Navigation lights on a sailboat

Navigation Rules, lights & bridges · Sailboats

Under sail at night a sailboat shows sidelights and a sternlight; under 20 meters (65.6 ft) they may be combined in one masthead tricolour. Once the engine is driving her, even with sails up, she is a power-driven vessel and must show power-boat lights (Inland Rules 3, 23, 25).

Commonly missed

A common error is motoring at night with only the tricolour lit. That shows other boats a sailing vessel when you are legally a power-driven vessel. Switch to the steaming light, sidelights and sternlight.
If your sidelights and sternlight are only at the masthead, you have no legal light set for motoring. Make sure deck-level sidelights and a sternlight (or a combined bow lantern plus sternlight) work too.

Under sail alone

A sailing vessel underway shows red and green sidelights and a white sternlight (Inland Rule 25(a)).
The rules count a boat as a sailing vessel only while she is under sail and any engine fitted is not being used to drive her (Inland Rule 3(c)).

Masthead tricolour and red-over-green

On a sailing vessel under 20 meters (65.6 ft), the sidelights and sternlight may be combined in one lantern at or near the top of the mast where it can best be seen (Inland Rule 25(b)).
The rules allow this combined lantern only for a vessel under sail. It is not a motoring light and not an anchor light (Inland Rules 23, 25(b), 30).
A sailing vessel may also show two all-round lights near the masthead, red above green, in addition to her sidelights and sternlight, but never together with the masthead tricolour (Inland Rule 25(c)).

Under engine, with or without sails

Any vessel propelled by machinery is a power-driven vessel, so a sailboat motoring or motor-sailing shows the power-driven set: masthead (steaming) light, sidelights and sternlight (Inland Rules 3(b), 23(a)).
Under 12 meters (39.4 ft), a sailboat under power may instead use the power-driven option of an all-round white light plus sidelights (Inland Rule 23(d)).
By day, motor-sailing calls for a black cone, point down, shown forward; see the day-shapes topic for the Inland exemption (Inland Rule 25(e)).

How far your lights must be seen

Under 12 meters (39.4 ft): sidelights 1 nautical mile; sternlight, masthead light and all-round lights 2 nautical miles (Inland Rule 22(c); 33 CFR 84.14).
12 meters to under 20 meters: sidelights, sternlight and all-round lights 2 nautical miles; masthead light 3 nautical miles (Inland Rule 22(b)).

The rules: Inland Rule 3 · Inland Rule 22 · Inland Rule 23 · Inland Rule 25 · Inland Rule 30 · COLREGS Rule 25 · 33 CFR 84.14

Sources (7)

ecfr.gov · ecfr.gov · ecfr.gov · navcen.uscg.gov · boatus.org · app.leg.wa.gov · ohiodnr.gov

A plain-language summary of federal rules for recreational boats, checked against the rules’ own text and a second source, and written in our own words. It isn’t legal advice. States add rules of their own, and rules change — the links above go to the current official text.