COLREGS Rule 25 — Navigation Lights
Sailing Vessel Underway — Navigation Lights (COLREGS Rule 25)
A sailing vessel underway under sail alone shows sidelights and a sternlight. Vessels under 20 meters have additional options including a combined tricolor lantern at the masthead and optional red-over-green all-around lights. A sailing vessel using its engine is a power-driven vessel and must show a black cone by day.
Condition: Underway under sail at night or in restricted visibility (engine not in use)
Navigation lights required
| Light | Color | Arc | Position |
|---|---|---|---|
| Port sidelight | Red | 112.5° | Port side, forward half of vessel |
| Starboard sidelight | Green | 112.5° | Starboard side, forward half of vessel |
| Sternlight | White | 135° | Stern, centerline |
| Combined tricolor lantern (optional, vessels under 20 m) | Red / Green / White | 360° (port 112.5° red, starboard 112.5° green, stern 135° white) | At or near the top of the mast |
| Red over green all-around lights (optional) | Red (top), Green (bottom) | 360° each | At or near the top of the mast, in a vertical line |
Combined tricolor lantern (optional, vessels under 20 m): Replaces separate sidelights and sternlight. Cannot be used simultaneously with the red-over-green optional lights or any other masthead lights.
Red over green all-around lights (optional): May not be used together with the combined tricolor lantern.
Dayshapes
| Shape | Position | When displayed |
|---|---|---|
| Black cone, apex downward | Forward, where it can best be seen | When proceeding under sail AND engine simultaneously (motor-sailing) |
Exceptions and size rules
- →A vessel under 7 m under sail may, if it is not practical to show the full light set, instead show an all-around white light and, if practicable, sidelights.
- →A vessel under oars may use sailing vessel lights or simply have a flashlight or lantern ready to prevent collision.
Inland Rules differences
- !US Inland Rules are identical to COLREGS for sailing vessel lights — no practical difference.
Common exam mistakes
- ✗Showing a white masthead light on a sailing vessel — sailing vessels under sail alone do NOT show a masthead light.
- ✗Using the combined tricolor lantern at the same time as the optional red-over-green all-around lights — these are mutually exclusive.
- ✗Forgetting the black cone by day when the engine is in use — a motor-sailing vessel is a power-driven vessel.
- ✗Applying sailing vessel lights when the engine is running — if the engine is in use, the vessel is power-driven regardless of whether sails are set.
USCG exam questions — Sailing Vessel Underway
These questions are drawn from the same pool used in real USCG licensing exams. Correct answers and explanations are shown.
1. A sailing vessel underway at night shall show:
- A.A tricolor light at the masthead only
- B.Sidelights, a sternlight, and a white masthead light
- C.Sidelights and a sternlight only✓
- D.Sidelights, a sternlight, and two all-round lights (red over green) at the masthead
Why: Rule 25(a) requires a sailing vessel underway to show sidelights and a sternlight only, so C is the mandatory minimum. The optional two all-round lights (red over green) at the masthead are authorized by Rule 25(c) — not 25(b), which is the combined tricolor lantern for vessels under 20m — and a white masthead light would falsely indicate a power-driven vessel.
2. A sailing vessel less than 20 meters in length may combine the sidelights and sternlight into:
- A.A single all-round white light
- B.A bicolor lantern at the bow
- C.An all-round red and green light at the stern
- D.A tricolor lantern at the masthead✓
Why: Rule 25(b) permits sailing vessels less than 20 meters to combine sidelights and sternlight into a tricolor lantern at or near the top of the mast. When this tricolor is used, the separate all-round red-over-green lights at the masthead must NOT also be shown.
3. A sailing vessel proceeding under sail AND using her engine shall display by day:
- A.A black ball shape forward
- B.A black cone with apex downward forward✓
- C.A black diamond shape
- D.No special day shape is required
Why: Rule 25(e) requires a sailing vessel proceeding under sail when also being propelled by machinery to show a conical shape, apex downwards, at the forward part of the vessel. This alerts other mariners that despite the sails, she is operating as a power-driven vessel for rules purposes.
4. A vessel under oars less than 7 meters in length shall, in lieu of prescribed lights, have ready at hand:
- A.A red flare
- B.A white flare only
- C.Sidelights and a sternlight are always required
- D.A white all-round electric torch or lighted lantern✓
Why: Rule 25(d)(ii) permits a vessel under oars less than 7 meters to show only the lights in Rule 25(a) or (b), but if this is not practicable, she shall have ready at hand an electric torch or lighted lantern showing a white light. This is a practical concession for small rowboats.
5. You observe a vessel showing only a tricolor lantern at the masthead. What type of vessel is this most likely to be?
- A.A power-driven vessel less than 12 meters in length
- B.A sailing vessel less than 20 meters in length underway✓
- C.A vessel at anchor with a single white light
- D.A pilot vessel on duty
Why: Rule 25(b) permits sailing vessels less than 20 meters to combine the sidelights and sternlight into a tricolor lantern at or near the masthead. The tricolor replaces the separate sidelights and stern light — it is never used with a white masthead light.
6. A sailing vessel underway may exhibit at or near the top of the mast where they can best be seen which combination lights?
- A.A combined lantern showing a red light over a green light✓
- B.A tri-color lantern showing red, green, and white sectors
- C.Separate red and green lights only
- D.A single all-round white light
Why: Under COLREGS Rule 25(c), a sailing vessel underway may — in addition to the sidelights and sternlight required by Rule 25(a) — exhibit at or near the top of the mast, where they can best be seen, two all-round lights in a vertical line, the upper red and the lower green. There is no length restriction on these optional lights (the under-20-meter limit applies instead to the separate Rule 25(b) combined tri-color masthead lantern, which may not be shown together with the 25(c) red-over-green lights).
7. A sailing vessel under 20 meters underway may use which simplified light configuration in lieu of separate sidelights and stern light?
- A.A tri-color lantern at the masthead showing red, green, and white sectors✓
- B.A combined red over green lantern at the masthead
- C.A single all-round white light and separate sidelights
- D.A single masthead light visible from all directions
Why: Rule 25(b) permits sailing vessels under 20 meters to use a single tri-color lantern at or near the masthead showing red to port, green to starboard, and white aft — replacing the need for separate sidelights and stern light.
8. A sailing vessel of less than 7 meters in length, if unable to exhibit the lights prescribed by Rule 25, shall exhibit what?
- A.An electric torch or lighted lantern showing a white light in sufficient time to prevent collision✓
- B.An all-round red light only
- C.Sidelights from a flashlight when another vessel approaches
- D.No light is required for vessels this small
Why: Rule 25(d) provides that sailing vessels under 7 meters and vessels under oars that cannot exhibit standard lights shall have ready an electric torch or lighted lantern showing a white light to display in sufficient time to prevent collision.
Frequently asked questions
- Does a sailing vessel ever show a masthead light?
- No — not when proceeding under sail alone. Sailing vessels show only sidelights and a sternlight (or a combined tricolor lantern). The white masthead light is a power-driven vessel light. If the sailing vessel is also running its engine, it becomes a power-driven vessel and must show a masthead light.
- What is the combined tricolor lantern and when can it be used?
- A combined tricolor lantern is a single fitting carried at or near the top of the mast that incorporates the red port sector (112.5°), green starboard sector (112.5°), and white stern sector (135°) in one unit. It is available only to sailing vessels under 20 meters and replaces the separate sidelights and sternlight. It cannot be used simultaneously with any other masthead lights or the optional red-over-green all-around lights.
- What dayshape must a motor-sailing vessel show?
- A sailing vessel proceeding under sail when also under power must exhibit a black conical shape, apex downward, forward where it can best be seen. This applies during daylight hours and signals to other vessels that the vessel has engine power available despite having sails set.
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