What lights does a sailing vessel under 20 metres show at night?

Sidelights (green to starboard, red to port) and a white sternlight. Under COLREG Rule 25 a sailing vessel under 20 m may combine these into a single tricolour lantern at the masthead instead of separate lights.

What lights does a sailboat show when motoring at night?

Once propelled by machinery a sailing vessel is a power-driven vessel under the rules. It shows a masthead light plus sidelights and sternlight, and by day exhibits a black cone point-down, per COLREG Rule 25(e).

Can a small sailboat use a flashlight instead of fixed lights?

A sailing vessel or vessel under oars less than 7 m, if it cannot show the prescribed lights, must have ready a white light (e.g. a torch) to show in time to prevent collision, under COLREG Rule 25(d)(ii).

What Lights Does a Sailboat Show at Night? (COLREG Rule 25)

At night, a sailboat is read entirely by its lights. Get them right and every other vessel knows what you are and which way you are heading; get them wrong and you become a guessing game on a dark horizon. The governing rule is short and specific, so let us start with the answer and then unpack it.

COLREG Rule 25 — Sailing vessels underway and vessels under oars. (Recepito in Italia con L. 1085/1977; mirrored for US inland waters at 33 CFR § 83.25.)

The short answer

A sailing vessel underway shows sidelights and a sternlight:

Green sidelight to starboard, covering an arc of 112.5°.
Red sidelight to port, covering 112.5°.
White sternlight astern, covering 135°.

That is the baseline every sailboat must satisfy. What changes is how those lights may be arranged, and that depends on the length of the boat.

Boats under 20 metres: the tricolour option

On a vessel of less than 20 metres the sidelights and sternlight may be combined into one tricolour lantern carried at or near the top of the mast. It is the same three sectors — red, green, white — gathered into a single fitting, and it is efficient: high up, visible at distance, and easy on the battery.

A sailing vessel of less than 20 m may combine the prescribed lights in one lantern carried at the top of the mast — COLREG Rule 25(b).

One important caveat: the masthead tricolour and the optional all-round red-over-green "sailing" lights at the masthead may not be shown at the same time. Choose one configuration.

The moment you start the engine, everything changes

This is the single most misunderstood point, and the one most likely to lose you marks on a licence exam — or, worse, mislead another skipper at sea. The instant your sails are assisted or replaced by the engine, you are no longer a sailing vessel under the rules. You become a power-driven vessel, and you must light yourself as one.

Switch off the tricolour (it is for sailing only).
Show a masthead light (white, forward-facing 225°), plus sidelights and sternlight at deck level.
By day, exhibit a black cone, point down, where it can best be seen.

A vessel proceeding under sail when also being propelled by machinery shall exhibit forward a conical shape, apex downwards — COLREG Rule 25(e).

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Very small boats: keep a torch ready

A sailing vessel or a vessel under oars of less than 7 metres, if it cannot show the lights above, is not left without obligation. It must have an electric torch or lighted lantern showing a white light ready to be exhibited in time to prevent a collision.

…shall have ready at hand an electric torch or lighted lantern showing a white light exhibited in sufficient time to prevent collision — COLREG Rule 25(d)(ii).

Quick reference

Sailing, any size: sidelights + sternlight.
Sailing, under 20 m: may use a masthead tricolour instead.
Motoring (engine on): masthead light + sidelights + sternlight; cone by day.
Under 7 m, no fixed lights: white torch ready to show.

And the rule above all rules: none of this relieves you of good seamanship. If showing or withholding a light helps avoid a collision in the moment, Rule 2 governs — practice and circumstances come first.

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FAQ

What lights does a sailboat under 20 m show at night?

Sidelights (green to starboard, red to port) and a white sternlight — which, under Rule 25(b), may be combined into a single masthead tricolour lantern.

What about when motoring?

You are then a power-driven vessel: masthead light plus sidelights and sternlight, and a black cone point-down by day (Rule 25(e)). Turn the tricolour off.

Is a flashlight ever enough?

Only for a sailing or rowing vessel under 7 m that cannot show fixed lights: it must have a white torch ready to show in time to prevent collision (Rule 25(d)(ii)).