Lights and Shapes of Special Vessels and How to Read Them

How to read a set of lights — the six-step script

In short: Read Lights and Shapes: Basic Rules, Arcs and Ranges first: it gives the arcs and ranges of every light used here. When you see lights, answer in a fixed order: type → length → aspect → special circumstances → underway → making way. Then take bearings.

1. Type of vessel — power-driven, sailing, fishing, NUC, RAM, CBD, pilot, towing… The coloured all-round lights tell you the type.
2. Length — one or two masthead lights (or one or two anchor lights) say under 50 m or probably 50 m and over. Many special displays give no length at all.
3. Aspect — which sidelight you see: green = her starboard side, red = her port side, both = head-on, sternlight only = you see her stern.
4. Special circumstances — towing with a tow over 200 m, gear out more than 150 m, obstruction on one side, mine clearance, aground.
5. Underway — not at anchor, not made fast to the shore, not aground (COLREG Rule 3(i)).
6. Making way — moving through the water. ❌ Trap: “making way” is not defined in Rule 3; only “underway” is.

• Then say: “I take a series of compass bearings to see if risk of collision exists” (COLREG Rule 7 — see Risk of Collision and Action to Avoid Collision).
• How to word it: if her lights prove she is moving, say “vessel making way”. If the lights look the same moving or stopped, say “vessel underway, probably making way”.
• Then decide who keeps out of whose way (COLREG Rule 18 — see Give-way, Stand-on and Responsibilities between Vessels).
• Ranges (COLREG Rule 22): the status lights of special vessels are all-round lights: 3 NM (50 m and over), 2 NM (under 50 m, including under 12 m). Masthead lights reach 6 NM on a big ship, so you often see her masthead lights before her red or green status lights.

Lights that look the same moving or stopped — PDV, sailing, CBD, pilot

In short: A power-driven vessel (PDV), a sailing vessel, a vessel constrained by her draught (CBD) and a pilot vessel show sidelights and sternlight whenever underway, moving or not. So from their lights you can only say “underway, probably making way”.

Power-driven vessel — Rule 23

• Masthead light, sidelights, sternlight. A second masthead light, aft and higher, is compulsory from 50 m (COLREG Rule 23(a)).
• Underway: yes. Making way: probably.
• Length: one masthead light = under 50 m. Two = probably 50 m or more — a shorter vessel may also show two.

Sailing vessel — Rule 25

• Sidelights and sternlight; no masthead light. Under 20 m they may be combined in one tricolour lantern at the masthead.
• Optional: red over green all-round at the masthead (not with the tricolour).
• Sailing and motoring at the same time is a power-driven vessel: by day she shows a cone, apex down (COLREG Rule 25(e)).
• Underway: yes. Making way: probably. Length: unknown — no masthead lights to count.

Constrained by her draught (CBD) — Rule 28

• A power-driven vessel: normal Rule 23 lights, and she may add three all-round red lights in a vertical line. By day: a cylinder. The display is optional.
• Cylinder size: diameter at least 0.6 m, height twice the diameter = 1.2 m × 0.6 m (COLREG Annex I §6).
• Reads like a PDV: underway, probably making way; length from her masthead lights (under 50 m, or probably 50 m and over).
• At anchor she shows normal anchor lights (COLREG Rule 30). Nothing then tells you she is draught-constrained.

Pilot vessel — Rule 29

• On pilotage duty: white over red all-round at or near the masthead. Underway: add sidelights and sternlight. At anchor: add the anchor light(s) or ball (COLREG Rule 30).
• No masthead light, even though she is power-driven.
• Making way: probably (sidelights stay on when she stops).
• Length: unknown while underway. At anchor, one or two anchor lights tell you under or over 50 m.
• Memory aid: “white over red, pilot ahead”.
• Off duty: lights of a similar vessel of her length (COLREG Rule 29(b)).

Lights that change when making way — NUC, RAM, fishing

In short: A vessel not under command (NUC), a vessel restricted in her ability to manoeuvre (RAM) and a fishing vessel switch sidelights and sternlight on only when making way. So for them you can say “vessel making way” or “not making way”.

Not under command (NUC) — Rule 27(a)

• Two all-round red lights in a vertical line. By day: two balls.
• Making way through the water: add sidelights and sternlight. Stopped: switch them off.
• No masthead lights, even if power-driven.
• Making way: you can tell.
• At anchor: you can’t tell. Two reds alone say she is stopped, not whether she is drifting or anchored. A vessel properly at anchor shows the Rule 30 anchor lights instead.
• Length: the two recognition lists disagree. One says NUC length “is known”; the other puts NUC among vessels whose length you cannot tell. Rule 27(a) gives her no masthead lights, so the NUC lights alone do not show length.
• NUC = unable to manoeuvre through some exceptional circumstance (Rule 3(f)). ❌ A planned engine shutdown is not NUC.

Restricted in her ability to manoeuvre (RAM) — Rule 27(b)

• Red–white–red all-round in a vertical line. By day: ball–diamond–ball.
• Making way: add masthead light(s), sidelights and sternlight. At anchor: add the Rule 30 anchor lights or ball.
• Making way: you can tell. At anchor: you can tell.
• Length: from her masthead lights when making way, or anchor lights when anchored. Stopped, with neither, you can’t tell.
• RAM is about the nature of the work (laying buoys or cables, dredging, surveying, replenishing underway, launching aircraft, some towing) — Rule 3(g).

RAM exceptions — dredging, diving, towing, mine clearance

• Dredging or underwater operations (Rule 27(d)): RAM lights, plus two red lights or two balls on the obstructed side and two green lights or two diamonds on the side where you may pass. At anchor these replace the anchor lights, so you can’t tell she is at anchor.
• Diving (Rule 27(e)): if she is too small for the full display, red–white–red lights and a rigid replica of flag “A”, at least 1 m high, visible all round. Her length and whether she is at anchor may not show.
• Towing (Rule 27(c)): towing lights + RAM lights. The towing display already carries sidelights and sternlight underway, so you can’t tell making way.
• Mine clearance (Rule 27(f)): PDV lights (Rule 23) or anchor lights (Rule 30), plus three all-round green lights or three balls: one at the foremast head, one at each end of the fore yard. Keep more than 1,000 m away. Can’t tell making way (PDV lights); can tell underway or at anchor; length is known from masthead or anchor lights.
• Under 12 m, Rule 27 signals are not required — except for diving (Rule 27(g)). Rule 27 signals are not distress signals (Rule 27(h)).

Vessel engaged in fishing — Rule 26

• Trawling: green over white. A masthead light aft and higher than the green: compulsory from 50 m, optional below. By day: two cones, apexes together.
• Fishing other than trawling: red over white, same day shape. Gear out more than 150 m: add an all-round white light or a cone apex up towards the gear.
• Making way: add sidelights and sternlight. Making way: you can tell.
• At anchor: you can’t tell. Underway or at anchor she shows only the fishing lights (Rule 26). With sidelights off, she may be at anchor or just stopped.
• Length: a trawler with the masthead light is probably 50 m or more. Fishing other than trawling has no masthead light: length unknown.
• ❌ Trap: there is no “fishing vessel” in the rules, only a vessel engaged in fishing. Trolling lines do not count (Rule 3(d)): a yacht trolling a line is not fishing. Not fishing = lights of her length only.

Towing and pushing — Rule 24

In short: Two masthead lights in a vertical line (three if the tow is longer than 200 m), sidelights, sternlight, and a yellow towing light above the sternlight. You can’t tell if she is making way.

• Tow length is measured from the stern of the tug to the after end of the tow. Over 200 m: a diamond by day, on the tug and on the tow. Exactly 200 m does not count.
• The tow shows sidelights and sternlight. An inconspicuous, partly submerged tow shows all-round white lights (3 NM, Rule 22(d)) and a diamond.
• Pushing ahead or alongside: two masthead lights, sidelights, sternlight; no towing light. A rigidly connected composite unit is one PDV (Rule 23 lights).
• Tug and tow hard to manoeuvre: she adds red–white–red (Rule 27(c)) and becomes RAM.
• Making way: probably (lights unchanged when stopped). On the bridge: three masthead lights and a yellow light aft → never cross close astern; the tow may be 200 m+ behind, unlit or hard to see.

Air-cushion vessels and WIG craft — Rule 23

In short: Both show normal PDV lights plus an all-round flashing light (120 or more flashes per minute, Rule 21(f)): yellow for an air-cushion vessel, red (high-intensity) for a WIG craft.

• Air-cushion vessel in non-displacement mode (on the cushion): all-round flashing yellow (COLREG Rule 23(b)).
• WIG craft (wing-in-ground) only while taking off, landing or flying near the surface: high-intensity all-round flashing red (COLREG Rule 23(c)). On the water she is a normal PDV.
• Making way: probably, like any PDV. Expect high speed: a flashing light closes fast.

At anchor and aground — Rule 30, and the can / can’t table

In short: At anchor: all-round white forward (and a lower one aft from 50 m), a ball by day. Aground: anchor lights + two all-round reds, or three balls. Some special vessels never show you they are anchored.

• Under 50 m: one all-round white where best seen. 100 m and over: also illuminate the decks.
• Aground: anchor lights + two red in a vertical line, or three balls by day. Not required under 12 m.
• Under 7 m at anchor away from channels, fairways and anchorages: no anchor light or shape needed.
• ❌ Don’t mix up: two reds alone = NUC; two reds + anchor lights = aground.

• “Can’t tell at anchor” covers fishing, CBD, RAM dredging and underwater operations (diving may not show it either) and NUC (her sidelights and sternlight are off, so two reds alone).