What is sound Rule 33?

Rule 33 is the equipment-for-sound-signals rule. It tells you which vessels must carry a whistle, bell, and gong so they can make the signals required elsewhere in the Navigation Rules.

Does a boat under 12 meters need a whistle under Rule 33?

No. A vessel under 12 meters is not obliged to carry the whistle, bell, or gong listed for larger vessels, but it must still have some efficient means of making a sound signal.

Is Rule 33 the same as the maneuvering and warning signals rule?

No. Rule 33 covers the equipment carried aboard. Rule 34 covers maneuvering and warning signals, and Rule 35 covers sound signals in restricted visibility.

Inland Rule 33 — Whistle, Bell & Gong Rules (33 CFR 83.33)

Rule text#

Source

Verbatim 33 CFR §83.33 as published in the Code of Federal Regulations — public domain, retrieved 2026-07-26.

(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.

Why it shows up on the exam#

Rule 33 is the equipment rule, not the maneuvering-signal rule. Memorise the 12 m, 20 m, and 100 m breakpoints before studying Rules 34 and 35.

Exam checkpoints#

12 m or more
Whistle
A vessel at least 12 meters long must carry a whistle that can make the prescribed sound signals.
20 m or more
Whistle + bell
At 20 meters, the bell is added to the whistle requirement. This is the most common exam breakpoint.
100 m or more
Whistle + bell + gong
At 100 meters, the vessel also needs a gong whose tone cannot be confused with the bell.

Rule 33 — common exam questions#

What is sound Rule 33?: Rule 33 is the equipment-for-sound-signals rule. It tells you which vessels must carry a whistle, bell, and gong so they can make the signals required elsewhere in the Navigation Rules.
Does a boat under 12 meters need a whistle under Rule 33?: No. A vessel under 12 meters is not obliged to carry the whistle, bell, or gong listed for larger vessels, but it must still have some efficient means of making a sound signal.
Is Rule 33 the same as the maneuvering and warning signals rule?: No. Rule 33 covers the equipment carried aboard. Rule 34 covers maneuvering and warning signals, and Rule 35 covers sound signals in restricted visibility.

Authoritative source#

Source links checked against the current public rule corpus on 2026-07-26.

33 CFR §83.33 — the section this text comes from, with its neighbours.
The Inland Navigation Rules are codified at 33 CFR Part 83 and are public domain. The international COLREGs text is published separately by the IMO.

Practice this rule#

One real exam question on this rule, cited to source. No sign-up.

Under 46 CFR §11.302, a seafarer who cannot demonstrate 1 year of sea service within the last 5 years to maintain basic training (BT) competence is required to do which of the following?

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Equipment for Sound Signals