Rule 25 — Lights for Sailing Vessels Underway and Vessels Under Oars

TL;DR — A sailing vessel underway shows sidelights and a sternlight; vessels under 20 m may combine those into a single tricolor lantern at the masthead, but never simultaneously with the optional red-over-green all-round pair. A vessel under oars need only show a white light if full sailing-vessel lights are not carried. 33 CFR §83.25

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What the Rule Says

The baseline requirement — all sailing vessels underway

Every sailing vessel underway, regardless of length, must exhibit sidelights and a sternlight. 33 CFR §83.25 The sidelights are defined as a green light to starboard and a red light to port, each covering 112.5° of arc from dead ahead to 22.5° abaft the beam on its respective side. 33 CFR §83.21 The sternlight is a white light covering 135° centered on dead aft. 33 CFR §83.21 These rules apply in all weathers. 33 CFR §83.20

The combined tricolor lantern option — vessels under 20 m

A sailing vessel of less than 20 meters in length may, instead of carrying separate sidelights and a sternlight, combine all three into a single lantern carried at or near the top of the mast where it can best be seen. 33 CFR §83.25 This is the familiar "tricolor" masthead lantern seen on offshore sailboats. It is an option, not a requirement — the vessel may instead carry the standard separate lights.

On a vessel of less than 20 meters in length, sidelights may in any case be combined in one lantern carried on the fore and aft centerline; on a vessel of less than 12 meters, that combined sidelight lantern shall be placed as nearly as practicable to the fore and aft centerline. 33 CFR §83.21

The optional red-over-green all-round pair — any sailing vessel underway

Any sailing vessel underway may, in addition to the sidelights and sternlight required by paragraph (a), exhibit at or near the top of the mast two all-round lights in a vertical line — the upper being red and the lower green. 33 CFR §83.25 These lights are purely optional and are intended to make the vessel more conspicuous to approaching traffic. An all-round light shows an unbroken light over 360° of the horizon. 33 CFR §83.21

Critical restriction: The red-over-green all-round pair shall NOT be exhibited in conjunction with the combined tricolor lantern permitted by paragraph (b). 33 CFR §83.25 A vessel under 20 m must choose one or the other — tricolor lantern alone, or separate sidelights/sternlight with the optional red-over-green pair. It cannot use both simultaneously.

Vessels under 7 meters — reduced obligation

A sailing vessel of less than 7 meters in length shall, if practicable, exhibit the lights prescribed in paragraph (a) or (b) — that is, the full sidelight/sternlight combination or the tricolor lantern. However, if she does not exhibit those lights, she shall exhibit an all-round white light, or have ready at hand an electric torch or lighted lantern showing a white light, which shall be exhibited in sufficient time to prevent collision. 33 CFR §83.25

The phrase "if practicable" acknowledges that very small sailing vessels — dinghies, day-sailers — may not be fitted with permanent navigation lights. The fallback is a white light, not darkness.

Vessels under oars

A vessel under oars may exhibit the lights prescribed for sailing vessels under Rule 25, but if she does not, she shall exhibit an all-round white light or have ready at hand an electric torch or lighted lantern showing a white light, which shall be exhibited in sufficient time to prevent collision. 33 CFR §83.25

Note the parallel structure: both the sub-7-meter sailing vessel and the vessel under oars share the same fallback — a white light exhibited in time to prevent collision. Neither is required to carry full navigation lights, but neither may simply show nothing.

Sailing vessel also propelled by machinery — the cone shape

A vessel proceeding under sail when also being propelled by machinery shall exhibit forward, where it can best be seen, a conical shape, apex downward. 33 CFR §83.25 This is a daytime requirement — shapes are complied with by day. 33 CFR §83.20 A vessel of less than 12 meters in length is not required to exhibit this shape, but may do so. 33 CFR §83.25 At night, a vessel under sail and power is treated as a power-driven vessel and must display power-driven vessel lights under Rule 23. 33 CFR §83.23

Minimum visibility ranges

The sidelights and sternlight carried by a sailing vessel must meet the minimum visibility ranges set by Rule 22. For a vessel of 12 meters or more but less than 50 meters: sidelights 2 miles, sternlight 2 miles. For a vessel of less than 12 meters: sidelights 1 mile, sternlight 2 miles. 33 CFR §83.22

When lights must be shown

Lights must be exhibited from sunset to sunrise. During that period, no other lights shall be exhibited that could be mistaken for prescribed lights, impair their visibility or distinctive character, or interfere with keeping a proper lookout. 33 CFR §83.20 If carried, lights shall also be exhibited from sunrise to sunset in restricted visibility, and may be exhibited in all other circumstances when deemed necessary. 33 CFR §83.20

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Why It Matters on the Exam

Exam questions on Rule 25 cluster around four areas:

1. The tricolor-vs.-red-over-green mutual exclusion. This is the most frequently tested point. Candidates must know that the combined tricolor lantern (paragraph b) and the optional red-over-green pair (paragraph c) are mutually exclusive. A vessel under 20 m using the tricolor cannot also show the red-over-green. 33 CFR §83.25

2. The sub-7-meter fallback. Questions will ask what a small sailing vessel must do if she cannot exhibit full navigation lights. The answer is an all-round white light, or a torch/lantern ready at hand to be shown in time to prevent collision — not simply nothing. 33 CFR §83.25

3. Vessels under oars. The rule treats rowing vessels identically to sub-7-meter sailing vessels for lighting purposes. A vessel under oars may use sailing-vessel lights, but if not, must have a white light ready. 33 CFR §83.25

4. The cone shape for motorsailing. Candidates must know the shape (cone, apex down, forward), the size threshold for exemption (under 12 m not required), and that it is a daytime requirement. 33 CFR §83.25 33 CFR §83.20

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Common Pitfalls

Pitfall 1 — Confusing the tricolor lantern with the red-over-green pair. The tricolor combines red sidelight, green sidelight, and white sternlight into one masthead lantern. The red-over-green pair are two separate all-round lights used in addition to the standard sidelights and sternlight. They serve different purposes and cannot be used together. 33 CFR §83.25

Pitfall 2 — Thinking the tricolor is available to all sailing vessels. The combined tricolor lantern option is available only to sailing vessels of less than 20 meters in length. A 25-meter sailing vessel must carry separate sidelights and a sternlight. 33 CFR §83.25

Pitfall 3 — Assuming a vessel under oars needs no lights at all. A vessel under oars that does not exhibit sailing-vessel lights must still exhibit an all-round white light or have a torch ready at hand. Showing nothing is not an option. 33 CFR §83.25

Pitfall 4 — Applying the cone-shape exemption incorrectly. The exemption from displaying the motorsailing cone applies to vessels of less than 12 meters — not less than 20 meters. Do not confuse this threshold with the tricolor lantern threshold of 20 meters. 33 CFR §83.25

Pitfall 5 — Forgetting that lights must be shown in restricted visibility during daylight. If a sailing vessel carries navigation lights, those lights shall also be exhibited from sunrise to sunset in restricted visibility. 33 CFR §83.20

Pitfall 6 — Confusing sidelight visibility ranges by vessel size. For vessels under 12 meters, sidelights need only be visible at 1 mile — not 2 miles. The sternlight for the same vessel still requires 2 miles. 33 CFR §83.22

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Quick Check

Q1 — A sailing vessel of 15 meters is underway at night. She wants to use the optional red-over-green all-round lights at the masthead. May she also use a combined tricolor lantern?

No. The red-over-green all-round pair shall not be exhibited in conjunction with the combined tricolor lantern. She must choose one configuration or the other. 33 CFR §83.25

Q2 — A 5-meter sailing dinghy is underway at night and has no installed navigation lights. What is the minimum she must do?

She shall exhibit an all-round white light, or have ready at hand an electric torch or lighted lantern showing a white light, which shall be exhibited in sufficient time to prevent collision. 33 CFR §83.25

Q3 — A vessel is proceeding under sail and also running her engine. What shape must she display, and is there any exemption?

She must display a conical shape, apex downward, forward where it can best be seen. A vessel of less than 12 meters in length is not required to exhibit this shape, but may do so. 33 CFR §83.25

Q4 — A person rowing a skiff at night does not have sailing-vessel lights installed. What must she do?

She shall exhibit an all-round white light or have ready at hand an electric torch or lighted lantern showing a white light, which shall be exhibited in sufficient time to prevent collision. 33 CFR §83.25

Q5 — At what minimum range must the sidelights of a 10-meter sailing vessel be visible?

1 mile. For a vessel of less than 12 meters in length, sidelights must be visible at a minimum range of 1 mile. 33 CFR §83.22

Q6 — A 30-meter sailing vessel is underway. May she use a combined tricolor lantern at the masthead in lieu of separate sidelights and a sternlight?

No. The combined tricolor lantern option is available only to sailing vessels of less than 20 meters in length. A 30-meter vessel must carry separate sidelights and a sternlight. 33 CFR §83.25

Q7 — It is 0900 and visibility has dropped to less than half a mile. A sailing vessel has navigation lights installed. Must she exhibit them?

Yes. Lights prescribed by the Rules shall, if carried, also be exhibited from sunrise to sunset in restricted visibility. 33 CFR §83.20