Module 7 of 7 · COLREG Bridge Simulator

Ship Lights & Day Shapes

Rules 23 through 31 — the universal visual language of vessels at night and in fog. A red over a white means a fishing vessel pulling nets. Two reds vertical means "not under command — keep clear." Three reds vertical means "constrained by my draught." Read these patterns and you read the sea.

Rule 23Rule 24Rule 25Rule 26Rule 27Rule 28Rule 29Rule 30Rule 31

Practice night recognition → Get the full course

Built for: everyone — universally tested in every maritime certificate exam from ICC and Day Skipper through Yachtmaster Coastal & Offshore, STCW Officer of the Watch, deck-officer revalidation, RYA examinations, and maritime academy oral exams. No skipper passes any exam without knowing this section cold.

The lights — read top to bottom, then horizontally

Each rule below shows the law text on the left and the matching simulator-rendered vessel on the right (port-beam aspect — 270° — so all distinguishing lights are visible). Click any image to view full size; scroll past this card for the full 8-aspect strips.

Rule 23 — Power-driven vessel under way

Masthead light — white, forward, showing 225° (from 22.5° abaft beam port through ahead to 22.5° abaft beam starboard).
Sidelights — red port, green starboard, each showing 112.5°.
Sternlight — white, showing 135° aft.
Vessels > 50 m show a second masthead light abaft and higher than the forward one.
Power-driven < 7 m and < 7 kn — exemption: all-round white only.
Air-cushion (hovercraft) in non-displacement mode: yellow flashing all-round.
WIG (Wing-In-Ground) craft: high-intensity all-round red flashing.

Power-driven vessel under way viewed from her port beam — COLREG Rule 23 night-recognition diagram — Rule 23 PDV

Power-driven vessel under 7 m and under 7 kn viewed from her port beam — COLREG Rule 23(d) night-recognition diagram — Rule 23(d) <7 m

Air-cushion vessel (hovercraft) in non-displacement mode viewed from her port beam — COLREG Rule 23(b) night-recognition diagram — Rule 23(b) hovercraft

WIG (Wing-In-Ground) craft on the water viewed from her port beam — COLREG Rule 23(c) night-recognition diagram — Rule 23(c) WIG

Rule 24 — Towing & pushing

Towing astern, tow length ≤ 200 m: two masthead lights vertically + sidelights + sternlight + yellow towing light above sternlight.
Tow length > 200 m: three masthead lights vertically; by day a diamond shape.
Vessel being towed: sidelights + sternlight; if tow > 200 m, day diamond.

Towing vessel — tow under 200 m viewed from her port beam — COLREG Rule 24 night-recognition diagram — Rule 24 — tow ≤ 200 m

Towing vessel — tow over 200 m viewed from her port beam — COLREG Rule 24(a)(i) night-recognition diagram — Rule 24(a)(i) — tow > 200 m

Rule 25 — Sailing vessels & vessels under oars

Sidelights + sternlight.
Optional red over green all-round at masthead.
< 20 m may combine in a tricolour at masthead.
Sailing vessel under power = power-driven vessel (must show masthead light); by day display a cone, point downward.

Sailing vessel under way viewed from her port beam — COLREG Rule 25 night-recognition diagram — Rule 25 — sailing

Sailing vessel under 20 m with masthead tricolour viewed from her port beam — COLREG Rule 25(b) night-recognition diagram — Rule 25(b) tricolour < 20 m

Sailing and motoring vessel (motor-sailing) viewed from her port beam — COLREG Rule 25(e) night-recognition diagram — Rule 25(e) — motor-sailing

Rule 26 — Fishing

Trawling: green over white all-round + sidelights + sternlight (if making way).
Other fishing: red over white all-round + sidelights + sternlight (if making way).
If gear extends > 150 m horizontally: an additional all-round white in that direction.
By day — two cones, points together (basket).

Trawling vessel — green over white viewed from her port beam — COLREG Rule 26 night-recognition diagram — Rule 26 — trawling

Fishing vessel (nets / lines, non-trawling) viewed from her port beam — COLREG Rule 26(c) night-recognition diagram — Rule 26(c) — non-trawling

Fishing vessel with outlying gear over 150 m viewed from her port beam — COLREG Rule 26(c)(ii) night-recognition diagram — Rule 26(c)(ii) — gear > 150 m

Rule 27 — NUC, RAM, dredgers & mine-clearance

NUC: two all-round red vertical + sidelights + sternlight if making way. By day: two black balls.
RAM: red-white-red all-round vertical + masthead lights + sidelights + sternlight. By day: ball-diamond-ball.
RAM at anchor: RAM lights + anchor lights.
Dredger / underwater operations (Rule 27(d)): RAM lights + 2 all-round red on the obstruction side + 2 all-round green on the safe-pass side.
Mine-clearance vessel (Rule 27(f)): power-driven lights + 3 all-round green (one at masthead, one at each yardarm).

Vessel not under command / restricted in ability to manoeuvre viewed from her port beam — COLREG Rule 27 night-recognition diagram — Rule 27 — NUC / RAM

Vessel not under command, not making way viewed from her port beam — COLREG Rule 27(a) night-recognition diagram — Rule 27(a) — NUC not making way

Vessel restricted in ability to manoeuvre, at anchor viewed from her port beam — COLREG Rule 27(b) night-recognition diagram — Rule 27(b) — RAM at anchor

Dredger or underwater operations vessel viewed from her port beam — COLREG Rule 27(d) night-recognition diagram — Rule 27(d) — dredger

Mine-clearance vessel viewed from her port beam — COLREG Rule 27(f) night-recognition diagram — Rule 27(f) — mine clearance

Rule 28 — Constrained by draught

In addition to power-driven lights: three all-round red vertical.
By day: a cylinder.

Vessel constrained by her draught (CBD) viewed from her port beam — COLREG Rule 28 night-recognition diagram — Rule 28 — CBD

Rule 29 — Pilot vessel on duty

White over red all-round at masthead + sidelights + sternlight if making way.
At anchor: anchor lights + the white-over-red.

Pilot vessel on duty viewed from her port beam — COLREG Rule 29 night-recognition diagram — Rule 29 — pilot vessel

Rule 30 — Anchored & aground

At anchor > 50 m: forward all-round white + aft all-round white at lower level. Day: black ball.
At anchor < 50 m: single forward all-round white. Day: single black ball.
Aground: anchor lights + two all-round red vertical. Day: three black balls vertical.
Vessels < 7 m anchored not in or near a fairway: lights/shapes not required.

Vessel at anchor viewed from her port beam — COLREG Rule 30 night-recognition diagram — Rule 30 — at anchor > 50 m

Vessel at anchor (under 50 m — single white forward) viewed from her port beam — COLREG Rule 30(b) night-recognition diagram — Rule 30(b) — at anchor < 50 m

Rule 31 — Seaplanes & WIG craft

Where impracticable to comply, lights and shapes shall be displayed as nearly as possible to those required for the corresponding power-driven vessel.

Seaplane on the water viewed from her port beam — COLREG Rule 31 night-recognition diagram — Rule 31 — seaplane

How the simulator drills it

Static charts in textbooks teach the patterns; sea conditions test recognition. The simulator presents:

Approach view — bow-on, stern-on, beam-on, oblique angles. Same vessel looks different from each.
Pattern → identify — you see the lights, you name the vessel and her status.
Vessel → predict pattern — given an AIS target type, what lights will you see from the approach angle?
Day-shape recognition — basket, cylinder, ball-diamond-ball, single ball, two balls, three balls vertical, cone point-down.
Composite scenarios — RAM towing > 200 m: identify both the RAM vertical pattern and the towing pattern in one target.

Common mistakes

Mistaking RAM red-white-red for fishing red-white — RAM has three lights, fishing has two. Always count vertically.
Forgetting the optional sailing-vessel red-over-green — it's at the masthead, not amidships, and confusion with port-sidelight pattern is common in cross-sections.
Counting sidelights as "all-round" — sidelights are 112.5° each, not 360°. From astern you see only the sternlight.
Anchored < 50 m showing aft white as well — the second white is required only for vessels > 50 m at anchor.
Sailing under engine without showing the cone by day or masthead at night — common yacht violation; technically a power-driven vessel.

📸 Night recognition gallery — every vessel, every aspect

Each row below shows one vessel type captured from 8 angles, every 45° of aspect. Use these to drill recognition — pick a row, study the silhouette progression as the ship presents her bow, beam, quarter, stern. All images rendered from the live SkipperCheck COLREG bridge simulator.

COLREG Rule 30 — Vessel at anchor �