Comparatifs
NUC vs RAM — the two reds that everyone mixes up
"Not under command" (NUC) and "restricted in ability to manoeuvre" (RAM) are the two highest priority vessel statuses in Rule 18 after vessels engaged in fishing or sailing. Their lights both involve all-round red — and that's where the confusion starts.
Below is the side-by-side that ends the confusion: definitions, lights, day shapes, exam scenarios where examiners swap them, and the priority order in Rule 18.
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NUC vs RAM — definitions, lights, shapes
| Aspect | NUC — Not Under Command | RAM — Restricted in Ability to Manoeuvre |
|---|---|---|
| Definition (Rule 3(f) / 3(g)) | A vessel which through some EXCEPTIONAL CIRCUMSTANCE is unable to manoeuvre as required by these Rules | A vessel which from the NATURE OF HER WORK is restricted in her ability to manoeuvre as required by these Rules |
| Typical cause | Engine failure, steering gear breakdown, severe weather damage | Cable-laying, dredging, mine-clearance, replenishment-at-sea, launching aircraft, towing unable to deviate |
| Lights (underway, when not making way) | TWO all-round RED lights in a vertical line | Red-WHITE-Red in a vertical line, all-round |
| Lights (underway, making way) | Two reds + sidelights + sternlight (NO masthead lights when not making way) | Red-white-red + masthead lights + sidelights + sternlight |
| Lights (anchored) | Two reds + anchor light | Red-white-red + anchor lights (no masthead) |
| Day shapes | Two black BALLS in a vertical line | Black BALL — DIAMOND — BALL in a vertical line |
| Priority in Rule 18 | Highest (after fishing/sailing only when in sight of those) | Second-highest — but ABOVE NUC in some interpretations because she is performing critical work |
| Sound signal in fog (Rule 35) | One prolonged + two short blasts every 2 minutes | Same: one prolonged + two short blasts every 2 minutes |
How to read the lights — the 60-second drill
Count the reds and look for the white. The shape tells you everything Rule 18 needs to know.
- Two reds in a vertical line, no white between them → NUC. Treat as the vessel of highest priority you have to keep clear of (after fishing and sailing if in sight).
- Red-white-red vertical line → RAM. She is busy doing essential work and is hard to move — give her even more sea room than NUC.
- Red-white-red PLUS additional lights/shapes on her side (e.g. red and green balls/diamonds + two-cones) → vessel restricted in ability to manoeuvre due to a specific operation: minesweeping (one black ball each side), dredging (red+green sides marking obstructed/clear water), towing operations unable to deviate.
- Three reds vertical (no whites) → constrained by draught (Rule 28), NOT NUC and NOT RAM — completely different rule with a lower priority than RAM.
- Confused on the water? Slow down and give wide berth. The lights matter, but "don't hit anyone" matters more.
Read the underlying rules
Frequently asked questions
What does "not under command" mean in COLREG?
Rule 3(f) defines "vessel not under command" as a vessel which through some exceptional circumstance is unable to manoeuvre as required by these Rules. Typical causes are engine failure, steering breakdown or storm damage. The exception is the operative word — equipment failure that the operator could have prevented is not a NUC condition.
What does "restricted in ability to manoeuvre" mean?
Rule 3(g) defines it as a vessel which from the nature of her work is restricted in her ability to manoeuvre as required. The non-exhaustive list in Rule 3(g) includes vessels engaged in laying / picking up cable or pipeline, dredging, surveying, underwater operations, replenishment at sea, launching or recovering aircraft, mine-clearance and towing operations that severely restrict their ability to deviate.
What is the difference between NUC and RAM lights?
NUC shows two all-round RED lights in a vertical line. RAM shows three all-round lights — RED, WHITE, RED — in a vertical line. Both add sidelights and sternlight when making way; only RAM adds masthead lights when making way. Day shapes: NUC shows two black balls; RAM shows ball-diamond-ball.
Which has priority — NUC or RAM?
Rule 18 places both above all power-driven and sailing vessels, but you should treat RAM with at least as much care — she is doing work she cannot abandon (cable laying, mine clearance) whereas NUC is in trouble but conceptually mobile once the trouble passes. Practical rule: keep well clear of both.
Is a fishing vessel NUC or RAM?
Neither by default. A fishing vessel has its own dedicated lights and day shapes (Rule 26) and its own slot in the Rule 18 priority hierarchy (BELOW NUC and RAM but ABOVE sailing and power-driven). A fishing vessel that suffers an exceptional breakdown can additionally show NUC lights — Rule 27(a) explicitly allows it.
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