Rule 27 · USCG Navigation Rules
Vessel not under command (NUC)
Two all-round red lights in a vertical line (two balls by day); sidelights and sternlight appear only when she is making way.
Situation
Viewpoint
Display
Drag to orbit freely, scroll or pinch to zoom — or use the viewpoint buttons above (keyboard friendly).
From the port bow you see:
- All-round red (upper)
- All-round red (lower)
→ Vessel not under command (NUC) — Underway, not making way, seen from the port bow.
Memory aid
“Red over red — the captain is dead (nobody is in control).”
What it means
Underway, not making way
Just the two reds — no masthead light, no sidelights, no sternlight. Through an exceptional circumstance (steering/engine failure) she cannot keep out of your way.
Making way through the water
Adds sidelights and a sternlight — but still NO masthead light. That missing masthead light is what separates a NUC from a vessel restricted in her ability to manoeuvre.
Day shapes
Two balls
Two balls in a vertical line where they can best be seen.
Light details
Underway, not making way
| Light | Colour | Arc | Position |
|---|---|---|---|
| All-round red (upper) | red | 360° all-round | Mast, vertical line (top) |
| All-round red (lower) | red | 360° all-round | Mast, vertical line (2nd from top) |
Making way through the water
| Light | Colour | Arc | Position |
|---|---|---|---|
| All-round red (upper) | red | 360° all-round | Mast, vertical line (top) |
| All-round red (lower) | red | 360° all-round | Mast, vertical line (2nd from top) |
| Port sidelight | red | 112.5° to port | Port side, deck level |
| Starboard sidelight | green | 112.5° to starboard | Starboard side, deck level |
| Sternlight | white | 135° aft | Stern |
2D profile
Labelled side view — works without WebGL and in print. Variant shown: Underway, not making way.
In fog, she sounds
Don’t confuse with…
Official source
Rule 27, reproduced from the public-domain COLREGs Rule 27(a) — USCG Navigation Rules. Diagrams and 3D scenes are original to boatrules.com.