane.