ColRegs Lights Cheat Sheet
For RYA Day Skipper, Yachtmaster, SRC, and STCW exams
Memorising twenty different vessel-light combinations the night before the exam is hopeless. Memorising the underlying pattern and a handful of mnemonics is straightforward. This is the cheat sheet — the rule that unlocks 70% of the syllabus, the mnemonics that handle the remaining 30%, and the common traps that catch examinees out.
The universal rule (memorise this first)
Every set of COLREGS navigation lights is built from the same six building blocks:
- Port = red (a coloured sidelight covering 112.5° from dead ahead to 22.5° abaft the beam on the port side)
- Starboard = green (the same arc on the starboard side)
- Masthead white — a forward-facing white arc, 225°, shown by every power-driven vessel underway
- Stern white — a rearward-facing white arc, 135°
- All-round white — visible 360°, used for anchor lights and some vessel-type identifiers
- All-round coloured (red, green, yellow) — used in vertical stacks to identify special vessel statuses
Masthead + sidelights + stern = power-driven underway. That single combination is the answer to most questions in any lights exam. Everything else is variations: remove the masthead and you have a sailing vessel; replace the sidelights with vertical stacks of coloured lights and you have a special-status vessel; add all-round whites and you have an anchored or large vessel.
Port and starboard — the trick
The classic exam trap: you see a vessel showing a single red sidelight. What side of you is it on?
The mistake everyone makes: they think about the other vessel, not themselves. The right approach is to remember:
“Red on your right — keep clear; she has right of way.”
If you see red on your right, that is her port sidelight showing from your starboard side. She is crossing from your right, you are the give-way vessel, and she has stand-on. The mnemonic mirrors “red right return” from IALA buoyage — which is intentional. Once you have one anchored, the other follows.
Common short forms used by RYA instructors:
- PR-SG — Port Red, Starboard Green (your own lights, looking forward)
- RRR — Red on Right = Risk (you are the give-way vessel)
- GGG — Green on Right = Go (the other vessel will keep clear)
Special-status vessels — the rhyming mnemonics
These are the classic memory aids passed between sailing-school students for fifty years. They are not pretty, but they work — which is why every RYA instructor still teaches them.
Not Under Command (NUC) — “Red over red, captain is dead”
Two vertical all-round red lights. NUC means the vessel cannot manoeuvre due to circumstances beyond her control — engine failure, steering failure, etc. She has top priority in collision-avoidance and you must keep clear. The mnemonic is grim but unforgettable.
Restricted in Ability to Manoeuvre (RAM) — “Red, white, red, restricted ahead”
Three vertical all-round lights: red on top, white in the middle, red on the bottom. RAM means the vessel is restricted due to the nature of her work — dredging, cable-laying, mine clearance, survey work. Distinct from NUC because the restriction is by choice/work, not failure.
Constrained by Draught (CBD) — “Three reds going down”
Three vertical all-round red lights. A power-driven vessel (typically a large tanker or container ship) is so deep she cannot safely deviate from her course. Treat like a RAM but in a deeper channel context. Common in approaches to commercial ports.
Trawling — “Green over white, trawling at night”
Two vertical all-round lights: green on top, white below. Trawling specifically means dragging fishing gear. Distinct from general fishing because trawling is a hazard in a defined direction (towards the trawl) and other vessels need to anticipate that.
Fishing (not trawling) — “Red over white, fishing at night”
Two vertical all-round lights: red on top, white below. Drift-net fishing, line-fishing, or other static gear. Often shows an additional all-round white horizontally in the direction of the gear if it extends more than 150 m from the vessel.
Pilot vessel — “White over red — pilot ahead”
Two vertical all-round lights: white on top, red below. A pilot vessel on duty showing where to find the pilot. Common around major commercial ports at handover times (early morning, dusk).
Aground — “Two reds — aground in bed”
Anchor lights (one or two all-round whites depending on length) plus two vertical all-round reds. A vessel aground signals her status so other vessels can both avoid her and consider whether to render assistance.
The vertical-stack pattern (the deeper trick)
Notice that every special-status vessel uses a vertical stack of two or three all-round lights. The stack tells you everything:
- Two reds = NUC (one of the worst — captain is dead)
- Red-white-red= RAM (working, can't deviate)
- Three reds = CBD (constrained by draught)
- Green-white = trawling
- Red-white = fishing (not trawling)
- White-red = pilot
A surprising amount of the lights syllabus comes down to: see the vertical stack, identify the colours, map to the vessel type. Examiners will sometimes show you a glimpse of just the stack without the sidelights — that's a deliberate test of whether you read the stack first or the position lights first.
Common exam traps
Trap 1: “A vessel showing two white masthead lights”
Two whites could mean (a) a power-driven vessel over 50 m, or (b) a vessel towing. The difference: a towing vessel also shows a yellow towing light and (usually) sidelights at a different height. The examiner is testing whether you considered both possibilities. Answer: “Either a power-driven vessel over 50 m, OR a vessel towing — additional information needed.”
Trap 2: Aground vs anchored vs NUC
All three involve all-round white lights and can have additional red lights. The disambiguator: an anchored vessel shows only whites. NUC shows only two reds. Aground shows both the anchor whites and two reds. If you see whites and reds together, think aground first.
Trap 3: Sailing vessel under power
A sailing vessel with her engine running is a power-driven vesselunder COLREGS — she must show a masthead white and follow power-driven rules even if her sails are up. Examiners love this. The mnemonic: “engine on, sail status gone.”
Trap 4: Tricolour lights on sailing vessels
A sailing vessel under 20 m may show a single combined tricolour light at the masthead (port red, starboard green, stern white in one fixture) instead ofseparate sidelights and stern light — but never both at the same time. Examiners ask which is permitted; the answer is “one or the other, never both.”
Trap 5: Distance and arc confusion
Sidelights cover 112.5° per side (total 225°). Sternlight covers 135°. Together they cover 360°. The mnemonic: “225 + 135 = 360 — you see one or the other from any angle.” The masthead white covers the same 225° forward arc as the sidelights combined.
Quick reference table
| Vessel | Lights | Mnemonic |
|---|---|---|
| Power-driven underway (under 50 m) | Masthead white, sidelights, sternlight | Standard — the ‘default’ arrangement |
| Power-driven underway (50 m+) | Two masthead whites (second higher and aft), sidelights, sternlight | ‘Big ship two whites’ |
| Sailing vessel underway | Sidelights + sternlight only (no masthead white) | No engine, no masthead |
| Vessel at anchor (under 50 m) | One all-round white | ‘One white, all night’ |
| Vessel at anchor (50 m+) | Two all-round whites (forward higher than aft) | ‘Big anchor, two whites’ |
| Not Under Command (NUC) | Two all-round reds (vertical) | ‘Red over red — captain is dead’ |
| Restricted in Ability to Manoeuvre (RAM) | Red, white, red all-round (vertical) | ‘Red, white, red — restricted ahead’ |
| Constrained by Draught (CBD) | Three all-round reds (vertical) + normal power-driven lights | ‘Three reds going down’ |
| Trawling | Green over white all-round | ‘Green over white, trawling at night’ |
| Fishing (not trawling) | Red over white all-round | ‘Red over white, fishing at night’ |
| Pilot vessel on duty | White over red all-round | ‘White over red — pilot ahead’ |
| Towing (tow under 200 m) | Two masthead whites (vertical) + sidelights + sternlight + yellow towing light | ‘Two whites = towing’ |
| Towing (tow over 200 m) | Three masthead whites (vertical) + the rest as above | ‘Three whites = long tow’ |
| Vessel aground | Anchor lights + two all-round reds (vertical) | ‘Two reds = aground in bed’ |
Test yourself
Mnemonics are a starting point — reflexive recall comes from repetition. The fastest way to lock these in is the interactive lights widget and the ColRegs quizzes: