Rule 23 · USCG Navigation Rules
Power-driven vessel under 12 m
May replace the masthead light and sternlight with a single all-round white light, keeping the sidelights.
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 white light
- red — Port sidelight
→ Power-driven vessel under 12 m — Underway (all-round white option), seen from the port bow.
US Inland difference
Identical under the Inland Rules: a power-driven vessel under 12 m may exhibit an all-round white light and sidelights in lieu of the Rule 23(a) lights.
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Memory aid
“Small and simple: one all-round white plus sidelights does the whole job under 12 m.”
What it means
Underway (all-round white option)
In lieu of the masthead light and sternlight. The all-round white (or masthead light) of a vessel under 12 m may be displaced from the centreline if centreline fitting is not practicable.
Day shapes
No special day shape — by day this vessel is recognised by sight, not by shapes.
Light details
| Light | Colour | Arc | Position |
|---|---|---|---|
| All-round white light | white | 360° all-round | Forward masthead position |
| Port sidelight | red | 112.5° to port | Port side, deck level |
| Starboard sidelight | green | 112.5° to starboard | Starboard side, deck level |
2D profile
Labelled side view — works without WebGL and in print. Variant shown: Underway (all-round white option).
In fog, she sounds
Don’t confuse with…
Official source
Rule 23, reproduced from the public-domain COLREGs Rule 23(d) — USCG Navigation Rules. Diagrams and 3D scenes are original to boatrules.com.