COLREGs · Rule 35 · 33 CFR §83.35
Sound Signals in Restricted Visibility
Power-driven making way: 1 prolonged every ≤2 min. Power-driven underway but stopped: 2 prolonged every ≤2 min. NUC, RAM, CBD, sailing, fishing, towing: 1 prolonged + 2 short every ≤2 min. At anchor: bell rung rapidly for 5 sec every ≤1 min (50 m+ adds gong aft).
What does Rule 35 actually say?#
Source
Practice this rule#
One real exam question on this rule, cited to source. No sign-up.
Under the Inland Rules, a vessel at anchor in restricted visibility may optionally sound which additional whistle signal to warn an approaching vessel?
How does Inland Rule 35 differ from COLREGs?#
Two differences. Inland Rule 35 reserves paragraph (d), where COLREGs places its own signal provision, and Inland adds paragraph (l), which excuses a vessel under 20 metres and a barge, canal boat, scow, or other nondescript craft from the anchor bell signal when anchored in a Coast Guard designated special anchorage area. The core signals — one prolonged, two prolonged, and one prolonged plus two short — are the same in both sets.
21 of 38 rules differ somewhere; the five the exam leans on are Rule 9, Rule 10, Rule 24, Rule 28 and Rule 34, side by side on Inland vs International Rules.
Why it shows up on the exam#
Rule 35 has at least 8 distinct fog-signal patterns. The bell-then-gong combo for vessels at anchor 50 m+ is a high-frequency exam target.
What does the exam actually test here?#
Power-driven vessel
One prolonged, or two if stopped
Making way through the water: one prolonged blast at intervals of not more than 2 minutes. Underway but stopped and making no way: two prolonged blasts in succession, about 2 seconds apart, at the same interval.
The one-prolonged-two-short group
NUC, RAM, sail, fishing, towing
A vessel not under command; restricted in her ability to maneuver, underway or at anchor; a sailing vessel; a vessel engaged in fishing, underway or at anchor; and a vessel towing or pushing all sound one prolonged followed by two short blasts at intervals of not more than 2 minutes. A manned vessel being towed — the last one, if there is more than one — sounds one prolonged followed by three short.
At anchor and aground
Bell, and gong if 100 m or more
At anchor: rapid ringing of the bell for about 5 seconds at intervals of not more than 1 minute; a vessel of 100 metres or more also sounds the gong aft for about 5 seconds immediately after. Aground: the same bell and gong signal plus three separate and distinct strokes on the bell immediately before and after the rapid ringing.
Rule 35 — common exam questions#
What fog signal does a power-driven vessel making way sound?
One prolonged blast at intervals of not more than 2 minutes (33 CFR §83.35(a)).
What is the difference between the underway and the stopped signal?
A power-driven vessel making way through the water sounds one prolonged blast; a power-driven vessel underway but stopped and making no way sounds two prolonged blasts in succession with about 2 seconds between them. Both at intervals of not more than 2 minutes (33 CFR §83.35(a) and (b)).
Which vessels sound one prolonged followed by two short blasts?
A vessel not under command; a vessel restricted in her ability to maneuver, whether underway or at anchor; a sailing vessel; a vessel engaged in fishing, whether underway or at anchor; and a vessel engaged in towing or pushing (33 CFR §83.35(c)).
What does a vessel at anchor sound in fog?
Rapid ringing of the bell for about 5 seconds at intervals of not more than 1 minute. A vessel of 100 metres or more rings the bell forward and immediately follows with the gong sounded rapidly for about 5 seconds aft. She may in addition sound one short, one prolonged, and one short blast to warn an approaching vessel (33 CFR §83.35(g)).
Do small vessels have to sound fog signals?
A vessel of less than 12 metres is not obliged to give the prescribed signals, but if she does not she must make some other efficient sound signal at intervals of not more than 2 minutes. A vessel of 12 metres or more but less than 20 metres is not obliged to give the bell signals, subject to the same substitute requirement (33 CFR §83.35(i) and (j)).
Authoritative source#
- 33 CFR §83.35 — this section with its neighbours. 33 CFR Part 83 is public domain; checked 2026-05-16.
- COLREGs Rule 35 is published by the IMO and is authoritative internationally.
Practise this rule against the real exam.
Real exam questions. No signup, no card.
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