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Rule 32: Definitions (Sound Signals) (COLREGS)

Last reviewed October 21, 2026

The short answer

Rule 32 defines the building blocks of sound signals. A short blast lasts about one second. A prolonged blast lasts four to six seconds. A whistle is any sound signaling appliance that can produce the prescribed blasts and meets the Annex III specifications.

The rule text

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

International Rules, U.S. Coast Guard Navigation Rules and Regulations Handbook (NAVCEN, 2024 corrected edition), Rule 32

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

International Rules, U.S. Coast Guard Navigation Rules and Regulations Handbook (NAVCEN, 2024 corrected edition), Rule 32

What it means on the water

  • Short blast: about 1 second (32(b)).
  • Prolonged blast: 4 to 6 seconds (32(c)).
  • These definitions apply to every signal in Rules 34 and 35.

International vs Inland

Same in both. Inland cites Annex III as 33 CFR Part 86.

Common exam traps

  • Calling a 3-second blast prolonged. Prolonged is 4 to 6 seconds.
  • Mixing up a short blast with the 5-second anchor bell.

Try 3 questions on Rule 32

  1. How long is a short blast?

    1. About 1 second
    2. 2 to 3 seconds
    3. 4 to 6 seconds
    4. 10 seconds
    Show answer

    A. About 1 second Rule 32(b).

  2. How long is a prolonged blast?

    1. About 1 second
    2. 2 seconds
    3. 4 to 6 seconds
    4. 8 to 10 seconds
    Show answer

    C. 4 to 6 seconds Rule 32(c).

  3. Where are whistle specifications?

    1. Annex I
    2. Annex II
    3. Annex III
    4. Annex IV
    Show answer

    C. Annex III Rule 32(a).

Frequently asked questions

What is a prolonged blast?

A blast of four to six seconds (Rule 32(c)).

What is a short blast?

About one second (Rule 32(b)).

Same Inland?

Yes.

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