COLREGs Rule 33: Equipment for sound signals on vessels

Last reviewed: October 14, 2026

Rule 33 sets the sound signal equipment a vessel must have, based on its length. A vessel of 12 meters or more must have a whistle. Bell and gong requirements start at 20 meters and 100 meters. A vessel of less than 12 meters that does not carry the appliances must have some other means of making an efficient sound signal. The International and Inland texts match, except that the Inland text refers to Annex III as 33 CFR part 86.

Applies toVessels, with the equipment depending on length: 12 meters or more, 20 meters or more, 100 meters or more, and less than 12 meters.

What it says

  1. A vessel of 12 meters or more in length must be provided with a whistle.

    COLREGs Rule 33(a)“A vessel of 12 meters or more in length shall be provided with a whistle”

  2. A vessel of 20 meters or more in length must be provided with a bell in addition to a whistle.

    COLREGs Rule 33(a)“a vessel of 20 meters or more in length shall be provided with a bell in addition to a whistle”

  3. A vessel of 100 meters or more in length must, in addition, be provided with a gong, whose tone and sound cannot be confused with that of the bell.

    COLREGs Rule 33(a)“a vessel of 100 meters or more in length shall, in addition, be provided with a gong, the tone and sound of which cannot be confused with that of the bell”

  4. International: The whistle, bell and gong must comply with the specifications in Annex III to these Regulations.

    COLREGs Rule 33(a)“The whistle, bell and gong shall comply with the specifications in Annex III to these Regulations.”

  5. Inland: The whistle, bell and gong must comply with the specifications in Annex III to these Rules (33 CFR part 86).

    COLREGs Rule 33(a)“The whistle, bell and gong shall comply with the specifications in Annex III to these Rules (33 CFR part 86).”

  6. The bell or gong or both may be replaced by other equipment having the same respective sound characteristics, but manual sounding of the prescribed signals must always be possible.

    COLREGs Rule 33(a)“The bell or gong or both may be replaced by other equipment having the same respective sound characteristics, provided that manual sounding of the prescribed signals shall always be possible.”

  7. A vessel of less than 12 meters in length is not obliged to carry the appliances in paragraph (a), but if it does not carry them, it must be provided with some other means of making an efficient sound signal.

    COLREGs Rule 33(b)“shall not be obliged to carry the sound signaling appliances prescribed in paragraph (a) of this Rule but if she does not, she shall be provided with some other means of making an efficient sound signal”

Common questions

What sound equipment must a vessel of 20 meters or more carry?

It must be provided with a bell in addition to a whistle. If it is 100 meters or more in length, it must also have a gong.

“a vessel of 20 meters or more in length shall be provided with a bell in addition to a whistle”

Can a bell or gong be replaced by other equipment?

Yes, the bell or gong or both may be replaced by other equipment having the same respective sound characteristics. Manual sounding of the prescribed signals must always be possible.

“The bell or gong or both may be replaced by other equipment having the same respective sound characteristics, provided that manual sounding of the prescribed signals shall always be possible.”

Does a vessel under 12 meters need a whistle, bell or gong?

No, it is not obliged to carry them. If it does not, it must be provided with some other means of making an efficient sound signal.

“A vessel of less than 12 meters in length shall not be obliged to carry the sound signaling appliances prescribed in paragraph (a) of this Rule”

The text of COLREGs Rule 33

U.S. Coast Guard, Navigation Rules and Regulations Handbook

Rule 33: Equipment for Sound Signals

International (COLREGs)

(a) A vessel of 12 meters or more in length shall be provided with a whistle, a vessel of 20 meters or more in length shall be provided with a bell in addition to a whistle, and a vessel of 100 meters or more in length shall, in addition, be provided with a gong, the tone and sound of which cannot be confused with that of the bell. The whistle, bell and gong shall comply with the specifications in Annex III to these Regulations. The bell or gong or both may be replaced by other equipment having the same respective sound characteristics, provided that manual sounding of the prescribed signals shall always be possible. (b) A vessel of less than 12 meters in length shall not be obliged to carry the sound signaling appliances prescribed in paragraph (a) of this Rule but if she does not, she shall be provided with some other means of making an efficient sound signal.

Inland Rules

Equipment for Sound Signals (a) A vessel of 12 meters or more in length shall be provided with a whistle, a vessel of 20 meters or more in length shall be provided with a bell in addition to a whistle, and a vessel of 100 meters or more in length shall, in addition, be provided with a gong, the tone and sound of which cannot be confused with that of the bell. The whistle, bell and gong shall comply with the specifications in Annex III to these Rules (33 CFR part 86). The bell or gong or both may be replaced by other equipment having the same respective sound characteristics, provided that manual sounding of the prescribed signals shall always be possible. (b) A vessel of less than 12 meters in length shall not be obliged to carry the sound signaling appliances prescribed in paragraph (a) of this Rule but if she does not, she shall be provided with some other means of making an efficient sound signal.

Sections it refers to

  • 33 CFR part 86

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.