COLREGs Rule 32: Definitions of whistle and blasts

Last reviewed: October 14, 2026

Rule 32 defines three terms: whistle, short blast and prolonged blast. A whistle must be able to produce the prescribed blasts and meet Annex III. A short blast lasts about one second and a prolonged blast lasts four to six seconds.

What it says

  1. International: A whistle is any sound signaling appliance that can produce the prescribed blasts and complies with the specifications in Annex III to these Regulations.

    COLREGs Rule 32(a)“The word whistle means any sound signaling appliance capable of producing the prescribed blasts and which complies with the specifications in Annex III to these Regulations.”

  2. Inland: A whistle is any sound signaling appliance that can produce the prescribed blasts and complies with specifications in Annex III to these Rules (33 CFR part 86).

    COLREGs Rule 32(a)“which complies with specifications in Annex III to these Rules (33 CFR part 86).”

  3. International: A short blast is a blast of about one second's duration.

    COLREGs Rule 32(b)“The term short blast means a blast of about one second’s duration.”

  4. Inland: A short blast is a blast of about 1 second's duration.

    COLREGs Rule 32(b)“The term short blast means a blast of about 1 second’s duration.”

  5. International: A prolonged blast is a blast of from four to six seconds' duration.

    COLREGs Rule 32(c)“The term prolonged blast means a blast of from four to six seconds’ duration.”

  6. Inland: A prolonged blast is a blast of from 4 to 6 seconds' duration.

    COLREGs Rule 32(c)“The term prolonged blast means a blast of from 4 to 6 seconds’ duration.”

Common questions

How long is a short blast?

A short blast is a blast of about one second's duration. The Inland text writes this as about 1 second's duration.

“The term short blast means a blast of about one second’s duration.”

How long is a prolonged blast?

A prolonged blast is a blast of from four to six seconds' duration. The Inland text writes this as from 4 to 6 seconds' duration.

“The term prolonged blast means a blast of from four to six seconds’ duration.”

What counts as a whistle under the Rules?

A whistle is any sound signaling appliance that can produce the prescribed blasts and meets the Annex III specifications.

“The word whistle means any sound signaling appliance capable of producing the prescribed blasts and which complies with the specifications in Annex III to these Regulations.”

The text of COLREGs Rule 32

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

Rule 32: Definitions

International (COLREGs)

(a) The word whistle means any sound signaling appliance capable of producing the prescribed blasts and which complies with the specifications in Annex III to these Regulations. (b) The term short blast means a blast of about one second’s duration. (c) The term prolonged blast means a blast of from four to six seconds’ duration.

Inland Rules

Definitions (a) The word whistle means any sound signaling appliance capable of producing the prescribed blasts and which complies with specifications in Annex III to these Rules (33 CFR part 86). (b) The term short blast means a blast of about 1 second’s duration. (c) The term prolonged blast means a blast of from 4 to 6 seconds’ duration.

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.