Rule 25 · USCG Navigation Rules
Sailing vessel under 20 m — tricolor lantern
A sailing vessel under 20 m may combine sidelights and sternlight in one red/green/white tricolor lantern at or near the masthead — under sail only.
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:
- Tricolor lantern — red, green and white sectors in one lamp — red sector
→ Sailing vessel under 20 m — tricolor lantern — Under sail alone (tricolor), seen from the port bow.
Memory aid
“One lantern at the masthead does all three jobs — but only under 20 m and only under sail alone.”
What it means
Under sail alone (tricolor)
One lantern, three sectors: red 112.5° to port, green 112.5° to starboard, white 135° aft. Never used together with the deck-level sidelights/sternlight, never with the red-over-green all-rounds, and NEVER when motorsailing.
Day shapes
No special day shape — by day this vessel is recognised by sight, not by shapes.
Light details
| Light | Colour | Arc | Position |
|---|---|---|---|
| Tricolor lantern — red, green and white sectors in one lamp | red / green / white | 360° in three sectors | Mast, vertical line (top) |
2D profile
Labelled side view — works without WebGL and in print. Variant shown: Under sail alone (tricolor).
In fog, she sounds
Don’t confuse with…
Official source
Rule 25, reproduced from the public-domain COLREGs Rule 25(b) — USCG Navigation Rules. Diagrams and 3D scenes are original to boatrules.com.