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Lights & Shapes

COLREG 20(a,c) · U.S. Coast Guard — International Navigation Rules (2024): (a) Rules in this part shall be complied with in all weathers. (c) The lights prescribed by these Rules shall, if carried, also be exhibited from sunrise to sunset in restricted visibility and may be exhibited in all other circumstances when it is deemed necessary.

Bow views at night: a power-driven vessel underway, a sailing vessel and a vessel at anchor.
Under power, under sail, at anchor — examples seen from ahead.
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Lights & Shapes — Cheat Sheet

Study selected light and day-shape configurations from Rules 23–30. Compare the four aspects and check the vessel type, length and operating condition against the rule. A visible pattern alone may fit more than one situation.

Open cheat sheet

Lights and shapes by vessel type (Rules 20–31)

Reading vessel lights — the framework that actually works

COLREG 21(a,b,c) · U.S. Coast Guard — International Navigation Rules (2024)

(a) Masthead light means a white light placed over the fore and aft centerline of the vessel showing an unbroken light over an arc of the horizon of 225° and so fixed as to show the light from right ahead to 22.5° abaft the beam on either side of the vessel.

(b) Sidelights means a green light on the starboard side and a red light on the port side each showing an unbroken light over an arc of the horizon of 112.5° and so fixed as to show the light from right ahead to 22.5° abaft the beam on its respective side.

In a vessel of less than 20 m in length the sidelights may be combined in one lantern carried on the fore and aft centerline of the vessel.

(c) Sternlight means a white light placed as nearly as practicable at the stern showing an unbroken light over an arc of the horizon of 135° and so fixed as to show the light 67.5° from right aft on each side of the vessel.

Day shapes: one ball indicates a vessel at anchor (Rule 30); two balls vertically indicate not under command (27); three balls vertically indicate aground (30). A cylinder is the optional shape for a vessel constrained by draught (28). Apply each rule’s conditions and small-vessel exemptions.

Rules 23–31 cover specific vessel categories: power-driven (23), towing and pushing (24), sailing and rowing (25), fishing (26), NUC and RAM (27), constrained by draught (28), pilot (29), anchored and aground (30), seaplanes and WIG (31).

Study selected light and day-shape configurations from Rules 23–30. Compare the four aspects and check the vessel type, length and operating condition against the rule. A visible pattern alone may fit more than one situation.

Fastest routes through the lights syllabus

Frequently asked questions

What are the basic navigation lights every power-driven vessel shows?
COLREG 23 · U.S. Coast Guard — International Navigation Rules (2024): (a) A power-driven vessel underway shall exhibit: (i) a masthead light forward; (ii) a second masthead light abaft of and higher than the forward one; except that a vessel of less than 50 meters in length shall not be obliged to exhibit such light but may do so; (iii) sidelights; and (iv) a sternlight. (b) An air-cushion vessel when operating in the non-displacement mode shall, in addition to the lights prescribed in paragraph (a) of this Rule, exhibit an all-round flashing yellow light. (c) A WIG craft only when taking off, landing and in flight near the surface shall, in addition to the lights prescribed in paragraph (a) of this Rule, exhibit a high intensity all-round flashing red light. (d) (i) A power-driven vessel of less than 12 meters in length may in lieu of the lights prescribed in paragraph (a) of this Rule exhibit an all-round white light and sidelights; (ii) a power-driven vessel of less than 7 meters in length whose maximum speed does not exceed 7 knots may in lieu of the lights prescribed in paragraph (a) of this Rule exhibit an all-round white light and shall, if practicable, also exhibit sidelights; (iii) the masthead light or all-round white light on a power-driven vessel of less than 12 meters in length may be displaced from the fore and aft centerline of the vessel if centerline fitting is not practicable, provided that the sidelights are combined in one lantern which shall be carried on the fore and aft centerline of the vessel or located as nearly as practicable in the same fore and aft line as the masthead light or the all-round white light.
What does white over red mean?
COLREG 29 · U.S. Coast Guard — International Navigation Rules (2024): (a) A vessel engaged on pilotage duty shall exhibit: (i) at or near the masthead, two all-round lights in a vertical line, the upper being white and the lower red; (ii) when underway, in addition, sidelights and a sternlight; (iii) when at anchor, in addition to the lights prescribed in subparagraph (i), the anchor light, lights, or shape prescribed in Rule 30 for vessels at anchor. (b) A pilot vessel when not engaged on pilotage duty shall exhibit the lights or shapes prescribed for a similar vessel of her length.
When does a sailing vessel show a black cone point-down?
COLREG 25(e) · U.S. Coast Guard — International Navigation Rules (2024): (e) A vessel proceeding under sail when also being propelled by machinery shall exhibit forward where it can best be seen a conical shape, apex downwards. COLREG 3(b,c) · U.S. Coast Guard — International Navigation Rules (2024): (b) The term power-driven vessel means any vessel propelled by machinery. (c) The term sailing vessel means any vessel under sail provided that propelling machinery, if fitted, is not being used.
What does a single black ball mean during the day?
Day shapes: one ball indicates a vessel at anchor (Rule 30); two balls vertically indicate not under command (27); three balls vertically indicate aground (30). A cylinder is the optional shape for a vessel constrained by draught (28). Apply each rule’s conditions and small-vessel exemptions.
Do I need to show lights during the day in restricted visibility?
COLREG 20(b,c) · U.S. Coast Guard — International Navigation Rules (2024): (b) The Rules concerning lights shall be complied with from sunset to sunrise, and during such times no other lights shall be exhibited, except such lights as cannot be mistaken for the lights specified in these Rules or do not impair their visibility or distinctive character, or interfere with the keeping of a proper look-out. (c) The lights prescribed by these Rules shall, if carried, also be exhibited from sunrise to sunset in restricted visibility and may be exhibited in all other circumstances when it is deemed necessary.