COLREGs Rule 23: Lights for power-driven vessels underway
Last reviewed: October 14, 2026
Rule 23 covers the lights shown by power-driven vessels underway. A vessel must show masthead lights, sidelights and a sternlight, with options for smaller vessels. The International and Inland rules differ on small vessels, flashing yellow light placement and Great Lakes vessels.
Applies toPower-driven vessels underway, with added lights for air-cushion vessels in the non-displacement mode and WIG craft taking off, landing and in flight near the surface.
What it says
A power-driven vessel underway must show a forward masthead light, sidelights and a sternlight, and a second masthead light unless it is under 50 meters long.
COLREGs Rule 23(a)(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;”
International: An air-cushion vessel operating in the non-displacement mode must also show an all-round flashing yellow light in addition to the paragraph (a) lights.
COLREGs Rule 23(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.”
Inland: An air-cushion vessel operating in the non-displacement mode must also show an all-round flashing yellow light where it can best be seen.
COLREGs Rule 23(b)“exhibit an all-round flashing yellow light where it can best be seen.”
A WIG craft must show a high intensity all-round flashing red light in addition to the paragraph (a) lights, only when taking off, landing and in flight near the surface.
COLREGs Rule 23(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”
International: A power-driven vessel under 7 meters long whose maximum speed does not exceed 7 knots may show an all-round white light instead of the paragraph (a) lights, and must also show sidelights if practicable.
COLREGs Rule 23(d)(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;”
Inland: A power-driven vessel under 12 meters long may show an all-round white light and sidelights instead of the paragraph (a) lights.
COLREGs Rule 23(d)“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.”
Inland: A power-driven vessel on the Great Lakes may carry an all-round white light instead of the second masthead light and sternlight, in the position of the second masthead light.
COLREGs Rule 23(e)“The light shall be carried in the position of the second masthead light and be visible at the same minimum range.”
Common questions
Does a vessel under 50 meters need a second masthead light?
No. A power-driven vessel under 50 meters long is not obliged to show the second masthead light, but it may show it.
“except that a vessel of less than 50 meters in length shall not be obliged to exhibit such light but may do so;”
What lights may a power-driven vessel under 12 meters show on Inland waters?
It may show an all-round white light and sidelights instead of the paragraph (a) lights.
“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.”
What light can a Great Lakes power-driven vessel use instead of two lights?
Inland: It may carry an all-round white light instead of the second masthead light and sternlight. The light must be carried in the position of the second masthead light.
“may carry an all- round white light in lieu of the second masthead light and sternlight prescribed in paragraph (a) of this Rule.”
The text of COLREGs Rule 23
U.S. Coast Guard, Navigation Rules and Regulations Handbook
Rule 23: Power-driven Vessels Underway
International (COLREGs)
(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. Power-driven vessel underway—50 meters or greater in length. Same for Inland.
(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. Air-cushion vessel when operating in the non-displacement mode—vessel less than 50 meters in length. Same for Inland.
(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. Power-driven vessel of less than 7 meters in length whose maximum speed does not exceed 7 knots. International only.
Inland Rules
Power-driven vessels underway
(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. Power-driven vessel underway—less than 50 meters in length. Same for International.
(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 where it can best be seen.
(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. Air-cushion vessel when operating in the displacement mode— vessel less than 50 meters in length. Same for International.
(d) 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. Power-driven vessel of less than 12 meters in length. Same for International.
(e) A power-driven vessel when operating on the Great Lakes may carry an all- round white light in lieu of the second masthead light and sternlight prescribed in paragraph (a) of this Rule. The light shall be carried in the position of the second masthead light and be visible at the same minimum range. Power-driven vessel on Great Lakes.
The plain-English explanation on this page was written with AI from the regulation text above and checked automatically before publishing: every quote appears in the text, every number comes from it, and a second model confirmed each statement adds nothing the text doesn't say. Regulation text current as of August 12, 2024. The regulation text governs. RegKnot is not affiliated with the U.S. Coast Guard.