Inland · Rule 33
Equipment for Sound Signals
Last verified: 2026-06-01
TL;DR
12 m+: whistle. 20 m+: whistle + bell. 100 m+: whistle + bell + gong (gong of different tone from bell). Smaller vessels are not obliged to carry these but must have some 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.
Authoritative source
Source links checked against the current public rule corpus on 2026-06-01.
Rule 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.
International parallel
COLREGs Rule 33 — Equipment for Sound Signals →More from Part D — Sound and Light Signals
Related drills
- Practise Rule 32 — Sound Signal Definitions
- Practise Rule 34 — Maneuvering and Warning Signals
- Practise Rule 35 — Sound Signals in Restricted Visibility
- Rule 36 — Signals to Attract Attention
Drill Inland Rule 33
Try the free Rules of the Road practice questions (no sign-in), or sign in to drill citation-backed questions on this rule with immediate feedback and the source chunk in a popover.